Who pays if the terrace leaks into the neighbour's flat?
It depends on who owns the structure and what caused the leak. If the terrace serves as the building's roof and the statutes treat it as a common element, the comunidad maintains the waterproofing as a structural component, while the paving and anything you have built on top is yours. If the leak starts from your alteration (new tiles, fixings that pierce the membrane, a badly detailed threshold), you and your insurance answer for it.
In real disputes the paperwork decides: statutes, nota simple, records of earlier waterproofing. So before touching the terrace, ask the administrador for them and photograph the existing state. If you live abroad you need one person on site to check in person, because leaks begin in your winter, when you are not there.
What layers make up a terrace waterproofing system
Top to bottom: finish (tile, timber, porcelain on pedestals), protection layer, waterproofing membrane, screed laid to falls, separating layer, insulation (in an inverted roof it sits above the membrane) and the structural slab. The membrane is the key element; the rest protect it and guide the water.
Choosing the membrane: liquid polyurethane or PMMA systems, bituminous sheets, EPDM, PVC or TPO. On a terrace with many junctions (complex shape, columns, glass walls) liquid systems are practical because they give a seamless surface. On large flat areas sheet membranes work well. What decides the result is not the brand but who forms the seams, corners and upstands, and how much protection goes on top.
Falls, drains and upstands: where leaks start
Leaks do not start mid-field but in the details: at walls, the threshold, drains, pipes and fixings. A flat terrace with no fall holds puddles, and the membrane ages faster under puddles. In practice you design a fall of around 1.5 to 2 percent towards the drains or a gutter, place the drains so water does not sit by the glass doors, and add an emergency overflow in case of blockage.
The upstand of the waterproofing up the walls is usually at least 15 cm above finished floor level, and at glass doors it is combined with linear drainage. Every fixing (balustrade posts, pergola, planters, solar panels) is planned in advance: either the post stands on a plinth that is waterproofed in its own right, or on a cast-in piece with a collar. Piercing a membrane later is far easier than finding where it leaks.
What is a flood test and when is it done?
A flood test checks the waterproofing with water before it is covered by the paving. Drains are plugged, the terrace is filled with a few centimetres of water and held usually for 24 to 48 hours, with the level marked in pen. If the level drops by more than evaporation explains, or a stain appears on the neighbour's ceiling, there is a defect, and it is found and sealed before the floor goes down.
It is done after the membrane and before the protection layer and finish, and recorded: date, level, photos, signature. Afterwards the drains are opened to confirm that water leaves freely. For a terrace above someone else's flat, agree with the neighbour that you can look at their ceiling: it is cheaper than lifting the floor later.
Can the threshold be flush with the terrace?
It can, but it is the most delicate junction: water at a glass door always looks for a gap. The scheme that works: the waterproofing runs under the door profile and rises above floor level, a linear drainage channel with a hidden grille sits in front of the door, the outdoor paving keeps a fall away from the door, and the interior floor stays a few centimetres above terrace level.
So "flush" to the eye and "flush" in the waterproofing are different things: under the clean threshold line there are two levels. The solution is designed together with the sliding-wall manufacturer, because the profile sets the height and the drainage. If the slab has no spare depth, the living-room screed has to be lowered or a podium built, and that must be known before the windows are ordered.
Mistakes that surface after the first winter
The first winter shows everything. The common mistakes: laying the floor without a flood test, not running the waterproofing up the walls, tiling over a drain and losing access to it, drilling pergola and balustrade fixings through the membrane without sealing, forming falls by eye and getting puddles, making seams in a hurry in rain or cold.
Cheap waterproofing under an expensive floor remains the costliest mistake: to correct it you must remove everything above. So in the estimate it is a separate line, and in the schedule beside it sit the flood test and the site supervision, not at the end of the job but before the floor is laid.
How often to replace waterproofing and how BCN YARD can help
Service life depends on the system and upkeep: a well-built membrane under protection lasts in practice 15 to 25 years, liquid systems usually less if they lack protection from sun and foot traffic. Signs to check: stains at the neighbour's, blistering, water under the paving, cracks at junctions. Once a year, clear the drains and inspect the joints after autumn.
BCN YARD handles terrace works in flats and penthouses in Russian and Spanish, with one person responsible for the site. We begin with a visit: looking at the condition, the documents and the options for the threshold and fixings. Then a phased estimate with a separate line for waterproofing and the test.
Frequently asked questions
Can new paving go over old waterproofing?
Sometimes, if the old system is sound and compatible with the new one. It is checked for blisters, cracks and adhesion, and a flood test is always done. If the terrace gets a new threshold, balustrade or pergola, the waterproofing is usually renewed, because every new junction has to be formed again.
Do you need permission to refurbish a penthouse terrace?
Replacing the paving and waterproofing within the existing footprint is usually handled as minor works with a notification, while changing the structure, adding a pergola or enclosing with glass needs separate approval. Always inform the comunidad, because the terrace may be the common roof, and check the regime with the district in advance.
Why does a leak show up months later?
Water travels along the slab and builds up in the screed and plaster until it soaks the ceiling into a visible stain. So the stain can appear away from the entry point and after a winter. The flood test and careful records of details during the works exist precisely so you do not have to hunt for the cause blind.