ᐅ Parapet construction on flat roofs

Created on: 20 Jun 2019 21:23
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blueturbo
We plan to build our house using 24 cm (9.5 inches) Poroton bricks. An external thermal insulation composite system (ETICS) will be applied on top. The flat roof will be a reinforced concrete slab.

Now, the question is about the construction of the parapet. The current offer for one row of Poroton bricks topped with a U-shaped form and ring beam is quite expensive.

My idea is to lay or glue two rows of sand-lime bricks on the last floor slab to reach the required parapet height of 50 cm (20 inches), and that should be sufficient. On top of that would come insulation, an OSB board, and then the aluminum flashing. The roof covering will be a bitumen membrane.

My question is: Is this solid masonry wall enough as a parapet, or do I need to cast a concrete ring beam as a finishing element? After all, only the wind load acts as a horizontal force on this 50 cm (20 inches) high wall panel.

I would appreciate some input.
Best regards, André
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guckuck2
29 Jun 2019 16:50
It won’t work without a parapet. Appropriate (sloped) insulation will still be applied on top of the concrete slab.

What do you mean by "really expensive"?

The parapet can also be constructed from reinforced concrete, basically cast together with the concrete slab.
tomtom7929 Jun 2019 20:27
When the ceiling is being poured, what speaks against leaving a few anchors sticking out and using them as reinforcement for the parapet?

But what price are we talking about here?

Also, something else that sounds strange: a bitumen membrane? Think it over carefully—it's better to go with EPDM, as it lasts longer and performs better.
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Matthias 40
29 Jun 2019 21:10
How much was the quote?
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guckuck2
29 Jun 2019 23:02
EPDM ... good luck finding a contractor who installs it in that size and with the necessary penetrations. And then it costs several thousand more in extra charges.
In my opinion, there is nothing wrong with the usual three-layer system.

I would also be interested to know what the parapet should cost.
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blueturbo
30 Jun 2019 22:37
For the parapet with a row of Poroton bricks and a concreted U-shell, I was around 100 euros per meter. I find that quite expensive.

The parapet cannot be poured at the same time as the slab. First, the slab would need to be cast, and then the upstand could be shuttered and concreted. The solution with the sand-lime bricks still sounds cost-effective and easy to build to me.