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Deck Slope


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When I was in architecture school I clearly remember one of my professors that said there is only one place that flat roofs don't leak. The answer-"In the middle of the desert where it does not rain"

1/8" per foot is the minimum that we use in our office. Whenever possible we use steeper pitches. If the structure is flat we add a tapered insulation system as part of the roofing system.

In high traffic areas we sometimes specify a fiberglass roof.

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Good Afternoon all,

During by construction days we always used 1/4" per foot as minimum for the movement of water. As it pertains to municipal code there was none although a negatively pitched deck would give you just as much trouble as soil would. The important thing is really that ledger board flashing is used and it is placed on the ledger board. So many times I see amatures place this on top of the deck boards which does nothing for water infiltration at the union of rim joist and the ledger board.


Appletree Home Inspections

West Bend, WI

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Originally posted by hausdok


I agree. 1/4 inch per foot is what I'd been taught for porches and balconies. Not sure it makes sense for a deck where the boards are spaced apart though. I'd be more concerned with the hardpan underneath in that case.



Personally, I'd be pretty po'd if my second floor walk deck was pitched 1/4" per foot. My 10' deck would drop 2 1/2". I would expect the builder to be able to make it water proof without sloping it. But... I live in the desert and don't have to worry about snow, ice, and rain every 3-5 days.

I think the design and slope really depends on the use, geography, and architectural constraints.

When I was a contractor in CT, we'd slope them at least 1/4", roof em' with EPDM, and build removeable "duck boards" that were sloped the opposite way, so you could actually hang out (with your deck furniture) on the deck. The duck boards could be removed to clean out leaves, etc, from the deck.

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In my day of hammering boards and planks, we carpenters always used to pitch the whole width about 3/4 to one inch (say for a twelve foot width)away from the building. It wasn't scientific or standard, it's just what we considered good practice and common sense.

I agree with Chris about the quarter inch to foot, it would make the tea in your glass look out of level.

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