Where to start when designing a roof terrace
A usable roof terrace is designed from its uses outward: first decide what will happen up there, then work out falls, drains, thresholds, balustrades and finishes. Every junction where the terrace meets a door, wall, balustrade or pipe is drawn in advance and assigned to someone responsible.
If you choose the tiles and furniture first and sort out the junctions later, some decisions will have to be revisited, and occasionally finished waterproofing has to be opened up again.
Uses and loads
Write down what the terrace will hold: dinners for eight, sun loungers, planters with trees, an outdoor kitchen, a hot tub, a pergola, outdoor air-conditioning units, solar panels. Draw the furniture to scale with the walkways between pieces, and mark where you need shade.
Heavy items, such as planters full of soil, a hot tub or a pergola on its own supports, are built into the engineer’s floor calculations at design stage. You cannot tell from looking at a terrace what load it will take. Putting a hot tub on the roof two years after handover, when it was never in the calculations, is a bad idea.
On the coast at Castelldefels and in the Garraf the wind can be strong. Light furniture blows away, and pergolas and awnings are anchored with wind load in mind.
Falls and drainage
Water has to run to the drains along a fall, not sit in puddles by the door. Two drains are better than one, or one drain plus an emergency overflow: if a single drain clogs with leaves, water goes where nobody expects it.
A good solution for terraces is a raised floor on adjustable pedestals. It hides the falls, gives a level surface and keeps the membrane and drains accessible underneath. Bonded tiles are cheaper, but the fall then shows, and reaching the waterproofing means lifting the finish.
The door threshold, the key junction
Waterproofing is turned up the wall and under the threshold to the height set by the CTE building code, and the designer builds that into the detail. If you want to step out onto the terrace without a step, that conflict is resolved in advance: with a recess in the floor slab across the terrace area and a linear drain grille in front of the door.
The decision is made before the concrete is poured, because the recess is part of the structure. A typical mistake: sliding doors ordered with a flush threshold over a slab with no recess. You then end up with either a step or a leak risk. What to agree before ordering windows and doors is covered in a separate guide.
Balustrades and fixings
Every balustrade fixing that goes through the waterproofing is a potential leak. It is better to side-fix posts or glass to the parapet, or to anchor plates installed before the membrane and detailed together with it. The balustrade height is set by the design according to the CTE, depending on the drop.
The parapet gets a coping with a drip edge. Without it, water runs down the façade and leaves streaks.
Services on the terrace
Sockets, lighting, a tap for watering and cleaning, automatic irrigation, power for the outdoor kitchen: all of these are pipes and cables that cross or run along the roof. Penetrations are grouped, sleeved and sealed according to the membrane system.
Outdoor units for a heat pump or air conditioning are noisy and vibrate. They should not sit next to the lounge area. Solar panels compete with the terrace for space, so you decide early which part of the roof is for panels and which is for people. In the house with a pool that we delivered between 2022 and 2024, the panels were likewise part of a single roof design.
Living with it after handover
Drains, access points and service penetrations must stay reachable. Do not cover them with fixed planters or built-in furniture without checking first. Keep photos of the membrane and junctions taken before the finish went down, together with the maintenance instructions: drains are cleaned every season and sealants are inspected every few years.
Roof waterproofing as a construction stage has its own guide.
Next step
To discuss it with BCN YARD, prepare the house drawings, photos or renders and a list of how you want to use the terrace. Structural details are developed by a competent design team, and we tie them in with finishes, services and the schedule. We reply within an hour and work in Russian and Spanish.