What Happens if your Framing Gets Rained on? (Learn to use a Moisture Meter)
Rain during framing is hard to avoid, so how do you know when a house is dry enough to move ahead with construction?
Q: What happens to the typical American house that’s built in a 4-6 month cycle?
A: The moisture in the framing lumber dries after a few months of heating/cooling and the house settles. This is indeed normal but it doesn’t need to be so pronounced.
First, let’s talk about the property of wood called Hygroscopy. Hygroscopy is the ability of a substance to attract and hold water molecules from the surrounding environment. This is achieved through either absorption or adsorption with the absorbing or adsorbing material becoming physically ‘changed’ somewhat, by an increase in volume, stickiness, or other physical characteristic of the material, as water molecules become ‘suspended’ between the material’s molecules in the process. (Source Wikipedia.org)
Most of the lumber used in my homes is kiln dried (KD), meaning it should arrive to the job site at a moisture content of 12-14%. Non-KD lumber or pressure-treated lumber generally has 15-19% moisture content. That 19% is a critical number as it’s a general consensus among the building-science experts that above 19% moisture content is the point where mold spores are activated and the rot processes start (assuming it stays above 19% for an extended period). Wood can absorb water up to 28-30% moisture content and is saturated at that point.
So, what happens if you close up framing that is still “wet”? You may see:
- Sheetrock cracks, nail pops, cracks in the sheetrock above windows/doors
- Floor squeaks, Stair squeaks
- In the worst case scenario, plumbing stacks can move, which could lead to Roof leaks
Now that you have a brief lesson on Wood Moisture Content let’s talk about what to look for in regards to Moisture Content for a home under construction. First, you as a Builder NEED to own a moisture meter. I like pin-based meters like the Extech model I currently use. Next, we want to ensure there is ZERO lumber in the house with a MC above 19%. 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.
|Pressure Treated Bottom Plate on a Concrete Slab reading 14.6% MC|
|I like to note the date & MC reading. That way if you have an elevated reading you can re-check as it comes down in MC.|
|My Extech M0220 Pin Based Moisture Meter reading this stud at 11.7% MC. Perfect.|
This testing is critical to really knowing what moisture content your wood is reading prior to hanging rock. As I said before you must get all readings less than 19%, but MY standard is all readings below 13-15% for my KD lumber and less than 17% for any green Pressure treated lumber. Once your home is completed and the heat/cooling equipment runs for a year it’s typical to see those studs reach equilibrium MC around 10-12%. That’s why I really want to see MC %’s below 15%. A small degree of drying is expected but when you get more than 5% MC loss the shrinkage of that lumber will show greater flaws in your finishes.
I’ll show you how to dry a wet house in a future post!
Best, Matt Risinger
Risinger Homes in Austin TX
Risinger Homes is a custom builder and whole-house remodeling contractor that specializes in architect-driven and fine-craftsmanship work. We utilize an in-house carpentry staff and the latest building science research to build dramatically more efficient, healthy and durable homes.
Be sure to check out my video blog on YouTube.