My neighbor recently had open cell foam sprayed on to the ceiling of his attic. We live in the south and so summer lasts a long time here. As part of the process, all vents to the attic were sealed. The temperature in his attic dropped a lot. From typical summertime attic temps to 85 degs in the summer. Impressive to be sure.
My question, as was his, is what are the downsides? He was told, and from what he read he believes, that the open-cell foam does breathe and moisture in the roof won’t be a problem. He says the temperature of the shingles isn’t actually much higher since they radiate heat much faster than they conducted heat into the attic.
Obviously he decided to go with the technique.
Does anyone have any opinions on this technology? Is it safe for the roof?
Based on my understanding of a smart attic, you’d want airflow through the attic, so vents are good. I cannot imagine sealing up any vents. If you want to insulate, you insulate the house from the attic, but allow the attic to breath as much as possible, and to match the outside temps as closely as possible. This minimizes condensation, moisture/humidity and allows all parts that expand and contract to move/expand at the same pace/rate.
Insulating the roof isn’t the issue, but it might not help anything if the space is unused, unheated and uncooled.
I’d say you insulate the heck out of the attic floor, sealing it off as much as possible from living space, and allow maximum airflow at all times of the year through the attic.
Roof insulation = somone has to determine if there is a return on the investment when done to a roof above a non-living space.
The idea is that since spray foam is so good at sealing the space from air infiltration, a spray-foamed attic becomes part of the interior of the house instead of the traditional vented attic that is considered an exterior space. There were a lot of concerns when they started promoting this several years ago. People were concerned that the manufacturers of roof materials wouldn’t honor warranties when their products were used on such roofs, but that hasn’t turned out to be an issue (I think most manufacturers have issued statements saying that their products can be used in this way). People were concerned about the lack of venting, but that is borne out of a misunderstanding of the design of a spray foamed attic, which doesn’t need ventilation. It’s interior space. Just as you don’t have ventilation in the walls of your bedroom, you don’t need it in a properly sealed spray foamed attic.
A sealed attic is different from living space in that it does NOT get the ventilation that, say, your bedroom does. It becomes a closed/confined/unvented space. Nothing good about these spaces. And it gets hot. Closed. Dark. Hot. Unvented.
I believe the gist of the change is that insulation moves from the floor of the attic to the ceiling, and instead of venting the attic itself you vent the whole house, but not to nearly the same degree.
Basically, attic venting doesn’t do much for radiated heat, and there will be enough leakage through gaps, air conditioning ducts and the like that it’s more efficient to insulate the attic. Also, the home doesn’t need all of that humidity coming in and potentially condensing on the ceiling.
Philster, sorry, and no offense. Perhaps I should have been more clear on who wrote that cite. Joseph Lstiburek, Ph.D., P.Eng. and ASHRAE Fellow, lives in and is licensed in Toronto. He appeared on the PBS series NOVA when they covered sick building syndrome, and I have the impression that he is reasonably well known and respected in the field of building science. The “in the South” line doesn’t have anything to do with American politics. It has to do with climate.
The problem is that building science in America has developed mainly to address the demands of cold climates. To give the most common example, vapor barriers tend to be placed on the inside of exterior walls. This makes sense in the North; it keeps water from entering the wall from the room side and condensing on the cold exterior sheathing. People build like this in the South as well though, and it can be disastrous. Hot moist air enters the wall cavity and condenses on the cold inside wall, promoting mold growth.
Moving the building envelope to enclose the attic is a little less established; Listrubek recommends it for New Orleans, but doesn’t recommend it for dryer areas with equivalent high temperatures. It still makes sense though, for the reasons he gives in the link I gave upthread.
I appreciate the comments and the links!
My neighbor in fact is turning parts of his attic into living-or at least cooled storage space. All the vents, roof, gable, and eave vents are sealed.
He loves it. He thinks the insulation has cut at least $100/mnth from his electric bill. At that rate the project pays for itself in 2 years.
And New Orleans is right across the lake from our house.
I get it, especially for humid/hot areas. An attic space or unfinished room below the roof are just problems waiting to happen, so I can see how that works in that environment.
It seems there is return on investment that is practical, if the numbers are correct.
