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Alloswing OSB to get wet at the construction site

Topic: 
Moisture Problems
Question: 

I am considering buying a new construction home built here in Vancouver. I noticed they are using the OSB for under the typical composition roof and behind the Hardiplank siding. OSB is all you see as its being built. I think that's ok from what I've read even though we are here in the rainy northwest, as long as the roof and Hardiplank siding are installed correctly. But they have like 5 homes being built at once and I did notice that when it rained about 3/10 of an inch last Thursday/Friday all that OSB was exposed to that rain on those homes while they are being built. Is that a concern? Thanks

Answer: 

Hello Rick,

Allowing OSB to get wet is not a wonderful idea but its done all the time. Most of the time there is very little harm and the material doesn't loose strength or any of its integrity. Under the best circumstances, the OSB sheathing is delivered to the site, installed and covered within a few days. Under such a scenario, moisture from rain etc. does not have the time to penetrate into the layers of wood strands or weaken the glue.

This is one good reason why good construction includes good organization and scheduling. There is very little that one can do to prevent a rain-storm but there is a lot that one can do to make sure that materials arrive on time and that the work progresses on schedule.

OSB that does get wet will tend to swell and delaminate first at the edges of the boards. This can be a real headache when one intends to install windows or doors with pre-manufactured liners. In such cases, the exact thickness of the walls can complicate final finishing work.

In cases where window liners are made out of drywall or the sill and liners are installed after the window and drywall installation, small differences in the thickness of the wall cause few if any problems.

All this maybe more then what you wanted to know and provides you little to terms of a ?bottom-line?. So, here is the bottom line:

  • The construction site should be neat and clean.
  • Work should progress with few interruptions.
  • The framing material should arrive within a few days of the start of the framing.
  • Once framing has started, work should not stop until the roof is on the house and been covered with the felt (tar paper) or the roofing material.
  • The wall sheathing should be covered with a moisture barrier.
  • If we are talking about a ?standard? sized home and in a project with several homes under construction, I would hope that the elapsed time from framing material delivery to roof and siding protection is no more than one month.

    George