My client has an old 1840s home that never had any kind of vapor/water barrier
rockinroger
| Posted in General Questions on
It is simply clapboard nailed to studs. He gutted the old plaster wall, and had the stud bays spray foamed directly onto the old clapboards. A few popped loose on the outside, so they re-nailed them.
My question is: will the foam retain moisture and cause the clapboards to rot, or will he be o.k.?
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Replies
Roger,
Oops! Cross that spray-foam contractor off your list.
This was a bad idea, for many reasons.
1. It will be nearly impossible to repair the clapboard or to remove any individual clapboards for future repairs.
2. Every time the siding gets wet, it will dry unevenly -- with almost no drying from the back side of the siding, and rapid drying on the sunny side -- leading to cupping and splitting.
3. The wall has no water-resistive barrier -- always a bad idea.
There is not too much you can do about these problems but live with them -- and fix the wall properly once the siding looks so bad that no one can stand to look at it anymore.
If it's closed cell foam the foam itself is the weather resistive barrier, but without back venting the clapboards are guaranteed to fail- it's only a matter of time.
If it's open cell foam the foam its NOT a WRB. Open cell foam can retain moisture, and the clapboards may fail even sooner than if it were closed cell foam. With open cell not only does it get the direct wetting from the exterior, it also gets interior side moisture drives accumulating in the siding.
Installing vinyl siding over the existing clapboards will extend their life almost indefinitely, since the vinyl siding is inherently backventilated and the much reduced moisture that makes it all the way to the old clapboard dries quickly into the air space between the vinyl and old clapboard.
Or, wait until the old clapboards fall apart, as Martin suggests, and when it comes time to strip them off it becomes an opportunity moment for installing insulating sheathing.
If the house has deep roof overhangs the clapboards on the upper part of the wall barely get direct wetting, and they may hang on for quite awhile. Depending on the house design, it may be possible to aethetically replace only the first story siding.