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Old 04-26-2014, 07:38 PM   #1
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Insulating an Attic - Spray Foam in the Rafters v. Cellulose on the Floor


My house is a single story ranch in Connecticut and it was built in 1957. The attic has about 4-5 inches of fiberglass insulation in the floor of the attic, but it is matted down after all these years. I believe I’m a losing a lot of heat through the attic so I want to fix this issue.

I have looked into blowing in cellulose insulation over the existing fiberglass insulation, but after speaking with a contractor there are a number of steps that need to happen first. The contractor told me that first they would have to seal (with some type of spray foam) all penetrations between the attic floor and the living space below. This includes any electrical wiring, plumbing pipes (vent stacks), and the chimney. They’d also install an insulated door over the pull down latter. Furthermore, there is an air handler for the air conditioning on the attic floor and there is also plywood down the center of the attic to allow a walking space in the attic to service the air handler and general storage. The cellulose cannot cover these areas the contractor told me they’d build barriers out of plywood around these areas keeping the cellulose out of these areas and also add a layer of rigid foam and another layer of plywood to add some additional insulation to these areas.

The contractor also offered another alternative, which he seemed to prefer and I think I prefer it too. He told me they could insulate the attic ceiling and the gable walls with open cell spray foam (I don wonder if closed cell spray foam is the better choice to achieve a higher R Value), which also needs to be coated with a fired retardant, which is also sprayed on like paint. He also indicated that when they fill the roof rafter bays and the gable wall stud bays that they would actually over fill these areas and cover the rafters and studs to add a greater thermal barrier. This all seems to be a good solution and the contractor suggested that this will make the attic cooler in the summer and warmer in the winter even though it is still not conditioned space. He also suggested the A/C air handler would not have to work as hard and may last longer.

We then discussed my exiting ridge vent, soffit vents, and roof fan. He told be the ridge vent would still exist, but it would not have a function and would be covered on the inside with the spray foam. The roof fan can be spray foamed over or I could remove it and patch the roof before they apply the spray foam. He also told me that the rafter bays would be completely filled with the spray foam so there would no longer be a need for air circulation in the rafters and no need for the ridge vent. The soffits would still have air circulation as they would install a barrier so the spray foam does NOT fill up the soffits.
Both alternatives are about the same price and I am leaning toward the spray foam.

One question I have is with the spray foam alternative do I need to remove the existing fiberglass insulation in the attic floor? The contractor said it can stay, but if I want they would also remove it for $1.00 per square foot by stuffing it into plastic bags and carting it through the house and out to the dumpster. I think it makes sense to remove the fiberglass because the paper backing, which for some reason is on both sides, is so dry and crumbling that I have a concern that it is a fire hazard.

Does this all make sense and what do you suggest?




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Old 04-27-2014, 12:12 PM   #2
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Insulating an Attic - Spray Foam in the Rafters v. Cellulose on the Floor


I would not convert that attic to a conditioned space.

Blowing in insulation after you air seal the floor will be much more cost effective and safe.

In order to put SPF on the underside of the roof, he will have to cover it with an intumescent paint and they are expensive as well as offensive to the nose/lungs.

You don't have to necessarily removing the fiberglass on the floor as long as it does not have any feces or urine in it from animals.

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Old 04-27-2014, 09:32 PM   #3
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Insulating an Attic - Spray Foam in the Rafters v. Cellulose on the Floor


I agree. Figure you have around R-16 there now, http://www.greenbuildingadvisor.com/...fiberglass.JPG

adding cellulose would bring it to (at least) code minimum of R-38; http://energycode.pnl.gov/EnergyCode...te=Connecticut

I am amazed they would be even close to the same price... the newer com. SPF is probably $$$ with a built-in, wish I had stock in that company.....http://www.dow.com/news/press-releas...icle/?id=6436;

You'd need about 3"SPF to get to R-20 (preventing condensation), per code, then other fill to standard code; http://www.buildingscience.com/docum...rchterm=attic+

Conditioned attic may require an impermeable membrane under the shingles and does reduce the asphalt shingle life-span by 10%; http://www.buildingscience.com/docum...on?full_view=1

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