Moisture Testing Houses on Dry Summer Days

“Can you moisture test a home on dry summer days? “… a common question clients ask in summer time.

Yes you can, but there’s a couple of things to consider. Before I explain further, here’s a photo of a major leak below a window that we detected on a hot dry Auckland day with thermal imaging and moisture meters… (You can see the mould stain on the internal side of fiber cement board)

The timber doesn't look too damaged does it?
The timber doesn't look too damaged does it?

This is a very common type of window leak that was caused be cracks opening up around where the plaster cladding meets the aluminium window frame. There were no visual signs of this leak on gib board, skirting or external cladding.

So can you detect moisture problems in houses when it hasn’t rained?

First of all, there is a difference between moisture and leaks. Moisture will accumulate in a wall (with no cavity), and penetrate into insulation as a result of a leak. Moisture will stay long term, even if you fix the source of the leak… and if the timber in the area is untreated, mould and decay will start to take place, and you won’t even know it. A pitched roof leak for example could be missed if it hasn’t rained for some time, as the air circulation in the ceiling space will potentially dry the leak out… but not so with trapped moisture in walls.

The moisture damage below the window above was due to lack of cladding maintenance around the windows… coupled with design issues.

Here’s part 2 of what happened with the job above:

The home owner got his local builder to take the gib board off where we had found the leak. The vendor then had the source of the problem fixed and they used a dehumidifier to dry the area out. He kept the area open and dry of two weeks before replacing the gib, plastering and painting. The reason he went ahead and closed it all back up is because the timber frame looked and felt dry… and the screwdriver didn’t go through the timber when he tested further. Then…

He called me back to do a ‘re-test’ and get a clean moisture report. Guess what? After all that time drying it out, the moisture readings came back at 60% (Well over 18 – 20% moisture that it should be). Why was this? The moisture was inside the untreated timber and couldn’t be ‘seen’. See, the window leak was running down the internal side of the cladding where the timber frame was touching, therefore the majority of the water was soaking in through the back on the timber and across… and didn’t leave much visual evidence on the side of the timber that could be viewed.

Now what?

The area is now getting pulled back apart and the timber is coming out. Ideally, he would have had it moisture tested before closing it back up.

Summary: Dehumidifiers won’t completely dry out moist untreated timber, and what ‘looks’ dry may not be… even if you can’t push a screwdriver through it.

Further info about how moisture can accumulate in walls HERE

Moisture Meter – Measuring Moisture Content of Wood

We have a serious moisture problem in this country when untreated timber comes into the picture!

The moisture content within timber has a very important bearing on the uses for that type of wood. Having a good understanding of how moisture and leaks effect timber types is therefore critical to determine utilization. Moisture meters are the fast way to read moisture levels in wood.

Here’s a quick lesson about wood moisture, how it works in timber… and why we have leaky homes and leaky buildings in NZ:

The makeup on wood is best described as 1000’s of tiny cells… and within those cells are cell walls and cavities. Heartwood and Sapwood in their raw form (freshly cut) are saturated with moisture, and you may have noticed this yourself when you cut down a tree. In between the saturated cells are very small spaces of air. Once the wood has been cut, and the drying out process of the timber begins, the first part of the cell to loose it’s moisture content is the cell cavity, and then the cell wall.

Important to understand: Once the moisture from the timber cell walls has completely evaporated and the timber itself has somewhat shrunk in the process, the woods moisture content will then be in equilibrium with its surroundings (EMC – Equilibrium Moisture Content).

Once the timber framework of your home has been put in place by the builder, from then on its integrity and life span will be subject to the variations in surrounding relative humidity (and to a lesser extent, temperature). In general, most countries around the world including New Zealand, will have wide variances in humidity between winter and summer months, therefore the Equilibrium Moisture Content of the timber will affected (swelling and shrinking) if it wasn’t originally dried to the average moisture content is will attain in use. That’s why moisture meters quickly help us to determine if the timber is either dried out, or wet.

Are you starting to get the picture about why the high moisture content in untreated timber is causing major issues here is NZ with leaky buildings?

How does temperature affect moisture readings?

Most companies will initially calibrate their moisture meters around 19 -21 degress. The problem with people who aren’t experienced and don’t know how to use a moisture meter correctly, is they aren’t aware of how to add or subject readings based on temperature corrections. The basic rule of thumb, is that you subtract 1 from the meter reading either way per 5 degrees in temperature variance (this only applies up to 70 degrees in temp). The best moisture meters for sale in NZ will have this correction feature as a function.

You should have knowledge about the different timber species used in NZ buildings prior to arriving at a benchmark moisture percentage to work with. Treated and untreated timber will require adjustments. Untreated timber will actually give the most true reading because there aren’t any chemical preservatives to throw the moisture reading out.

We use a moisture meter to test NZ houses daily, and it works out cheaper for us to do the moisture inspection for you then buying one for yourself. 

(Source: Some of the above info was provided by NZ Forest Research Institute)