During the past week in my area, it's rained almost non-stop for 3 days. And although I haven’t started building, I was thinking I’d be pretty nervous if I had started building. What if my house was being framed and got exposed to all that rain? It got me to wondering… Is it ok if it rains while your house is being framed and before the house is dried in? Remember, "dried in" means that the building shell has been completed.
A dried in house includes: 1) all the exterior walls of the house, along with house wrap or some other moisture barrier 2) the roof sheathing with an appropriate water proof roof covering, and 3) coverings for any openings, including window or doors openings. These steps keep out wind, rain, and snow so that weather-sensitive materials both inside and outside the house are protected from weather damage.
Again, I wondered if it’s okay for a home’s frame to be rained on? And if not, what you can you do if it rains before your house is dried in? I did a little research and here’s what I found.
There are many articles out there written by builders who say it’s perfectly ok if your home’s frame gets rained on. They say it happens all the time and they simply continue the building process without much thought about the damp or wet framing lumber, and without much change to the normal building schedule. Those builders say they’ve been building houses in the rain for years and it has never posed any problems with rot, mold or cosmetics.
That sounded a little too good to be true -- a little hard for me to believe since so many articles that I’ve read have said that water and moisture are the greatest enemies of any home. That moisture cause more problem in construction than almost anything else. So why would a wet house frame not be a problem? I dug a little deeper.
I found an article on Fine Homebuilding.com that actually warns against moving ahead with construction if you have a significantly damp house frame.
The article says that framing lumber can attract and hold water and that water within the lumber changes the wood’s characteristics. Water makes wood swell. And the problem with using damp, swollen lumber for the frame of your house is that the lumber will eventually shrink back towards it normal size after the house is complete and the heating and cooling systems have run for a few months. This shrinkage causes the house to settle or shift more than usual.
Here’s a what can happen if you use damp lumber and the house settles more than usual.
-Drywall cracks and nail pops. Nail pops are when you see the heads of nails literally popping through the surface of the drywall
-Floor squeaks and Stair squeaks
-Plumbing waste lines and vents that can shift, leading to roof leaks.
-Mold and rot, if moisture content in lumber is too high.
What should you do if it’s been raining on your framing lumber?
Before you proceed with installing drywall, test the moisture content of the framing lumber with a moisture meter. The Fine Homebuilding article recommends the Extech MO220 Wood Moisture Detector, which is currently less than $150 on Amazon. You might want to invest in a moisture meter for the construction of your home, then sell it on Craig's List or some other site when your house is completed.
Alternatively, you might ask your framing carpenter and builder if they have a moisture meter and if they can test your framing lumber while you are on-site, right before the sheetrock/drywall is installed. You’ll want to be on-site when the lumber is tested just to verify the moisture content for yourself. And insist that the house frame be tested in several different areas.
So what’s our target moisture content?
It’s 19% or less. No lumber in your house should have moisture content above 19%. The article says “This is a hard rule, if you are getting readings on your moisture meter above 19% then cancel your sheetrock hang crew till it’s all below that 19% threshold.”
The reason you want your lumber to have 19% or less moisture content is because building science experts say that moisture content consistently above 19% can cause mold spores in lumber to be activated, starting the rotting process.
Although you can accept a lumber moisture content reading of 19%, ideally you should aim for moisture content below 15% for kiln dried lumber, and less than 17% for any green pressure treated lumber.
The lower the moisture content readings, less lumber drying and shrinkage will take place over time, and as a result, you’ll see fewer settling flaws in your drywall, such as those drywall cracks and nail pops.
What do you do if your house frame has a moisture content above 19%? First and foremost, do not proceed with installing your drywall until the wood’s moisture content is 19% or less. I know I just said that, but that is such an important point, it bears repeating.
If you’re using oriented strand board/OSB for your sheathing and it gets so wet that it swells or puffs up, it will unfortunately need to be replaced.
If you live in an especially rainy or humid climate, consider using plywood sheathing instead of OSB. Although plywood is usually more expensive than OSB, plywood is more resistant to moisture damage.
Here are the four main ways you get wet framing lumber to dry:
1. Wait it out.
2. Use Fans
3. Use a dehumidifier
4. Use heat
Wet lumber will naturally dry out if given enough time. If the outdoor temperatures are above 60 degrees F, it usually takes about 4 weeks for moisture content to decrease about 4%.
It might take 6-12 weeks for a 4% drop if its cold and rainy. And if it’s below freezing, it might take many months.
If you live in a cold, damp climate or if you simply want to speed up the drying process, you can use one of the other methods: Fans, a dehumidifier or heat.
Carpet blower/drying fans, or some other powerful fans, increase air movement and decrease drying time. Keep the fans running 24/7, if possible, with window and door openings closed. These fans are very effective, but can be expensive. So make sure you secure the fans to the house frame with chains and padlocks. You might ask your framing carpenter or builder if they have fans that can be used for drying the house frame. Or check local supply or big box stores for fan rentals.
If the outside temperature is above 45 degrees F during the day, fans can typically decrease the moisture content of framing lumber about 0.5-1% per day. So you’ll need about a week, or a little more, to go from the 20% moisture content range to 14-15% or below.
In addition the fans, you could also ask your builder or framer about a running dehumidifier to help dry your house frame.
Finally, you might want to use heat to dry your lumber if you live in a climate where your wet lumber has frozen. But don’t use propane heaters inside the house for drying wood. A propane heater can add 1 gallon of moisture to the air for every hour of run time.
Instead of putting heaters inside the house, heat should ideally be generated OUTSIDE the house and then dry, hot air blown inside the house. If live in a very cold climate, ask your framing carpenter what heater he recommends for drying your framing lumber.
So, in summary, yes it matters if your house frames gets rained on. You should test the moisture content of the lumber with a moisture meter before drywall is hung. Definitely postpone drywall installation if moisture content is above 19%, but if possible shoot for moisture content of less than 15% for kiln dried lumber and less than 17% for pressure treated lumber.
Well, that all I have for you this week. I hope you learned as much as I did. Come back next week for another edition of Build Your House Yourself University-- BYHYU.