| Author | Message | ||
     jolynn Citizen Username: Unixiscool Post Number: 42 Registered: 2-2005  |
Hello, I am interested in gathering information on spray foam insulation for my attic roof and walls. I just had the old horse hair insulation removed and I am about to get a new roof so I will be starting with a clean slate. Has anyone used this? I heard that if you use spray foam you don't have to vent your roof, is this true? That would be a bonus for us since we don't have vents in our siding under the roof line. Is there anyone you would recommend to do this job? Thanks | ||
| Jgberkeley Citizen Username: Jgberkeley Post Number: 4645 Registered: 5-2001 |
This Old House had a show that featured the use of Spray Foam Insulation. I've not seen it around, but if you contact TOH, perhaps they can point you the way. | ||
| jolynn Citizen Username: Unixiscool Post Number: 43 Registered: 2-2005 |
Eek, I just read on TOH that spray foam can cost 4 times more then fiberglass. Hmmm, plan B. The one concern I have with fiberglass is that my roof was built with 2 X 6's and the best R-value I can get is R-21. Would it be logical to put ridged foam insulation below the rafters after I have filled the space between them with fiberglass? Is there a better solution I am just missing? Thanks | ||
| Jgberkeley Citizen Username: Jgberkeley Post Number: 4647 Registered: 5-2001 |
If you are talking about a typical attic where you have a floor, (ceiling joists) and the 'A' frame for the roof; you insulate the floor. You do not insulate the rafters, the 'A' frame. To do so will cause your roof to cook off years sooner than it should. If you must insulate the rafters, (Building an attic room) you need to provide vent channels and ridge vents, and I always incluce a power vent fan. | ||
| MittenReckitt Citizen Username: Mittenreckitt Post Number: 94 Registered: 4-2006 |
Is this a reasonable DIY job? Or is this one that should be handled by a professional - any hazards of handling insulation material? | ||
| Jgberkeley Citizen Username: Jgberkeley Post Number: 4651 Registered: 5-2001 |
In my opinion, this is a more than reasonable DIY job. Wear a standard dust mask and gloves. Have fun. George | ||
| Travis Citizen Username: Travis Post Number: 469 Registered: 6-2004  |
It is a myth that not ventilating the roof deck will cook the attic. That myth has been disproven by scientific tests. In fact insulating the roof deck will improve energy efficiency if you have an air handler in the attic. There are arguments for not insulating the roof deck: there is less square footage if you just insulate the attic floor, and you can spot leaks in the roof deck if it is not covered with insulation. If you do insulate the roof deck, putting in baffles for ventilation can still help dry it out in the event of roof leaks (or even just snow melting on the roof). Ridge and soffit vents are useless if you add mechanical ventilation, it short-circuits the air flow over the roof deck. There was a fascinating research paper that I saw once on the origin of ventilating attics in US houses. It was pushed by insulation companies who were seeing condensation problems in Minnesota. Remember that next time you see a ventilated attic in Texas. There is no scientific basis for saying that ventilation prolongs the span of your roof shingles, no matter what the shingle companies say. The 300:1 rule you hear about? Someone just pulled that number out of their •••, and it just kept being repeated. Fiberglass is basically junk for insulation purposes. And it may eventually be banned as a dangerous substance. Remember, everybody was happily playing with asbestos for decades before they banned it. Cellulose is better than FG, but there are growing worries about fire-retardent PDBEs and their effect on brain development. Levels are much higher in the US than anywhere else. Is this why 1 in 2 Americans does not know what year 9/11 happened, and 1 in 20 don't know what date? If you want to just insulate your attic floor, 5-1/2" is not enough. If you want to use the attic space for storage, one thing you could try doing is laying a second set of floor joists on top of the attic joists, perpendicular to the original. This will not only give you a higher R-value, it'll isolate the thermal bridging to the intersection points of the joists. But the key to insulation is: stop air leaks. This is the big win with foam (if done right). | ||
| Kevin Supporter Username: Kevin Post Number: 851 Registered: 2-2002 |
For you insulation experts... The unfinished part of my attic doesn't have enough space to stand up in, so I don't want to lay a second set of floor joists for insulation. Besides cost issue (because it is probably expensive) is there any reason why you cannot use a polyisocyanurate sheathing like Dow's Thermax between the joists on the attic floor, seal the seams, and then cover the floor with plywood? Thermax insulates with an R-value of 6.5 at 1" and it is approved for interior use without a thermal barrier. You can get the sheets in many different thicknesses depending on what will fit between the joists. http://www.dow.com/styrofoam/na/thermax/whychoose.htm | ||
| jolynn Citizen Username: Unixiscool Post Number: 46 Registered: 2-2005 |
The attic floor is finished and has old blown in insulation already. But it is really old and I am afraid it might be asbestos. I am looking to insulate the attic roof. Some day we may want to use it for living space and I think it will also help in keeping the rest of the house warmer. Currently 5-1/2" is all I have to work with so I am trying to come up with the most effective solution. Jolynn | ||
| JC Citizen Username: Demolitionman Post Number: 62 Registered: 6-2006 |
www.claytondemo.biz "We are your solution" | ||
| Darren Say Grrrrrrrr Citizen Username: Darrensager Post Number: 552 Registered: 11-2001 |
Kevin, From what I understand you cannot use Thermax for indoor use in the way you'd like to use it. | ||
| Travis Citizen Username: Travis Post Number: 470 Registered: 6-2004 |
Kevin: Not an expert, just a poor dumb HO. I don't know why you can't use Thermax in the way you describe, perhaps Darren could elaborate. I have put styrofoam panels between studs and sealed with spray foam; it is a lot of work. I could not use spray foam because the house has no building wrap, so the foam would just come oozing out of the siding. AFAIK code does not require thermal barrier in an unfinished attic, though it really depends on how AHJ interprets UBC. Why not just spray closed cell foam which has about the same R-rating as thermax, and will seal air leaks to boot? The max you can spray with closed cell foam is 4" at a time, otherwise it fries. Jolynn: There should be no asbestos in old blown-in, unless it is vermiculite. But you should not have insulation on both the floor and the roof deck, that can lead to condensation problems. The idea with insulating the roof deck is bringing the attic into the building envelope and maintaining it at the same temperature as the rest of the house. You may also want to consider some ventilation, say a low-cfm bathroom fan (say Panasonic or Fantech) running indefinitely and ventilating to outside, to prevent moisture build-up. |
