# Radiant in slab new garage build



## hondaracer2oo4 (Mar 7, 2016)

Hey guys, building a new garage this spring. 28x40 3 bay with full frost walls and poured floor. I am looking to install radiant heat in the floor. I know that I will have to basically make a foam tub to pour the floor in so that I have my underslab insulation and my thermal break to the frost walls. My question is how to do the thermal break to the frost wall? I have seen some drawings of a stepped in frost wall 6 inches below the floor height so that the frost wall insulation will have the stud wall land over it and you will have a fully poured floor all the way out to the stud wall. I think this is doable but what about where the cars pull in through the bay doors, how do I insulated the floor from the frost walls there?


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## 700renegade (Mar 7, 2016)

Here is how I did my 60'x60' with 2x8 stick walls ( 17' sidewall ).

Place the top of the 4' frost wall 6" above the finished floor.  this keeps the sill boards high and dry where they belong and an internal concrete 'curb' so if you push something against the wall with a skidsteer or something, the wall isn't affected.

Make sure the backfill inside the foundation is compacted correctly.  if you leave this up to a low bidder you are asking for trouble with hollow spots along wall and in corners.  do it yourself.

Put down your 2" or 3" of styrofoam on base, and run a 6" strip (or whatever your slab thickness ) of 1/2" dow foam glued to the frost wall.  half inch is plenty for a thermal break.  I put 1.5" dow against the outside of the frost wall before that was backfilled.

Your internal slab is floating with the exception of at the service doors and overhead doors.  Notch the frost wall down 13" or so.  Run an inch of dow over top of that wall for a thermal break.  In my case I poured my floor half way ( 4" ) to bear on the wall, the exterior floating slab lies on the outside 4".  Yes, you will have 5 or 6 inches of heated slab hanging out beyond your OH doors, but your weatherstripping is always on a thawed slab.

Most importantly, make sure you budget for an inch of spray foam into the wall cavity as part of your wall insulation.


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## hondaracer2oo4 (Mar 7, 2016)

Thank you for your insight, everything makes sense around the garage doors and the service door. My only questions is about the 1/2 inch foam board against the frost wall around the inside perimeter. So you will always have a 1/2 inch of foam board exposed and even with the floor around the perimeter?


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## 700renegade (Mar 8, 2016)

In truth, I used regular impregnated expansion joint material instead of 1/2" dow.  You seemed more concerned on the thermal break than I was, so I suggested the 1/2" Dow.  I was happy with the black expansion joint stuff. I was ( and am ) concerned with where the pressures go when a 60x60 slab is heated and expands inside my foundation walls.  I think there is enough initial shrinkage in the slab cure that it doesn't get tight.

Yes the bond breaker is visible.  Doesn't cause me a bit of problem.  Most of my walls have shelving, workbench, table saws, etc, etc pushed up against them.  If you were really anal you could use a zip strip on top of the foam, and fill in that gap with a bunch of grey SikkaFlex sealant for cosmetic reasons.

One other lesson I wish I paid more attention to:  Make sure you pitch OUT the concrete edge at the OH doors enough.  In my case, in a driving rain, the water sneaks itself under the weather seal and into the shed.  Not a huge problem as I have trench drains, but it still irritates me.  Also we didn't nip out the concrete far enough to the sides, so I had to diamond grind the floor at the outermost 3" of my OH doors to get them to sit down tight.

Sticking that stem wall 6" above grade prevents a lot of problems in the future.


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## hondaracer2oo4 (Mar 8, 2016)

Thank you for your insight. Everyone says that a thermal break at the frost walls from the slab is an absolute must for a heated slab. But they all depict and show a 2 inch thick piece of foam board that sits against the frost wall and sits level with the floor slab, but no one talks about how this works in a garage where the floor is exposed. I see that some depict notching the frost wall when pouring the frost walls and then the foam sits in the notch and falling under the bottom of the stud wall but then you see the side of the foam if the frost wall ends 6 inches above the floor. Some others suggested a 45 degree bevel on the foam and then the floor would pour all the way to te wall but you would have a very weak edge. That approach makes no sense to me.


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## Karl_northwind (Mar 9, 2016)

standard would be 1" and tape the top at a 45 degree to be zero thickness at the top edge.  I would do something similar, stopping the slab under the door, and having a small separate pour outside to make the apron.  the thermal leakage in that 8" exposed to the outside is not small.


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## leon (Mar 9, 2016)

hondaracer2oo4 said:


> Hey guys, building a new garage this spring. 28x40 3 bay with full frost walls and poured floor. I am looking to install radiant heat in the floor. I know that I will have to basically make a foam tub to pour the floor in so that I have my underslab insulation and my thermal break to the frost walls. My question is how to do the thermal break to the frost wall? I have seen some drawings of a stepped in frost wall 6 inches below the floor height so that the frost wall insulation will have the stud wall land over it and you will have a fully poured floor all the way out to the stud wall. I think this is doable but what about where the cars pull in through the bay doors, how do I insulated the floor from the frost walls there?


=============================================================================================

Assuming your insulating the walls; and ceiling to an R 32 have you compared the cost per square foot of in floor heat 
at 12, 16, 18, 24, 32 and 36 inch spacing versus a number of hot water radiators on a single loop system for the three walls and hot water to air ceiling hung heaters on a second loop that would only activate when the doors open the entire system could be heated and used at a much lower temperature.  

I always worry about concrete floors in garages especially if they are not scored properly or installed properly with felt expansion joints and or floor drains. The entire slab foats unless it is properly installed with expansion joints and felt or the proper amount of rebar for the entire slabs square area. 

The so called "builder" that installed my fathers garage slab incorrectly and it looks like a spiderweb with all the cracks because it was not installed properly with a score slot or expansion joints.

At least with radiators the piping is exposed and you can find the leaks if you know you have them.

Another thing to consider is forced air heat in a large garage like that when comparing the cost per square foot as the registers can be placed in the ceiling and near the overhead doors if desired.

The other advantage is the registers can be closed and only a certain number of them left open by the overhead doors if desired to counteract the loss of heat as quickly as possible.

The thing is that heat is going to leave your garage the minute an overhead door is open and it will take a long time for the slab to recover. 

By having new steel or surplus cast iron radiators installed the heat loss is gradual and not massive and the heat in the garage will be back up to temperature sooner as the radiators are the only thing shedding head versus the entire slab.

You could install the radiators along both walls and have more than enough heat for the garage as the radiators are about 150 BTU per square foot of area in heating area for each radiator section and many large surplus radiators are still saved rather than scrapped.



I could see heating the apron on a separate loop if there is an ice buildup in your case but not having floor heat.


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## Highbeam (Mar 9, 2016)

hondaracer2oo4 said:


> Some others suggested a 45 degree bevel on the foam and then the floor would pour all the way to te wall but you would have a very weak edge. That approach makes no sense to me.



Oh no, this makes perfect sense. I used 2" on the edge with the top cut at 45. Works great. See, you won't load that edge and even if you do it is quite thick all the way to the razor edge.

Whether or not to use floor heat in a garage is another issue. I never hooked up my 1800 LF of tubes in the 5 years since I built the shop. Woodstove works great and after you insulate very well, it never freezes.


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## jebatty (Mar 10, 2016)

Very pleased with my decision for in-floor, 12" OC, in my 32 x 48 x 14 shop. My Tarm and 1000 gal storage tank (well insulated) also is in the shop. 2" foam under entire floor, and 2" perimeter foam as well. Floor heat is set at constant 61F with a differential of 1F. 35,000 Btuh input into the floor via a mixing valve set at 100F. What I really like is the lack of drafts and the warm floor. I stubbed in plumbing to add an overhead hot water unit heater, but never installed it. Shop temp stays very comfortable no matter what the outside weather conditions may be, from calm to windy, regardless of outside temp (-35F design temp). Floor responds very slowly to temp changes, which keeps very even heat in the shop. 

Maybe I was a bit lucky, but after six years not a single floor crack, even hair-line, except in the sawed crack lines, and the cracks that formed are barely visible. I think keeping the floor warm with insulation underneath basically eliminates expansion/contraction and floor cracking.


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## hondaracer2oo4 (Mar 10, 2016)

All of the responses are great, I am certianlly looking for opinions both ways as well. I figured that you only get one chance to put the radiant in, if I never use it I never use it but I wont regret not putting it in the floor. I plan to heat the garage to 45-50 degrees all the time and place a modine or similar up in one corner for when I want to bring the garage up to temp. What did everyone else do about the thermal break around the garage door apron area? Just lay down 2 inch on the top of the frost wall where the floor will get poured over and up the sides of the frost wall at the edge of the door frame? Same for the man door? Anyone do the thermal break somehow across the apron to separate it from the outside?


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## Karl_northwind (Mar 10, 2016)

hondaracer2oo4 said:


> All of the responses are great, I am certianlly looking for opinions both ways as well. I figured that you only get one chance to put the radiant in, if I never use it I never use it but I wont regret not putting it in the floor. I plan to heat the garage to 45-50 degrees all the time and place a modine or similar up in one corner for when I want to bring the garage up to temp. What did everyone else do about the thermal break around the garage door apron area? Just lay down 2 inch on the top of the frost wall where the floor will get poured over and up the sides of the frost wall at the edge of the door frame? Same for the man door? Anyone do the thermal break somehow across the apron to separate it from the outside?


I saw a great detail for that at last week at a conference.  it essentially was to continue the perimeter 1" inside insulation right across the door opening under the seal for the OH door.  it was cut to a taper at the top, and then had a heavy rubber seal gasket glued on top.  the outside apron portion was poured on top of the frost wall separately. the IR camera photos were most impressive.  wish I'd done that.


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## Karl_northwind (Mar 10, 2016)

The question of whether to do in-floor or not is the real question.  it basically comes down to how you are going to use the space.  occasional use space that will be left to freeze, minimal insulation, don't bother.  it takes too long to come up to temperature to use it for a weekend.  if it has to be kept at a steady 50 degrees all the time, and you have or can do pretty good insulation, in floor is a great way to go.


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## Buzz Saw (Mar 10, 2016)

Karl_northwind said:


> I saw a great detail for that at last week at a conference.  it essentially was to continue the perimeter 1" inside insulation right across the door opening under the seal for the OH door.  it was cut to a taper at the top, and then had a heavy rubber seal gasket glued on top.  the outside apron portion was poured on top of the frost wall separately. the IR camera photos were most impressive.  wish I'd done that.


Do you have any pictures or diagrams of this method? I kind of follow the idea but a picture would really help.


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## hondaracer2oo4 (Mar 11, 2016)

The walls are going to be 2x6 with r21 fiberglass( I am maticulous about fitting it correctly with no gaps or compressions. The cieling is going to be 16 on center 16 deep I joists with r38 insulation in them. Good windows and doors. I will build an insulted trap door to the second floor. So the garage will be well insulated and all gaps in the framing wil be chaulked or foamed. Should be a tight well insulated space. I want to keep it at 45-50 all the time with the slab. A modine in a corner would bring it to 60 during the times when I would be out there. I just think that the slab is the most efficient option to keep the garage at that 45-50


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## hondaracer2oo4 (Mar 11, 2016)

I am in New Hampshire so yes it is cold. So I guess the 45 bevel cut is the way to go for the thermal break to the frost wall. With the drop downs in th frost wall for the man door and garage doors I will lay foam down on the bottom if the drop down and bevel cut pieces on the side of the frost wall. Everyone seems to have a different technique for doing the thermal break under where the garage door lands on the apron. I am not a fan of using foam board up to a point and then using some sort of chaulking to fill the gap the rest of the way to floor level, I am concerned about the longevity of that technique with cars driving over it but maybe I am just being to cautious. I do like te rubber strips to seperate the floor from the drive up apron but does it provide a good thermal break? If anyone has pictures of their foundation in progress I would love to see them. Is the glycol nescasary in the floor loops?


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## leon (Mar 11, 2016)

Greetings,

Antifreeze is used in heated car wash floors to keep them and 
the aprons hot and drying constantly.

If you use the steel or cast iron radiators you will have less work and 
the garage will stay warmer longer simply because of the radiators 
shedding heat. If you place foil insulation board behind them to reflect
the heat you will be even warmer in the garage.

Running a single pipe heating loop with cast iron or steel radiators is both 
cost effective and allows for quicker recovery as the radiators store a 
huge amount of heat in the water and even keeping the water at 
60 degrees translates into a huge heat bonanza if you place the steel 
or cast iron radiators on the three closed walls using foil backed insulation 
board and piping is simple as the pipe follows the walls and over the doors 
to the modine if used and then back to your boiler.  

You can save money and invest in sand mix concrete slab with more 
rebar and mesh too to make it stronger. You just have to make sure 
you have a felt slab separator every eight feet or so to protect the 
slabs from cracking and spidering. 

I could see spending money on heating the garage apron as that is where 
a lot of ice will build up from opening and closing the overhead doors.

As long as you follow the building code for the climate, snow load and 
the local zoning codes you should not have many issues with heating your project.


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## hondaracer2oo4 (Mar 11, 2016)

Is a heated slab not the most efficient way to keep a space at an even consistent temp?


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## Karl_northwind (Mar 11, 2016)

hondaracer2oo4 said:


> Is a heated slab not the most efficient way to keep a space at an even consistent temp?



heated slab is.  and 100,000 lbs of concrete holds a whole lot of heat, and will bring the air temperature right back up when the OH door closes.  fair chance the heating loop won't even turn on.


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## Karl_northwind (Mar 11, 2016)

Buzz Saw said:


> Do you have any pictures or diagrams of this method? I kind of follow the idea but a picture would really help.


none that I can share, as they're not mine.  the general idea is to do the same bevel up to the slab top, and do a pour inside and one outside.  home depot sells  a heavy rubber air seal for under garage doors that would cover any gap nicely.


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## hondaracer2oo4 (Mar 11, 2016)

So I am a little confused about the bevel under where the garage door lands and then you said to put a rubber strip from Home Depot to fill the gap? Are you saying to just bring the foam up to a half inch or so below what will be the final floor grade Hieght and then fill the gap with the Home Depot rubber to bring it level with the floor ?


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## Fred61 (Mar 12, 2016)

Well, I have never done this on any slab I've poured even though my policy over the last few years is to always install tubing on every one but this problem has kept me awake a few times. If I were to pour another slab (which is highly unlikely) I would lay a rugged piece of angle iron 2 inches X whatever the concrete thickness is under the door. Tuck my foam insulation behind the angle iron which doubles as my form. The 2" dimension covers the form. Then pour the floor. This will give you a nice straight and flat jam for your door seal. Then pour the apron separately. Be sure to pin it well to the top of the frost wall.
When I was a youngster back in the 50s and 60s I worked in my dad's shop which he always kept warm with oil hot air heat but I was always cold. Here it s 2016 and my lower legs and ankles are just starting to thaw out. Remember, it's not how hot but how comfortable. When you open the big roll up door long enough to get a vehicle in, you're only loosing some warm air which is so low mass that it will re-heat before you notice it. You could easily drop the temperature 3 to 5 degrees with radiant and still feel comfortable.
The perimeter foam insulation cut at 45 degrees works well. Just remember to have a good supply of good porous backfill there for your excavator operator to tap and don't turn your back on him. Be sure he brings his compactor and USES IT. Words of experience!


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## hondaracer2oo4 (Mar 12, 2016)

That piece of angle iron standing up with the 2 inch leg covering the top of the foam is a good idea to protect the top of the foam. I find it odd that some people don't think that a heated slab is the most efficient way to keep a well insulated garage at an even constant heat. Since I will be likely using anti freeze in the system since it seems like people think that it is best practice and using a flat plate to isolate myself the system does anyone see any reason not to use regular aqua pex vs o2 barrier pex?


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## Buzz Saw (Mar 12, 2016)

I'm going to use  PERT.  It's made for radiant floor heat. 1/2" is about $0.35 / foot.


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## Fred61 (Mar 12, 2016)

Right or wrong, one thing I do when pouring, is pressurize my loops to 25 psi during and keep the pressure on a few days after the pour. Keeps the tubing from getting crushed and also reduces the pressure on the concrete when heat is applied. No spider cracks here!


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## Highbeam (Mar 18, 2016)

hondaracer2oo4 said:


> Is a heated slab not the most efficient way to keep a space at an even consistent temp?



A heated slab is not "efficient". The heated slab is just the delivery device. You can send water to the slab heated by burning 100 dollar bills and it will be the least efficient way to heat your shop that I can imagine.


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## huffdawg (Mar 18, 2016)

Here's a graph that  shows what my heated floor has been doing for the last 48 hrs. It  is 36x24 ,4 loops @ approx 150' 1/2" hepex on 9" centres. The insulation underneath the 6" slab is 2" high density styrofoam boards. I didnt use any on the sides. when the concrete dries it shrinks and there is a 1/4" air gap around the perimeter. Also we dont get frost below the surface here very often..  It heats roughly 1800 sq ft.


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## 700renegade (Mar 23, 2016)

Hondaracer,

I don't like to bash other's opinions, but have to opine here.



leon said:


> The thing is that heat is going to leave your garage the minute an overhead door is open and it will take a long time for the slab to recover.





leon said:


> If you use the steel or cast iron radiators you will have less work and
> the garage will stay warmer longer simply because of the radiators
> shedding heat.



The misdirection in those statement proves that he's never had the fortune to work in a shop with a heated floor.  Find me one person that's installed a properly working in floor heat system and regretted it, and I'll mail you $100.


Lets do some high school math:
What is the highest mass element in your shed:  the concrete floor by a factor of 10.  Your 6" slab would weigh 250,000#
A 28x40x14 shed contains 1160# of air. If you left your OH door open long enough to exchange every molecule of inside air with the outside, you would have lost an 'astounding' 11,000 BTU of heat in the air.  BIG WHOOP.  That takes 2# of wood to burn to replace.  Assuming it gets inserted via your floor it lowers it's temp by 0.044 degrees.

A shop with a heated floor returns to a comfortable workplace in almost a mystical fashion the instant the door is closed.

I'll offer some advice - don't pony up $ too soon for the Modine to bump the shed temp up from 50* to 60* on occasion.  You will never use it.  Scouts Honor.  Heat your shed with the floor to 55* instead and you will be much happier and take very little more energy.  Spend the modine money towards the $2000 it would take to spray foam the walls 1".

Hydronic floor heat and spray foam are an unbeatable combo.


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## leon (Mar 23, 2016)

UM let say me say first that I never insult anyone or their opinions on this forum 
nor do I feel the need to. I was not misdirecting him either.

He also stated he was not going to heat the building all the time at a higher temperature
and a steel or cast iron radiator used for heating could be set with a manual thermostat 
on each radiator and keep the building at a comfortable temperature effectively, 

Heat goes to cold that is simple physics. You can cool a building down by opening an
overhead door. Your heat source has to have enough hydronic heat energy available to heat the 
open area back to the desired temperature. 

by properly insulating it to an R32 or higher the garage will not require much heat and number radiators 
would heat the building easily.

The more heavily an out building or for that matter any building is insulated the better it is 
at retaining heat and it loses less heat with standby losses due to windows or doors or overhead doors.
AND the faster it will come back the desired temperature. 

I said using steel radiators of any size was much less work and much less plumbing 
to fuss with that was my main point. A slab that is insulated from frost will hold plenty 
of heat from radiators or a Zurn hot water to air garage heater.

I also mentioned the apron to the garages doors is ideally where he would want tubing anyway to
eliminate ice buildups as that is where there is going to be a lot of ice anyway if read what I posted. 

He has not mentioned tubing spacing and whether he is going to use the so called thermal concrete 
either that adds to the cost which is something I explained extensively in my other posts.

A lot of buildings with overhead doors are heated with hanging steam radiators or steel or cast iron radiators and 
I also mentioned that by installing aluminum foam board insulation behind the radiators will push even more heat into
the building more effectively. 

A simple pipe run is all that is needed with hot water to air garage heater if desired for his use as he is not heating living space and we do not know his budget either or even if he has considered the tubing spacing nor has he mentioned it.


It would be better for him to obtain the books Classic Hydronics and Pumping Away before he spends any money on this.

OH and by by the way you can find a leak much easier with radiators than you can with in floor heating which requires you to shut the lights off pull down the shades and put a cat in there and it will lay down on the warmest spot in the garage or the room or run around with a stethescope to find it unless you buy the very expensive pex with a wire tracer in it. then you have to dig it up....................


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## maple1 (Mar 24, 2016)

*Your heat source has to have enough hydronic heat energy available to heat the 
open area back to the desired temperature. *

That is true. But you will need a LOT of radiators to match the heat energy (thermal mass) of a heated slab, all running a lot warmer water temps than a slab would.


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## leon (Mar 24, 2016)

Hello Maple One,


The BTU per gallon issue again rears its ugly head and 
since water cannot carry more than 10K BTU per gallon
no matter the temperature, that is the major issue. 
The larger the radiator in square feet the greater the amount of 
heat it can provide and they can provide 150 BTU per square foot 
of area or more. 
A long low radiator can provide the user with lots of heat quickly,
especially with steam or hot water with manual thermostat 
mounted on the radiator OF ANY SIZE.


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## Karl_northwind (Mar 24, 2016)

leon said:


> Hello Maple One,
> 
> 
> The BTU per gallon issue again rears its ugly head and
> ...



One gallon per minute at a 20 degree drop yields 10,000 btu per hour.  if you can operate at a  wider temperature drop, you have more heat available.  40 degrees drop=20,000 btu per GPM. 

you are correct, the larger the radiator, the more heat it can provide.  one the size of the slab will therefore be the best. (at low water temperature) 
and with the heat stored in the slab, it will recover more quickly without additional heat input.  

a long low radiator cannot be "of any size".  it has to be sized based on the available water temperature and heat load, which would include: heat lost by opening the door, bringing in an 8000 lb truck that is below zeroF and covered in ice and snow, and bring it to room temperature.  a slab will excel at that.


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## Fred61 (Mar 24, 2016)

Heat is also stored in everything else within the heated area including tools, machines and everything else that's heavier than air making the heat lost in the air exchange a non issue. That 8000 lbs. of cold steel will radiate somewhat but that's where in slab shines because that heat you're standing on overcomes or at least neutralizes that radiation. It's not temperature, it's comfort.


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## leon (Mar 24, 2016)

Karl_northwind said:


> One gallon per minute at a 20 degree drop yields 10,000 btu per hour.  if you can operate at a  wider temperature drop, you have more heat available.  40 degrees drop=20,000 btu per GPM.
> 
> you are correct, the larger the radiator, the more heat it can provide.  one the size of the slab will therefore be the best. (at low water temperature)
> and with the heat stored in the slab, it will recover more quickly without additional heat input.
> ...


========================================================================================

What I ment and glossed over was the fact that the garage he wants is 28 by 40 and is 1,120 square feet in area and 
a seven tube radiator that is 20 inches tall will have 4.25 square feet of radiation per section and that equals 264 sections of radiation equivalent to his proposed garages square area. He can line the three walls with surplus cleaned and tested radiators and accomplish the same thing and reuse perfectly good radiators that would end up at the smelter otherwise. 

If he skimps on insulating he saves nothing by installing floor heat. A small zurn heater wil provide plenty of heat to go along with salvaged hot water radiators at less total cost 

The plumbing is simple and faster as one continuous loop of galvanized or black iron pipe can be used to his advantage to the floor connection to his radiators across the door header then to his other radiators and the hanging heater and then to his apron and then to the forest eater.  

Why make it more expensive than one needs to? lots of garages have hot water radiators and Zurn water to air heaters.


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## maple1 (Mar 25, 2016)

I'm not sure it would be that much or any more expensive. Four rolls of pex & 2 manifolds, vs. an uncertain number of radiators and an overhead heater plus the plumbing for all of it? I see used rads here for sale quite often, but they're certainly not giving them away.


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## Karl_northwind (Mar 25, 2016)

not to mention all the wall space that is not available for things now.  Laying 1200 feet of pipe for a simple rectangular slab will take 2 guys a couple hours to lay out and put down.  and if you use cheap 02 per you can spend about $800 for the materials for that and be done.   you will spend that and more for enough radiators not to mention the time to clean, test, etc.  
it also does a nice job of drying out the floor.


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## leon (Mar 25, 2016)

Hello Maple1, Karl_Northwind,

It all boils down to an economics/opportunity cost problem.


minuses

1. buying thermally enhanced concrete
2. plastic anchor sheets for the Pex
3. Oxygen barrier pex
4. stone mix 
5. concrete shrinkage during and after curing if the slab is not saturated and kept wet 
using heavy canvas tarp and a thick layer of straw applied to hold tarp down and to 
hold moisture to increase slab strength during the curing process

Assuming: in both instances:
slab on grade construction stone backfill to below grade elevation 

1. slab is properly insulated against frost
2. foundation footers are dug to proper depth 
3. top soil is stripped away to actual depth of slab
4. crushed stone is laid in footer trench to support perimeter footer
5. rebar is installed to increase strength of footer foundation.  
6. foil backed insulation board is installed prior to pouring concrete in footers and for slab pour
7. 6000 Lb. sand mix with rebar tied into concrete mesh  

Not knowing what spacing is desired for the in floor heat loops or the inside diameter of the 
oxygen barrier PEX is another issue entirely.


Plusses:

1.surplus salvaged and tested radiators are used.
2. all plumbing connections are exposed 
3. less work as simple single pipe run is used with two connections(in/out) 
to slab apron and water to air Zurn heater at door way 
4. each radiator will have a manual thermostat allowing the shop to stay at a low
temperature when not in use.

====================================================================================


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## maple1 (Mar 25, 2016)

All those minuses should be done anyway, no matter how you heat the garage - except that if not putting pex in the floor, you don't need numbers 2 & 3, or course. And 'thermally enhanced concrete'? I don't know what that is.

Then if doing pex, the only ones I've seen done didn't use 'anchor sheets' (also not sure what those are even), they just tied the pex to the mesh - and used the same concrete mix as if not putting pex in. So the only added cost to the slab was the pex, and the time to lay it out & tie to the mesh. Slab should be insulated either way.

I've even been involved in a hockey rink build where the opposite was done - the floor was cooled. They just laid the pipe out & tied to the mesh. Piping was bigger than for infloor heat, but otherwise done the same way as heated slabs I have seen done. We have one heated slab in a small building here, also done same way. 

'Surplus' still costs - can't find used cast rads around here for less than $100 each, if that. Not tested, just pulled from old houses. If they are less, they are leakers & look like they should go for scrap.

Also, how do you control the heat in each rad with its own thermostat if it's all in one run/zone?


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## Buzz Saw (Mar 25, 2016)

leon said:


> It all boils down to an economics/opportunity cost problem.



I disagree.  It comes down to preferences, comfort, and usability of the building.  

The whole purpose of in slab in great heat without hearing and no visual appearance.  Maybe rads are your thing but I don't want them taking up valuable wall space in my workshop/man cave/garage/party center.


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## 700renegade (Mar 25, 2016)

It appears Leon in incapable of understanding that the original poster has already decided to install in floor heat and is looking for some advice in detailing his thermal breaks.
Leon please start your own post on "the many advantages of wall hung used cast iron radiators over in-floor heat" and we can all leave Hondaracer alone.


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## leon (Mar 25, 2016)

Hello Maple one,

Each radiator could have its own thermostatic radiator control valve that is connected to the lower tapping and the water flow would continue on to the next radiator or one radiators thermostatic control valve could control an entire wall of radiators if each wall had its own loop and had reflective foam board insulation to push the heat back into the open area rather than towards the exterior wall.   

A cast iron radiator can be heated using lower temperature water and for than matter will soak up the heat from the daylight coming through a window and you can run them at 100 degrees water temperature very efficiently using smaller piping. 

As far as lost usable space goes the area above a radiator lends itself well to shelving does it not it?

We  still do not know what size PEX he wants to use or the spacing or what his desired EDR "Equivalent direct radiation" is for what whatever he plans so were spitting in the wind here and for that matter he may just be trolling for information. 



To each his or her own


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## Buzz Saw (Mar 25, 2016)

@ HondaRacer2oo4, I'm pouring my building next week and have decided to put 2" foam directly under where the overhead door comes in contact with the floor.  I'm going to leave about 1" concretrete on top and use the expansion joint (when I pour the approach)for the thermal break for the top 1" of concrete.

This is the best solution I can come up.  I'll try and post some pics once I form the doors.


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## hondaracer2oo4 (Mar 25, 2016)

This thread has certainly generated some great conversation. 

Buzz saw, please grab some pics if you can. I will personably copy your approach.

Leon, I get that you love radiators. I think they have there place, I tried to convince my wife for one in the entry way in our house and one in the living room. The one in the entry way would quickly recover heat lost to opening the door. The one in the living room would be like a wood stove. She wouldn't bite on either. I don't want radiators taking up wall space in my garage. I would use a single hot water modine if I didn't go with in slab radiant. But I am going with in slab radiant, I don't know what your talking about with all that special concrete and special drying procedures. I have read a lot from very reputable in floor radiant slab company's and they mention non of that stuff. I will be using 1/2 pex attached to the mesh on the underside 12 inches on center. I will use concrete bricks to hold the mesh off the insulation. I will be using 6 mil vapor barrier first. Then 2 inch xps foam board under the slab and 2 inch xps around the frost wall on the interior to isolate the slab from the frost wall. I will probably do what buzz saw does to thermal break the apron. Should cost me around 1500 if not less. I am using recycled xps by the way at .25 cents per square foot. Helps lower the cost a lot.


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## Fred61 (Mar 26, 2016)

I would worry that the bricks that you use for spacers would weaken the concrete and invite cracking. The best way to space the mesh away from the insulation is to hook it and pull it up into the mix while pouring. This has always been the method for bringing the mesh up whether there is pex or not. There are concrete hoes made especially for this with a hook welded to the back. If you don't have one you can use a potato hook. You just must be careful not to pull it up too far. Take your time. There are some drivers that will rush you and some that will work at the pace you demand.


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## Fred61 (Mar 26, 2016)

Also, don't forget to order their highest pressure floor mix.


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## Buzz Saw (Mar 26, 2016)

Fred61 said:


> Also, don't forget to order their highest pressure floor mix.


Have any examples? 4,000psi?


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## Fred61 (Mar 26, 2016)

I used 3000 on my last pour and didn't get any cracking on my 6 inch slab but 4000 would give you a good margin of safety.


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## Buzz Saw (Mar 26, 2016)

Honda, here is what I've come up with so far.  I think it's going to work out pretty well.  Still need to backfill and put a string on the front of the 2x4 to get it straight.

This summer I'm pour the approach.  Until  the approach is poured I'll use 2x8's and plywood to protect the edge from breaking out.  I will not be driving on it until the approach is poured.


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## Buzz Saw (Mar 26, 2016)

Fred61 said:


> I used 3000 on my last pour and didn't get any cracking on my 6 inch slab but 4000 would give you a good margin of safety.


My uncle(who is also doing the pour) said 4,000 psi with fiber mesh is the norm for floors like mine.


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## hondaracer2oo4 (Mar 26, 2016)

Looking good. So it looks like you will have two inches or so of concrete over the top of the foam board at the garage door?


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## Buzz Saw (Mar 26, 2016)

I was trying for 1.5" but things didn't quite work out that way.  I still think it's going to work OK.


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## Fred61 (Mar 27, 2016)

I guess the one thing that would concern me is that the 2 inches over the insulation is only supported (attached) on one side. Concrete strength is poor when subjected to bend pressures. It's strength is in compression.


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## Karl_northwind (Mar 27, 2016)

looks nice.  unless you drop a corner of a mill or something on that edge, you won't have a problem.  fiber is awesome stuff.   you or your concrete contractor can get little wire "chairs" to set the 6x6 mesh on right before the pour.


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## woodsmaster (Mar 27, 2016)

I skimmed threw this post and wanted to add my 2 cents.

1. I don't think you would save much, if any money going radiators verses in floor.
2.  Special thermally enhanced concrete is not necessary in my opinion.
3. you should try to let the slab dry slowly weather or not you have heat in the floor.
4. as long as you have re-mesh in the floor so the concrete cant shift if it cracks its more than likely not going to leak weather it cracks or not. Don't ask how I know  When I cut the cement I did't know the cuts needed to go continuously from one side to other so I have a couple of cracks. no worries.
5. with in floor heat, the building will stay warm for days even without a fire going.
6. It is going to take a day or two to raise the temperature significantly if you need quick heat often it may not be the best option.
7. They sell spacers to put under the remesh to keep it spaced properly in the floor. tie the tubing to the remesh and use the spacers and you don't have to worry about having it to deep or not deep enough and cutting into it when you cut the concrete.

I have in floor heat in my shop and love it. I would also like to add a modine type heater for times when I'd like to raise the temp fast. sometimes I'm away from home most of the day for weeks at a time sometimes and turn the heat back to save on wood.


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## Buzz Saw (Mar 27, 2016)

Fred61 said:


> I guess the one thing that would concern me is that the 2 inches over the insulation is only supported (attached) on one side. Concrete strength is poor when subjected to bend pressures. It's strength is in compression.


I've though about drilling a hole and putting  some rebar through  the form to support the 2" when I pour the approach.


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## maple1 (Mar 28, 2016)

I have a question. Trying to educate myself a bit - I am hoping to build myself a garage in the next couple years or so.

What would be the issue, if you poured the approach & floor all in the same pour? Just run the concrete out the doorway - an extension of the floor?


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## Buzz Saw (Mar 28, 2016)

maple1 said:


> I have a question. Trying to educate myself a bit - I am hoping to build myself a garage in the next couple years or so.
> 
> What would be the issue, if you poured the approach & floor all in the same pour? Just run the concrete out the doorway - an extension of the floor?



Things to consider:

1.Cost - I understand in the end it's going to be the same cost, or slightly more, but In my case I'm  limited by money on hand.

2. Thermal Break - No sure how reliably   keep the foam board and expansion joint in place during the pour.  

3. Not sure how big of an approach I want/need yet.

4. Timing - I need this project to move forward so I get some interior work done. We are going to temporarily live in this building while we rehab the house.  House project starts real soon.

So nothing is wrong with pouring it all at once if you can overcome the issues/don't apply to you.  If this was just an unheated storage/machine shed it would be poured all at once.


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## gfirkus (Mar 28, 2016)

your approach needs to be separate. Don't use rebar from garage slab to approach either. Bad deal. The approach is a floating slab and will move up and down between seasons.


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## Buzz Saw (Mar 28, 2016)

gfirkus said:


> your approach needs to be separate. Don't use rebar from garage slab to approach either. Bad deal. The approach is a floating slab and will move up and down between seasons.


Never thought of the approach heaving.  Good call.


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## 700renegade (Mar 28, 2016)

Buzz Saw said:


> I'm pouring my building next week and have decided to put 2" foam directly under where the overhead door comes in contact with the floor. I'm going to leave about 1" concretrete on top and use the expansion joint (when I pour the approach)for the thermal break for the top 1" of concrete.


Buzz saw, what is your garage door going to seal against if that skinny strip of concrete cracks out of there ( which is possible since it's bearing on compressible foam ) ?  Also, since your future exterior slab could frost heave do you really want it doing so right at the face of your door?

Personally I'd push that heated slab out at least a few inches past the door and live with the few BTU lost out there.  You could always pull in your pex a touch at the OH doors so the slab temp is a bit lower there to start with.

Also, a trick I've used on commercial apron pours ( exterior slab on grade ) is to put them on foam board for the first 12 feet.  start with a 4' strip of 2" thick, then lay a 4' strip of 1", then finish with a 4' strip of 1/2".  This does a decent job of limiting frost penetration into the subgrade near the building face so It doesn't heave ( as much ).  The point of tapering the foam is to gradually transition to the unprotected state.  Anytime you introduce a different subgrade condition onto the slab you are asking for a crack to form.  Also never make the mistake in clayey or silty soils of putting a big layer of gravel under the exterior slab, as it is an invitation to heaving.  Concrete right on compacted native clay soil is superior to building a bathtub full of water under your slab.


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## hondaracer2oo4 (Mar 28, 2016)

Interesting points renegade. For one, the foam is stronger in compression psi than most compacted sub grades are I believe. Interesting point about the clay being better than a 6 inch lift of 3/4 gravel compacted. The consensus it seems is that the 6 inch of gravel is necessary for a capillary break to keep the moisture from wicking up through the slab or bringing the moisture and soaking the underside of the vapor barrier.


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## Buzz Saw (Mar 28, 2016)

700renegade said:


> Buzz saw, what is your garage door going to seal against if that skinny strip of concrete cracks out of there ( which is possible since it's bearing on compressible foam ) ?
> 
> Also, since your future exterior slab could frost heave do you really want it doing so right at the face of your door.



Worse comes to worse I'll cut out that strip and install some square tubing to take it's place.  Granted it could happen but I think it will be ok as long as I have an approach when I drive over it.  In 2 inches of run I gain 2 inches of fall bring my concrete to 4" pretty quickly. 

The future exterior slab will also have an expansion joint to give me a 1/2" buffer, so I'm not sure if a heaving slab would affect the door.  

Also since I do have a decently sizable  compacted stone lift I do intend on running a tile under the lift to drain water before I pour the approach.

Sounds good on paper.....Hope it works in real life........       This is my "you have me questioning things" face. [emoji52]


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## 700renegade (Mar 29, 2016)

Buzz Saw said:


> I'm not sure if a heaving slab would affect the door.


Since we are thinking......  if it does heave, when you get a late winter driving rain against your OH door, and the water sheets down the door, where does the water go?
A. into the shed
B. Possibly worse - into the joint and soaks under the exterior slab, so that tomorrow the slab heaves a bit higher still.

I've seen my mother-in-laws garage door trim torn clean off the shed by her slab heaving 3".  Brother-in-law was well meaning and perplexed "gee I put nearly two feet of sand under that slab, I can't believe this is happening!"   I had to draw him a diagram of the bathtub full of water he unintentionally created.

I design streets and highways for a living and I don't think most people realize there is almost zero concern for the strength of the subgrade when designing a concrete pavement.  What matters?  Uniformity, Uniformity, Uniformity.......and after that, thickness.   A perfectly uniform subgrade is critical to a slabs long term performance.  There is only one reason we put a foot or more of gravel base under the concrete - it is ONLY so that the trucks and the paver have a spot to drive on that keeps them from leaving ruts before the concrete goes down.  Why do you put gravel under your shed floor?  It has nothing to do with the floor strength, but it sure is handy to level out so you can achieve the holy grail of uniformity.

Buzz Saw has no option but to float the slab.  Hondaracer (with a frost wall) has an option to:
> Run the interior slab past the door 6" and put plenty of pitch away ( keep driving rain away from coming inside)
> bear the exterior slab on the outer 3" of the frost wall ( so it cannot settle )
> put foam under the outside slab ( limit frost penetration so it does not frost heave )

Note that all the discussion of 2" foam thermal breaks ( which I consider a tad excessive, just me.... ) makes detailing out a good solid transition to your apron more difficult.  You only have an 8" wide wall to bear on.


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## Buzz Saw (Mar 29, 2016)

Now the gears are really turning.  I have till Thursday morning to make changes.  I  could move the 2x4 out 3" and cut the foam off and move it out.... But then I would have to dig out some of the stone holding my foam in place so I can compact it.     What to do......[emoji20]


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## Fred61 (Mar 30, 2016)

Not only do you need to worry about driving rain. You need to worry about splash that will occur every time it rains because your door is on the drip side of the building as opposed to being on the gable end.


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## Buzz Saw (Mar 30, 2016)

Fred61 said:


> Not only do you need to worry about driving rain. You need to worry about splash that will occur every time it rains because your door is on the drip side of the building as opposed to being on the gable end.


With gutters how does this differ from the gable end?


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## huffdawg (Mar 30, 2016)

I just cut the foam off and overlapped the floor foam and the wire mesh to the edge of the form. I don't think that triangle piece of foam is giving you much rvalue anyway


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## Fred61 (Mar 30, 2016)

Buzz Saw said:


> With gutters how does this differ from the gable end?


I assumed I was seeing a metal roof. I don't know much about Ohio weather but in Vermont the snow sliding off the roof takes them down every winter.


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## Karl_northwind (Mar 30, 2016)

huffdawg said:


> I just cut the foam off and overlapped the floor foam and the wire mesh to the edge of the form. I don't think that triangle piece of foam is giving you much rvalue anyway


it's not about straight R value, it's about breaking the thermal contact. 1/4" of foam is way better insulator than 1/4" of concrete. it'll make a big difference.  a piece of treated wood will do it as well.


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## huffdawg (Mar 30, 2016)

Karl_northwind said:


> it's not about straight R value, it's about breaking the thermal contact. 1/4" of foam is way better insulator than 1/4" of concrete. it'll make a big difference.  a piece of treated wood will do it as well.


Ya good point.. I dont think I lose a whole lot of heat through mine though, its 6" thick and the tubing is held back 18" from the opening..  I prolly lose a lot more heat through the 10-6 x 10   2" insulated  overhead door..  but you guys get a lot colder winters than us .


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## 711mhw (Mar 30, 2016)

woodsmaster said:


> 7. They sell spacers to put under the remesh to keep it spaced properly in the floor. tie the tubing to the remesh and use the spacers and you don't have to worry about having it to deep or not deep enough and cutting into it when you cut the concrete.


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## lotawood (Mar 31, 2016)

711mhw is that a re-pour over existing concrete?  Is there insulation underneath?


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## 711mhw (Apr 1, 2016)

That was some weird insulation with a 1/2" of concrete on it. Used material from an industrial type flat roof. It was 2" of blue DOW with the 1/2" 'crete, I think used for insulation and "ballast" instead of loose stones. T&G all 4 sides and strong & cheap.
But no, not a re pour over existing. 
I had some left over and made a stay in place forms for another slab, it provided the stregnth for a form, with 2" of insulation and a nice exposed aggregate type of durable finish for the portion that was above grade, all in one!


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## 711mhw (Apr 1, 2016)

Not the best pic, but it has a decent finish and is a good solution for exterior insulation on frost wall type const.
I cut the foam back to apply the treated 2x6 plate that also held the panels in place for the pour.


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## 711mhw (Apr 1, 2016)

Forgot the damn pic!


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## woodsmaster (Apr 3, 2016)

Fred61 said:


> I assumed I was seeing a metal roof. I don't know much about Ohio weather but in Vermont the snow sliding off the roof takes them down every winter.


 Then they weren't installed right. the gutters have to be lower than the roof so the snow will slide over them. then you can  put snow jacks on the roof also and that will keep most of the snow from sliding off and it will melt into the gutter.


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## Buzz Saw (Apr 3, 2016)

woodsmaster said:


> Then they weren't installed right. the gutters have to be lower than the roof so the snow will slide over them. then you can  put snow jacks on the roof also and that will keep most of the snow from sliding off and it will melt into the gutter.


I still need to add the snow Jacks to my roof.  I might do the single piece of angle instead of the individual jacks.


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## Buzz Saw (Apr 3, 2016)

Well after much debate, consideration, and input from multiple sources I decided to remove the foam in the OH doorways and push the concrete out to the edge of the building.


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