Rooftop pool on a house: calculation, waterproofing, guarding

Rooftop pool on a house: where it starts

A rooftop pool on a house starts with a calculation, not a sketch. Water is heavy: a metre of depth puts a tonne on every square metre, plus the weight of the shell, lining and people. So first a structural engineer checks the slab, columns and foundation, and only then do we settle the size and depth of the pool. In a new house the load is designed in from the start, and then a rooftop pool costs hardly more than one on the plot. In an existing house the slab often has to be strengthened, or the pool gets smaller.

Calculation and structure

• survey of the slab, columns and foundation;
• calculation of the load from water, shell, people and seismic action;
• the shell rests on beams or columns, not on the screed;
• movement joints between the shell and the roof;
• space for the plant room on the roof or on the floor below.

We design the slab under a pool as a separate structure; more on floor slabs on the floor slabs page. In Batumi seismic action adds requirements: the water in the shell sloshes during a tremor, and this is also allowed for in the calculation.

Two lines of waterproofing

A leak from a rooftop pool runs into living rooms, so the waterproofing is done in two lines. The first is a roofing membrane under the shell, as on a usable roof; the second is the liquid-applied waterproofing inside the shell itself. Each line is water-tested before the next layer, and every pipe penetration through the slab gets flanges and sleeves. Where the structure allows, we leave access for inspection under the shell.

Plunge pool or a large one

A terrace or the roof of an apartment often has no spare load capacity for a large pool. Then we install a 2.5×4 m plunge pool in stainless steel or composite: shallow, for cooling off in the heat and relaxing rather than swimming. It is lighter, quicker to install and can stand on supports that transfer the load to the columns. The roof of an apartment building requires the owners' consent and a permit, and we check this before the design.

Getting everything up there

Concrete goes up to the roof by concrete pump, and reinforcement, glass and equipment by crane. In Batumi's dense streets the space for the crane and pump has to be agreed in advance, sometimes with the street closed for a day. A finished plunge pool shell is lifted by crane in one piece, so its size is limited by the crane's capacity and reach. All this goes into the schedule and estimate before work starts.

Guarding, wind and the view

At height the wind is stronger than at ground level; it blows water out of an overflow gutter and cools it. We make the guarding along the roof edge in glass so it does not block the view; more on the glass railings page. A glass pool wall, through which the water can be seen from the side, is made only of laminated toughened glass to a calculation. An overflow design on a roof looks striking, but its tank also has to go somewhere and its weight has to be calculated.

How much a rooftop pool costs

A turnkey rooftop pool to a structural design costs from 3 840 ₾ per m² of water surface, a 2.5×4 m plunge pool for a terrace or roof from 48 000 ₾. A slab survey and load calculation from 2 520 ₾, double waterproofing under the shell from 130 ₾ per m². A glass pool wall from 12 000 ₾ per m², an overflow pool from 3 180 ₾ per m². A heat pump from 11 400 ₾, an underwater light from 840 ₾. The final cost is set after the calculation and an agreed estimate.