Concrete patio floor at same elevation as interior finish floor
I have two questions, regarding a covered patio for the new home we’re building outside of Vancouver, Canada (climate zone 4c). We’d like the concrete patio floor to be flush with the interior finish floor, so there’s not a significant step when going outside. The patio is covered, so snow and rain should not be a serious problem. The concrete slab is suspended over a bed of free draining gravel.
My builder isn’t sure whether flush decks are permissible, but I’m confident that I’ve seen them before around here. I’ve got a question in to our building envelope engineer, but wanted to ask the question here to see if anyone already knew the answers.
My questions are:
1. Does the BC building code permit decks that are flush with the finish floor?
2. Is the detail I’ve shown below with the copper flashing and drainage tubes a good one?
Thanks!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Peter,
Yes flush slabs are legal under the BCBC. The requirements for a certain distance from grade to the framing are generally interpreted as being for yards (soil, vegetation). Paved entrances, garage doors, etc. can be flush.
That detail looks problematic. It's a common situation on lots of condo buildings, but is complicated by the attachment of the slab to the foundation. Is the connection necessary for some reason?
Thanks for the reply, Malcolm. I'm glad to hear that flush slabs are allowed.
The footings are already poured, and most the foundation wall forms and rebar are in place. The foundation walls in this area have an extra rows of rebar to bend 90 degrees and create the 4 inch ledge for the deck slab to sit upon (that deck slab will be poured later). The builder intends to pour the foundation walls this coming week.
I realized a few days ago that the architectural drawings showed a step down to the patio, but my wife and I had it in our minds that the patio was to be flush. And so I'm trying to get this sorted out before the foundation walls are poured, hoping there's some reasonable way we can achieve the flush deck we imagined.
What about if in addition to the detail I showed, we also put some sort of drainage tubes in between the foundation wall and the suspended slab, as shown (and maybe add a second flashing that follows the foundation wall down). This would create an effect somewhat similar to if the slab were not connected.
Do you have any other suggestion on how best to make this work, assuming we went ahead and poured the foundation walls as currently planned with the 4" ledge for the suspended slab to sit on? I am speaking about this to our building envelope engineer on Tuesday, but I want to know what I'm talking about when I meet with him.
Best,
Peter
Peter,
My worry is that the small drainage tubes could block and that the consequences would be damage to the interior finished floor, which is not protected by the sill-pan.
I'd favour a drainage system that remained assessable to be cleaned and inspected. I would build a trench-drain into the finished top slab connected through several 2" ABS pipes through the structural slab. Something like this:
I see you're point -- you're worried about bulk water that might want to come inside, while I thought the slope of the deck would resolve that. I like the serviceable drain idea (a trench drain connected to several 1-1/2" ABS pipes through the structural slap). It sounds like I could make that work without having to change the 4" ledge of the foundation wall.
In the areas beside the door opening, where it is wall instead, would a similar drain be necessary? I think the answer is "no" because the flashing can extend up the wall to protect the interior. Would you agree?
Yes, I'm imagining a window cleaner who decides to first rinse the glazing down with a hose.
I agree the flashing should protect the walls fine where there is no door.
One concern though is there are three materials all on different parts of the galvanic scale used in close proximity. The concrete, aluminium door frame, and copper flashing. They need to be separated, or other materials used, to avoid corrosion.
Thanks again for the thoughtful answer, Malcolm. That's another good point about the different materials used in close proximity. I think I have enough info now to have an intelligent conversation with the building envelope engineer and builder about how we should proceed.
Peter,
One other alternative you might consider that would simplify things a lot would be to substitute pavers on plastic spacers for the top slab. The space under the pavers is a drainage plane, and you can easily remove them to do any necessary maintenance.
This is a photo of a deck I used them on in a slightly different situation over a membrane:
That's a beautiful home (and yard)!
We will keep this option in mind. Thanks again.
I second Malcolm, and suggest going the stone paver route. You can get large 2'x2' limestone pavers that look great and have a similar feel to concrete. It's pretty instant, vs concrete you have to get a "concrete artist" in to do the pour and powertrowel or polish and details to get I looking good. Just my personal opinion on good looking concrete is dependent on the person's doing the work.
The pavers will give a grid pattern but you'll get very good drainage and it essentially replaces the need and hassle for the linear drain. I think its more practical and it would be significantly easier to install as well.
The top deck with the pavers would be level, which is also a nice look, but note you'll have to slope and daylight the suspended slab underneath before it gets poured. Also you'll have to waterproof that slab, ideally with a polyurethane roll on membrane.