re-insulating old attic
Hello. This is my first post, thank you.
I am currently tearing apart the walls of my attic built in 1930's. The insulation (Kimsul brand) has been there for probably 50+ years and most of it just crumbles to dust when poked at. It was covered over with particle board which has long since warped and sagged. The roof itself has 2x6 rafters with 24" centers and 4 sides of the house coming up to a point. There are 1x8 planks as sheathing on the outside with ¼-inch gaps between them. All the wood seems to be in fairly good shape except for a few splits and some knots falling out. Not sure what kind of insulation (if any) is under the floorboards (tongue & groove boards nailed down sound like they'd be a pain to tear up). So my questions are:
1) Are the gaps between the outside planks intentional for ventilating/breathing purposes or should I attempt to fill them in with spray foam or something? (The only vents I know of are a couple at the peak of the roof. There are a couple windows that can be opened for inside ventilation.)
2) I would like to use both insulation and radiant barrier to keep the attic temperature tolerable during summer. I was thinking of using Roxul up against the underside of the roof, then staple AtticFoil to the rafters over the Roxul, then cover with (cheap) paneling. Would this work well or should I put the radiant barrier on the underside of the roof then the insulation over that? And is Roxul worth the 3x price over fiberglass? (I live in Ohio with summer temps in 80's/90's often with high humidity; winters in 20's/30's)
Suggestions would be helpful since this is my first insulation work and I obviously don't want to waste money doing it the wrong way.
The gaps in the roof boards are not a problem. Air must be allowed to travel from soffet vents to the peak vents. So you could put in 4" insulation and still leave a gap between that and the roof boards. I would build a flat ceiling so air from every bay can get to the vents at the peak.
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