osb Sheathing w/ 3/4" rigid insulation over 1x6 planks

[Dave Chapple]

When a roof needs sheathing over 1x6 original butted planks, is it possible to put rigid insulation over the panks and osb ply on top of that?

How is an old planked roof resheathed and still pass code?

Because this is a vaulted ceiling, rafters and planks visible from inside the house, triflex black underlayment would be used.

So next question; if rafters are not on 24" centers, say wider (aprox 38", this is an old house) how would you attempt a nailing pattern? And with what nail? The specified 8D Common is too big.

possible solution:
1x4 sleepers nailed to rafters with 8d regular nails over stapled triflex black fabric. cut foam to fit sections. Overlay with 4x8 osb, ofset. preferably stapled with wide crown 1.5" staples, into sleepers. No nailing on butt ends of plywood possible.

[Garry Sorrells]

First off use plywood not OSB, personal preference for quality.

Second, Nailing but end of plywood means that the plywood has to be cut to have ends fall on rafters. If the ends are not secured they will bow up and you will have some real issues to deal with.

Third, What you need is a good roofing contractor. . But, the good roofer will have your answer and it will not be cheap or quick.

Fourth get more than one good roofer that knows what they are doing to quote job and design installation.

You will have attachment issues due to the old wood. Which is why you really need a good roofer who knows what will hold for your application.

Old house = old code most of the time

[Andy Wuenschel]

Have been a non-member here for awhile, but login instructions are asking me to make a post. So here it goes:
I would be extremely cautious about putting that much additional weight (plywood) on an old non-conforming roof, whithout having a structural analysis on the rafters, walls, and foundation.
Don't you need a permit with an engineering stamp to modify a roof like that?