Spray foam insulation in attic

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  #1  
Old 04-20-02, 05:39 AM
MsAnnie
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Spray foam insulation in attic

I am working on a 50-year old cape (in New England) that is structurally sound - just needs lots of TLC (and money!) Lack of insulation in the attic is high on my list to fix. The ceiling is going to be replaced on the second floor, so it's a good time to do the right thing. A contractor explained the benefits of spray foam polyurethane insulation on the underside of the roof and the walls of the second story and dormers - putting a "cap" on the house. He says the goal is to keep the attic close to the same temperature as the house - seal off the infiltration of outside air - which contradicts all I have read about ventilation to keep the attic the same temp as outside. He says no need for ventilation to be put in - soffit vents, etc. But all my reading says that it's important to ventilate moisture from the attic as well. He says moisture is not a problem with this method - no need for vapor barriers, no need for anything on the attic floor other than maybe some plywood to give me some storage space. This method is more expensive and I will have to sacrifice something else - but it's worth it if it makes such a difference in comfort and energy. My remodeling projects are moving from the inside out. The house will be getting a new roof and siding in about 3 years. But with the second floor work I'm doing now, it seems to make sense to tackle the insulation task now as well. Help!
 
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  #2  
Old 04-20-02, 10:37 AM
Conserve NRG
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Insulating between the rafters against the roof sheathing will move your thermal barrier to the roof line instead of having it at the ceiling. In essence you will be paying to heat the attic (heat may rise within the home through indirect bypasses into the attic-this is called stack effect).
In addition, if for any reason you may have to replace your roof sheathing in the future, installing foam may make the job more difficult. In fact, it may destroy/damage the installed foam. In which case you may have to have the foam reinstalled after the roof sheathing was replaced/repaired.
In any case, I would not recommend this proceedure.
However, kneewalls would be a great area for insulating with foam.
 
  #3  
Old 04-22-02, 10:03 AM
Edinpitt
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You may have noticed that I am wrestling with similar issues. We recently bought a 60 year old cape, and I am finding it a challenge to insulate for both Pittsburgh winters and summers. I will add my voice the the idea that polyurethane in the rafters doesn't sound like a great idea. Now, I don't have a lot of experience, but almost all the web pages dealing with this sort of thing advocate insulating the attic floors over the first and second floor living spaces, the knee walls and the sloped ceiling (if you have them ... do you?). there already was, in our house, 2 inches of rock wool in all those places. I saw no reason that fiberglass couldn't be used for additional insulation, and that is what I am in the process of doing (I am held up by jammed door to the second floor attic). I think it will end up costing me maybe around $200 for the whole project, though among other things I may end up trying to be creative and make 2 inch (R-7) insulation from 6 or 8 inch insulation, in four foot lengths to add on my 2 x 4 knee walls (which already have the 2 inches of rockwool). So I don't think you need to spend so much on materials to insulate, though labor is a different matter. You might want to consult with a different contractor if possible. There might a reason why ventilation is a bad idea. Apparently cape's do not have the best ventilation, because the air has to pass through the limited space of the rafters between the sloped ceiling and the roof. My rafters are 6 inch, so I am planning to add 2 inches of fiberglass to the 2 inches already there. The air will have a wee 2 inch pathway, the minimum recommended. To make matters worse, my top ventilation consists of some under sized gable vents. You may have limited or no access to the soffits to put in venting. Still, if your summers are not too bad, if you have only soffit vents (or can put them in) and gable vents and at least R-13 on the knee walls and sloped ceilings (with, like triple that on the flat surfaces), I suspect you would be alright, and still not break the bank. I have plans for either a radiant barrier or some powered ventilation, or both, which will raise my cost. Actually, even if your summers are a bit warm, if you can hold out until you do add a roof, you could add a continuous ridge vent at that time, and probably address the top ventilaiton issues.
Ed
 
  #4  
Old 04-22-02, 10:27 AM
MsAnnie
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Thank you both for all your help. I have eliminated the spray foam idea - even though I coincidentally saw and episode of This Old House where they used it. So it sounds like batting in the entire attic floor - but staying clear of the sheathing is the way to go. The attic has no ventilation right now and the soffit looks too small to add vents. We had a heat spell last week and the second floor was very uncomfortable! Someone suggested I just get the batting down in the attic for now - that should make a significant improvement, and maybe some gable vents. Then in a couple of years, when I replace the siding and the roof, do a proper insulation job - blowing into the walls and putting in attic vents, maybe extending the rafters to provide a larger soffit area. What is a radiant barrier? I don't mind spending a few more bucks if it really helps.
 
  #5  
Old 04-22-02, 02:39 PM
Edinpitt
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Um, a radiant barrier is aparently a essentially aluminum foil backed with some material, stapled to the rafters. I would suggest a google search, and I was bantering back and forth in a previous post (Latest dumb idea - radiant barrier) a few days ago. Radiant barriers apparently get used in the south a lot, and there is some question whether they make the house colder in winter. My thought had been to use maybe $20 worth of aluminum foil in the side attics, something more permanent in the sloped ceiling and a lot of insulation in the top attic. I think I might need powered ventilation up top, though, if I did. Real radiant barrier's cost a bit more, probably comparable to what insulation costs, and they require a lot of ventilation. Just finding a way to add soffit vents and gable vents might help. And Conserve NRG's post (Old thinking/New thinking ...) would seem to concern us as well. Good luck, and let me know if anything works.
Ed
 
  #6  
Old 04-23-02, 07:20 AM
gjtoth
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Have you given thought to Radiance paint?
 
  #7  
Old 05-02-02, 07:51 PM
Gary Gray
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MSAnnie, sorry you decided against the idea of spray foam insulation on the underside of your rafters. The latest technology suggests that a building is most effectivly insulated by limiting air infiltration (air changes per hour) which is best controlled by spray foam. Your contractor who suggested that you totally seal your attic area and add it to your conditioned air space had the correct idea. Spray foam insulations prevent air infiltration restrict vapor drive and provide real world "R" value which traditional insulation cannot. Spray foam also allows a down sized HVAC unit because of the number of air changes. I was a participant today at a blower door test in South Carolina where the house was tested for air infiltration. THe results indicate an infiltration level of .09changes of air volume per hour. The house is a 5,000sqft tri-level new construction on the ocean. Reps from the local utilities and from Energy Star were on hand as well as the spray foam contractor. This kind of result projects an energy usage in this area of less than $1400.00 per year for HVAC. Because the house is so tight possitive mechanical ventilation is required. Fresh air MUST be brought in and the Air Conditioner needed to be down sized. If the AC is left at the same tonnage that Fiberglass requires, it will short cycle and never run long enough to remove the humidity which is put in the air in normal living conditions. Cooking, showers, laundry, dishwasher etc. Fresh air is brought in through the use of ducts into the airhandler plenum whereit is filtered and conditioned and sent to the living space including the attic. In this way you actually achieve a slightly possitive pressure in the house and you are able to control for the first time your indoor air quality. No more pollen, dust, or outside pollution of any kind. Thus a healthier, quieter. more comfortable home. Revisit the idea of using spray foam. There is no equal in the home insulation market today!
 
  #8  
Old 05-02-02, 09:35 PM
Conserve NRG
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So Gary, What your saying is that MsAnnie should move her thermal barrier to the roof line and pay to heat her attic? It sounds counter productive from a conservationalist point-of-view. If she has an open attic wouldn't installing the foam insulation at the ceiling perform the same function of blocking thermal bypasses? This would also permit future roof work to be performed without damaging it and prevent MsAnnie from having to heat an unconditioned area. No?
Also insulating with foam on the underside of a slate roof with open batten seems like a bad idea. The moisture that tends to leech beneath slate shingles and disipate through the open batten would have no where to go, and would essentially rot the batten board.
 
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