I've read not to put plastic under a deck. What can I do?

closed as unclear what you're asking by mmathis, JPhi1618, ThreePhaseEel, Daniel Griscom, Machavity Nov 4 '17 at 18:46

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  • Can you post a picture of your deck? Be sure to include a picture of where it contacts the ground. – Machavity Nov 1 '17 at 19:04
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    Are you sure it's moisture from underneath the deck and not water sitting on the top that's causing the rot? I regularly find decking which was laid very close together and over time the gaps have disappeared (timber swells, debris fills the gaps etc.) and then water sits on top working its way into the screw holes and any end grain. – handyman Nov 1 '17 at 21:03
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    Incidentally, burying screws deep into the decking to get a 'good hold' also leads to rot. Imagine a screw with a little pocket of water sitting on top of it and soaking into all that lovely micro torn grain... We always leave the screws flush with the top these days and call in a year later to further tighten them once the decking has settled in (if necessary). With expensive, good looking screws laid to a line, it's virtually a feature. – handyman Nov 1 '17 at 21:06

Plastic is okay underneath but not touching the deck's joists, i.e. on the ground. Put gravel on top to keep it in position. Secondly, ensure that there is a good airflow over the top of the gravel and under the deck structure. Never put anything between the deck structure and the decking material.

Ensure the ground is properly prepared under the deck structure/plastic sheeting by making sure water will not pool. I.e. slope everything away to surrounding ground or drainage.

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