Insulating an attic for finsih

ddave23

We are in the process of finishing our attic, and we are about to start to insulate with fiberglass Insulation.

I had few questions in regards to the soffit vents and roof rafters and how to use the insulation.
How should the installation be done around these? I have read a few things, but not sure the proper way to insulate the attic. The soffit vents are located behind the newly framed knee walls. They come about 12 inches from the floor (which was insulated) do I start my insulation after the soffit vent? How far up the wall should the insulation go? I was told not to go the top of the roof because of the roof rafters?

Sorry, first time home owner, and trying to get a better understanding on how it is done.

Thanks for your help.

Densec

Hi Dave,

I am researching the same thing. Found this PDF http://www.southface.org/web/resourc...lings_4pdf.pdf
which may help. I think one big thing is putting baffles in before the insulation so the is proper ventilation.

Hope that helps.

I am trying to figure out which way the paper on the insulation should face to roof or to inside. My gut says toward inside.

Good luck,

Dennis

Scuba_Dave

Kraft paper should face inside for NJ

I use the baffles for soffit venting

Densec

Thanks Scuba Dave!

Gary in WA

Densec, sorry I didn't see your question in the other post until now. As Dave said for the vapor retarder. This article on v.b., towards the bottom, fig. 20?: http://www.buildingscience.com/docum...gs?full_view=1
You know the baffles are only needed for loose fill and too thick batts, near the soffit vents? If you furr the rafters down and use the baffles as Dave suggested. Here is one I use for Capes, notice under the knee wall: http://www.homeenergy.org/archive/he...95/950309.html
If you already knew this- no harm, no foul...
Be safe, Gary

Densec

Thanks Gary! There is a lot of great info in those links. I understand that if I use the correct thickness there would still be room for air flow, but how do you keep the batts in place so they allow air flow behind them?

Scuba_Dave

Iuse rafter baffles to allow for air flow along the roof sheathing
I like to put as much insulation in as I can
The batts usually just staple in place with kraft faced ??

Gary in WA

You would furr the rafters out to match the insulation and use the baffles. Staple the facing tabs to the edges of the furring, not inside. --- place the insulation very carefully --- pre-fluff it before installing: http://www.homeenergy.org/archive/he...99/991110.html
Be safe, Gary

Densec

Hi Gary,

Thanks for your help. What does "furr the rafters" mean? Sorry this is all new to me.

Also, were you saying that even if you use the overstuffed batts or loose fill for the rafters you would only need the baffles near the soffits? Is the idea that the air flows from the soffits to the ridge vent? I was thinking that if I do use the baffles I would use them all the way up to the ridge vent, otherwise the overstuffed batts would cut off the air circulation after the baffle. Am I way off here?

I am forgetting that gravity is on my side so if I use thinner bats, I guess they would just hang, resting on the drywall and leave a passage way for air from the soffit to the ridge vent. Is that correct?

Thanks Again,

Dennis

Gary in WA

Furring is adding wood, 2x4 or such, to the bottom of the existing rafters to make them thicker. I incorrectly stated to let the insulation make your air space, you need the baffles all the way up to keep the air out of the insulation. For fiberglass to work it needs dead air (no movement) space. You need the rated thickness for the r-value for your locale. Staple batt's flange to the outside edge of the framing, not the inside face. Leave about two inches between baffles as you install them as per directions. Sorry for the inaccurate information, I'm glad you checked back.
Be safe, Gary

Densec

Thanks for all the info Gary. Much appreciated!!