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Moisture content in new vs. old wood

Greg Labbe | Posted in General Questions on

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.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Greg,
    It's easy to get misleading MC readings with pin-type moisture meters. Here are some links with more information:

    http://www.buildingpreservation.com/index.php?option=com_content&view=article&id=115:use-of-electrical-moisture-meters&catid=7&Itemid=84
    "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!"

    http://www.bigelowsite.com/aracnetlive/wood/articles/Wood_Moisture_Impedance.pdf
    "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."

  2. Greg Labbe | | #2

    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!

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