I’m building a two story addition to my house at the momement which will have a roof garden on top, and the plan is pour concrete for the patio. Basically looking for anyone who has done this before and has any lessons learnt the hard way, so that I don’t have to.
The supporting floor is 9 1/2 super TJ’s (the stronger ones) with 1 1/8 T&G ply on top of this. The current thought is to cover the ply with an elastomeric membrane, then a layout a 16″ o.c. grid of #3 re-bar and pour about 3″ of light weight concrete, with a both a color and Kalmatron additive, which is an additive that increases strength and decreases porsity (similar to Xypex).
Any thoughts or comments would be appreciated.
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You don't say what your span is, but there is a channeled steel base product (think HEAVY corregated) for this kind of application. I don't recall the name of it, but it looks like scaled down sheetpiling that is used for revcetments, dikes and the like.
The steel serves as the underlayment and structural support, is covered with a waterproofing membrane system and then the concrete.
You also need to design the path for water runoff from weather or sprinklers.
I'm always a little leery of a framed wood base for something like you describe unless it's built more like a bridge or dock frame.
There are a number of really good waterproof membrane systems available....not the kind you get at a big box or local lumber yard....more likely available through industrial suppliers or retailers, like tile or masonry suppliers that serve commercial and industrial builders.
>> The supporting floor is 9 1/2 super TJ's (the stronger ones) with 1 1/8 T&G ply on top of this. <<
What is a super TJI's?
Regardless of what they are, were they designed to handle what you want to do? If not you can't do it unless you get it designed and build them up to handle all the weight you want to put on them.
Who engineered the I-joist system? More importantly or specifically, was the I-joist system designed specifically to carry this substantial additional load? What the he11 is a 'Super TJI'? A 3" concrete slab with a garden on top is a pretty heavy thing.
I worked on a couple of condominium projects that used slabs over membranes. But after watching crews with concrete saws and jackhammers trying to find leaks, I now always specify pavers.
When you say "the current thought"... whose current thought is that?
You need to get an engineer to size the framing for the load. You most likely need to slope the top of the framing so that your deck has pitch, rather than being flat. The membrane over the decking is the right idea. I don't know the concrete additive you speak of, but are you proposing to have waterproof concrete?
Drainage details around the edges are important... you going to have railings, parapets, or what?
I would seriously consider hiring a waterproofing contractor. I would also seriously consider a paver-on-pedestal system instead of a slab.
The roof has been engineered, stamped, through the city and is being inspected. The deck will be slopped to a roof drain (with overflow), there will be paprapet walls and the membrane will lap up those walls at least 8", with the building paper lapped over the membrane (not stapled at the very bottom!)
I was more looking for thoughts on the concrete pour and membrane system, i.e. does anyone have a particular type or manufacturer of membrane they think would work, any other. Or does anyone have any thoughts on the concrete mix. The Kalmatron makes the concrete waterproof in theory (although I would never rely on that to make a deck waterproof for a whole host of reasons, but it all helps).
Thanks
Are you saying that it's being inspected to see if it can handle the weight? Or was it designed and past inspections with all the weight of the concrete from the start? I'm just asking this because you said that this concrete was your current thought but then you said it's been past already and being inspected. It sounds like you thought of this after it was designed and past by the town.
Joe Carola
This is new constrution that I'm building right now.
79912.9
Read over my comments about the deck I'm currently doing.
You'd better have a structural engineer design the framing. "Super TJI" sounds like you met "Super Salesman".