Workshop Insulation

[jadefox]

The old rule was R19 is used on 5.5" material (2x6), R11 on typical 3.5" (2x4). I guess the insulation guys have figured out how to increase the R value on each (R21/R13) With a true 2x4 I guess R15 might work. You haven't mentioned your heating supply yet.

Probably a rinnai, although would love to find a wood burning solution.

 

[Rustyiron]

So 3" of Pollyiso with R-13 for the exterior walls?

Yes, insulation is your friend! It get's to a point of diminishing return on your money, but the f/g is just so cheap and easy after doing the "cut & fit" foam, and with the exception of this last freak price drop in fuel/energy cost's always go's up.
My construction just allowed (unintentionally) the space to fill the stud bay with r-13 on top of the foam.

 

[Rustyiron]

Probably a rinnai, although would love to find a wood burning solution.

I have radiant heat, with a wood gasification boiler.

 

[jadefox]

Yes, insulation is your friend! It get's to a point of diminishing return on your money, but the f/g is just so cheap and easy after doing the "cut & fit" foam, and with the exception of this last freak price drop in fuel/energy cost's always go's up.
My construction just allowed (unintentionally) the space to fill the stud bay with r-13 on top of the foam.

I can build out the exterior wall enough to probably 6" deep. Did you leave and air gap between the rigid and the exterior wall? I won't get to installing Tyvek under the new siding until next summer.

 

[sailfast]

That rigid polly-iso is equal to spray foam, (per inch) good stuff. Cut & fit tightly and use "can foam" to seal the edges & any joints. I used 2 layers of 1.5" and had enough room left for 3.5" of f/g. I would use 2 layers at the exteror walls to put your dew point in the insulation to avoid moisture issues.
Lucky your in Maine, you can check out "hot & cold" radio with host Tom Gocze on the radio 101.3 Augusta on Sat. mornings starting at 8:00. All sorts of great building info, and you can call in with your questions.

False economy in that plan.
It is not at all equal and you will have air barrier and moisture problems.
Costs more than getting the foam to begin with.

 

[jadefox]

False economy in that plan.
It is not at all equal and you will have air barrier and moisture problems.
Costs more than getting the foam to begin with.

Our plan, given that the exterior wall sheathing (vertical boards) and siding (horizontal boards) is both "barn built and old" (i.e., plenty of sunlight coming through), is to treat it like an old building with no sheathing. From outside to inside, we're thinking air gap, rigid foam, batt insulation, interior panelling. Does that sound sound?

 

[Rustyiron]

False economy in that plan.
It is not at all equal and you will have air barrier and moisture problems.
Costs more than getting the foam to begin with.

Not at all. reclaimed p-iso foam @ .25 a board foot compared to $1 bd/ft (in our area) for sprayed in closed cell. The edges & joints are sealed, there is no air movement carrying conditioned air through the wall cavity for condensation concerns. I would agree that there is nothing better than a spray in foam job, period. This is a very close second at a fraction of the cost depending on what you attribute your labor at.

 

[Rustyiron]

I can build out the exterior wall enough to probably 6" deep. Did you leave and air gap between the rigid and the exterior wall? I won't get to installing Tyvek under the new siding until next summer.

No, this was new construction, 2x6 studs with a 2x purlin or wall girt to fasten the "barn metal" to. Tyvek, all taped under the metal. 1st layer of foam runs horizontally between the wall girts, foamed & sealed all the edges, then the 2nd layer vertically in the stud bay, again all sealed. This left 4" for f/g. Now for the insulation purist, there is some wood to wood (where the vertical & horiz. framing intersect) areas that have no insulation at all, and this lowers the overall wall insulation value, but this is a shop and the insulation was an afterthought.

 

[jadefox]

Not at all. reclaimed p-iso foam @ .25 a board foot compared to $1 bd/ft (in our area) for sprayed in closed cell. The edges & joints are sealed, there is no air movement carrying conditioned air through the wall cavity for condensation concerns. I would agree that there is nothing better than a spray in foam job, period. This is a very close second at a fraction of the cost depending on what you attribute your labor at.

Thanks! We're definitely not doing spray-in for this project for reasons already discussed, so I appreciate your feedback on other options.