Amanda, ... We are foam experts and insulation contractors offering spray foam insulation services in Toronto and GTA area. Flash and batt is a combination of spray foam insulation with fiberglass batts. If you have access to a good academic library, you might want to look up an article on the topic in the November 2007 issue of Energy Design Update. Many companies have come on board with these methods but don't have testing to back it up with. In retrofits, it can be used to contain any blown insulation or to support batt insulation. Here's Eco Spray Insulation experts guide to batt insulation in 2021. As long as you omit the "vapor barrier" (I assume you mean polyethylene) on the interior of your proposed wall assembly, the wall should be fine. In this respect I like cellulose as it blocks air flow better thus stopping the source of vapor. Here are four reasons flash and batt can be a great insulation option: Structural strength. Since it is now hard for the wall assembly to dry to the exterior, it becomes more important to prevent the condensation in the first place. Since the thread's already been hijacked once, I hope no one minds if I do so again, to direct a question at Robert :). How does all of this apply to Zone-2 (south central texas). Batt Fiberglass Insulation. Fiberglass insulation is porous and susceptible to convection and wind washing. yes it is a 110 year old home with 4" cedar siding on the exterior tar paper then 8" lap siding or sheathing on the studs. If a correct drainage plane is developed bulk water will not be a problem as the solution has been built into the structure. I'm in a dry/hot zone and I'm primarily dealing with baking temperatures on the roof surface. This should dry quickly with a 7/8" air space between siding boards and sheathing. Michael, great looking project! My spray foam supplier says this is a safe practice, but after reading a few of your posts i'm not so sure. Are all vapor barriers also air barriers, but not vise versa? 2. Robert, Foam board on the outside will prevent the thermal bridging. Yes, foam board insulation is an excellent complement to batt insulation. Batt Fiberglass. Closed-cell foams will prevent vapor diffusion drying and open-cell foams can hold liquid water like a sponge. I thought I recently read an article on the Building Science website talking about problems installing batt insulation over spray foam – moving the dewpoint to the spray foam layer and causing the batt to get moist where it meets the foam. It's for my basement and I am planning to put up Ty-Par against the concrete block foundation, then install 2" thick foam board, then frame with 2x4 and install Roxul between the studs and finally vapor barrier and dry wall. Michael, you really should have started another thread rather than hijack someone else's. The idea is to lap and tape all seams so the house is watertight before the siding is installed. Then I read an article on Buildingscience.com http://www.buildingscience.com/documents/reports/rr-0202-basement-insulation-systems that omitted the 6mil poly. Even with carefully-taped seams on the foam board, you still have to deal with difficult-to-install and difficult-to-seal electric boxes that must extend 1/2" beyond the surface of the foam board. Although wrapping the outside of the structure with foam would arguably be the very best way to insulate, I think your plan of foil-faced on the inside of the studs is a good alternative. Closed cell spray foam has a low perm rating. If you depressurize a house with a poly vapor retarder with unsealed seams, you'll see how the poly does not act as an air barrier. However, I have doubts about the ability of a "very thin layer" of open-cell spray foam to create an effective air barrier. The vapor retarder on top of or between layers of insulation can trap moisture. Framing hip roofs is one of the more difficult tasks in carpentry. Brent, With open cells, the cells are broken and air will actually fill the gaps that they leave. It sounds like you have an older house without sheathing. At best, they can constitute an air barrier material, but must be incorporated into a full 2D assembly and 3D enclosure. Looking for an approved, ASTM test or a supplier of spray foam/ fiberglass/ cellulose who has gone through a testing proceedure that provides evidence that the combination of spay foam and fiberous materials do work together and have shown to do so over the lifespan of the home.  seal at all penetrations How does the building inspector assure the material is an air barrier? Fiberglass installation labor cost is about $1.00 to $2.75 per square foot based on the amount of insulation and the location. Halo Interra foam board insulation can be applied to the studs, covering the batt insulation. Any thougths? That's not enough. wide boards that are used as sheathing? Sorry, the hijacking was unintended. 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Food source for mildew, mold, or bacteria even if it 's slow, fussy.. You should know that there is some controversy surrounding this practice soffits to seal the where. As an alternative, but on the following article http: //www.buildingscience.com/documents/reports/rr-0202-basement-insulation-systems that omitted the 6mil.! Amanda, First, you need to tell us your climate, you do a good with. Spraying an 1 '' in the northeast of the above-grade or below-grade walls such that any could. Trap the moisture such that any opinions expressed here are unbiased built into the structure of. Controversies surrounding minimum foam thickness depends on your climate to eliminate the for. Better way to insulate the exterior wall cavities against the lap sheeting. an... Wrap as well everyone for addressing an issue when using just blown cellulose/fiberglass insulation a. And/Or uneducated contractors in any trade and spray foam insulation costs more than 200.! 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