Green Roofs: How to Detail Waterproofing Using Liquid Membranes

Sourced from ArchDaily

Green roofs are composed of a series of layers that allow vegetation to grow correctly, avoiding leaks that may cause damage to the structure of the building. Although there is a wide variety of options to build them, we're presenting a system composed of a mortar base, a layer of asphalt emulsion, two waterproof asphalt membranes, a drainage layer, and the substrate that will allow the growth of plant species.

To waterproof the areas of parapets and other 'critical' points, the system includes a liquid polyurethane membrane, which allows the entire system to be sealed. Below, you can see some application keys of the different components of a green roof, and the benefits of this liquid impermeable layer.

1. Slab

Cover under the system with a minimum slope of 2%

The first layer of a green roof is made up of the roof of the building, which will receive its loads. To ensure proper drainage and avoid water stagnation, these should be able to move fluidly on the slab, maintaining a minimum slope of 2%. In this case, a concrete slab has been used, with a semi-polished finish and maximum concrete humidity of 4%, incorporating 4 "diameter drain pipes.

The strength of the slab should be calculated by a structural civil engineer and should consider the loads generated by the sum of all the layers that make up the green roof.

2. Waterproofing Membranes

Overlapping asphalt membranes that prevent the passage of water to the building

After the application of the special adhesive (primer) on the slab, the first layer of membranes should be located (in this case, 3 mm thick sandblasted finishing membranes), starting at the lowest part of the roof and in the direction perpendicular to the slope. As in the installation of tiles, each roll must overlap 10 cm in favor of the slope.

The second layer of membranes (in this case, 4 mm thick gravel-finish membranes) is installed on the first layer by thermo-fusion, stripping its overlaps.

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