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Attic brace change

Hello I would like to add some unconditioned storage room in my attic,maybe later on down the road add on a room and a dormer. My house was built in 1948 2x4 roof rafters 24inches on center 17’7inches long, peak height is 9 foot. Ceiling joist are also 2x4. Currently there are braces from mid way through the rafter to the center of the attic no purlin. I would like to remove the braces and add a knee wall and collar ties in its place. I don’t know how high the knee wall needs ton and how low the collar ties will be to support the roof. I can send pics if needed but the site won’t let me upload them.

Thank You

Re: Attic brace change


This sounds like an early attempt at stressed trusses. 2X4 rafters and joists on 24 inch centers are grossly undersized. Without that diagonal from the midpoint of the rafters to the center of the ceiling everything would be sagging! If you remove that diagonal you're asking for a disaster. It is what gives the roof/ceiling structure what ridgidity it has.

I yield to the professional carpenters who contribute here, but I would not cut those diagonals without some really good advice as to beefing up the floor and rafters, especially since you intend to place weight from storage up there.

Re: Attic brace change

I second that.

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