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Posted By mdaniel,
Jan 8, 2010 at 7:41 PM
That's an interesting thought.
We're in the process of a 7000 sq. ft new build and we are doing this very same process of "flash and batt" in the side walls, However, our foam coating is 2 inches w/ fiberglass batts on top of that. Personally, for where we live and length of heating season, I kind of think that only 1/2 in. is a bit light-but it a diff. climate it probably would be okay. The sub said that we'll accomplish at least an R-28 value in our sidewalls, brings the cost down not going the full 5 1/2 for the sidewalls.
Another option that I've heard of people doing, don't know how well it works, is to fill the joist cavities with batts or other techniques, and then put up an inch or two thick layer of foam boards on the underside of the joists, being careful to tape and seal all seams, penetrations and so forth...
StackedLumber, What kind of foam are you using? Open cell or closed cell? Open cell at 5.5" should yeild around R-20. Cl;osed cell at 3" should be close to R-21.
I believe it's a urethane spray foam which I believe is a closed cell foam, but I may be mistaken and can ask the sub cont. on Monday for the exact details and specs., but I'm almost positive that the urethane spray foam in considered "closed cell". We having done a full 3", only 2" plus batting on top of that.
The explanation I got from the sub was this. It is a closed cell foam that yields (supposedly) a 7-7.2 per inch R value. So what they are doing is a 2 inch application of the foam and then R-12 batts on top of the foam. I told him by my math that would give us r-26, not r-28 and he answered-I guess you could say that.
Anyways, overall i think the point is that the spray foam goes leaps and bounds into eliminating drafts and other "unwanted" guests (flies, ladybugs, etc. etc.) from entering the sidewalls. To me, insulation should be about eliminating air infiltration just as much as heat retention.
Jim, would you recommend using DPC in a cathedral ceiling? I've always worried about the effects of small roof leaks soaking into the cellulose and causing a catastrophic ceiling failure when the wallboard finally gives way. Is that a reasonable concern?
I feel compelled to add my $0.02 worth.
There is an article which gives details on how and why Sprayed Polyurethane Foam is so good, and cites a number of real world scenarios. Some of the information in the article addresses several of the claims of writers in this thread. With data and evidence from several actual jobs which (a) supports some of the writers in the thread, and (b) shoots holes in claims of other writers in the thread. I shall let the article speak for itself. Link to the article is:
SPF in between your studs will increase the racking strength of your walls by a factor of 3x to 4x - you will have a stronger house.
SPF will function as a sound insulator. Do you live in a city? - you will hear less traffic noise.
Anyone who says that you should not put SPF in your ceiling or attic or cathedral ceiling is simply letting you know of their ignorance - reading the above article certainly disabused ME of MY ignorance!
My wife and I have researched this for several years, and we would not even consider anything other than Closed-cell (this means 3 pounds per cubic foot density) Sprayed Polyurethane Foam. We have a good friend who is an architect tell us that if we used SPF in the 25' high gothic arches of our barn-to-be-home we MUST (her emphasis) leave the 2' space between every fourth or fifth arch open (no insulation), from floor to roof peak, so the house could breathe. My wife and I looked at each other in total disbelief - and with those respective looks we silently communicated, "she just talked herself out of designing our home."...and she did not even know what her ignorance had cost her.
I have other links to a variety of sites where various well respected agencies report data on various positive aspects of SPF, not even touched on here. If you'd like them I can send them to you - and I'll let you post them here if you'd like.
Email address is --- email@example.com.
There's nothing more satisfying than knowing you have made a well-informed decision.
I read more in this thread, and found the below and other similar comments to be of great interst....
"Another option is to do what is called a “flash and batt”. This is where they come in and just put a thin coating of the foam, say 1/2” or so to seal everything up and then install traditional fiberglass batts. This also can be done using netting and loose fill if you choose. Another thing to consider is to make sure all the HVAC and Duct work is in the conditioned space. Makes a big difference. On a current project we are doing, we have to foam the roof deck so that attic is part of the conditioned space just for the HVAC. And install and ignition barrier as there is no sheetrock over the insulation.
Good Luck, Michael"
I agree with Michael........with one minor modification, have them spray Closed-cell SPF at 1 and a half inch...then the fiberglass batts.
The articles I've read present convincing arguments that this is an inexpensive and very viable alternative to 3" of SPF.
When cost is an issue, this oughta be a superb choice.
If I were building a new house I would have cellulose installed in walls and attick. there is a methed of spraying it in the stud cavities on walls slightly damp and then it dries crisp and then they brush it off flush
with studs with a power rolling brush. It wont settle. It has boric acid in it to deter bugs, and most important it's not flamable like spray foam! Its allso much cheaper than foam and fiberglass. No voids like are commen in fiberglass batts. Foam is a good product but if you use it make sure you have ventalation or you will have mold problems. Im a contractor and I prefer cellulose.
Hello, Interesting post, particularly so since you are a contractor. My wife and I have spent a great deal of time researching insulation alternatives, and we find a strong consensus that at least one inch of Closed-Cell Foam Insulation can be an excellent and very likely the best investment one can make in their home. This is based on some essential assumptions. Assuming you are using some common siding and roofing...The foaming must be done (a) after the rough-in of electric and plumbing, (b) after the siding is on, (c) after the roofing is done, and (d) perhaps also after HVAC ducting is done.
The one inch of closed-cell foam will plug any and all holes, will function as an air barrier and as a vapor barrier - thus eliminating the necessity of purchasing and installing TYVEK or an equivalent 'house wrap'. (After installing your Tyvek house wrap, which is supposed to function as your air and vapor barrier, you will punch several thousand holes in it when you put on your siding, how wise is that?!). See also this link for compelling information from a site where they are not selling insulation, just presenting facts, as well as information from users as well as contractors...http://www.monolithic.com/stories/foam-chapter-04
If you apply the one inch of closed-cell foam after you do (a) through (d) mentioned above you will have an impenetrable seal of your home. Is it not true that moisture-laden air movement through insulation is the source of the water (and nutrients carried as 'dust' with the air/moisture mix) which the mold must have to grow? The one inch of closed-cell foam stops all those air-leaks, and stops convective flow of moisture-laden air. With this air movement stopped you need not worry about mold. Now the home owner can proceed with adding more foam if money is not an object, or they may choose to add a less expensive alternative insulation to fill the remainder of the wall, ceiling, attic cavities.
I do like your idea of spraying the cellulose into a moistened cavity. I have read in numerous places that a 'skin' will form much as you describe, and additionally that settling will be at worst minimal. I can understand that the cellulose could be better than fiberglass batts (paper-backed or not), no matter how careful the installers of the fiberglass batts were. Wouldn't it therefore be wise(est) from an economical perspective to use 1" of Sprayed, Closed-cell Foam, then use 'your' cellulose application to complete filling the cavity?
Have you ever done a side-by-side comparison of closed-cell foam vs cellulose - one house done with foam and another very similar style and square footage home done with cellulose? Have you ever done a side-by-side comparison of a home where they used just 1" of closed-cell form + cellulose for the remainder vs just cellulose? It would be very interesting to get a year's energy use data on those homes and compare. I wonder if anyone reading this thread has any personal information to share, or if anyone reading this knows where to 'send' us all for actual comparative data.....????
I do not believe there will be a problem with mold if you use Sprayed, Closed-cell Foam. Everything out there argues very strongly that it will not be a problem. The above link addresses this issue fairly well.
Wanted to respond to your post. I'm not an insulation contractor so I don't have the numbers to compare, but there have been blower door tests done. If you go to the Nu-wool website you may be able to find the info there.
I Know they foam any cracks and around electrical boxes etc. before sprying the cellulose. Netting is used on walls that dont have a backing on to spray such an interior bath wall you may want insulated. Don't know if
cellulose would stick to foam or not. I would use house wrap regardless to repeal any water that may get behind siding. It is also made from100% recycled material and takes 10 times less energy to produce than fiberglass
Has anyone had any experience with a Direct Under Roof Spray? We have an unfinished attic. It was roofed in the last couple years (before we bough it). Who ever roofed it, just roofed over the slat bords and did not put down new decking. I can see the underside of the shingles from inside the attic. There is no venting in the roof at all. I was told a direct roof spray would be my best option. The big question I have is when its time for a new roof, the foam will be bonded to the old shingle bottoms so when tey are removed and the new roofing/decking applied they will leave an air gap. Unvented air gaps = moisure created by dew points right? But if the foam is a vapor barrier from the house side, then no moisture should be able to come through the house and get trapped? Am I too worried about this? The other option is to do a shitlowd of work and cut in vents where they can go the I will lose over an inch of insulting space. WHich I only have 5 inches of anyway. We plan to finish the attic at some point.
Interesting query. I will speak with the gentleman who will spray our roof (outside application), and get his take on this. He has been using SPF for over a decade, and likely has run across your situation - we'll see.
Regarding your concern about unvented air gaps, and in particular the situation present 15 years from now after a tear-off and re-roofing job. I don't believe this should present a problem, since I am certain you are correct that the foam acts as your vapor (and water) barrier INside, thus you won't have any moisture problems at all.
I cannot imagine that going to the trouble of creating a boatload of vents would be necessary.
I will post again once I get a reply from the guy doing our spraying.
Sincerely, Hankovitch in SW Wisconsin
Wow Thanks so much. That would be great!
I received the reply from Scott Waste, of NES Building Solutions.
If you have additional questions, I am sure he would communicate with you.
You may reach Scott Waste by email at [firstname.lastname@example.org]
And his Web Site is http://nesbuildingsolutions.com/
Below is Scott's email to me.............
Hank, What you and this home owner are talking about is what we call a "hot roof system".
I believe in the system for insulating - as I did it to my own house over 7 years ago .
When you apply the closed cell foam to the underside of the roof deck you are creating a non-vented attic and or air space. Please note also that this technique for applying will void many of the shingle manufacturers' warranty. I hope at least the roofer laid down tar paper, then the shingles.
Note that during tear-off of the shingles at a later date they will just have to be a bit careful not to 'pull' or just 'rip out' the nails... but more to tear or cut along the top of roof boards to try to cut off nails of possible, and to thereby minimize disturbing or damaging the foam.
By using closed cell foam they will get a vapor barrier and air barrier all in 1 system --- at a depth of 2 inches or more of foam.
Another option they have is to install air shoots from the eve to the ridge and then make sure they have eve vents and a ridge vent. Then spray the closed cell foam on the underside of these 'air shoots'. This must be done in every cavity. If they have different pitches and or dormers, then you will have fewer cavities that can be vented by this technique.
A final idea (assuming the roofers did not put tar paper over roof decking before shingling) would be to put tar paper on the underside of the decking prior to foaming.....extra work, but do-able.
A note added by Hank - perhaps if the roof boards are pretty tight (let us say gaps between boards a quarter inch or so), then perpaps they could apply the foam, and not worry TOO MUCH when they do the eventual shingle tear-off some years from now.
Hankovitch in SW Wisconsin
Building Science corp. has some good information on insulation options. There are several good articles in the Digests section of their website. For roofs, this document may be helpful.
http://www.buildingscience.com/documents/digests/bsd-115-wood-pitched-roof-construction/?searchterm=pitched roof insulation
general ventilation primer:
I had some Icynene, open cell, sprayed in our ceiling cavities and think it's great. Im writing in because of the "Flash and Batt" idea. I sprayed my propane storage tanks with closed cell foam and ran into problems. When I sprayed the foam on the tanks it did not loft. The reason was that the tanks adsorbed some of the heat that the foam self generates to loft.
How this applies to Flash and Batt. In reading up on foam installation there are many thing that can effect the quality of the job. One rule of thumb is to spray product on, in, 2 to 3 inch layers. This is directly related to the exothermic reaction ( I was taught that word by a Boiler Room Member I'm not that sharp ) of the foam's 2 part properties. If you go less than 2 inches you don't have enough foam to complete the reaction. Not enough foam mass to build up it's own internal heat to loft. If you go with 4/5/6" you can cook your finished product and have cracks etc.
The other problem was mentioned in a previous post, it puts the vapor barrier on the wrong side of the fiberglass. Yes you can make a case that there won't be any air movement because of the foam but.........
Like any professionally installed product applicators experience, ambient temperature and humidity also play a factor.
I have also read about spraying the underside of the roof. That is a correct application and vents are not required. You need to make sure you get the complete roof and end walls down to the walls below because you will now have warm moist air in attic space and if you have any voids you will get condensation or ice build up at those points. Then mold.
Icynene has a great web site for Q & A that you can read up on. Where you don't want to foam is any where there is a possibility of a leak. Under tubs, washers and the like. It does afford nice noise dampening characteristics but if there is a leak the water needs to get out and not get trapped in or on the foam. This will create a mold situation.
What was the temperature of your tanks when sprayed? I sprayed my tank and didnt have any problems. Spray the ubderside of the roof deck with closed cell( 4-5") to make it a hot roof. When its time to replace the shingles it might take a bit longer to trim any foam down that has filled the gaps, use some ice and water sheild and find a shingle manufacturer that does warranty there shingles( Certainteed, Elk are the oly two i know of right now). Then REAP the benefits.
Note: Do not use open cell, you dont have enough rafter depth to get the required R-value.
Tanks were some where about 80+F. They were warm to the touch. I know the product I got was fresh and I had it to the proper temp before spraying but frankly the second coat didn't loft the way it should of either. The only up side was that the manufacturer gave the local distributor a freebie kit so when all said and done I have about 3" to 4" of coverage.
Have a good one Rob.