Spray foam insulation installation
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I've heard mixed opinions (and they all seem to be opinions) that you either DO NOT put spray foam between the roof rafters, or it is OK to put spray foam between the rafters.
I was in a house the other day that was loaded with spray foam - it was put everywhere, and I mean LOADED on. The house, still being built, was probably 10 degrees cooler inside than out, and it even had the windows open (no wall coverings up yet). It seemed to be pretty effective.
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@unknownuser said:
I've heard mixed opinions (and they all seem to be opinions) that you either DO NOT put spray foam between the roof rafters, or it is OK to put spray foam between the rafters.
I was in a house the other day that was loaded with spray foam - it was put everywhere, and I mean LOADED on. The house, still being built, was probably 10 degrees cooler inside than out, and it even had the windows open (no wall coverings up yet). It seemed to be pretty effective.
depends on the detailing, climate, if house has an air exchanger, roof build up, etc. etc.
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It IS very effective... BUT if your geographic area is prone to certain climatic conditions and there isn't an adequate vapor-barrier on the warm side of the insulation and/or ventilation [to the outside] of the 'void'; and there are very humid internal conditions [e.g. showers without really good ventilation]... then in cold winters you can get interstitial-condensation forming on the rafters' surfaces on the cool side; if these voids are not appropriately ventilated and/or treated with preservatives, at the least you can get molds forming or, even worse, fungal-rot affecting structural members...
Your architect should advise...
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House is in south east Texas, Washington County, about 2.5 hours from the coast, in the start (south east corner) of the Texas Hill county. High humidity is expected.
I haven't seen what is going to the attic yet for special air handling or venting. -
I concur with TIG. If it's packed too tight (I.e. no air movement) mold in High Humid High moisture areas is a real problem. Here in the Mountain west, we're pretty dry--well not this year-- but we get a lot of snow. I did batt in the walls and attic blow in. Foam for around the windows and such.
Good Luck.
By the way . .. I was checking google maps last night on an Ipad and noticed that the Google satellite did a fly over of my lot after I had dug my hole for the foundation --so I can see the start of my house on google! That means they flew over my area last July. Kinda trippy!
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In addition to what TIG said, I would add that some manufacturers of asphalt based roof shingles could have a problem with this if the roof deck has no other way to dissipate heat from direct and prolonged sunshine. It could contribute to shorter service life and loss of whatever warranty is available. If this is indeed a concern, you may have to consider a "cold" roof, one in which the nail base (the nailable deck) is isolated from the rafters with "sleepers", strips of wood placed in staggered purlin fashion. The contiguous space the sleepers occupy allow some convection and some radiation to occur between them. It is called a cold roof because in northern snowy climates you want to minimize snow melt from house heat, as it becomes hazardous when it sloughs off. At least that is my understanding.
Back to the insulation. If you had a way of spraying the foam onto a membrane held down and away from the deck, and as TIG said, ventilate this chamber between the rafters, you are less likely to damage the shingles.
Even if you use metal or ceramic shingles/tiles/panels, you will need something like ice and water shield membrane beneath these "invincible" roof protectors, as the membrane is the real roof and the shingles are the protectors. -
The roof in this case is an aluminum (think tin, standing seam) roof.
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Then, consider the ice and water shield membrane. And, hopefully, your standing seam system uses concealed anchorage. No exposed fasteners.
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If you haven't already done so, pop over to the FineHomeBuilding website and do some reading over there. Lots of good stuff.
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@tim said:
If you haven't already done so, pop over to the FineHomeBuilding website and do some reading over there. Lots of good stuff.
There is an FHB related site:
http://www.greenbuildingadvisor.com/book/export/html/14955
http://www.finehomebuilding.com/PDF/Free/021189072.pdf
http://forums.finehomebuilding.com/breaktime/energy-heating-insulation/spray-foam-insulation-8There are different solutions depending on climate. It does make a very tight house which is a very good thing but does require proper detailing and the aforementioned air exchange solution.
If you can afford it, it is the best insulation, it does require different approaches and solutions to ensure you don't have problems down the road. (this is also true of every other type of insulation)
With the metal roof you will likely not have to worry about roof issues but I would want to have an air gap for ventilation to reduce the amount of heat transferred to the structure. There are many ways of achieving this either by adding a second layer of sheathing with a spacer to create air channels or by the traditional chutes on the underside and then spray foam over them.
Creating a complete envelope and having the entire HVAC system in the conditioned space will ensure better efficiency and the sealing and insulation values you can achieve will offset any increase in the volume of the conditioned space.
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