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Renovating 3rd flr Cape Cod - insulation/airflow question


I'm renovating my son's attic room and am stuck.

The room is in Pittsburgh on the 3rd floor of building with a cape-cod style roof (i.e. NO soffits). The previous owners had the following:
- insulation between all rafters
- roof vents in the plenum spaces outside the knee wall
- roof fan that evacuates the peak space
- a peak vent

I want to provide my son with a better environment (even though we have a high-eff. A/C his room gets warm in the summer). I am also concerned about doing this right to fix the ice dams I get in the winter (caused by tears/fallen insulation batts) and avoid mold.

I had the following ideas:

1) Just fix the existing insulation, install a vapor barrier in the warm spaces (there is just the paper backing now)and move on.

2) Tear out the existing insulation, install rafter venting, back that with radiant barrier Mylar followed with fiberglass. Roof fan would draw air up underneath the roof deck, fresh air drawn in by the peak vent and the little square roof vents (doesn't seem ideal to me)

3) Foam.

I can do the first two myself, and have nothing against hiring someone to do the third.

I have researched this quite a bit (including older posts here) and have found that the consensus seems to be that 'there is no good way to deal with a cape cod'.



Re: Renovating 3rd flr Cape Cod - insulation/airflow question

I gather there is existing sheetrock you are not taking down. I have done a combo installation where a cellulose contractor packed cellulose into the enclosed cavity and we foamed the exposed rafters behind the kneewall. Ice dams are caused by hot air getting to the underside of the roof and I don't think you will ever solve it with fiberglass.

Re: Renovating 3rd flr Cape Cod - insulation/airflow question


No sheetrock, just wallboard. I am gutting the space. From my recent research, it seems the way to go with this space is closed-cell spray foam, and seal off the pot vents and roof fan.

No warm air with moisture can get to the underside of the roof deck, not sure about the performance with solar (radiant) loading though.

I've been checking out the DIY kits for foam, they are somewhat expensive ($900 for the space at only 1" of foam).

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