Q&A / 

Rain Soaked Framing Lumber

DEAR TIM: My new home is under construction and the roof is not complete. Our area has received record rainfall for days and days. More rain is in the forecast. Is my house ruined? Will the wood rot? Should I be concerned about mold or any other problems? Is there anything a builder can do to minimize damage to lumber caused by rain and standing puddles on wood floors? Sara G., Trenton, NJ

DEAR SARA: I doubt that your house is ruined by the heavy and persistent rainfall. You would be shocked how much abuse framing lumber and engineered lumber can take when Mother Nature turns on her faucet. The glues used to bond layers of wood in exterior-grade plywood and the strands of wood in exterior-grade oriented strand board (OSB) are made to resist water. The actual solid lumber used by many builders for walls, floor joists and roof trusses is naturally resistant to rapid decay by water.

But these facts do not give you or your builder an unlimited license to allow water to saturate the lumber or stand in puddles on the flat floor surfaces for weeks or months on end. As soon as the moisture content in wood reaches in excess of 20%, decay and staining can begin. The greater likelihood is that you will begin to see mold growth long before the wood starts to decay. Often there is an abundance of mold spores in the air at just about every construction site. These spores just need water to start their growth process and some molds can form in as little as 48 hours after getting wet.

My own home was rained upon several times as I built it. I distinctly remember the house getting soaked for several days before the sun came out. As soon as the rain stopped I used a large squeegee to get the standing water off the floor surfaces. Because I kept the jobsite clean on a regular basis, there were no wood scraps or piles of absorbent sawdust that would trap moisture. Once the standing water was off the floors and the sun came out, the wood would dry rapidly with no mold growth, decay or warping.

The lumber on the jobsite that is at the greatest risk of mold growth or decay is that lumber which is stacked closely together. Often delivery trucks dump piles of lumber on the ground with just a thin 2x4 under the pile. In many instances the pile of lumber is in direct contact with the soil. If water gets between pieces of lumber or sheets of plywood and/or OSB, it will not easily evaporate. For this reason, it is very important that lumber deliveries be scheduled so that the lumber is used by the carpenters within days, not weeks. Lumber that does sit on the jobsite should be off the ground at least four inches and be covered by a tarp that protects it from rainfall. But the tarp should not be wrapped tightly around the stacked lumber. Water vapor from the ground can build up under the tarp and condense into liquid water.

Builders can also take extra precautions to protect framing lumber. Water repellents can be applied to flat expanses of plywood or OSB subflooring. These liquid water-repellent products are easy to apply when no walls are erected on the flat subfloors. Plywood and OSB that are treated in this manner will rarely swell and delaminate.

Framing lumber such as 2x4s, 2x6s and floor joists can be sprayed with borate solutions. The borate chemicals are not toxic to humans or other mammals, but they are highly toxic to many species of wood fungi that cause wood rot. Termites also dislike lumber treated with borates. It is best to soak the lumber in borate solutions to get the full treatment, but spraying the borate on lumber that is in place will offer a fairly high level of protection until such time as the house can be roofed.

Mold growth on framing lumber is a common occurrence. The mold can be killed in any number of ways and should be killed before the lumber is covered with any finished wall or ceiling materials. The Environmental Protection Agency (EPA) has suggested guidelines for mold removal that can be performed by the average person. You can find these helpful tips at www.epa.gov.

Serious damage can happen to houses under construction that are exposed to long periods of wet weather. Light, dry snow and ice are not nearly as bad as standing water. Cold weather slows the growth process of most organisms including wood fungi and most molds. But snow can be easily removed from the flat surfaces of homes under construction and this should be done as soon as possible after the storm has concluded. Once temperatures rise, the snow will melt and turn into liquid water.

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13 Responses to Rain Soaked Framing Lumber

  1. Hi there. Hope you can answer a concern I have. Building a home threw a company, wood delivered almost three weeks ago, and still sitting packed together. It should all go up with in next 3-4 days. Do you agree I should have major concerns with this and should I tell them how mad this makes me. Also should I ask for something in writing for extra coverage on mold , if it causes problems down the line.

  2. Pretty good description of mold. However, mentioning the role of light vs. dark conditions would enhance article. Underneath of bottom plate of framed walls is an ideal spot for mold to grow. Water and darkness are often both present.

  3. My house is under construction. it is insulated and dry walled but untaped, during a monsoon the paper came off the roof caused severe water damage in 5 different rooms. Is it possible to dry out the insulation and drywall or should I insist the builder replace it to prevent future mold in the walls.

  4. Thank you for your info. My house has exposed floor boards. I woke to the sound of rain, Sunday morning. I did have tarps here covering less important things. I put those tarps over wet floor boards just before the rain really started pelting down. I was able to cover the whole area but I could not dry up under the tarps yet, until this rain stops. How long can I leave this. I also have a mold spray product. Should I use that after it dries? Again thank you.

  5. We have a 5 year old home and it is built near the Ozarks so there is a lot of rock. The entire home is built on a slope so there is a crawl space under the whole home. When it rains a lot we get water coming up from under the ground into the crawl space and we see quite a bit of standing water around the edges and where you enter the crawl space (about 7 feet tall). There is a plastic barrier with rock on top but it has come up through that. The water usually goes away within a week but I'm worried about mold etc from standing water. How would you fix this? I've read where you could pour sand and then another layer of rock around the edges where the water collects. W/out paying for another barrier and then more rock over the top of 3000sq feet of space what would you recommend? Thanks

  6. What does the mold look like? Our house has been framed and we have experienced extreme rain during the entire 2 months. The bottom of the wood frame that touches the floor boards is black about 1-2 inches throughout the house. Is that mold?

  7. We recently had the old wood trim, facia and soffit on the exterior of our home wrapped with aluminum. The installer did it in the rain and covered soaking wet wood. This was in October in Michigan, so it will not get warm again for a very long time. He assured me that the boards would dry out in a matter of a few days (even though everything was caulked). Can someone please shed some light on this? Mold almost killed me this spring and I am so anxious about what is going on behind that metal!!

    • Rachel, you'll probably be okay. Even though the aluminum was caulked in places, there's plenty of openings and gaps where this water can evaporate and be released to the atmosphere.

  8. My home is almost a year old. After moving in a strong musky odor showed up in master closet.
    When building we came to see progress and for two straight weekends a few inches of water sat upstairs with no where to go. Roof was on, walls up but no where for water to escape. The second weekend we brought a broom and in front of house my husband pushed the wAter down the stairs. We kept on builder and he reassured us he would take care of it. Could this be what I'm smelling?
    The builder is finally coming out Monday to cut into floor and part of walk downstairs sons the wall is pulling down and cracking.

    What should I do? I've had to fight and fight for this builder to take me serious.

  9. We are in the process of building a home. The builder just finished with the foundation and frame around the foundation but we had a 4 to 6 inches of snow on the ground. Can the snow and cold cause a damage to the plywood?

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