note that all my comments are on common practices and materials I see in my 10+ years in the efficiency business. this is not to say one product is superior over another, just itrw here in La. concerning flash & batt: I've never seen anyone do flash and batt. to get the foam company to apply such a small amount turns companies statewide off. instead they talk the homeowner into full depth..or close approximation in 2x4 walls. also note that I've never recommended foam sprayed walls, and if they go that route..foam has to completely fill the stud bay..overfill with open cell & shave flat with stud faces. never seen flash and batt on attic side of ceilings either. If you could get a company to flash & batt walls it would entail a second trip to do again a minimal cost job to do attic floor. here we don't do fiberous insulations against rooflines so flash & BIBS wouldn't be installed. I wonder why would a foam company make multiple trips to the same site where they are making mininal dollars? even if they did foam & batts or blown..it is usually different crews. so you would have multiple trips and tie up two crews. now if it was for a bulider with several projects a year..that would work. but for a homeowner with one house at most every several years..just don't see it happening. maybe in Austin Texas. I try to be that bridge that brings homeowners and trades people together. so that is my pov in all this. people in my trade are unbiased and only sell efficiency so although we don't have a material dog in the fight its the efficiency that we fight for. Davd cary & lzerarc Yes builders do use tyvek & foam sheathing. because they don't understand clearly what the end goal is. if a builder has upgraded from felt to housewrap..that to them is a big step. and now you want them to skip the housewrap?? land of mercy!! you tryin to put them out of business? LOL! here we have hurricanes. solid sheated walls with osb & cdx is the norm. putting 1" polyisocyanurate foam sheathing over the solid sheated walls and taping all the seams..tape has to adhere to CLEAN and DRY surfaces.. sealing any holes mades by trades people before then installing cladding has been our most cost effective wall to date. follow with conventional insulation on interiorr of walls and air tight drywall. you've got high performance wall. R-7 foam sheathing..R-13 to R-15 insulation..not bad for a 2x4 wall. of course air sealing also includes sealing sole plates to slabs or subfloors, proper flashing & sealing of windows and doors. Air sealing ceilings..that is a whole other post. we do walls well..but ceilings! recessed lights that aren't ICAT holes for supply boxes returns..bath vent fans..stove vents.. speakers.. and wire and plumbing penetrations. the air sealing is in the details. but it pays back in comfort, smaller tonnage hvac, better indoor air quality. another post would be fresh air requirements & how exactly do do it. here is a link to my utility co-op's energy efficiency design for new homes. while it isn't as comprehensive as I pushed for it does show lots of good information. pay special attention to the exterior wall composition. you'll see that since so many builders INSIST on housewraps that they specify that it be next to studs and sheathing over tyvek. in general: designers/architects really let us down in that they don't design with hvac & ductwraps in the conditioned space. or incorperate accurate load calcs into the house when it is in design stages. maybe some do..but I've had several architects incorperate my spec sheet word for word onto thier plans. MY spec sheets. hell, they went to college for years, IMO they should have a clue...but just my angst there! trades people should seal holes they make as they make them. hvac should be comperhensively sized..not just rule of thumb. insulators should learn where to put the foam and educate themselves in thermal boundry locations. in a perfect world. continuing education for everyone! LOL! best of luck.

the purpose of the air space is to allow porous insulation to dry if it gets wet As well, in cold climates it is supposed to keep the roof cold and prevent ice damming; in hot climates, a vented attic reduces the heat on the roof surface and lessens the load on cooling equipment. Fibrous insulation subject to a convective current, as in an attic, has a reduced effectiveness vis-a-vis solid insulation materials. "Convective heat loss in insulation is rare, but it can occur when large temperature differences above and below insulation create tiny air currents (called "convection loops") within the insulation. Studies have shown that convective heat loss can occur with lighter density loose-fill fiberglass at the very low attic temperatures possible in extremely cold climates. Depending on the attic temperature, the insulation's measured R-value could decrease by as much as 50%" (See link below.) I have been in vented attics in winter watching the swirling snowflakes coming in from all those mandated vents. If the whole thing were sealed in the first place, the snow wouldn't be coming in. If prices were the same, I'd go for a sealed attic next time. I don't know if I have the energy to explain to the trades how to do it. Old dogs do not like learning new tricks. Here is a link that might be useful: Energy Guide

I read some very interesting info about vented and un-vented crawlspaces in the following document: http://www.huduser.org/Publications/pdf/moisturehomes.pdf It's a big read, but definitely worth it if you are concerned about moisture and mold issues. It also has some good stuff on vapor barriers, esp. regarding homes in humid regions such as the South East. I am still a little unsure as to whether we should actually have the vapor barrier facing AWAY from the living space, since my DH and I live in a primarily humid 'cooling' climate, where most of the year, outside humidity is greater than that inside. Moisture issues are important to consider if you are insulating your crawlspace. If you are not careful, you might end up with mold under your house, which we had, and is not pleasant! A 6mm plastic barrier is recommened for covering dirt crawlspaces to prevent moisture evaporating from the ground up. HTH

The one under the roof keeps outside heat from coming in whereas the one over the insulation keeps outside cold from getting in. Does anyone have any thoughts on this theory? Anyone tried to verify it? It's radiant barrier, it doesn't keep the cold out it keeps the heat in the home OR the heat out in the summer. Heat moves from hot to cold, not cold to hot. Heat is energy, cold is the lack of energy. Energy moves around. Shades of hot or in terms of radiation moves from hot to surfaces that are less hot. (or you could say from warm to cool). The problem is: this is more complex than what the video goes in to talking about. That's inherently the problem with DIY products... most of the time they play on the ignorance of people. (This sort of thing is often times presented to me as something to sell.... but because I know better they then turn this kind of stuff into a DIY product.) Because this guy is selling a product, he's only going to tell you how great and simple it is. He wants to sell this product to as many people as possible. You have to do the prep work as I suggested earlier up in the thread... but once you do the prep work reinsulating properly, proper ventilation etc. the need for radiant barrier is greatly reduced. The reason I know this: I own a home that doesn't have any radiant barrier on it and it resides in a hot and sticky climate. Ventilation + Proper Insulation and that's really all you need. Radiant barrier can help... but without proper insulation + ventilation it probably won't make that much difference. A ridge vent by itself will not provide adequate roof ventilation; there must be eave vents to allow air to enter and rise to the ridge and escape. yep, too many people focus on getting the heat to escape and don't realize they have to replace that air that is leaving with cooler air. If the cooler air has no way in, well that hot air isn't going anywhere either... just sit in there and get hotter still. I know we'll put a roof mounted fan in there and force that heat out. LOL.