Sister 2x4 rafters and other issues
Hello. I have a small cape style house built in the 1920's. The attic was finished long ago but is in serious need of updating. I already removed the rigged up knob and tube up there so the place won't burn down but now I must turn my attention to the structure itself.
The roof rafters are 2x4's and spaced about 18 OC. The span is 10 feet. I can't see any obvious signs of sagging from outside.There is no knee wall crawl space in this area I'm working on. The floor extends all the way to the outer wall, which is about 2 feet high at the rafter/top plate junction.
This area I'm working on had flimsy wood paneling covering the rafters. No drywall or plaster. Behind was old Kimsul insualtion that was hanging loose and falling apart. I found the roof decking was wet in some areas, mostly towards the eave area. Some mold. It dried rapidly after removing the paneling and insulation. The flat ceiling above is drywall.
I want to possibly sister on some 2x6's or even 2x8's to strengthen things up and allow room for more insulation and also ventilation and then drywall over it. There are no soffit vents but I can add them easily enough. I've done a lot of research and even posted on some other forums and there are so many options and opinions on how to do things, I'm sorta lost lol. Any tips or thoughts appreciated!
Your house sounds like it is balloon framed. The 2x4 rafters may be the full 2"x4" and stronger than today's 2x4s. I'm assuming the roof sheathing is boards, not plywood. What is above that, slate, asphalt shingles, maybe two different types of roofing?
When you say a 10' span, do you mean the run from the o/s wall horizontally to the center of the room below the ridge board, or do you mean the length of the rafter?
You have more than one issue here. The area of the mold sounds like it was caused by ice dams. The mold needs to be addressed immediately, which means you need new roof covering. It also sounds like you have inadequate roof venting.
2x6 rafters tacked to the side of the existing rafters will give you some depth for a little insulation, but obviously more depth means more insulation.
Dead load should not be an issue here, as there are probably full 1" boards on the roof and plaster on the ceiling. Drywall will be lighter than plaster and, if the sheathing is in bad shape, plywood will be lighter than the boards.
Hope that gives you some food for thought
I THINK there are two layers of asphalt shingles. For the span I measured from o/s wall to center of house under ridge, yes.
As far as ice dams go, we do get pretty good ones. I use a roof rake to minimize this but it’s hard to keep up sometimes. What puzzles me is the wet area dried right up after removing the insulation so I thought it was a condensation issue. The insulation under there was worthless.
The center flat part of the ceiling is drywall. No plaster anywhere in the house. It’s all old 1921 “Sheetrock” covered with newer stuff in most places.
There are 4 vents at the ridge. No gable venting. The whole half story is sorta crappy and should really be sliced off and rebuilt….lol….but we may move in a couple years so I just want to make it a bit more livable up there and prevent mold/rot issues.....
Here's a (crappy) diagram of what I think the insulation/ventilation layout should be......
Had some pretty good ice daming recently and the underside of the roof decking is still dry. So the dampness must have been from lack of ventilation?
Seeing the 2nd floor overall is inadequate by modern standards as far as head room, floor space, and structure, now thinking I may just tack 2x2's onto the exisiting 2x4 rafters, stuff baffles and R13 in there, drywall it and call it a day. It will still be a huge improvement over how this area was before.
A total overhaul is not possible at the moment and I'd hate to dump a bunch of money and time into the area I'm working on and then have to tear it all out again later if we rebuild the 2nd floor. This is how it's set up now:
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