barn insulation

[littleboss]

Got a shop in southern Colorado that I need to insulate. It’s 2×6 stud walls 12′ tall with the center being about 20′ tall. Pix of barn is attached. Walls are wrapped in OSB and then steel lap siding. The best I can tell there is no building wrap. Spray foam is too expensive so I am thinking fiberglass in the walls and after I put a loft and ceiling in it, have cellulose blown in the attic. Mice are bad there so I think the cellulose is treated. I have read that fiberglass has air currents flowing through it which reduces R value. Thoughts on either using a plastic vapor barrier on top of the fiberglass or using 2″ of pink foam in the wall cavities first (caulk around them to make air tight) then add the fiberglass and OSB or tin to cover the walls? Also what about attic venting? Thanks

 

[jack stand]

I'm digging your view!
Your kinda right about the FG except it should be any "air movement through the wall cavity (this is what the wrap is for) will reduce the r value. An 1 1/2" - 2" layer of foam cut and fit in each stud bay and (can) foamed around the edges will block any air infiltration and leave you with room for FG and +/- R 28 wall depending on which foam you choose.
There are places that sell used foam sheets from a commercial re-roofing jobs, (usually polyiso that's around a r7.5/inch) for under half the new price.
If you're diligent and maybe willing to drive a bit you can find it.
There are very dense alternatives to FG, Roxull is one where I believe that will not let air pass through it. It might be worth investigating if you have a house wrap but it's unlikely to have been included with the original purpose of your "ag" building especially if it's 10-15 years old.

 

[billconner]

Why not cellulose in walls? Dense packed. Very effective and least expensive.

I'd probably put poly on inside but necessity is based on use and moisture. If old slab floor without vapor barrier, probably a moisture source.

 

[littleboss]

I'm digging your view!
Your kinda right about the FG except it should be any "air movement through the wall cavity (this is what the wrap is for) will reduce the r value. An 1 1/2" - 2" layer of foam cut and fit in each stud bay and (can) foamed around the edges will block any air infiltration and leave you with room for FG and +/- R 28 wall depending on which foam you choose.
There are places that sell used foam sheets from a commercial re-roofing jobs, (usually polyiso that's around a r7.5/inch) for under half the new price.
If you're diligent and maybe willing to drive a bit you can find it.
There are very dense alternatives to FG, Roxull is one where I believe that will not let air pass through it. It might be worth investigating if you have a house wrap but it's unlikely to have been included with the original purpose of your "ag" building especially if it's 10-15 years old.

Thanks. Sangre de Cristo mountains in southern Colorado........... The barn came with the place when we bought it It was built in the late 90's. No house wrap and probably no insulation under or around the slab. 2" of pink foam board for the walls was what I was thinking. As you said I could cut the foam board to fit loose then seal it with foam in a can. Then if that wasn't enough I could add fiberglass on top.

 

[littleboss]

Why not cellulose in walls? Dense packed. Very effective and least expensive.

I'd probably put poly on inside but necessity is based on use and moisture. If old slab floor without vapor barrier, probably a moisture source.

Only problem with cellulose is it settles. You would have to have access to the top of the walls to add more down the road

 

[billconner]

Only problem with cellulose is it settles. You would have to have access to the top of the walls to add more down the road

Dense packed cellulose doesn't settle.

Dense-Pack Cellulose Insulation Done Right - Fine Homebuilding

Dense-pack cellulose is great at stopping air movement and managing moisture. Learn how to install dense-pack cellulose insulation correctly.

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[C-S-H]

Is there an air gap with some ventilation between your exterior steel cladding and the OSB sheathing? If not you may be stuck with what you have. The OSB needs to breathe to both sides, or if only one side then you need to build-in a means for prevention of condensation in the wall assembly.

If the OSB can breathe to the outside, you could use all batt insulation in the wall cavity. You could also use XPS against the OSB plus batt insulation as long as the R-value of the the XPS is >30% of the total R-value of the insulation in climate zone 5B. Your interior wall finish needs to be vapor semi-permeable, so drywall and latex paint or various membranes can be used if tin interior cladding is used. The tin needs to be able to breathe through gaps or perforations or you are into another wall layup design problem.

 

[littleboss]

Is there an air gap with some ventilation between your exterior steel cladding and the OSB sheathing? If not you may be stuck with what you have. The OSB needs to breathe to both sides, or if only one side then you need to build-in a means for prevention of condensation in the wall assembly.

If the OSB can breathe to the outside, you could use all batt insulation in the wall cavity. You could also use XPS against the OSB plus batt insulation as long as the R-value of the the XPS is >30% of the total R-value of the insulation in climate zone 5B. Your interior wall finish needs to be vapor semi-permeable, so drywall and latex paint or various membranes can be used if tin interior cladding is used. The tin needs to be able to breathe through gaps or perforations or you are into another wall layup design problem.

Sorry, I missed this response. As far as I can tell the only air gap would be where each piece of lap siding overlaps. Nothing visual but it can't be air tight.

I am now thinking just 3-4" of pink foam board.
I could do 2" of pink foam (R10) then unfaced fiberglass R15 for a poor boys "flash and batt" system. I would have to leave the fiberglass off until I was ready to cover it due to the mice

Thoughts? Thanks

 

[jollygreengiant]

Put your batts in first then do the rigid foam over top of the studs. That will save you a lot of labour cutting foam for each stud bay, and with the right type of foam applied on top of the studs you can use that as your vapour barrier. It will also give you better efficiency as the foam will prevent thermal bridging from the studs to your interior finish.

 

[littleboss]

Put your batts in first then do the rigid foam over top of the studs. That will save you a lot of labour cutting foam for each stud bay, and with the right type of foam applied on top of the studs you can use that as your vapour barrier. It will also give you better efficiency as the foam will prevent thermal bridging from the studs to your interior finish.

I don't understand enough about vapor barriers to know if this is ok or not. With the "flash and batt" method that me and

C-S-H are talking about the 2" of foam provides the vapor barrier.​

 

[jollygreengiant]

When you do the flash and batt method, with the foam on the inside of the cavity against the OSB, you need to be careful that you're not using a foam board that is vapour impermeable or vapour semi-impermeable. Which a lot of foam boards are. In your climate, one where you'll be mainly heating, you want your vapour control layer on the inside of the wall, underneath your interior finish product. That will stop any vapour before it enters the wall cavity, and the wall can dry to the outside.

 

[billconner]

you want your vapour control layer on the inside of the wall, underneath your interior finish product. That will stop any vapour before it enters the wall cavity, and the wall can dry to the outside

I usually say the same thing but wonder if with siding, house wrap, and OSB, or taped ZIP stuff, if it can really dry outward. The flash and batt with spray foam on sheathing thick enough to keep inner surface above dew point, and then batt's or whatever inside, just seems easier to maintain a drying inward condition. And I'd prefer cellulose since it's hydroscopic vs fiberglass or mineral wool, both hydrophobic. At a conference talking to Joe Lstiburek and he made the point that throw a cup of water into fiberglass and you end up with a cup of water on the sill. Do same with cellulose and water disappears. The cellulose will dry better over time without rot and mold. (He also said foam and concrete are the least problematic walls. Makes ICF attractive.)

 

[jollygreengiant]

I usually say the same thing but wonder if with siding, house wrap, and OSB, or taped ZIP stuff, if it can really dry outward. The flash and batt with spray foam on sheathing thick enough to keep inner surface above dew point, and then batt's or whatever inside, just seems easier to maintain a drying inward condition. And I'd prefer cellulose since it's hydroscopic vs fiberglass or mineral wool, both hydrophobic. At a conference talking to Joe Lstiburek and he made the point that throw a cup of water into fiberglass and you end up with a cup of water on the sill. Do same with cellulose and water disappears. The cellulose will dry better over time without rot and mold. (He also said foam and concrete are the least problematic walls. Makes ICF attractive.)

I used to think the same in regards to OSB but the more I looked into it the more I discovered that OSB is actually fairly permeable to water vapour. It changes based on humidity, but IIRC at 50% humidity it has something like 2.0 perms which is considered semi vapour permeable. But it rises to over 10 perms once you get up to higher humidity ranges. I think the main problem with OSB is bulk water getting on it, but that can be solved by using a housewrap. After that it should be easy to escape as siding is very open, at least when installed correctly. It's the combination of materials that allows the wall to dry to the outside. You won't get any drying to the inside in a climate where you are mainly heating the inside space; vapour drive will be from inside to outside when heating.

Now having said all this I'm not a building materials scientist or anything like that. This is simply the result of a very deep dive down a rather large rabbit hole before I took the outside of my house down to the studs. This is also based on my climate area, SW Ontario, where we are primarily heating.

 

[billconner]

It's the "continuous insulation", with code bias in favor of it, that seems to force you to allow it to drive inward. And yes, it's seasonal drying, which I think is OK.

Rain screen siding systems would seem to be a plus for drying outward.

 

[littleboss]

Pink foamular board = Virtually impervious to moisture. FOAMULAR® XPS insulation boards have up to 13X more resistance to water than EPS insulation.