How to waterproof the flat roof of a terrace/slab?

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We are building a new house and are currently working on a terrace. We would like to build it over our garage, which should have a flat roof. The height of the structure inside is 14 cm, the balcony door has no threshold, so there is also 14 cm for the structure outside.

Currently, the floor slab is not sloped. In fact, a sloped screed is/was planned to extend over 7 m. The architect advises a 0 degree roof, which is more of a pain in the stomach for us, so now a sloped screed. XPS 40mm insulation will be used, and there will be a foil and fleece on top, so the structure will be 43mm, which is already a given. Everything else is exposed. Do you have any ideas on that?

As far as covering, we're pretty flexible.



Insulating the slopes and then raising the terrace. It's best to collect water in a cistern. In fact, you plan such details before you start work. But it's more of an "easier exercise.

  • The cistern is a good idea.

Sloped screed with insulation or sloped insulation are both possible and common.

But I have yet to see how you get to those heights?

If the door has to be without sleepers and a slope of 2° is needed for 7m, I assume away from the door, then you already have a 14cm difference in height due to the slope alone. In this case there is no more room for flooring, so you have to switch to a roof with a 0° slope angle, which is certainly technically feasible without any problems, but will incur additional costs.

  • Sloped insulation with a 2 degree slope is rather out of the question. Do you have any ideas about coverage? We were already thinking about a 1 degree slope for the screed so that we would have at least some slope and then do a relatively thin structure on top. That would leave 7cm – 4.3cm -> 2.7cm on the pavement.
  • Slope insulation would be preferable in terms of structural thickness to a screed. And, again, if you do have a slope of 7m from the door, at 2% 0.0 is the place for flooring. But you can also make a counter gradient so that the water goes to the gutter in the middle of the roof (impact on the space below) or to the gutter, which in turn leads to the downspout.

In the upright position. The water runs along the sidewalk, and the slope underneath is leveled so the sidewalk is level.

  • Is 1% slope enough and what would you recommend for a sidewalk with a 2.7 cm slope?
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