Hot Roof. Interested in opinions

[Michael Weber]

I need additional insulation in my attic space as well as needing to increase attic ventilation. I have a square hip room that comes to a peak. I was thinking of opening up the peak and adding a cupola along with more eave vents for the ventilation part and adding cellulose for additional insulation. I ran across something called a "Hot Roof" where the insulation (foam most likely)
is sprayed on the underside of the roof decking. Not sure what else is involved with this process or how well it actually works. I understand it is particularly helpful where the HVAC unit and duct work are located in the attic which is my situation. I live in Arkansas and it gets hot and humid in the summer. Does getting a hot roof mean that ventilation is no longer needed or even counter productive? Would I need to seal off the existing minimal roof venting? If there was say 8 inches of foam on the roof deck and the attic unventilated do you think the attic would remain reasonably cool on a hot humid sunny day? Not sure about the ability of the deck insulation to really keep the attic cool. If it matters, the house is two story and the attic is unused as a living area. Anyone with experience good or bad or just an opinion of why one option is better than the other? House is a work in progress and there may be a need for additional roof openings in the future.

[Tom Winship]

Michael,
I looked at this down here a couple of years ago. I had a guy from the local utility company says that it works. Fairly expensive, I think but had a pretty good payback as I recall.
The thing that he said that impressed me was that he had been in attics on a 100 degree day and the attic was 80 degrees.
As I recall, you have to remove the existing insulation in the attic. I would check with your local utility company. They have guys that work with builders and are up on the latest.

[Myk Rian]

It was one of the home shows that foamed the underside of the roof on a house. It was going to be used as living space.
Their other thought was to put in all kinds of roof vents, and let the air circulate through it. That was if the space would be just an attic.
It was to keep ice dams from forming.

I have wondered if insulating under the deck would have any effect on the life of the shingles.

[Brian Elfert]

On the Holmes Inspection TV show if they reinsulate an attic they generally put down an inch or so of spray foam that totally seals any air leaks and then cellulose over that. You have your HVAC in the attic so that probably changes things.

If I ever build another new home I will probably do the spray foam things in my attic. I only know of one house in Minnesota with HVAC in the attic. HVAC is generally in the basement.

[David G Baker]

I frequently watch Holmes on Homes and feel terrified at the thoughts of trusting a contractor to do any work on my house. The person that owned my house prior to my buying it had re-did the roof, I didn't like the looks of it so I had a new one put on. The old roof had to be removed down to the trusses. There was no roofing felt on the roof, the OSB that was installed was originally 5/8" thick had swollen up to around 3/4' thick, the 1x8" original roof boards had to be removed due to rotting and mold, the soffets had no openings for venting and the insulation was crammed into the space where the openings should have been. A roofing job that should have cost me around $5000 cost me $11,000.

[Mike Archambeau]

There is a lot of information available on this very topic on the Fine Homebuilding site. It is a fairly complex topic so there are no simple or fast answers. But if you are interested in engineering a solution that will save you some energy costs as well as extend the life of your home, the knowledge you glean from that site will allow you to do it right the first time.

[Larry Edgerton]

http://jlc.buysub.com/index.php/review/product/list/id/191

This book is probably one of the better real world references for what you are thinking and offers other solutions as well.

Also do some research on what that will do to your shingles if you have asphalt shingles. Heat buildup is a problem that a spray foam insulator will not tell you about. Some shingle manufacturers void their warrenty if there is no ventilation under the roof decking. The temps in a southern sun with no way for heat to escape are very high indeed.

Larry

[Myk Rian]

We had the roof stripped and re-shingled about 4 years ago. The living quarters roofs are un-insulated, but the garage/shop has fiberglass under the deck. Helps during these cold northern winters, as I heat the garage.
During the summer, I've measured as much as 140º inside the roof peak. No idea what the shingles temp is. I have a fan that exhausts the garage through a roof vent to help cool it down to about 95º on those hot days. So far, the roof still looks good. I stay off it as much as possible, only being up there to clean the gutters in the fall.



http://jlc.buysub.com/index.php/review/product/list/id/191

This book is probably one of the better real world references for what you are thinking and offers other solutions as well.

Also do some research on what that will do to your shingles if you have asphalt shingles. Heat buildup is a problem that a spray foam insulator will not tell you about. Some shingle manufacturers void their warrenty if there is no ventilation under the roof decking. The temps in a southern sun with no way for heat to escape are very high indeed.

Larry

[Michael Weber]

Thank you all for your input.