Should a raised deck be built with a grade to it?

by Rick
(Calgary, Canada)

I have a 14 foot deep deck over a walk out basement that runs the length of my house. I am planning to re-floor the deck with sheeting and a duradeck type of product. Does the deck need to have a grade to allow any rain / snow to run off or should it be level? Currently it has 6" wide boards spaced 1/4" apart on it.

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Oct 24, 2010
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Slope on deck is critical
by: Editor - Rich Bergman

Yes, this is a very important issue. Minimum slope recommend is 1/4" per 12" or per foot. This works out to be about 2% (0.25/12). But your local climate should be taken into consideration. For example, 2% might be fine in southern California where rain is less frequent. But in Seattle you might want to increase that to 3/8" per 12" (foot) (0.375/12) which is about 3%.

In Calgary you have a generally drier climate, just west of the Rockies, just east of the prairies so 2% should be perfect. But you have very cold snaps in the winter followed by warm Chinook winds so your installer has to use very good quality adhesive to secure the vinyl membrane, do very good quality double welds.

Double welding includes a first weld underneath the overlapping pieces in the first pass. Then the second pass is the full and final weld. That is needed to really get it right. Well trained installers know this.

Also make sure you lap the vinyl up the wall of the house, under the siding at least 6-8" and depending on the thickness of the material you may need a cant strip so the material stays adhered to the sheathing. 60 mil will require cant strips.

And make sure there are good drip edges. The drip edge ensure water drips cleanly away from the fascia. Without that the water will dribble down the fascia and water stain it over time reducing life span and looks dirty all the time. But if he uses a thick vinyl it is tougher to get the 90 degree bend to say stuck to the drip edge. So discuss this thoroughly with your installer. Nothing worse than paying a good dollar for your new deck and a year later it starts to peel away from the drip edge. It is metal so it may require a better glue than for the wood sheathing. Hope this helps.

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