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handymandan
Attick insulation

I have questions about attick insulation. I currently have fiberglass in the rafters. I'm getting conflicting information. Can I spray foam the roof rafters? Which will completely seal off the attick? Will this damage the shingles? Or am I better off to install more fiber glass?

Thanks, Erie PA

keith3267
Re: Attick insulation

Most people are better off just adding fiberglass over the existing insulation. Unless you are turning the attic into living space, the results from spraying insulation between the rafters will be very disappointing to you.

Remember you also have to do the gable ends if you do the rafters so you are looking at something like a 30% to 50% increase in the area to be insulated, depending on your roof pitch, plus the premium price for foam. The additional fiberglass will payback much sooner.

Oops, I just reread your post, you have insulation in the rafters now, why? All your insulation should be in and over the joists unless it is living space.

handymandan
Re: Attick insulation

Sorry,it is in floor joists,sounds like our best bet and least expensive is to add some more on top?

keith3267
Re: Attick insulation

Yes, add over the existing.

Just so you understand what the benefits will be, the typical house looses about 30% of its heat through the ceiling. Walls account for about 20%, windows and doors, 20%, infiltration 20% and floors 10%. This is not universal, those numbers are very flexible, for example a two story house looses more through the walls and less through the ceiling. Someone who has added a lot of insulation to the ceiling without upgrading anything else will see the ceiling have less than average losses as a percent of total.

If your house is typical, or close to it and you double your attic insulation, you could expect a savings on your heating bill of around 15%. Remember that the heating bill is only part of your total utility bill. You can often get a decent payback with weatherstripping if your current weatherstripping is not adequate.

Insulation can make a home much more comfortable by reducing the temperature swings and drafts, but done solely for the goal of saving money, it is easy to spend far more than you will ever recover.

LeonardHomes
Re: Attick insulation
handymandan wrote:

I have questions about attick insulation. I currently have fiberglass in the rafters. I'm getting conflicting information. Can I spray foam the roof rafters? Which will completely seal off the attick? Will this damage the shingles? Or am I better off to install more fiber glass?

Thanks, Erie PA

Some of the information provided here is only accounting for heat loss , which is only half the equation , heat gain is the other half .

The most economical bang for your buck would be to simply add more insulation on top of the existing , increasing the R value up to R40. Before doing so , seal all penetrations into the attic preventing air movement to and from the living space and attic. This will reduce heat gain/loss by another 15%.

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