Helpful? 0

Moisture content in new vs. old wood

My question is about moisture content of new versus 100 year old wood found in an attic.

I was recently in an attic and noticed dripping condensation in the vintage home's attic. The dimensional lumber planking used as roof sheathing had a few new white pine planks installed. With a pin type moisture meter, the MC in the new white pine was 22%. In the adjacent softwood (SPF?) the MC was twice at 40%.

Does an attic do funky things to wood long term? Certainly the sap has dripped out over repeated summer heat and maybe the wood has a greater capacity to absorb moisture?

The meter suggests no number over 30MC should be trusted. I also should have corrected for temperature and for species.

The new planks laced in with the old plank roof sheathing.44.36 KB
Mystery wood (SPF) with 40+MC43.58 KB
New pine with 20+MC38.08 KB
Asked by Greg Labbe
Posted Tue, 12/31/2013 - 08:50
Edited Tue, 12/31/2013 - 10:18


2 Answers

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Helpful? 1

It's easy to get misleading MC readings with pin-type moisture meters. Here are some links with more information:
"The actual readings also depend on the area of contact of the probes/electrodes with the substrate. For example you will get much higher readings on a material where the probes can fully penetrate than on a similar material with similar moisture factors where the probes cannot fully penetrate. Therefore, do not try to make simple comparative readings between substrates - these meters are qualitative and it may just be reflecting the probe contacts and nothing else!"
"Even insulated pins cannot be used successfully on lumber with free water on the surface because the water will follow the pins as they penetrate the wood, giving a very high miseading moisture reading."

Answered by Martin Holladay, GBA Advisor
Posted Tue, 12/31/2013 - 09:14

Helpful? 0

Surface condensation was felt too so surface readings were probably short circuiting! Thanks for the feedback Martin and a Happy New Year to you too!

Answered by Greg Labbe
Posted Tue, 12/31/2013 - 16:20

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