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drewdin 03-18-2013 08:43 AM

Insulating the Attic
Do i just insulate the attic floor or am I supposed to insulate the attic roof? Thanks

CallMeVilla 03-18-2013 09:00 AM

Logical question. Assuming you have proper ventilation from the eaves, Just insulate between the attic joists. If you insulate between the attic floor joists, you are not required to insulate the attic rafters. Don't skimp! Attics take more insulation than exterior walls. Most of the home's energy (cold or hot) escapes through the roof. Check your local codes and go an extra step. You'll be happy with the outcome.


Fireguy5674 03-18-2013 09:19 AM

If you have a "normal" home with insulation in the sidewalls and attic vents of some sort you would insulate the area between and above the ceiling joists and leave the rest of the attic uninsulated and open to air flow. The area where you live dictates how much insulation is needed in the attic. That is conventionally the way homes have been built and insulated for years. There is now new thinking concerning the need for ventilating attics and ways of insulating those spaces. One popular, although more expensive alternative, is to have foam insulation applied to the bottom of the roof deck and all gable ends etc foamed to create an air tight insulated space of the attic. The claim is this causes less than a 5 degree temperature increase to the roof deck and helps the house heat and cool better particularly if you have heating and cooling duct work in the attic. Go to the internet and look up two part insulating foam. There are volumes of information concerning the subject if you are interested. You can olso have foam applied in a conventional way between the ceiling joists. You can buy loose insulation and blow it in with a blower supplied by the place where you buy your insulation and do the project yourself. They should assist you with how much you need and how to blow it in.

nealtw 03-18-2013 10:14 AM

If you are insulating the ceiling make sure you have soffet vents and install air shoots against the roof deck to keep air moving.

Fireguy: Insulating the roof in a cold zone is questionable, as the one spot that will have the least amount of insulation is above exterior wall and there is no longer any air flow to carry heat away. Ice dams can become a problem.

Fireguy5674 03-18-2013 10:20 AM

Yeah Neal I know there are many factors to be looked at. I don't think I have ever seen that one talked about in all the all the stuff I have read. If you design a home for foam insulation probably increase the heal height at the wall plate to compensate.

My son-in-law was getting mold in the upper corner of their bedroom on the outside wall. Finally tracked it down to lack of blown-in insulation at the wall plate and inadequate bathroom ventilation causing constant condensation from the cold spot and high humidity in the room. When we added onto his house we redid insulation/ventilation to fix the problem.

drewdin 03-18-2013 10:34 AM

I live in Boston so it gets cold and hot as hell here always with a ton of humidity. Right now i don't have any insulation in my attic, just had the ridge and soffit vents added last year (House is from 1927). I want to make sure that when i do put insulation up there I do the right thing.

I know I need at least 18" of insulation on the attic floor, and I can only do the ceiling bays that dont have the airvents on the side.

Is there a specific insulation you guys recommend? Thanks

nealtw 03-18-2013 12:56 PM

Air shoots are 4 ft long, you staple them to the roof sheeting and intall a little batt insulation over that wall. That will stop the loose insulation from falling into the vent and prevent the wind from blowing the loose around.

drewdin 03-18-2013 02:39 PM

right now I have them goin 4' up the side, ill need to add more 4' extensions to the ridgevent and then cover that with insulation?

CallMeVilla 03-18-2013 02:40 PM

I think the Boston Insulation Code calls for R38 minimum in the attic for new construction. Get there or higher if you can. You MUST have the chutes Neal is recommending to guarantee proper ventilation. Which kind of insulation you use it optional ... blown-in is popular but has to be carefully applied for good coverage. Inspect carefully.

Fireguy5674 03-19-2013 08:40 AM

I checked the R value of blown in cellulose. If Villa is correct and Boston calls for an R-38 attic rating then you must use 10" of blown in cellulose to meet that standard. I would use more. It is hard to get to much insulation. Make a stick with a mark at whatever depth you decide to use and keep checking the depth of your insulation as you install it. Make sure you plenty out against the outside edges as you go to keep that edge from being to cool or hot.

If you already have 4' air shoots then you should not need any more length. All the shoots are for is to keep the insulation from obtructing air flow from your soffit vents into the attic space. By placing batt insulation or any kind of barrier that keeps your blown-in insulation from falling out into your soffit and plugging your vents you have done all that is required to keep the air moving up through your soffit vents, through your air shoots and out the peak of your roof. I have used fan fold siding backer nailed on the outside of wall sheeting and trimmed to fit against the air shoot to hold insulation from falling into the soffit area. If your soffits are already in place that will probably not work for you, but you can most likely get the batt insulation in that area.

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