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1/8" slope on walkable surface?

G

gnarkill283

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Nov 15, 2017
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New York
We have a stamped concrete deck on a roof with drains (and emergency overflow drains) flush with the concrete finish. The slope to the drains is no greater than 1/4" (to a foot) since its a walkable surface and no less than 1/8" since that is the minimum for drainage. We are receiving comments that 1/8" is too little of a slope for drainage and 1/2" should be maintained. First off 1/2" doesn't meet ada cross slope requirements of 1:48 or 2% max and how would one maintain 1/2" throughout a large deck that is not perfectly square? If 1/2" is maintained, the top of slope to some drains will be higher than others and you can't have bump ups on a walkable surface. Appreciate any help - thanks
 
The least slope of the various roof covering types is 1/8" per foot. If the concrete roof covering is being done after the fact and would qualify as a re-roof, there is no minimum slope required as long as the roof drains.
 
ICE said:
The least slope of the various roof covering types is 1/8" per foot. If the concrete roof covering is being done after the fact and would qualify as a re-roof, there is no minimum slope required as long as the roof drains
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This is all new construction
 
Is this a slab poured over a waterproofing membrane? If so, there should be subslab drainage at the membrane as well (similar to a shower drain detail). Emergency overflow drains should be a couple inches above the slab.
 
Paul Sweet said:
Is this a slab poured over a waterproofing membrane? If so, there should be subslab drainage at the membrane as well (similar to a shower drain detail). Emergency overflow drains should be a couple inches above the slab.
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Yes - the emergency drains are spaced away from the main drain following the slope - how far would it have to be to meet code? If the slope is 1/8" then 8' away would mean its an inch higher than the main drain - is that enough height difference?
 
In Ca. the plumbing code requires the secondary drain to be a minimum two inches above the roof surface.
 
When i was in high rise construction about a hunnert years ago, we poured a porous concrete surface over a waterproof membrane on the roof of the building. I don’t remember the details, but the concrete batch plant came up with the mix design. We poured a 2x2 ft sample for the customer to approve, put it on saw horses so we could pour a bucket of water through it while they used a stop watch to calculate the porosity. Surprised everybody, the water ran through the concrete like it wasn’t there.
 
1/8" per foot roof slope used to be typical. The codes increased it to 1/4" sometime in the 1990s, probably because roof deflections would cause water to puddle on a 1/8" slope. I don't know of any code requirement for a 1/2" slope. It would be best to try to get a 1/4" slope to minimize the chance of puddles which could freeze in the winter and cause a slipping hazard for people.
 
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