A walkable «inverted» flat roof: the insulation sits above the waterproofing, which stays protected, and the walking surface is made of stone or porcelain pavers laid on adjustable pedestals. Rainwater drops through the joints between the pavers, runs over the insulation and reaches the outlets following the fall of the screed below. It is the liveable terrace: inspectable, draining and well insulated.
Technical section of the system, from inside (left) to outside (right).
A walkable «inverted» flat roof: the insulation sits above the waterproofing, which stays protected, and the walking surface is made of stone or porcelain pavers laid on adjustable pedestals. Rainwater drops through the joints between the pavers, runs over the insulation and reaches the outlets following the fall of the screed below. It is the liveable terrace: inspectable, draining and well insulated.
A walkable flat roof is a terrace. It is built «inverted»: unlike the traditional roof, the insulation is laid above the waterproofing membrane instead of below, so the membrane is protected from sun, frost and foot traffic and lasts much longer.
The walking surface is made of pavers (stone, porcelain, concrete) resting on adjustable pedestals. Between one paver and the next the water passes and falls into the space below the floor, where it runs freely to the outlets: the floor is «floating» and draining. The pedestals, adjustable in height, create a perfectly level surface even over the falls.
Under everything, a screed gives the fall (≈ 1.5-2%) to the outlets; on it the waterproofing membrane makes the seal, turned up at the edges and around the drains. The water runs at two levels — above the insulation and, above all, on the membrane — so the outlets and overflows must be sized and inspectable.
Being walkable, the structure and the floor must be checked for the service loads. The advantage of the floating floor is maintenance: the pavers are lifted to inspect the membrane and clean the cavity without demolition. At the edges, parapets and a high enough upstand of the membrane are needed.
In the traditional roof the membrane is on top, exposed to sun, frost and foot traffic: it ages, cracks and loses its seal. In the «inverted» roof the order is reversed: the insulation (XPS, which does not fear water) is laid over the membrane, protecting it from UV, thermal shock and impact. The membrane works cool and sheltered, and lasts far longer; the floating floor above, removable, also makes it inspectable. A little efficiency is traded — water runs over the insulation — for much greater durability.
The pavers rest at their corners on an adjustable pedestal, with an open joint between them: rainwater drops straight through into the cavity below and runs over the insulation to the outlets. The pedestal head levels the floor and keeps the pavers off the insulation, so the surface stays dry and flat.
At the parapet the waterproofing is turned up well above the finished floor — the upstand — and capped, so wind-driven water cannot get behind it. The pavers stop short of the wall, leaving a drainage margin; a coping protects the top of the parapet.
Informational links to the regulatory framework. Always verify the current text on the official source.
A ready-to-edit DOCX from this system’s data — build-up, performance, and cited regulations with their current in-force status. Courtesy draft, free.