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Mike nichting
Posted: Apr 09, 2012 03:20 PM
upstate new york attic
I have a 3000 square foot commerical building that was built in 1950. It has one floor. The attic is complete untouched. Drop ceilings were installed in half of the building and insulation was placed on top of the ceiling tiles.

I love the whole concept of foam and want to put a three inch layer of phone accross the entire attic floor. My contractor tells me that if I use high density foam and foam not only the floor but also the gable ends, that I don't need to ventilate the roof (which is currently unventilated).

1) Is it true that I won't have to ventilate? Seems like 140 degrees in that area can't be good.
2) does he have to foam the entire gable ends. It seems to me that if he just goes a couple of feet up, he should be good to go.
3) Any other suggestions?

Thanks for any help!
Posted: Apr 09, 2012 10:51 PM
If you are going to spray the attic floor, spraying the gables is pointless. If you are going to spray the underside of the roof deck, you must spray the gables also. This system will require no ventilation and give you a conditioned attic. It will not be 140 degrees up there. I would recommend a minimum of 4" of closed cell foam.
Mike nichting
Posted: Apr 10, 2012 08:17 AM
Thanks very much for the response.

Sorry for the extra question but why 4 versus 3?
Posted: Apr 11, 2012 09:33 PM
Simply for more R-value. Foam will stop your air infiltration but you still need the "R". Depending on brand of foam you'll get an aged R-value between R6.4 and R7 per inch. The foam I spray (per the ICC report) will get you :3=21, 4=28 5=34, 5 1/2 =38 (code required). I have sprayed 3" in a roof by customer request with no complaints. Upstate N.Y. can get pretty chilly. I'm in central Maine and stongly recommend 4"-5" and have been doing more 5 1/2" applications since we finally adopted the 2009 codes. Hope this helps.
Mike nichting
Posted: Apr 16, 2012 09:01 AM
Thanks again.

I was just at lowes this weekend and see that batts of r-30+ are pretty cheap. Does it make sense to spray an inch of foam and then lay down batts of high r value insulation to save money?
Mike nichting
Posted: Apr 16, 2012 09:20 AM
I retract my last question. I see that there are other forums that address it.

I have another question though. Is it better to spray the attic floor or the ceiling (the inside of where the shingles are attached). There is less area on the ceiling floor.


Posted: Apr 16, 2012 09:10 PM
As far as hybrid systems go, especially in Upstate N.Y. I am strongly against them. Remember that the bitterness of poor quality lingers long after the sweetness of low price is gone.
As far as the roof deck vs. the attic floor. I prefer the roof deck. According to most building scientists it is the perfered method. Although end use of the space and roof pitch may not make it economically feasible.
Spraying the underside of the roof deck will give you a conditioned space (ie: it won't be 140 in the summer or below 0 in the winter.)
Mike nichting
Posted: Apr 17, 2012 07:52 AM
Thanks very much for the help.

Seems to me the the closer I spray to the living space the better able the foam will trap the heat in the living space.

With that said I think I will spray the attic floor and then vent the space above big time. What do you think?

Thanks again!

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