eps or epx foam under slab

[eauzonedan]

Curtis:
This is how I handled it on my Northern Wis Shop. I used a 1' high perimiter curb wall formed as part of the slab to allow me to go with 9' clear interior height and still use 8' studs/sheet goods. That approach also allowed me to better match surrounding grades and still keep the siding from being too close to the ground. If you read the fine print on the load capacity of the foams - they tell you to de-rate the stated capacity to 1/3 the nominal carrying capacity for continuous loading. So I upped the foam to the 60 psi rated stuff under the perimiter load bearing areas of the building that carried the weight from the upper floor and roof (the area of the slab perimiter typically thickened for that very reason). It's readily available from anybody that would supplly comercial building materials. The 25 psi foams should have plenty of capacity if the only loading is the floor slab (and not the building loads). I wrapped the full perimiter area of concrete with 4" of rigid also....... Have yet to fire the in-floor up, so can't tell you how well the heat loss worked, but after two years there is no sniff of any cracking. My thought was better safe than sorry ........after the building is up it's pretty tough to try to re-do . The foam doesn't like UV for long exposure, so I covered it with alluminum and installed a z strip to keep the rain off it. Ended up looking pretty decent. I only ran a single piece of 2" between the O/H doors and the aprons. Thought the 4" gap to be a bit strong if driving over it. Good Luck!
Dan

 

[Bret Chase]

I used EPS under my slabs and it is fine. You have to make sure to get the higher density EPS for under the slab though. Under the slab is 1.5 lb foam, the foam I used on the inside of the basement walls is 1.0 lb.
This is the company I got my foam from. (broken link removed to http://www.thermalfoams.com/default.asp) They were very helpful.

No, the regular blue dow foam is just fine.... it gives you the same 3000#/sq.ft as the assumed ground load..... there is generally no need to go to Dow Hiload 100... (14,400PSF) at $108 a sheet...

 

[BoilerMan]

Personally I have to say, I'm glad the IBC hasn't made it this far north. I was just at a town meeting and we voted out the MUBC as we are a towm of less than 4,000 residents. It's interesting that a "human occupancy" has to have a frost wall, but a "detached building" can be monolithic. The base (gravel) has all to do with the frost's heaving force and foam can stop frost penetration. Drainage is also a deciding factor, I'm on blue (hard) ledge and excivated a foot of topsoil and filled and leveled with bank run gravel. To me a monolithic slab is stronger as it's all one pour and the load bearing is transferred into the "floor surface" to further spread out the building load, rebar should be bent into the thickened edge and all tied to the lateral rebar in the shollow footer making it much stronger than a sepetate footer and floating slab IMHO. But I can't tell the code that.............. This is America isn't it.
Rant over, I'm still fired up from the town meeting about this subject, and none of the selectmen having building skills.

TS

 

[Fred61]

Rant over, I'm still fired up from the town meeting about this subject, and none of the selectmen having building skills​

Most of our laws/rules are made by people who don't know crap about the subject.

 

[ewdudley]

To me a monolithic slab is stronger as it's all one pour and the load bearing is transferred into the "floor surface" to further spread out the building load, rebar should be bent into the thickened edge and all tied to the lateral rebar in the shollow footer making it much stronger than a sepetate footer and floating slab IMHO. But I can't tell the code that.............. This is America isn't it.

I was making the same argument to my code enforcement officer here in NY and he said code is footers 42" below grade. But he liked the idea and said he might be able to do something if I came back with more engineering to back it up.

Meanwhile he dug into the NY code and found a section that covered insulated grade beams specifically as an approved alternative to footers.

So 'everybody knows' footers are required, including the zone enforcement experts, but it is possible that what everybody knows is contradicted by the actual code. And it is possible that a building inspector might go the extra mile if you're lucky enough that they turn out to be an ally.

Here's some photos of the forming. Unfortunately all the gravel work and the horizontal insulation were covered over by the time I got around to taking photos, but the basic idea is to have tiled drainage below a gravel layer with the insulation next, extending 2' down and away from the base of a 1' x 1' reinforced insulated concrete beam. (Would have much preferred Dow blue board but couldn't get what I needed in the time frame available.)

http://summerwages.blogspot.com/

 

[BoilerMan]

Nice work EWD! There are few to no sturctures in that era here, most go back to 1880s with a huge boom in the roaring 20s and again in the 60s. I used the Pink "Owens Corning" board as that is what my building supplier carried at the time. I was not aware of any differences other than color and manufacturer O.C. vs. Dow.

TS

 

[ewdudley]

I used the Pink "Owens Corning" board as that is what my building supplier carried at the time. I was not aware of any differences other than color and manufacturer O.C. vs. Dow.

Before I built the shed over where the 'rain harvesting system' tanks are, I used a bunch of scrap insulation board to cover the area where the pipes came in to the house. I used gravel, then plastic, then insulation, then more plastic, topped off with a couple inches of grave. With rain water and snow melt from above and condensation from below, it completely failed to keep the insulation dry.

There was a mix of Dow blue and Corning pink, and when I dug the mess up to do the shed the Dow blue was crisp and bone dry while the pink was flexible and water-logged, so that's where I get my opinion. But I am betting that the pink will do the job if it's kept well drained.

 

[BoilerMan]

Gulp...........

TS

 

[ewdudley]

Gulp...........

TS

I wouldn't be too worried, I had built that patio off to the right a few years before and used pink to form the 48" concrete footings. When we did the shed I exposed some of that. Backfilled with gravel and under the wide eaves the pink was in real good shape. I'm just saying given a choice blue is better in adverse conditions.

 

[Bob Rohr]

Here is a link to some excellent reading and codes regarding underslab insulation.

(broken link removed to http://www.healthyheating.com/Radiant_heating_designs/insulating-underslabs.htm#.UWBuqnD6pJ0)


Consider also having a bug repellent sprayed before insulating. Here in Missouri I detected 3 different bugs boring into my Blueboard and also the foam ICfs I used for the foundation. It seems warm conditions under a slab are a big draw for bugs to take up residence.

Also consider a tight tube spacing. I'd even go to 6" on center so you could run that slab with supply temperatures as low as possible, perhaps 90F. To really leverage your tank output charge to 180- 190, and run it down to 90F with good insulation and tight tube spacing. That provides for a 100 degree ∆T from your tank temperature!

 

[Floydian]

Here is a link to some excellent reading and codes regarding underslab insulation. (broken link removed to http://www.healthyheating.com/Radiant_heating_designs/insulating-underslabs.htm#.UWBuqnD6pJ0)

My favorite paragraph from the above link:

"When you build to code you essentially get a “D” grade – that is, you didn’t fail but you missed the opportunity to earn an A or A+. If you don’t understand the words, ‘missed opportunity” then you have never considered what it takes to increase the insulation under a concrete slab after it has been poured."

Noah

 

[nate379]

Looks way better than current codes around here for a SOG

how did you get that past codes?

We used 2" XPS foam under my house and garage when the slab was poured. I forget the brand now, but it was about 1/2 the price of the blue board. Something around $18 a sheet vs $36

 

[Bret Chase]

Personally I have to say, I'm glad the IBC hasn't made it this far north. I was just at a town meeting and we voted out the MUBC as we are a towm of less than 4,000 residents. It's interesting that a "human occupancy" has to have a frost wall, but a "detached building" can be monolithic. The base (gravel) has all to do with the frost's heaving force and foam can stop frost penetration. Drainage is also a deciding factor, I'm on blue (hard) ledge and excivated a foot of topsoil and filled and leveled with bank run gravel. To me a monolithic slab is stronger as it's all one pour and the load bearing is transferred into the "floor surface" to further spread out the building load, rebar should be bent into the thickened edge and all tied to the lateral rebar in the shollow footer making it much stronger than a sepetate footer and floating slab IMHO. But I can't tell the code that.............. This is America isn't it.
Rant over, I'm still fired up from the town meeting about this subject, and none of the selectmen having building skills.

TS

The worst of the IBC was the 2000 edition, which is what Sanford had adopted for a while... it added at LEAST 20% to the cost of the building for basically NO benefit whatsoever... During that era, I put up a building by the airport... the code driven design ended up requiring the purlins to be 18" OC.... and this building stands next to 20# buildings from the 70's... and their 6' purlin spacing... and those 40 year old buildings, with 2" insulation are still standing.

monolithic slabs have their purpose, but they are certainly NOT stronger from a load bearing and seismic perspective.

 

[Bret Chase]

Here is a link to some excellent reading and codes regarding underslab insulation.

(broken link removed to http://www.healthyheating.com/Radiant_heating_designs/insulating-underslabs.htm#.UWBuqnD6pJ0)


Consider also having a bug repellent sprayed before insulating. Here in Missouri I detected 3 different bugs boring into my Blueboard and also the foam ICfs I used for the foundation. It seems warm conditions under a slab are a big draw for bugs to take up residence.

Also consider a tight tube spacing. I'd even go to 6" on center so you could run that slab with supply temperatures as low as possible, perhaps 90F. To really leverage your tank output charge to 180- 190, and run it down to 90F with good insulation and tight tube spacing. That provides for a 100 degree ∆T from your tank temperature!

This is why I like Tuff-R (Polyisocyanurate) for below ground.... if the bugs eat it, they die... lol

 

[Bret Chase]

Looks way better than current codes around here for a SOG



We used 2" XPS foam under my house and garage when the slab was poured. I forget the brand now, but it was about 1/2 the price of the blue board. Something around $18 a sheet vs $36

My comment about codes had nothing to do with the insulation... it was with the monolithic slab and a complete lack of a frost wall, which is generally mandatory in this state...

 

[BoilerMan]

This is why I like Tuff-R (Polyisocyanurate) for below ground.... if the bugs eat it, they die... lol

Ployiso, takes on water and is NOT for below grade at all. The fact that Dow puts the aluminum over it is to keep the moisture from destroying the R-value, it is water permiable.

TS

 

[Bret Chase]

Ployiso, takes on water and is NOT for below grade at all. The fact that Dow puts the aluminum over it is to keep the moisture from destroying the R-value, it is water permiable.

TS

it still makes bugs die...

 

[nate379]

Must be something new. I lived in Maine for almost 20 years....

My comment about codes had nothing to do with the insulation... it was with the monolithic slab and a complete lack of a frost wall, which is generally mandatory in this state...

 

[Bret Chase]

Must be something new. I lived in Maine for almost 20 years....

well... I've seen exactly one monolithic slab... with a "human occupation" use, since 1989....

 

[nate379]

I can think of 5 or 6 just in the town I grew up... a town of about 2000 people. Don't really have building codes "per say" though.

That photo with the insulation is exactly how my house and garage is, as well as most of the 12 houses in my neighborhood.

 

[BoilerMan]

I've lived in Maine all my life, and I can speak of more than a dozen monolithic slabs that are for "humans"........ My house, uncle's place, old apartment we lived in before we built, some friends from church, come to think of it, it's only commercial buildings that I've with floating slabs and footings. Slab houses are not at all common around here, the houses I speak of are all under 20 years old. There are many, if not all garages are monolithic pours though.

My reasoning for a slab:
I'm an electrician and I've been way too many wet, damp, flooded basements, which are useless IMHO
Wet radiant heat with high mass is unparrelled for comfort and inherrant storage for wood heat
No blasting required if ledge is close to surface
Radon which is rampent in our area
Simplified construction for novice (me) builders who do everything themselves
Keeps my hoarding temdencies in check LOL

Bottom line is insulate under any slab even if you don't plan to heat the building, because someday someone may turn it into living space and I lived in a converted two car garage (apartment mentioned above) with carpet right over that cold uninsulated concrete and it ain't no fun............

TS

 

[nate379]

My Dad did not insulate or vapor barrier the slab in the first garage he built. In the summer it sweats so bad that you have to squeegee the water out. Even with a fan going and doors/windows left open it does it. Most of his tools are equipment are pretty rusty from that.

Garage #2 he put 6 mil plastic down and no problems. The 2 garages are about 50ft apart.

 

[Bret Chase]

I've lived in Maine all my life, and I can speak of more than a dozen monolithic slabs that are for "humans"........ My house, uncle's place, old apartment we lived in before we built, some friends from church, come to think of it, it's only commercial buildings that I've with floating slabs and footings. Slab houses are not at all common around here, the houses I speak of are all under 20 years old. There are many, if not all garages are monolithic pours though.

My reasoning for a slab:
I'm an electrician and I've been way too many wet, damp, flooded basements, which are useless IMHO
Wet radiant heat with high mass is unparrelled for comfort and inherrant storage for wood heat
No blasting required if ledge is close to surface
Radon which is rampent in our area
Simplified construction for novice (me) builders who do everything themselves
Keeps my hoarding temdencies in check LOL

Bottom line is insulate under any slab even if you don't plan to heat the building, because someday someone may turn it into living space and I lived in a converted two car garage (apartment mentioned above) with carpet right over that cold uninsulated concrete and it ain't no fun............

TS

I'm not arguing against insulating under a slab... at all.... it's been S.O.P. for us for many, many years.... but we still do have to build to the print/specs... if the specs call for insulation only in the outer 4'.... that's what they get... I hear owner complaints all the time.... All I can tell them is that their building is operating as designed, I built what they paid me to build. Getting blamed for what the architect designed... I just *love* that one.... but anywho...

I've got one of those damp cellars.... not a basement.... the cellar in my nearly 150 year old home has a rubble/granite foundation and a dirt floor. it's damp all the time, but is only really wet in the spring. the house leaks so much air that Radon really isn't a concern for me... it might in the future as I tighten this thing up.

 

[Highbeam]

Back to the OP of the thread... You can certainly use EPS, the white stuff, under the slab. The manufacturer rates their product for this application. It works great and is much cheaper than XPS (pink/blue). I bought the 25 psi EPS from the factory and put it under my 30x60 slab with radiant heat tubes.

 

[curtis]

Back to the OP of the thread... You can certainly use EPS, the white stuff, under the slab. The manufacturer rates their product for this application. It works great and is much cheaper than XPS (pink/blue). I bought the 25 psi EPS from the factory and put it under my 30x60 slab with radiant heat tubes.

Thanks highbeam, are you by chance a member on garagejournal? I think i remeber that name from there about topics just like this.