framing and decking

I am installing Doug fir for my decking and have been told to hold each board tight with no gap. Then when the lumber dries out there will be about a 1/4" gap...

My concern is that in the winter the wet weather will swell the boards and they will be touching again holding the moisture and causing rot...

Also in securing the boards with two screws on each joist will that cause the boards to split in the center by not allowing them to shrink inward as they dry?

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Oct 26, 2010
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by: Editor - Rich Bergman

It really depends on the moisture content of the boards when you install them. If they are already very wet, you should not have much to worry about if they are tight together.

But if they are dry, say 5-10% m.C. then you will certainly have a problem when the rains come. I have never ever seen a deck board split in the middle because it had two screws holding it to a joist. The movement or shrinkage is not that severe. Yes there is tension in a board but a 5.5" board might shrink 1/8" on each side for a total loss of 1/4". The board should never split because of that.

That being said you will often see surface cracks in boards from weathering, drying, shrinking, etc but not enough to pull a board apart.

Pine tends to be a bad culprit for this because it moves a lot and is less stable then say a cedar or a redwood. But those species can also show moderate surface cracking or splintering if subjected to enough temperature and moisture extremes.

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