# Insulation calculations



## Ashful (Dec 8, 2014)

I'm converting an old'ish (1850's?) carriage barn on my property to heated and insulated shop and storage space.  Heating will be via dual mini-split.  Building envelope is 1200 sq.ft. heated plus 300 sq.ft. unheated space.  Spray foam is high on the list of insulating options, given style of construction.

I'm trying to make choices on how thick to go with insulation (eg. R7 per inch in closed cell foam) on walls and ceilings, and whether to make unheated space part of insulated envelope, and even what garage doors to buy (R9's that look nice or R16's that don't).  I'd like to find a set of formulae I could use in determining how much to spend on the insulation, in various areas (doors, walls, roof), versus how much those extra BTU's will cost me in heating.  Any good on-line calculators or sites describing trade-offs, that you can recommend?

Thanks!


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## Bret Chase (Dec 8, 2014)

how is the barn framed?


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## Ashful (Dec 8, 2014)

Original frame is 8" x 6" sills with 6" x 6" posts and beams, and 3" knee braces.  Standard 19th century timber framing, at least for our locale.  I failed to notice what type of mill the timber was sawn on, but now that you ask, I should try to do so before it's all covered up!  Being a barn, things are somewhat dirty and it has been wet at some point in it's past... the saw mill marks are not abundantly apparent.


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## Ashful (Dec 8, 2014)

Before:






Now:


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## midwestcoast (Dec 9, 2014)

Did you try googling Heat Load Calculators that HVAC folks use?


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## Circus (Dec 9, 2014)

Insulation has a deminishing return as thickness go's up. From R1 to R19 savings can be 500% but from R19 to R38 savings might be 5%. Investigate fiberglass batts for pole buildings. Maybe house wrap against the inside of the exterior wall prior to insulating to prevent drafts circumventing the insulation.
There are insulating calculators and ideas here.   http://www.builditsolar.com/  Hit the references tab.


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## Bret Chase (Dec 9, 2014)

Joful said:


> Original frame is 8" x 6" sills with 6" x 6" posts and beams, and 3" knee braces.  Standard 19th century timber framing, at least for our locale.  I failed to notice what type of mill the timber was sawn on, but now that you ask, I should try to do so before it's all covered up!  Being a barn, things are somewhat dirty and it has been wet at some point in it's past... the saw mill marks are not abundantly apparent.




Here we'd call that "3/4 framed"... it's framed the same as my barn... timber framed walls with conventional or raftered roof instead of king rafter and purlin.

if it was me... I'd not spray and stuff it all with XPS or polyiso rigid.  I would not, under any circumstances spray the ceiling, because that metal roofing will have to be replaced at some point, and it does need to be able to move.

In a former life, my occupation involved installing/removing/replacing metal roofing... measured in acres.  I've had to pull off a couple of roofs that were foamed in place.... it easily took 3 to 4 times as long to replace... and the all the advantages of spraying were destroyed.

I would put 4" in the wall and 6" in the roof.

my uncles has the same JD855.. nice little tractor


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## brian89gp (Dec 9, 2014)

I like the HVAC-calc software.


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## Ashful (Dec 9, 2014)

Thanks, guys!  Never heard the "3/4 framed" term Bret, but it makes sense.  Not many king-post houses around here, but my family did own one for generations (1692 - 1993).  I only see timbered roof framing in the 18th century (1700's) houses, and almost all of them were redone with rafters in the 19th century.  This barn is almost certainly mid 19th century, not earlier.

I also have my reservations about spray foaming.  I'd never use it on a historical house, and even dislike the idea of spraying the timber on this barn, for the sake that someone may want to remove my "modern" work generations from now.  With regard to the metal roof, I had been given the impression it peels pretty easily off closed-cell foam, but maybe I was mislead there.  I do have an old friend who does blown-in cellulose, so I'll have him in to take a look at this.  I don't think the construction I have will play well with the strengths and weaknesses of blown-in.

Bats are always an option, but I'd have to put some more thought into how deep to stuff it (sheathing to wallboard distance varies substantially), and the job may be more DIY, as I don't know of any contractors around here who still use bats.  I did my last such barn completely myself, but have very little time these days for DIY.  Time is much more precious than money, at this point in my life.


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## Bret Chase (Dec 10, 2014)

with a lift or two of sheet foam... that barn could be knocked out pretty fast.

Contractors around here use whatever the architect/engineer calls for, be it bats, sheet foam, dense-pack, cellulose, blown in, etc...

metal roofing does peel off *relatively* easy... but that's not the main problem. the larger problems are having to shave off ALL of the highs left in the spray foam... because unless you manage to get the exact same crew, with the exact same panels, at the exact same temperature... the highs won't line up. also... that seal between the foam and the metal is gone... moisture will crawl up it, and damage the underside of the panels. AT least with sheet foam... if applied to the underside of the roof strapping... will allow air to move underneath the panels and carry moisture away... keeping the panels dry.

like I said... been there, done that.


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## Firewood Bandit (Dec 10, 2014)

I think you would get more bang for your buck by stopping in air infiltration.  Tyvek wrap is good stuff as well as sealing possible leak points.

A couple of years ago we had an energy audit done.  They had us seal box sill and the tops of the drywall going into the attic.


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## Warm_in_NH (Dec 10, 2014)

If you do want to spray the roof, I would suggest an air chase below the metal. You can do this with 1" strip of wood down the sides of the rafters, put rigid foam to that leading the 1" gap between rigid and "strapping" then spray away. 
Allows it to breathe, you get an air tight seal, max r value and you can replace the roof without issues.
A little more labor but worth it, there's a good chance that roof will condensate and eventually ruin the fiberglass, really needs some venting prior to any insulation.


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## semipro (Dec 10, 2014)

midwestcoast said:


> Did you try googling Heat Load Calculators that HVAC folks use?


I believe you're thinking of "Manual J".


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## semipro (Dec 10, 2014)

I'd suggest  foam board insulation with an attached radiant barrier be installed along the bottoms of the rafters (radiant barrier up) for the roof. 
It will be relatively easy to install and likely less expensive and problematic than spray foam.


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## Ashful (Dec 13, 2014)

Follow-up:  Spoke with an old friend today, who is a blown-in cellulose contractor.  He did not feel cellulose was the best option for my walls, as the studs are spaced off the sheathing.  He said he would spray foam the walls.  He also said he could do the roof, but again probably not the best option for my circumstances.

He agreed with the comments above (Bret, NH) on not spraying right to the metal roof, and suggested pinning rigid foam board to the underside of the furring strips to which the roof is fastened in each rafter bay, and then spraying to that foam board.  He seemed to have several concerns with condensation dripping off the bottom side of the metal roof, no matter what insulation I used, so I guess vapor barrier behind the wall board is key.

Outside will be wrapped, although exact product has not yet been selected.

As mentioned framing in gable end walls is set in 3" from exterior sheathing, so if I use bats I can either go 6" deep, or just allow dead air space between bats and sheathing.  That might not be a bad way to go, after all.

Thoughts?


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## Warm_in_NH (Dec 14, 2014)

The "professional" builders that built my house a strapped the rafters then did metal. I have a cold attic with a full vapor barrier between it and living space. The metal condensates in the winter. It'll build frost until it warms up enough to run down the proper vent and eventually drip through my kitchen window trim. Happens twice a winter, unloads about a quart of water, annoying. VERY confusing the first year I owned the house.

Torn on the best way to fix it. Either rigid air chase and spray foam, or pull all the metal, sheath it, strap it, metal and on the inside proper vent and more insulation.

Don't imagine you'll be generating too much moisture in the barn but it's something to keep in mind.


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## Ashful (Dec 14, 2014)

Running equipment in the attached shed, and even occasionally in the barn, will be about the extent of my moisture generation.  We won't be cooking out there.  Then again, any air infiltration between the metal roof and insulation will bring in moisture from outside.

I trust this guy.  He's been insulating higher end custom homes for 35 years, including the 1994 addition to my own house (wasn't mine then).  I just wish I got a more detailed plan from him, but we were only talking on the phone, he wasn't here.


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## woodgeek (Dec 18, 2014)

Agree with the friend's plan for walls and roof.

A few rules of thumb:

To get BTU/h, its is simply  = Area(sq ft)*DeltaT(°F)/(R-value).  To get BTU/yr it is simply Area(sqft)*24(h/day)*HDD/R-value, where HDD is heating degree days for your location....say 4500±500 in Philly burbs.  You can add up the different segments of the building (with their estimated areas and r-values) in a SS trivially to get a total, and see how different changes affect the bottom line.  The free online calc do just this, and nothing more.  The fancier methods are not free.

Air infiltration will increase the heating load in a leaky building by 100 to 150% over the above (making insulation kinda pointless), if the building is 'snug' it might still add 50%, if it is carefully airsealed I would still add 20%.

You can prob neglect BTU losses to the slab in the above, but the floor will be cold.

The math above doesn't like insulating some areas more than others....insulating half at R-11 and half at R-22 is a waste.  The exceptions would be heat rising, and the roof being cold from radiation....more in the roof can make sense.

Garage door manufacturers are poorly regulated re their insulation value....most numbers are notoriously inaccurate, with the highest numbers being the biggest cheats.  They also leak a LOT of air....look for the doors that you would judge to be most airtight, and if they have 1+ inches of foam, pick those.


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## Bret Chase (Dec 18, 2014)

I forgot about the garage door question.  If it was me...  I would find your local Overhead Door branch.  The doors are not cheap, but they are the real deal.  Every project I have worked on since '89 (commercial and residential) that required a garage door, got one from OHD.  They are orders of magnitude better than the crap doors you can get from Home Depot or Lowe's..


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## Ashful (Dec 18, 2014)

I'm going to be dropping some substantial coin on the doors, mostly due to cosmetic reasoning, and fitting odd-size openings without framing them down to fit smaller standard doors.  I'd love to go with some of the stamped steel doors rated R-16, accurate or not, but they just don't look good on this barn.  So, doors will be machined T&G construction, but using polystyrene backed PVC components.  They're rated R-9, which ain't great... but like woodgeek said, air infiltration is likely the larger problem.  Door installation is being handled by a local door company who seems to be very good, and does a lot of similar heated shops, and weatherstripping is being addressed.

The working plan for the roof is to cut sheets of foam board, exact material not yet selected, to fit between each rafter.  These will be stapled to under side of the furring strips to which the metal roof is attached, allowing ventilation between roof and insulation, and preventing the problems mentioned above with roof replacement.  We will then spray foam to the foam board and rafters, and cover with OSB for wall board.

Walls, could be bats or sprayed, but due to air infiltration, I'm really leaning toward sprayed.  I still haven't seen many opinions on having insulation sprayed against outside sheathing, versus bats on the interior framing.  There is up to 11" space between wallboard (new interior framing) and outside sheathing.

Building will be wrapped in house wrap (Tyvek or similar), with vertical furring strips and horizontal wood siding, outside of that.  So, we'll have the usual siding, air space, drainage plane, sheathing, insulation, wall board, construction... the only question being location of that insulation and vapor barrier.  I do have some concerns in that regard, with closed cell spray foam on sheathing, and a large air space between wall board and spray foam, but I guess it's standard practice...


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## woodgeek (Dec 18, 2014)

Joful said:


> The working plan for the roof is to cut sheets of foam board, exact material not yet selected, to fit between each rafter.  These will be stapled to under side of the furring strips to which the metal roof is attached, allowing ventilation between roof and insulation, and preventing the problems mentioned above with roof replacement.  We will then spray foam to the foam board and rafters, and cover with OSB for wall board.
> 
> Walls, could be bats or sprayed, but due to air infiltration, I'm really leaning toward sprayed.  I still haven't seen many opinions on having insulation sprayed against outside sheathing, versus bats on the interior framing.  There is up to 11" space between wallboard (new interior framing) and outside sheathing.



Sounds like a plan....for cheap foam board, you can buy 'used' from: http://www.insulationdepot.com/  and save money and be 'green'.  

That outfit doesn't do small lots, usually trucks a large shipment, but it sounds like you want a lot of foam board, and don't care if its a little scuffed.

Depending on price, it might make sense to go as thick as possible on the board, and then go thin on the spray-foam for airsealing and hitting the rafters.   Remember that poly-iso loses R-value in extreme cold....if the used XPS is not much more, I would go for that, esp if you were going thin on the sprayfoam


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## semipro (Dec 18, 2014)

I'm not understanding why both foam board and spray foam are proposed for the roof.  Unless things have changed recently, board foam is less expensive per volume and can easily be air sealed when installed using canned foam.  
Perhaps the justification is labor costs?


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## woodgeek (Dec 18, 2014)

Cutting and airsealing 14" strips of foamboard is going to be labor intensive (costly), and the rafters still provide a thermal bridge.  Just sprayfoaming it will be material intensive (costly), might need a couple passes to get to target R-value (more labor), and result in an unvented roof assembly.  On a big job, I suspect a table saw could be set up to rip the boards quickly, cutting them all underwidth slightly so they go right up quickly.  A thinner coating of sprayfoam on the rafters (and the joints with the sheets) would be a quick way to airseal the whole thing and defeat the rafter thermal bridges, and minimizing the use of expensive spray foam.

I'm thinking 4" of (used,cheap) XPS sheet + 1" of sprayfoam and 1" of sprayfoam over the rafters = R-25-30 assembly value, and prob cheaper than 5" of sprayfoam on the deck (undesirable) and 1" on the rafters.  I think the foamers have tools for shaving the excess of the lower edges off the rafters quickly, to mount the OSB.

Of course, since you are doing an OSB ceiling, you could fit 2" foam sheet, do the OSB, and blow the cavity with cellulose.  Might be the cheapest route, though you'd have to have a plan for sealing, like taping the foam joints with each other and to the rafters.


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## Ashful (Dec 18, 2014)

Great ideas, guys.  But in this case, up-front cost (within reason) is not a big issue... my free time is.  I can pay a guy to sprayfoam this whole joint in a day, and it's a minimal investment of my time.  I'm only agreeing to do the foam board so that I can keep the sprayfoam off the underside of the metal roof, and avoid headaches down the road.

I had planned to use thin foam board (eg.1/2") so I can just cut clean with a utility knife, rather than dealing with the mess of ripping heavier sheets on the table saw or bandsaw.  I also already have estimates in the work from two spray foam guys, based on doing 3.5" (R25) in the roof, and it's probably easier to just go with what was quoted than re-figure for less foam / more board.

Do you see any issue with using thinner board?  Thoughts on foil back (foil facing roof with 1" air gap) vs. non-foil back?


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## woodgeek (Dec 18, 2014)

If you were going to do the foam sheet and OSB yourself, you could still go a little thicker on the foam, cut it easily (I can do 1" easily if I have fresh blades), and have a cellulose guy fill the cavity cheaply.  You could use the savings to pay your next light bill, or maybe two.    Of course, you would have to tape the foam sheets to the rafters, and that is time, unless you pay the kid nextdoor to do it.

This of course comes down not to money, but if you wanted to avoid a sprayfoam sol'n due personal preference.  Also, don't believe the R-7/in stuff, after it ages/outgases for a while, it'll bottom out around R-5.  At 3.5" thick and some residual bridging from the rafters, it could be well under R-20 for the assy.

If the cellulose was thicker it could easily get a higher final R-value.  If you were going to heat it with a mini, that might be useful if you were near the limit of a single unit.


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## Ashful (Dec 18, 2014)

Interesting... 

I can't tape to the joists, because they're rough sawn.  I was just going to pneumatic staple them to the furring strips and let the spray foam be the vapor barrier.  I do have concerns about interior humidity reaching the underside of that cold metal roof, which is part of what steered me away from cellulose and toward closed cell foam.

Light bill?    December is a big month for us... too many outside lights.


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## woodgeek (Dec 18, 2014)

I think the spray foam plan will make a robust assy.


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## semipro (Dec 18, 2014)

Just tossing out another idea (which I hate to do because I irritate myself 2nd guessing plans  )
This would be easy to install, would act as vapor retarder/barrier, allow plenty of roof ventilation, and address thermal bridging issues.  The foam been the rafters could be omitted if a lesser R value was okay.
In general I'm a big fan of cellulose but not where water is more likely to enter (like roofs). 






Edit: foam panels with OSB already attached can also be purchased.


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## Ashful (Dec 19, 2014)

I like that, semipro, and have actually been looking at doing a foam layer under rafters, but headroom is already a little tight.  I don't think I want to spare the room for it.  Also, was looking at maybe recessing ceiling (would have to use drywall instead of OSB) between rafters.  This plays well with spray foam.


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## Ashful (Dec 30, 2014)

Just coming back to this, after being away doing other things awhile.  I think I went about this entire thing wrong.  I came here asking questions to make my chosen (spray foam) method of insulating work.  I should have asked how one might best insulate this structure, as spray foam may not be the best course.

So, let me lay it out there... this is an 1850'ish timberframe barn, photos above, with new-work second floor and interior framed walls, new doors and windows, etc.  Roof is raised seam metal (agricultural screw-down type) on 1x3 purlins, on 2x6 rough joists.  New 2x4 framing within old structure, with framing for gable end walls (structural) set in several inches from sheathing, creating wall cavity depth of 6" - 10".  New 2x4 framing on front and rear broad walls is against sheathing (not structural), and notched around all old timber knee braces, nailers, etc.

New windows and doors to be installed, followed by house wrap (TBD), then furring and wood siding.  Had considered just using fiberglass batts for insulation, but concerns with condensation due to cold metal roof and air infiltration (sheathing will be old and leaky 2x6, not plywood) pushed me toward spray foam.  I think this is a good choice, but am admittedly not the most educated on these matters.  One thing I do dislike about spray foam is its permanence, in that this is an old structure, and some future owner 100 years from now may not appreciate having 2014 spray foam stuck to their 1850's timberframe.

How would you insulate this structure?


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## woodgeek (Dec 31, 2014)

Or the 2014 sprayfoam may have crumbled to dust in 30-40 years.

Missing info...do you intend to heat this structure 24/7, so it makes sense to give it house levels of insulation, or do you want a shop you can heat quickly from time to time, leading to a low thermal mass, lower R value design?


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## mellow (Jan 6, 2015)

woodgeek said:


> Sounds like a plan....for cheap foam board, you can buy 'used' from: http://www.insulationdepot.com/  and save money and be 'green'.
> 
> That outfit doesn't do small lots, usually trucks a large shipment, but it sounds like you want a lot of foam board, and don't care if its a little scuffed.



Just a heads up I tried getting a quote from them for 2000 sq ft of board, the guy got my info and said they had a site in Western MD they were pulling board out of and could bring it to me, never heard back from him, he sounded like they only want HUGE industrial jobs.   Just an FYI.


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## Ashful (Jan 6, 2015)

Thanks, Mellow.  After talking this over with two friends who both work for builders, they're recommending I just stay simple and go with fiberglass bats.  One recommended styrene baffles in the rafter spans behind the bats, and the other liked the idea of cutting foam board to go in behind the bats.

On a more interesting note, I did some calculations on loss due to garage doors of various R-value.  I'll post that info tonight.  I was surprised how little the difference was between R9 and R16.  In fact, it's almost irrelevant in terms of heating cost, until you go real low, like < R4.  This is of course based only on ~140 sq.ft. of door, not the entire barn.


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## woodgeek (Jan 6, 2015)

Yar.  Your insulation cost goes like R-value, and your savings go like the reciprocal...1/R-value (which is U-value)

16 is a lot more than 9 that is more than 1 (R-vaules), but 1/16 is not very different than 1/9 when compared to 1 (U-value) .

Same as going to a 30 mpg car from a 20 mpg car saves a lot less gas than going from a 10 mpg car to a 20.


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## woodgeek (Jan 6, 2015)

Ok, nothing wrong with fiberglass.  The FG haters might talk about convection induced R-value drop at low temps.  In our climate with FG batts (versus Wisconsin with loosefill FG) NOT a problem.  Without a baffle there might be some wind-washing loss of R-value...don't know if its worth the effort/cost of doing prefab or DIY baffles.

I would insist, however, on a careful air-barrier.  Stapled FG Kraft paper does NOT count.  IF however, you taped all the Kraft paper seams (including the staples and any tears during install) and then OSB'ed under I suppose it would be ok.

Do they make tongue and groove edged OSB to keep the seams lined up?

How deep are your joists again?

One tip....sometimes different thickness batts are the same price, and compressing the 'thicker' batt (to a higher final FG density) does yield slightly higher R-value per inch, and is less likely to collapse (in my imagination) than a ultra-low density product.  I've done that myself.


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## Ashful (Jan 6, 2015)

woodgeek said:


> Ok, nothing wrong with fiberglass.  The FG haters might talk about convection induced R-value drop at low temps.  In our climate with FG batts (versus Wisconsin with loosefill FG) NOT a problem.  Without a baffle there might be some wind-washing loss of R-value...don't know if its worth the effort/cost of doing prefab or DIY baffles.
> 
> I would insist, however, on a careful air-barrier.  Stapled FG Kraft paper does NOT count.  IF however, you taped all the Kraft paper seams (including the staples and any tears during install) and then OSB'ed under I suppose it would be ok.
> 
> ...


I do remember you mentioning compressed batts before.  Definitely worth consideration, in a vaulted ceiling install.

Joists are full 2 x 6 rough sawn.

I have only seen T&G OSB in 3/4" thickness for subfloors, never in 7/16" thickness for a ceiling or wallboard install, but I'm sure someone must make it.  I just don't know how easy it would be to purchase.

Re:  air barrier.  This is where I come back around to the spray foam.  The only time I will have appreciable indoor humidity is when I'm painting, as this shop has no kitchens or baths, but air infiltration can still cause havoc in terms of condensation.  Closed cell spray foam is absolutely superior, in this regard... but 100 years of building with batts has shown they can work well enough when installed simply with stapled paper barrier.  What am I missing?


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## woodgeek (Jan 6, 2015)

Forget the idea of a vapor barrier...you want an air barrier....little cracks and seams can move a lot of heated air, and bypass the insulation.  In 70-80 years of stick building with batts, houses had 100% higher heat loss due to poor airsealing!

The seams in the OSB and the gaps under the stapled Kraft paper will (in typical construction) leak enough air to largely defeat the insulation.  

You need to at least decide on what the air barrier will be, and then try to make it continuous. You are not going to tyvek the place, or put in a taped layer of poly, or tape or caulk all the OSB seams.  Being careful with the Kraft paper...overlapping the paper edges and taping the seams, should provide a decent air barrier without too much added effort or cost.

Regular OSB is fine of course....I was just free-associating....


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## Ashful (Jan 6, 2015)

Woodgeek, I will be tyvek'ing the outside walls, before installing new siding.  Existing (leaky) siding will become sheathing.  However, you are correct on the roof, it's steel on purlins on joists.  If doing batts in roof, it would be cutting 1" foam to fit between joists, then batts with stapled Kraft.  I could spray foam (canned) seams of 1" foam board to joists, but I'd worry about this becoming a secondary vapor barrier, and trapping moisture.  I think it best to have a single vapor barrier at sheathing.

I could do a secondary barrier at sheating, eg. tyvek or poly sheeting.  I really know nothing about modern building science, beyond the basic principles of condensation, 100% of my work has been repairing old construction.


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## Ashful (Jan 6, 2015)

This related thread may be of interest to those reading here.  I graphically show what woodgeek was describing in post #35.

https://www.hearth.com/talk/threads/overhead-door-insulation-calculations.138654/


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## woodgeek (Jan 7, 2015)

So, on the side walls, you can tape the tyvek seams with....tyvek tape, and that is your air barrier.  Even taped tyvek needs to be lapped carefully for drainage, esp around windows, but I expect you are an expert on that. No problem with the air barrier being on the outside (in this case) because tyvek is vapor permeable.

Assuming you want to vent the steel roof, you will need a good airbarrier on the (sloped) ceiling plane because any leaks in that plane will have ready access to the vented cavity, wind driven pressure, etc. 

I'm assuming you want to go as simple/fast as possible....sounds like thin polyiso stapled to the roof purlins.  If all you want to do is define a venting space (by keeping the FG from pushing up to the roofing) I'd go with 1/2" xps or polyiso, which would also avoid windwashing the FG.  I'd cut the foam all the same width, enough under the joist spacing so that each piece does not need to be custom fit (PITA). If you define your air barrier at the Kraft paper, then the (0.25"?) gaps on the sides of the polyiso don't matter.  And allow the FG to dry to the vented space.  But, to be a broken record, I would tape the Kraft seams if you are going to rely on it being your primary air barrier.

At 6" overall (old lumber dimensions)  you'd prob get R-20 center of cavity, maybe R-15 with thermal bridging by the joists.  Certainly not code, but workable if airsealed.  If you wanted to go to higher R.....you could put some polyiso under the joists, and 2" would get you to R27 or so.  You'ld need longer screws for the OSB, is all.  Or you could spring for foam-OSB bonded panels and save a step (if you can source them).  In the foam case you could not sweat the Kraft paper at all (or get unfaced) and tape the foam seams as an airbarrier.

IF R-15 is good enough for you....the FG seems like a simple and 'conventional' solution.  If you want significantly more than that, you are back to where the thread started....building up sheet foam, the joists, or going spray foam.

You will have to detail the transition from vented roof assy to your wall assy carefully to connect the air barriers.


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## Hansson (Jan 9, 2015)

This is a pretty good page for calculate U-value.
http://www.energiberakning.se/
Go to U-Value. Press the English flag


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## Ashful (Jan 15, 2015)

Okay... roof insulation finalized, thanks to a lot of back-room help from woodgeek.  Here's the plan:

1.  1" XPS sheets cut 22" wide and fastened to underside of purlins.  Also fastened to top side of collar ties (to create small flat ceiling in second floor space), and boxed in around soffits.
2.  R-30 closed-cell spray foam on XPS in each rafter bay.  The XPS is really just there to keep the spray foam off the underside of roof, and facilitate future roof replacement.
3.  7/16" OSB ceiling, pref T&G, if it can be sourced.
4.  UltraVent product (soft brillo pad type material) installed under ridge vent, to keep out critters, insects, snow.
5.  Corrugations caulked shut (could not source a prefab trim-board for this roof) at soffit, and louvered vents installed at underside of soffit.

Ideally, it would have been nice to just spray foam to the roof, and eliminate need to ventilate, along with any concern of condensation.  However, semipro's comment about roof replacement got to me, as I surely would replace with a different roof system, when the time comes.

I still need to decide on a secondary barrier behind OSB, but decided to not worry about thermal bridging.  Calculations showed thermal bridging bringing the assembly down from R-35 to R-25, which will only amount to $5 per year of additional heating cost, given the temperatures I intend to maintain.


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## woodgeek (Jan 16, 2015)

I don't know what you mean by secondary barrier....if its sprayfoam, the assembly is airsealed and vapor impermeable.  The joists can dry to both sides.

You can also go to 1/2" foam board, saves money and even easier to cut, tack, etc.


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## semipro (Jan 16, 2015)

Joful said:


> However, semipro's comment about roof replacement got to me, as I surely would replace with a different roof system, when the time comes


That credit belongs to Bret Chase, post 7. 
I appreciate the thought though.


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## woodgeek (Jan 16, 2015)

Re the thermal bridging, when you replace the roof in 25 years, you can (1) see if the spray foam shrank (2) add another layer of sheet foam as underlayment to the new roof to bring it to R-50, and (3) get an energy rebate for the upinsulation from the Bieber administration (don't ask).


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## Ashful (Jan 16, 2015)

semipro said:


> That credit belongs to Bret Chase, post 7.
> I appreciate the thought though.


You are correct!  Sorry, Bret!

1/2" foam board... what I originally suggested.  I thought I had let you talk me into going thicker, tho!  



woodgeek said:


> ... and (3) get an energy rebate for the upinsulation from the Bieber administration (don't ask).


"Ronald Reagan? The actor?  Then who's vice president? Jerry Lewis?  I suppose Jane Wyman is the First Lady!"  - Dr. Emmett Brown


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## woodgeek (Jan 16, 2015)

Joful said:


> "Ronald Reagan? The actor?  Then who's vice president? Jerry Lewis?  I suppose Jane Wyman is the First Lady!"  - Dr. Emmett Brown



In an enlightened future, ScarJo would be veep. Might make the SOTU speech even harder to follow.


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## Ashful (Jan 20, 2015)

Next up... how to handle ceiling / insulation around a lighted cupola.  Cupola has windows on all sides, and is sealed tight on air, insects, etc., but not insulated.  It straddles a vented ridge, as shown in photos.

Ridge and soffits are vented, with foam board and spray foam on purlins, as previously discussed.  There will be collar ties, and a ceiling, approximately as shown in the attached sketch.  Roofing is opened up to cupola (i.e. prior owner cut hole in roof to allow cupola lighting into barn).  Initial thought is to make the lighted cupola part of the un-insulated attic space, sealed off from the heated space.  Pro's are ease of construction, and better insulation.  Con's are loss of light, and a potential place for insects (stink bugs, hornets, etc.) to congregate out of sight.

Thoughts?


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## ironpony (Jan 21, 2015)

seal the cupola off from the attic with a trap door on bottom of cupola, so you still have access. then leave as part of attic space.


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## woodgeek (Jan 21, 2015)

I like daylighting.  Maintain the opening and cover it with a transparent sheetgood like plexi, suntuff or lexan twinwall.  Or even coroplast from a sign store.  Will diffuse the light, and provide enough insulation.  Cover the inside walls of the cupola shaft with foil or glossy white paint beforehand for better throughput.


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## Ashful (Jan 21, 2015)

I was going to do as ironpony suggests, but that's an interesting idea, woodgeek.  There will be large double-hung windows at each end, and it's primarily storage space, so daylight is not a huge issue.  However, definitely something worth consideration.  I was going to have a trap door for access anyway, so swapping from an insulated panel to something transluscent should not be a problem.


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## semipro (Jan 21, 2015)

I've been thinking of stuffing a translucent bubble wrap "lasagna" into some of our skylights with a transparent separator below to support it, a mod of Woodgeek's suggestion. . 
The bubble wrap should insulate well but I suspect its not designed to hold up to light long term and light transmission would suffer as more layers of bubble wrap were added.


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## Oldman47 (Jan 28, 2015)

I see you got advice from friends to use glass batts. You already know about Roxul batts for use in block off plates but those things insulate better than glass batts and are made for a nice snug fit in a standard wall. My new home has R-23 batts in the 2x6 wall sections and R15 batts in the 2x4 sections. (I used a double wall with 2x6 outer wall, then a vapor barrier and 2x4 inner wall.) Compare that to R-19 in glass in a 2x6 wall and R13 glass in a 2x4 wall. In addition to better insulation the stuff also sheds water fairly well, not perfectly, and does not degrade like glass does. To use it you would need to install a separate moisture barrier like 4 mil plastic but unless you consider kraft faced batts as an adequate barrier you will do that with glass too. Just some things to think about.


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## Ashful (Mar 9, 2015)

Interesting question for the foam board in the rafter bays.  If you recall, the plan is to fasten foam board to underside of purlins, and then spray foam to the foam board, 3.5" thick in each rafter bay.  The roof deck (purlin space) will be vented at soffit and ridge.

Do I want to go with foil face on this foam board?  My thinking is that, given solar loading on a dark'ish metal roof, this barn has always run hot.  I'm in a mid-Atlantic clime, and so we normally go with heating theory of placing vapor barrier toward the inside.  Here, I'm spray foaming with closed cell, which is a vapor barrier in itself, but fact remains it will be warmer under that roof deck (outside of insulation) than inside the building, most of the year.  Also, people who have insulated under metal roofs, as I'm doing, have often reported condensation problems under roof deck.  So, foil faced XPS (foil to outside), might be a good idea, in my mind.  If nothing else, it's a drip pan (albeit, not a very good one), taking any condensation back down to soffit.

Thoughts?

On windows, already got 6 Andersen 400-series double-hungs, a lighted entry door, and garage doors that are 1/3 glass.  There will be lots of natural lighting!


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## Ashful (May 31, 2015)

Figured it's time to post some follow-up, here.  Preparing for the 3" closed-cell foam to be sprayed on Tuesday, which means I'm making all final adjustments to wiring, cribbing to which wallboard will attach, etc.  Will post more photos over the next few days... in the mean time, here's a lot of wiring!  This will be a workshop space, hence the mils of AWG-10/2 and AWG-12/3.












Later today, I'll get some photos of the foam board I installed in each rafter bay, and between collar ties (still finishing it, actually), as a backer for spraying the foam.  That will add another 1" of insulation, so this will be one well-insulated barn... surely overkill for the 55F heat / 85F cool thermostat settings I'll have out there.

Note end wall cavities are 7" - 12" deep, completely inside original timber frame.  So, there's no thermal bridging due to studs... foam will fill in completely behind the 2x4's, which are spaced off sheathing.


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## Ashful (Jun 2, 2015)

It has begun:


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## woodgeek (Jun 3, 2015)

Did you decide to the keep the cupola open for daylighting, or seal it off?

Or a translucent 'trapdoor'?


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## Ashful (Jun 3, 2015)

There will be a trapdoor for access, and I haven't decided on foamed OSB solid panel vs. translucent, just yet.  My thinking is that this area will be undoubtedly an insect graveyard, and so if I go translucent glass, I may get some light but will be looking at dead bug silhouettes.  Insulative value of foamed OSB is also better, so that's the direction I was leaning.


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