What Builders Should Know About Moisture in Wood Framing
When a moisture failure happens on a construction site, whose fault is it?
Whether warped door openings, loose joints and fastenings, or mold, the construction business is often liable—unfortunately.
So how can you, as an industry expert, avoid these kinds of problems? You want to work quickly and efficiently to accomplish as many projects as possible. But how do you also protect your hard work and keep your reputation intact?
Understanding moisture’s impact on wood framing can help answer these questions. We’ll look at:
- Why does moisture content matter for framing?
- What is an acceptable moisture content for framing?
- How to measure the moisture content at this stage of construction
- How to deal with wet framing
So, first things first—why moisture matters.
Why does moisture content matter for framing?
Framing materials with too high of a moisture content can lead to wood failures. And wood failures may mean extra time, labor, and material costs—and even legal trouble—for your homebuilding business.
Shrinkage is the main result of having wood with too high of moisture levels.
Here’s the science:
As a hygroscopic material, wood shrinks as it’s affected by moisture in its environment. It’ll continue to release moisture until it reaches the equilibrium moisture content (EMC), the moisture content that matches the surrounding temperature and humidity levels.
This means that if your wood for framing hasn’t dried to the EMC before construction, it’ll continue to dry—and shrink—after the framing is finished. Shrinkage occurs “primarily in horizontal members such as wall plates and floor joists.”1
And it can be noticeable if the wood dries more than 5 percentage points.2
According to the USDA Wood Handbook, it can lead to many other unintended consequences, such as3:
- Cracks in the drywall
- Nail pops
- Roof truss uplift
- Open joints
- Warped door openings
- Uneven floors
- Loose joints and fastenings
Construction expert Matt Risinger also points out that “in a worst case scenario, plumbing stacks can be pushed around, leading to water leaks.”4
And with these problems, a construction business can run into legal issues. If a high moisture level results in mold growth, or the wood warps way out of specifications, construction company owners may find themselves in lawsuits. Which means their reputations could suffer, too.
That’s why it’s not uncommon for contractors, particularly those from companies that have been sued in the past, to take homeowners around and show meter readings with a quality moisture meter.
Indeed, using a moisture meter is an excellent precaution.
Let’s look at the kinds of readings you should get to prevent problems.
What is an acceptable moisture content for framing?
The industry standard for acceptable moisture content (MC) in wood framing varies depending on the location. But typically, the number is somewhere between 9 and 14% MC.
One construction engineering company, which specializes in moisture issues, uses the following criteria to determine whether a moisture content reading could contribute to problems:
- 16–20% indicates excess moisture that could be a cause for concern.
- 20–28% indicates a risk of decay and mold.
The Canadian Wood Council, in the booklet Moisture and Wood-Frame Buildings, has a more generous criteria. It considers a piece of wood “dry” if it’s under 19% moisture content. Above 28%—the fiber saturation point—wood has the potential for decay, meaning it begins to break down. But wood usually stabilizes between 12 and 18% MC when it’s outside.5
Of course, the exact number will depend on your region’s EMC.
For exterior wood, the Wood Handbook recommends:
- An average of 9% (7–12%) in the dry southwest part of the United States
- An average of 12% (9–14%) in damp, coastal areas or anywhere else in the country6
Note that some construction workers prefer to use wetter lumber because it’s easier to nail into place. The trade-off is that they have to deal with some shrinkage when the wood dries out. Others choose to dry the lumber all the way before using it. Yes, they may have to work harder to nail the frame, but they minimize moisture problems later on.
What matters most, though, is that the materials of the building envelope are dry before other materials are put on or over them.
Once the framing has dried to the EMC, it’s ready for OSB, drywall/sheetrock, insulation, and subflooring. Be sure to check the manufacturer’s requirements for your specific building materials.
But now that we understand the importance of wood MC, how can we check it quickly and easily?
How to measure the moisture content of wood framing
Measuring moisture content in wood framing is as simple as pulling out a wood moisture meter. Choose a quality meter that provides consistent and accurate readings.
You’ll have two main options: a pin meter or a pinless meter.
Pin meters can do the job, but keep in mind that they will leave small pinholes in the wood you measure. Furthermore, pushing the meter in for each measurement can be tedious when you have a large load of wood.
In contrast, a pinless meter will allow you to check large amounts of wood in very little time.
Once you have your pinless moisture meter, press it firmly on the wood, allowing the electromagnetic sensor to scan its moisture content. Test from the center of the board rather than just the ends or the edges that tend to be drier.
The number of boards you’ll need to check will depend on how those boards are used.
For example, if you’re building a laminated beam for structural purposes, measure every board along the entire length of the beam. One wet spot could mean a defect that causes the entire beam to be rejected.
In other cases, you may only need to check a representative amount of boards. But it all depends on how serious the flaws would be if the moisture pockets were not detected. It’s better to err on the side of caution.
You’ll also want to check moisture content at various stages in the process. Here are some details on timing.
When should moisture content be measured?
Measure the moisture content of framing materials at least (1) before purchase, (2) when the wood arrives on site, and (3) before putting insulation and drywall. If you’re waiting for the framing to dry, you’ll want to check it every few days for progress, too.
But what if you’re buying framing lumber that is supposedly kiln dried and ready to use? What if it comes from a reputable sawmill?
Regardless, do your due diligence and check the moisture content of the wood for yourself. The last thing you want is to end up with wood that is far from the moisture content you were told it would be. Then, all the responsibility will fall on you.
Once the frame is up and under a cover, check it again.7 Is it ready for insulation and drywall, per the manufacturer’s requirements?
At this stage in the building process, it’s absolutely essential for the wood to be at the right moisture content. Putting insulation and drywall in too soon could result in excess moisture getting trapped in the walls, which could lead to problems later on.
If the framing is not dry enough—perhaps it got rained or snowed on before the roof was finished—then what? Let’s walk through what you need to do to dry it.
How to deal with wet framing
The main step to handling wet framing is getting it dried out. We’re going to look at ways to dry framing, whether it’s new framing that got rained on or old framing that was exposed to flooding.
In the case of new framing, simply give it the time it needs to dry. One of the main contributors to improper drying is construction workers being in a rush to put on drywall and insulation.8
The timing depends on the climate.
In the experience of Matt Risinger, a builder for over 20 years, framing can dry quite quickly in a warm climate. It may only take a few weeks of air drying. But if the weather is cold, that number could be much longer: 6–12 weeks. If humidity is particularly high (above 60%), he also recommends closing windows and using a dehumidifier to help in the process.9
In fact, three elements help with drying out framing10:
- Venting—having fans inside and at open windows or doors to circulate air
- Heating—running furnaces or space heaters
But what if the wood is wetter due to a flood or major leak?
How to dry out wet framing after a flood
Just like wet framing in the building process, wet framing after a flood needs sufficient time to dry. However, if a finished house floods, some extra steps are necessary:
- Pull off the wall and floor coverings, drywall, and wet insulation.
- Clean any mold spores (which you can avoid if you deal with the flooding immediately). Use a detergent, followed by a solution of 1 cup of chlorine bleach to 1 gallon of water. Let the bleach sit wet for about 10 minutes on the wood before letting it dry.11
- Make sure the MC is at an appropriate range (at least 13–15%) before making any repairs.12
Then, the drying process.
Flood Recovery: Dry Out Before Rebuilding recommends the same three elements for drying that we mentioned earlier: ventilation, heat, and dehumidifiers.
Use a wood moisture meter to check the progress and know when the framing is sufficiently dry.
Safeguard your work against moisture issues
Using a wood moisture meter on-site has the potential to save you from many moisture issues during construction.
But you may be thinking, I don’t want to add another step to my process! That’s more time out of my already-full schedule!
Adding an extra step to your process is never ideal. But checking for moisture content is a step that’s guaranteed to save time, money, and your reputation in the long run.
You’ll be able to ensure your building materials are at the right moisture content at purchase and at the time of building. And if the framing is rained on before you get the roof on, a moisture meter will indicate when the wood is dry enough for drywall and insulation.
All of that means you’ll be giving your client a high-quality building.
And for yourself? Confidence in your work and a good reputation.
It all starts with a simple moisture meter. See Bessemeter’s pinless moisture meters to find a budget-friendly, high-quality option for your business.
- Canadian Wood Council, Moisture and Wood-Frame Buildings, p. 5. (↑)
- Simpson, William, “Drying and Control of Moisture Content and Dimensional Changes,” Wood Handbook, Ch. 13, USDA. (↑)
- Simpson, 12-18. (↑)
- Risinger, Matt, “Drying Wet Framing,” The Journal of Light Construction. (↑)
- Moisture and Wood-Frame Buildings, p. 4. (↑)
- Simpson, 12-5. (↑)
- Risinger, “Drying Wet Framing.” (↑)
- Ibid. (↑)
- Ibid. (↑)
- Moisture and Wood-Frame Buildings, p. 18. (↑)
- “Dry Wood Framing in Flooded Homes before Rebuilding,” Iowa State University. (↑)
- “Use Moisture Meters to Determine When Structures Are Dried Out and Ready for Rebuilding,” Nebraska Extension, Institute of Agriculture and Natural Resources at the University of Nebraska–Lincoln. (↑)