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I am renovated, rebuilding and adding on to a thirty year old or so haouse. The builder recommends using a sprayed in eurathane insulation (like corbond) as opposed to what we plan, envelop type walls. We have been enveloping the house, (exterior walls are 2×4, 16″ o.c., r-13 fb insulation) by adding a second insulated stud wall inside of the exterior walls, as we go, room by room.
Thoughts, experience, comment on the sprayed-in stuff? Relative costs, insulating values, makers and distributors?
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i've done double wall.. wouldn't do it anymore..if i want an energy wall i use 1" EPS (1.5 lb/cf)
b on the inside
then furr the inside horizontal 16" oc..
then blow dense pak cellulose thru the foam .. with regular 1/2" sheathing outside..
we also do about an R-50 attic / cathedral ceiling..
double wall still has a lot of air leaks unless you're blowing dens pak.. so it's very un-cost effective....
.. i think the energy wall i described above is superior to a sprayed foam and more cost effective..
b but hey, whadda i no ?
*Tim, Having used Corbond (brandname) and worked with several other spray-on foam insulations, I am not a big fan of that application. Given the choice by design or by option, I specify dense-pack cells or if unavailable blown-in fiberglass bibb system.The topic is open for much discussion, but I believe the exterior wall needs to breath. This can be achieved without suffering air-infiltration by using dense pack cells, and to a lesser degree using blown-in fiberglass. Spray-on foams do not breath and on a few remodels I have done, I noticed seperatation from stud- framing to allow air-infiltration. Also I have read several reports of R-value loss with the spray-on foams over a relatively short time. I prefer a double wall framing (staggered studs ) but do not think it is cost effective on a remodel, especially given the reduction in floor space and added expence of rewiring, window extensions, etc. Mike's point about EPS sheets is an option, but again you loose breathabilty.What I have done on my own reconstructed house and several other projects both new and remodeled, is to do a dense-pack into existing std walls then use denys foil as a radiant barrier. The denys foil is stapled to the face of the studs, then 1x strapping is ru over which your drywall or other wall surface. This will give you about R-15 for a standard 2x4 wall plus the radiant barrier which will help with heat retention. The wall insulation may not be the best, but your cost-effective tratments would be better spent in better, more efficient windows, window coverings, tighting up air infiltration at doors and windows, insulating the floor if possible/necessary and especially adding more insulation to roof/attic space.walk gooddavid
*is there a sheet insulation product at 3/4" thickness available to go between the furring or is the airspace required to be effective?brian
*Brian, If you are trying to achieve a radiant barrier, you need to leave the airspace (3/4- 1" ) for it to be effective. Usually when strapping or using furring over the added sheet insulation as Mike was discussing, it is not necessary to fill in the space. You again maintain and air space that contributes to heat retention, but it is not necessary asyou are working more with R-value than a radiant barrier.Adding an additional 3/4" EPS sheet could be used, and increase the R-value, but it is generally not done. I have seen the drywall applied directly over the EPS or HDPS sheets using longer screws. But the finish product of drywall showed more waveyness and variation of the wall surface than I can achieve with furring .walk gooddavid
*The remodel includes new siding (fiber-cement) new windows and doors (Pella insulsheild) and new roofing (40 year asphalt) as well as some structural mods and minor additions. Basically, a new shell. Plumbing, electrical (not including a new underground service), hvac, insulation, interior partions and interior finishing to be DIMyself.As I have been going through the interior of the house, room by room, I have been doubling the exterior walls, with staggered seams and using fiberglass bats with no vapor barrier. I live in heavy woods with lots of moisture and breathability/dry-ability is an important issue. Wiring or re-wiring is not an issue, as most of the house is getting rewired as I go. The house (among many problems of poor layout, poorer construction and 30 years of no maintenance) is poorly circuited. Also, the loss of the floor space is not particularly a concern for me. Cost effectiveness is a concern, but so is the ability of being able to do this myself, when time and budget allow. Floors are over a semiconditioned basement and unconditioned crawlspace. Over the crawlspace, they are insulated. When the project is complete, I plan on doing some air door testing and sealing up.As far as cells, go, I haven't seen it at my local home store. The fg batts are very available and convenient to install piecemeal, like I am doing. With 2 layers of r-15, exterior and interior wall materials, I get about r-33 out of my present scheme. EPS is readily available. Does dense pack cellulose come in a "batt" form? To be honest, I'm not real familiar with cells.Mike, how do you blow cells through foam? If I understand what your saying, I would end up with a wall that consists of exterior siding, sheathing, 2x4 studs 16" o.c. with dense pack cells, 1" eps between (5/4?) furring strips horizontal, 16" o.c. and interior, which in my case will be 1/2" gwb. What kind of an R-value will this yield? What is an approximate cost?David, having used Corbond, how much did it cost?
*Brian, Around here in SW Montana, CORBOND runs about $1.50/sgft x 3" thickness which is standard for 2 x 4 walls. Cells run a little less than half that. R-value comparison based on claimed R-value are CORBOND r-22 ; cells R-13.For a 2 x 6 wall, the standard is 2"of CORBOND with R-11 fiberglass batts for the same $1.50/sq ; claimed R-value is 25. For cells the cost is about $.85/sq with a claimed R-value of 22.Cellulose has the advantage of filling in every nook, cranny and void thus eliminating air infiltration. CORBOND will fill some spaces but will seal up most of the air infiltration. The problems of seperation arise when you have shrinkage in your framing or cold and/or wet framing at the time of installation. Cellulose is better at negating these problems.I am assuming that your house has CDX sheathing. With your new fiber-cement siding and existing sheathing, you are creating a pretty impermeable membrane on the exterior side of your house. When moisture travels through the walls and reachs it's dewpoint, condensation will result and since there is no place for the water to go it will be absorbed by the framing and sill plate of your wall. Serious dryrot is a good potential. It is a major problem with building today. CORBOND may help bty providing a sealed interior before the dew point if it maintains it's integrity. In any event, I think you would be wise to consider an air exchange system plumbed into the entire house which will help mitigate moisture without substantial heat loss.You can use 6mil poly on the inside of your walls as a vapour retarder, but I have found better success with sealing my drywall well when installed; caulk your edges to the studs, caulk around any openings in the drywall such as outlets, window jambs, and use a good quality Vapour barrier primer when you paint your walls and ceilings.walk gooddavid