Waterproofing exterior stairs over living space?

[Sea Ranch]

Greetings.

I'm planning to pull down my existing deck (rear of house, off main floor, about 8 feet above grade) and replace with a larger deck which I would enclose beneath and turn into shop/garage space. The house's back door will open onto this deck and there will be an exterior set of stairs to the left, running alongside the house, down to the back yard.

This set of stairs will run down overtop of enclosed shop space (at least 7 of 10 steps would be over shop space).

Question: what would be the best way to waterproof these steps?

The main deck surface will probably be some type of "Duradek". I am led to believe (and can imagine) that putting the main waterproofing membrane directly over the steps - attempting to seal the space below by sealing the staircase - would be a nightmare of corners and seams. [:-bigeyes

It's been suggested that I place stringers and steps over a slope, which slope would be waterproofed much like it was a "roof". The staircase over this slope/roof would be left as open as possible (to make cleaning out the inevitable debris that falls through them as easy as possible). In other words, build with a "roof slope" in place of a staircase, and install stringers and treads afterward, suspended over top of the "roof slope".

Thoughts, hints, tips, concerns? Would I use a torched-on cap, asphalt shingles (which are on the main house roof), some more Duradek on the slope . . . or an entirely different approach??

Thanks for your comments . . .

Randy

(This is the same structure I've started a post on over in the Building Science section . . . "How to design & vent deck-over-living-space?" [])

[Jim Katen]

First of all, do yourself a big favor and build the deck a good 7" below the door threshold. This will allow you to flash everything properly. Everyone always make the mistake of building these things flush with or only an inch or two below the threshold. This is madness.

Next, do yourself another favor and push the stairway out past the end of the building. As you say, trying to waterproof a stairway with Duradek would be a nightmare and using one of the liquid applied membranes just wouldn't work.

If you build a sloped roof under the stairway, it's going to look really retarded and you'll have to remove the stairway to recover it someday. It's a dumb design.

[Sea Ranch]

Thanks, Jim; somehow I knew I'd get a no-holds-barred answer from you []

Of course, moving the deck even lower than it already is would make headroom in the shop, well . . . even lower than it already is.

And, unfortunately, I don't have enough width on my house to get both an adequate sized deck/shop across the back and have the stairs not extend past the end of the house and out into my driveway. Stairs could be relocated to a new location off the deck, but would then ruin the natural and convenient flow of traffic in/out, up/down.

So, I am probably stuck with this "dumb" design. Certainly, it's a little unorthodox. But that's often what "renovations" and additions are, by virtue of not having been planned afore-time when the original house was built.

[inspector57]

Splurge and use quality metal roof (i.e. standing seam) then place a steel stairway over the roof with as much clearance as possible. Done properly it should last a lifetime.

[Jim Katen]

Thanks, Jim; somehow I knew I'd get a no-holds-barred answer from you []

Of course, moving the deck even lower than it already is would make headroom in the shop, well . . . even lower than it already is.

If it just isn't possible, then build a roof or at least an overhang over the door to limit the amount of wind-blown rain that will stress the threshold. Also, make sure that you run the duradek all the way underneath the door threshold and turn it up at the rear and sides of the threshold to create dams.

And, unfortunately, I don't have enough width on my house to get both an adequate sized deck/shop across the back and have the stairs not extend past the end of the house and out into my driveway. Stairs could be relocated to a new location off the deck, but would then ruin the natural and convenient flow of traffic in/out, up/down.

So, I am probably stuck with this "dumb" design. Certainly, it's a little unorthodox. But that's often what "renovations" and additions are, by virtue of not having been planned afore-time when the original house was built.

If you absolutely must have a 3' deep closet with a ceiling that slopes down to the floor, then do your sloped roof thing and use a granule-coated modified bitumen material. They make torch-down, cold-process, and self-adhering versions. Avoid the self-adhering version if you do the work during cold weather. Also, be sure to make the stairway removable so that you can replace the roof in 30 years.

[Jim Katen]

Splurge and use quality metal roof (i.e. standing seam) then place a steel stairway over the roof with as much clearance as possible. Done properly it should last a lifetime.

I didn't see Jim's reply when I typed mine. I like his idea better.

[Garet]

Is the stair off the deck an absolute requirement? The most simple solution would be to eliminate it. Lots of elevated decks like this don't have direct access to the yard.