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Old 10-01-2009, 10:06 AM   #1
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Protecting Joists and Beams with Bituthene

a contractor friend recommends I cover all my joists and beams of my deck (which is PTW) with a Bituthene type flashing. he says this will prevent any chance over moisture getting in cracks between joints and causing rot. Im imagining its another $100 of material which is nothing compared to the total cost and labor I put into it.

does anybody see any issues with doing this, one concern is it could trap harmless moisture that my PTW would absorb and allow to slowly dry and instead my decking would be subjected to this, is that a ridiculous thought?
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Old 10-01-2009, 11:46 PM   #2
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I have been recommending that also. If the water between the decking runs off the joists, rather than into them, I think they will last longer and be stronger while it is raining (think lighter). The decking will not absorb the water that weeps under them if they are back primed. If not, the decking wood won't sponge as much water because it won't have a chance to pool as with a porous surface below. The nails (fasteners) will not allow water in their holes because of the self-sealing quality of the material. The gang nails or bolts holding built-up beams together will get less water if you flare the bottom 1/4" of material out on each side to shed water. The bottom 1/2", pinch to create a fold aiming down. I run a bead of caulk under the ledger, on the outside bottom edge- continuous, to shed water dripping off the ledger/flashing above. If treated wood, treat all cut ends during construction as this will stop water there. Just in case:,M1
Be safe, Gary
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