Living Smart: Is it OK to install a roof in the rain?

McClatchy-Tribune Information Services

Dear Angie: Is it OK to install a new roof while itís raining? Iím having a new roof installed over 20-year old (Oriented Strand Board) sheathing. It started raining during the install. Good news is that they did a section at a time, so the OSB was exposed to fairly light rain/drizzle for about a half hour before peel and stick membrane was installed. Is that a problem?

 Dear Sailor:  A reputable contractor keeps tabs on the weather and wonít begin installing a roof if itís raining or expected to rain. Doing so puts workers at risk of falling off a wet roof and unnecessarily exposes your home to damage for which they may be held liable.

The OSB treatment

That doesnít mean that an unexpected rain or drizzle, as you indicated, wonít occur during the roof replacement. If it starts to rain or drizzle, the roofers should act quickly to cover your OSB ó most likely with a tarp.

One of the roofing pros we spoke with says mist wonít affect OSB any more than the humidity that OSB absorbs on a hot day. OSB isnít extremely sensitive to small amounts of water because resin and wax is manufactured into the layered product. Also, the edges of the panels are treated with a sealant to resist moisture penetration. 

Up on the roof ó watch out for wet or wrinkled decks

That said, pros say a new roof should never be installed over wet wood or a wrinkled barrier. Doing so goes against the building codes in most communities and the shingles wonít adhere.

When a roof deck is exposed to water and absorbs enough to swell, it should be allowed to dry out before any roofing material is applied to avoid trapping moisture under the roof material that could cause the edges to swell or buckle. 

If your contractor discovers damaged decking while installing your roof, it should be sanded or replaced before the new roof is applied. They should also make sure to properly vent the roof.

Check before you hire a roofing contractor

Because many states donít require roofing contractors to be licensed, experts recommend checking your local building codes or meeting with a building inspector before hiring a roofing contractor. Read reviews on Angieís List to find an experienced roofer who does quality work and carries liability insurance. Before you hire anyone, ask what precautions the roofer will take if it starts to rain when they are installing the roof and come to an agreement before the job begins.