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Not required under some codes

Posted by homebild on July 11th, 2004 08:03 PM
In reply to local practice by Phil on July 10th, 2004 04:18 PM [Go to top of thread]

A secondary weather barrier is not required under vinyl siding in many cases.

Many manufacturers of vinyl siding do not require it and building codes don't usually require what manufacturer's do not.

The International Residential Code (part of the ICC) does not require any type of secondary weather membrane under horizontally installed vinyl siding for OSB or plywood. (Table R703.4 of the 2003 IRC just so Glenn Goode doesn't have hissy fit...:) )

Should you use a secondary weather barrier to stop sun and wind blown moisture?

Most researchers agree you should, but there is evidence that a house properly flashed, sealed and caulked does not need to have a secondary membrane especially for OSB and plywood sheathed homes and can act just as well without it.

Think about it, T1-11 is nothing but a plywood sheathing and is never covered with a secondary weather barrier and not required to have one behind it either.

Since a vertical drainage plain (like the sheathing on your house) has nearly 100% runoff and does not hold or pool water, rot problems usually indicate flashing problems instead.

Tyvek is NOT the product to use over OSB because the surfactants in the adhesives actually break down the surface tension of liquid water which is what in fact is what makes Tyvek 'waterproof'. Lose the surface tension of liquid water and Tyvek is really no water proofing barrier at all.

You can use tar paper and some other products as others have mentioned.

Helpful link:

But from a manufacturers and building code standpoint, it really isn't required to have anything behind vinyl siding and still have a properly built home.

So if you are looking for a cause to your problems, it likely may not be because you have no weather barrier behind your vinyl and you may not have any legal standing aginst the builder or anyone if your vinyl manufacture or building code does not require it.

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