A damp patch on a top-floor ceiling is almost never directly below the point where the roof is damaged. Water gets under the covering, travels along the fall of the screed and through the insulation, and comes out wherever it finds a gap in the slab — sometimes several metres from the source. That is why patching over the stain does not help: a rain or two later the patch is back, often somewhere new.
Below are the causes we come across most often on Tbilisi roofs. The order roughly follows how common they are.
1. Water ponds on the roof
A flat roof is never truly flat: it needs a fall towards the drains, usually of 1.5–2% or more. If the screed was laid without a fall or has sagged, puddles remain after rain. Where water stands for days, the covering ages many times faster: the bitumen washes out, the seams soften, and in winter ice tears the material apart. Puddles that have not drained a day after the rain are the first sign of a future leak.
2. Upstands at parapets and walls
The most common place for leaks. The covering must be carried at least 250 mm up the vertical surface, fixed with an edge bar and capped with a flashing. In practice the membrane is often carried up only 5–10 cm, left unfixed, or it peels away from the wall over time. Water runs in behind the edge and down the wall into the building — leaks appear along external walls and in the corners of top-floor rooms.
3. Drains and outlets
A drain is a hole in the roof, and everything around it has to be watertight. Typical problems: the drain is blocked with leaves and water ponds around it; there is no clamping flange and the covering is simply brought up to the pipe; the drain is recessed below the level of the covering but the upstand around it has not been reinforced. One blocked outlet turns a section of roof into a pool.
4. Penetrations for pipes, aerials and air conditioners
Over time a roof acquires things that were not there when the building went up: outdoor air-conditioner units, aerials, vent outlets, cables. They are fixed to the slab through the covering, and every fixing is a potential hole. The sealant around pipes dries out within two or three seasons. During an inspection we check every penetration separately: they are small but very common sources of water.
5. Seams in roll materials
On torch-on and PVC roofs water most often gets in through the seams: the overlap is narrower than the standard, the seam is not welded along its full length, or the material was damp or cold when laid and there is no bond. From outside such a seam may look intact — it is checked with a spatula or a seam probe, and on PVC with a vacuum bell.
6. Mechanical damage
Walking on the roof in hard-soled shoes, installing equipment, a dropped tool, ice being chipped off — all of this leaves punctures that cannot be seen from the ground. Soft coverings on walkable roofs with no protective layer are especially vulnerable.
7. The building's expansion joint
Where a building is divided into blocks, the slabs move relative to one another — with temperature and settlement. If the joint is simply covered with the same material as the rest of the roof, the covering tears at the first movement. An expansion joint needs its own detail: a flexible tape or profile that keeps its freedom of movement, and a sealant designed for stretching.
8. The covering has reached the end of its life
Every material has a lifespan: bitumen cracks under ultraviolet light, blisters appear under the covering (that is vapour from moisture in the insulation), the granules fall off. If the roof is more than 10–15 years old and has never been repaired, leaks are a matter of time rather than of one specific defect. Here it is important to make an honest judgement: repair over the top, or start again.
How an engineer checks this
During an inspection we work from the rooms up to the roof: first a map of the stains from below — where, when and after what the water appears. Then the roof from above: the fall and the puddles, every upstand, every drain and penetration, the seams, the blisters. If the source is not obvious, we flood the roof with water section by section and watch where it shows up. And we make a control opening: is the insulation wet, is the old covering still bonded to the base. We photograph everything.
The result is a written report: where the water comes from, what to do and an estimate per m². The inspection costs 100 ₾; if you order the work from us, we deduct it from the estimate. The report stays with you either way.