Rain Water Drainage on Deck

by Paul Houston
(United Kingdom)

I had a 4m x 3m softwood deck built last summer. All in all a good job. The problem I have now is standing rain water in some areas. It takes days to dry out.

It seems that the deck is too level and there is only a gap of about 1mm between boards.

How could I resolve this problem other than lifting the boards and shimming up to create a slope?

I have been thinking about drilling a few small holes in the board to drain rain water or is it possible to route the grooves out gradually deeper so that the rain will run of the end of the boards...

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Jun 21, 2016
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Deck drainage holes between boards
by: Paule

I have three two year old cedar decks. The lowest one was not sloped properly. I plan to drill some holes between the deck boards to help drain the water. Not in the middle of a board, but where the boards meet. What do you think?

Editor's Comments

Not sure if the odd hole drilled between the deck boards will be sufficient. It sounds like your boards are tight up against each other. If water is pooling in between them you might also consider using a circular saw and ripping a long cut right between the boards to assist drainage.

It might not be wide enough but it would certainly look better and in theory would be more effective.

Dec 09, 2009
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Fixing a Poorly Sloped Deck
by: Editor - Rich Bergman

There is not a lot of good news I can offer you about this problem because the heart of the problem is the frame was not set properly to create the right amount of slope.

The proper amount of slope is about 1/4" per 12" or in metric terms that should be about 6mm for every 30cm.

But there are some things you can do to mitigate and improve, although not entirely fix the problem.

Here are my thoughts. If you can't change the slope of the deck then it sounds like your deck boards are much too close to each other.

By increasing the gap it might, and I stress might, allow some of the standing water to drain off the deck board by the sides.

I would not drill hole in your deck boards. If you want to do that you may as well just rip them off and buy new decking and nail or glue and screw shim boards along the entire length of each joist to recreate the correct slope. That is ultimately the best solution but the most inconvenient.

Back to the gaps between the decking boards. You could by a small router and get a bit to re-edge the boards. This will be a bit tricky because you want the edging to be straight.

You may be able to use a fence that comes with your router to ensure consistency particularly if the router bit does not have a guide bearing.

All of these solutions are not perfect, exception re-sloping the joists. But the might improve things a bit.

If anyone else has some better ideas please help this fellow out with some other good suggestions.

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