A(nother) Home in the (different) Woods

[radioman]

Interesting. Any reason you sprayed the "attic floor" rather than the underside of the roof? We are looking at foaming the attic in the future but I had only looked at foaming the underside of the roof deck (vs foaming the "floor" of the attic).

Thanks

Aaron Z

DONT foam roofs that has asphalt shingles on it. It will shorten the life considerably. Around here, its best to put up drywall in the ceiling and spray foam on top then blow in loose cellulose for best protection. I would only foam undersides of roofs if you need the attic space to be livable and you have HVAC mechanicals up there.

 

[EddieWalker]

DONT foam roofs that has asphalt shingles on it. It will shorten the life considerably. Around here, its best to put up drywall in the ceiling and spray foam on top then blow in loose cellulose for best protection. I would only foam undersides of roofs if you need the attic space to be livable and you have HVAC mechanicals up there.

What about a metal roof? Is there any problem spraying directly to the underside of a metal roof?

Eddie

 

[radioman]

What about a metal roof? Is there any problem spraying directly to the underside of a metal roof?

Eddie

Its kinda a tricky question eddie. Are you thinking open cell or close cell foam? Is this for a attic space in house or in a open barn? Are you in the northern climate or south? The northern climate is more susceptible to condensation then the south. Do you need roof support? closed cell is stronger then open cell.
SO -- what now? you know that open cell can soak moisture if exposed to the humid air. closed cell doesnt. However closed cell is expensive so now what? IF you want to install open cell in attic space of house, and it has a metal roof on top of osb sheathing - the only time its possible is to make the attic space air tight, no air gaps etc. you would want to test this with a air blower. This is the only way i know of to make sure the wood doesnt rot with open cell. I dont think its a good idea in a open barn. If you guys already have open cell sprayed on, fear not - just enclose the ceiling in the north climates.

 

[Fiziksgeek]

Back on post 178, you show that in the great room, they are spraying some closed cell on the underside of the roof deck, and and then filling the rest of the bay with blown in. Doesn't this put the vapor barrier on the wrong side?

 

[dstig1]

The foam setup we did is acceptable practice. It is foaming the underside of the roof deck (yes with asphalt shingles) with closed cell foam. It requires a minimum R value of a vapor impermeable insulation to do this. In my area that is R25. 4" of 2 lb closed cell foam meets that requirement. That then becomes the vapor barrier. The cellulose then just adds R value, and no vapor barrier is installed below the cellulose (or you would make a vapor trap - very bad). The goal is to keep the condensing surface above the dewpoint. You do that by blocking vapor to keep the humidity down, and insulating it to keep the temp on the moist side up. That is what the closed cell foam does, but it needs to be thick enough, and fully sealed up/continuous. In this case the first condensing surface is the underside of the foam, and because of the vapor-impermeable insulation above it, it will always remain above the dewpoint.

Spraying foam under shingles sometimes gets a bad rap as Radioman suggested. There is a feeling that all roof decks need to be vented by a number of people in the building industry, but there is really no negative effect on the shingles from doing this method. This is not to be confused with an unvented roof deck over an ATTIC SPACE. That will kill shingles in a short time as the temps will skyrocket in the enclosed space. The big difference with spraying directly on the deck, is there is no air space to act like a greenhouse. A number of studies have measured shingle temps with vented and unvented spaces like mine. The differences amount only a degree or 2 higher on the unvented one (again - no attic space below), and this is well within the temp ratings of the shingles. Now most manufactures will not warranty shingles installed this way (several used to), but then getting a building materials warranty to be honored is almost impossible in any case. They will always blame "poor installation technique" to try and weasel out of it.

As you can see, I did a ton of research on this before moving forward, and I have zero concern with this method. Open cell is a very bad idea in this application. Closed cell is the correct choice. Check out the link I posted to Eddie a page or two back.

 

[Fiziksgeek]

Fair enough. I have almost no experience, and this is the first I've heard of that method of insulation. I know you need at least 2 inches of closed cell to make a vapor barrier. And in the traditional attic space, I've seen lots of people do the 2" to seal everything up, then blown in whatever of top to get up to the desired R value. So I would believe that when reversing the order, you would need more, hence the 4" requirements. I've also heard that sometimes, with older homes, they will wrap them with foam board (taped seams) from the outside when residing the house. But this also has the potential to trap moisture in the walls, so I know there is a minimum thickness also, 3" I thought....so I guess it all makes sense...

The foam setup we did is acceptable practice. It is foaming the underside of the roof deck (yes with asphalt shingles) with closed cell foam. It requires a minimum R value of a vapor impermeable insulation to do this. In my area that is R25. 4" of 2 lb closed cell foam meets that requirement. That then becomes the vapor barrier. The cellulose then just adds R value, and no vapor barrier is installed below the cellulose (or you would make a vapor trap - very bad). The goal is to keep the condensing surface above the dewpoint. You do that by blocking vapor to keep the humidity down, and insulating it to keep the temp on the moist side up. That is what the closed cell foam does, but it needs to be thick enough, and fully sealed up/continuous. In this case the first condensing surface is the underside of the foam, and because of the vapor-impermeable insulation above it, it will always remain above the dewpoint.

 

[dstig1]

The amount of foam insulation you need to do this varies with climate zone. The colder the zone, the more you need to keep the deck and insulation surface above the dewpoint. In your zone, it might be 2" - I didn't look it up but southern new england tends to be a lot milder than here. The issue is similar when doing exterior foam as you note. For example, i could have done 4" of sheet foam on top of the roof deck, which would have been the same. I decided not to do it that way as this was a lot easier from a construction standpoint, but that was the initial plan.

 

[Fiziksgeek]

I agree, if you have the ability to do it from the inside, that's the way to go. Putting foam board on top of the roof deck is good for adding insulation to existing homes. I may be headed that way myself. My house was built in ~1985, and the family room has a vaulted ceiling, and less than desired insulation. I installed a wood insert in the family room fireplace that hadn't ever been used, keeping the room much warmer than in the first 25 years of the home's life, ice damns became a problem. In order to get insulation in there, I am either ripping down the ceiling, or tearing up the roof...

 

[dstig1]

There are advantages to doing it on the exterior. The biggest one is zero thermal bridges. Solid insulation all the way. Hard to beat that in many ways...

 

[dstig1]

Subfloor over radiant on main level

Got a pallet and a half of subfloor sheets delivered to put on over the main level floor over the concrete. It took 2-3 weeks to wrap that up, but it went down pretty good. Had some help on a couple weekends, and did some myself during the week on evenings. It was interesting as the sleepers we put in were so diced up by having to fit around the tubes, that it took time to mark each sheet as to where you could drive a screw before you placed it and secured it. All in all it worked out decently, but like everything, it just took time to get done. Fitting all the angles in the master bath was probably the most time-consuming single part of this. The subfloor is glued and screwed down, and then end result is pretty impressive. With the combination of the initial subfloor, 1.5" of concrete and the second subfloor over it, the main level floor is absolutely rock solid. It doesn't bounce at all or make a bit of noise when you walk on it. The reason for the second subfloor is to have something to attach the finish floor to. Most of the main level is going to be wood floor, and this will work well for that, plus as a base to build up with backer board for tile.

I thought I had more pictures of this in process ( I swear I do..) but I cannot find many them so we will have to go with this for now. You can see the subfloor in place in some of the upcoming interior shots, too. We started in the great room, and here it is over half done. This zipped along pretty decently, until we hit the master bathroom which had a lot of 45 degree angles in it. That took a lot of time, as noted.