Plywood sheathing, moisture...
So for some time I've been worrying about moisture within the ply sheathing. Water got in before the final roof sheeting went on and because the foil faced insulation on the outside won't allow moisture vapour to pass through then any water within the ply has to evaporate to inside the building. So whenever possible all the doors and windows are open to get a good drying breeze moving through. I had in mind that I was looking to get the moisture content down to around 14%, which is where fully seasoned wood will settle, and over the last few weeks I've been prodding around with a moisture meter to see how close we are (see pic.). The solid timber studs are mostly 14-15%, possibly because they're exposed on three sides, but the ply has been 16-19% with odd patches between 20 and 26%. So I put in a call to the TRADA technical helpline (www.trada.org.uk), a trade body who offer free advice about timber. Apparently the 'magic number' is 20% - above that timber is vulnerable to fungal and insect attack, below that is seen to be OK. So that was a green light to crack on and fit the insulation between the purlins... for the odd patches where moisture is still above 20% I'll use an electric fan to speed up the air movement...
5/20/2019 06:45:52 am
Here is great solution i found. Thanks for sharing your experience. Also Roof Purlin may be a solution on this point.
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Mike Hawkins is a co-op member and is responsible for the design and management of the build. He'll also live in it when its finished - hooray! He teaches future architects at Leicester DeMontfort and Birmingham City universities.