How much spray foam in shop ceiling?

[pamike]

I have a 40 x 36 shop I am finishing up. I have a metal ceiling that is screwed to the bottom cord of the trusses. I would like to have the backside of the ceiling spray foam insulated. I talked to a local guy and he recommended 3" of closed cell foam. He said he could do thicker but that 3" is the best bang for the buck. The walls currently have 4" of open cell.
Anybody spray foam a ceiling? Is 3" enough? Or should I go with more?
I have radiant floor heat. Not planning to heat the shop real warm, but I am looking to build a very efficient shop.

 

[runningbird]

I just had mine foamed. its a wood frame building, ended up with about 5 inches on the ceiling. It's only been a week and my shop is not done yet but daytime temps have been mid 60's and night time low 20's. when I went in the shop the other morning it was 55 inside.

 

[LX-Markham]

I forget now, but I think it was 4" closed cell 2 lb foam (R24?) on the ceiling of mine

 

[theoldwizard1]

The real answer is "as much as you can afford".

The most heat loss is through the ceiling/roof.

 

[d300]

Although 3" of closed cell foam is only rated at about R25 the biggest benefit is that the roof will be sealed and it will feel like more. Having the walls sprayed is huge.
My house has 6" in the roof assembly and it is very easy to heat/cool. My shop has 6-8" of open cell and, as big as the building is, the unit heater dosen't run much to keep it at 60° even when the outside temps are below freezing.

Buy as much as you can afford.

 

[PaulKTM350]

2" closed cell is about the same as 4" open cell R wise. Closed cell is on the high end of cost also. It really seals up the space.

 

[86turbodsl]

One thing i think maybe nobody else caught here, is you said you screwed the ceiling to the bottom chord, which means it's the interior ceiling of the barn.
There's no point in putting that much foam in. Just spray a flash coat to seal it and top with as much (cheap) cellulose as you want. Your pocketbook will thank you.

 

[pamike]

2" closed cell is about the same as 4" open cell R wise. Closed cell is on the high end of cost also. It really seals up the space.

So if I got 3" open open it would have similar feel of d300 open cell at twice the height. Sounds like 3" might be plenty...

 

[pamike]

One thing i think maybe nobody else caught here, is you said you screwed the ceiling to the bottom chord, which means it's the interior ceiling of the barn.
There's no point in putting that much foam in. Just spray a flash coat to seal it and top with as much (cheap) cellulose as you want. Your pocketbook will thank you.

I don't want loose cellulose up there because I want to be able to access utilities and what not easily.
You are right, money wise that would be the best bet, but for my application its foam only...

 

[d300]

I have had several buildings over the years that I have had foamed. What I have learned is.... closed cell is about 2x the cost of open cell...closed cell R-value is about 2x higher per inch than open... open cell is better at sound absorption than closed (this is why I used lots of open cell in the shop)....closed cell (high density) is alot harder to dent/tear/remove...both seal the building very well, no air infiltration....UV attacks the open cell faster than closed cell.
YRMV

 

[stm317]

Open cell foam can have issues with moisture. Metal buildings tend to condensate and sweat, especially the underside of the roof. You don't want that condensation dripping down on your ceiling if possible, and you definitely don't want it dripping onto open cell foam. You need to have a plan for moisture.

 

[yeldogt]

In my area it was common to do 2" at a pass .... and it happens that 2" is enough for condensation in my climate. Doing a flash and batt system was very cost effective vs doing the full 4" needed for code.

Because of advancements w/ the foam -- doing the full 4" is not as big a labor jump over doing 2" -- mostly just the product cost. So the last few jobs I have done have been full 4" foam. I was really impressed w/ 2" of foam.

All insulation is diminishing returns -- especially with foam. Why -- because that first thin coat is sealing the building in ways no other product can ... after it's coated .. it's jsut a question of R value. And that's all climate based. Spec builders (where they build the same house over and over) say that 2" of foam is better in my area vs 2x6 walls filled with conventional.

I would take the 3" -- why not spray the roof deck?

 

[rburke65]

How much money do you want to spend?

 

[pamike]

I can do 4 in of closed cell for 4k.

 

[JohnnieMo]

One thing i think maybe nobody else caught here, is you said you screwed the ceiling to the bottom chord, which means it's the interior ceiling of the barn.
There's no point in putting that much foam in. Just spray a flash coat to seal it and top with as much (cheap) cellulose as you want. Your pocketbook will thank you.

I second this. I also thought I wanted to retain access up there, but it just ended up being a nightmare. In my case I was using batting and plastic vapour barrier, but I would still suggest you blow in cellulose after a thin layer of the spray foam.

 

[rburke65]

And I'll vote for this also. Spray foam a thin layer and then cellulose of fiber batts. But this might be areal chore since you will be up there walking around on all that. Spray it!