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old roof is 30" oc

7719 Views 7 Replies 3 Participants Last post by  sun ray
I'm replacing the asphalt shingle roof on my 650 sq ft, 86 year old house. The existing sheathing consists of 1x6 boards. I am replacing the really bad ones. But the rafters are 30 inches apart. I am want to put plywood over the top of the existing 1x6's. I am worried that the extra weight from plywood would create a problem for the old house.
Does anyone know what plywood size is best?
Would H clips help with the sheathing's structure?
How do I deal with the problem of the 8ft plywood not aligning with the rafters?
Any other suggestions or hints?

Thank you,
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Where are you located?
Snow load?
What size rafters?
What is the span?

I'd install new rafters in the middle of the 30" distance between the existing rafters
That is way beyond current codes
Unless you have trusses installed?
Are the ceiling joists in the attic also 2x4?
Any signs of sagging anywhere?

18' length may equal 14' actual span
You are looking at maybe just over a 2x8 to get a 14' span for a rafter

The Span is the distance between the inside wall & the ridge
labelled "half span" in this pic

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It sounds like you have a truss system
These are engineered to for more support then a normal stick framed 2x4 roof
So you may not need any more rafters
And if it has not sagged in 86 years......and no snow :thumbsup:

Some roofs use 1/2" plywood as sheathing, I like 3/4"
You have 1x6 - even thicker - more support
Is there a reason you want the plywood?

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