We survey what is under the surface
Before anything is quoted we establish what the existing waterproofing is, what condition it is in and where the water is meant to go, because that decides the price far more than the boards do.
Property Enhancements / Terraces & Decking
Roof Terraces, Balconies and Decking in London
Roof terraces, balconies and garden decking built across South and West London, with the waterproofing under the deck treated as part of the job rather than as another trade problem.
Get a terrace surveyA terrace is only as good as what is under it
A roof terrace or a balcony is a flat roof with a floor on top of it, and the layer under the boards is what decides whether the room below stays dry. That single fact is why K & M Roofing Solutions builds terraces at all: we are certified flat roofing contractors, so on our jobs the waterproofing is the part we are most confident about rather than the part that gets covered up and hoped for.
It is also the usual reason terraces fail. A decking specialist arrives, finds an existing surface, lays a deck on top of it and leaves. Nobody has established whether the waterproofing underneath was sound, whether the falls still move water to the outlet, or whether the fixings have just been driven through the only thing keeping the flat below dry. The deck looks finished on the day, and the ceiling underneath tells the truth eighteen months later.
So we do it in the order the building needs rather than the order that gets a deck down fastest. Survey what is under the surface first, put the waterproofing and the falls right, then build the structure and lay the boards. On a garden deck at ground level none of that applies and the job is straightforward. Over a habitable room it is the whole job.
If the surface under your terrace has already failed, or you are not sure what is under there at all, that is a flat roof question before it is a decking one, and our flat roof repair and waterproofing page covers how the covering is assessed and what the options are.
Where a terrace has to be waterproofed over an occupied flat with nothing torn off and no hot works on the roof, a cold-applied liquid system certified to ETA-23/0735 is usually the answer, and we are certified applicators of it.
Benefits
Why a roofing contractor builds a better terrace
Waterproofing first, boards last
The membrane and the falls are completed and checked while they are still visible and reachable, rather than being buried under a deck that would have to come up again to correct them.
Nothing driven through the membrane
Over a habitable room the deck is supported off the waterproofing rather than fixed through it, because every fastener through a membrane is a hole that has to stay sealed for the life of the terrace.
Designed to be lifted again
A terrace deck is built so sections can be taken up to reach the outlet and the membrane underneath, which is what turns a future inspection into an afternoon instead of a demolition.
What we offer
What we build
Three of these sit over something, and one does not. That distinction is what changes the specification and the price.
Roof terraces
Usable terrace space over a flat roof, a rear extension, a dormer or the top of a building, where the deck is the walking surface and the waterproofing below it is the roof. This is the work we do most and the reason this page exists: the roof and the terrace are the same project, carried out by the same team.
Balconies
Existing balconies re-decked and re-waterproofed, including the junction with the building, the threshold at the door and the upstands at the edges. Balconies are small, which misleads people: almost all of the difficulty is concentrated in the details around the perimeter rather than in the middle.
Garden and ground level decking
Decking laid in a garden, on a patio or across a level change, with a supporting structure sized and set out for the ground it sits on. Nothing here is over a room, so the waterproofing question falls away and what matters instead is ventilation under the boards and drainage away from the house wall.
Composite decking
Composite boards are the usual choice on a roof terrace because they do not need annual treatment, they hold their colour and they behave predictably underfoot when wet. They also move with temperature more than timber does, so the setting out has to allow for expansion rather than pinning the boards tight to an edge.
Glass balustrades
Frameless and framed glass balustrades where the terrace needs an edge protection and the view is the point of the terrace. How the balustrade is fixed matters as much as the glass: on a terrace over a room the fixing has to be carried by the structure without perforating the waterproof layer beneath it.
Waterproofing under the deck
The layer that makes the difference, put right before anything is built on top of it. Where the deck sits over a habitable room this is a flat roof in every sense, and it is specified, installed and guaranteed as one.
See flat roof repair and waterproofingScope
What we check before quoting a terrace
- What the existing waterproof layer actually is, and its condition
- Whether the deck below is dry, or holding water from an earlier leak
- The falls, and whether water still reaches the outlet
- The outlet itself: size, position and whether it is blocked
- Upstand heights at every edge, wall and threshold
- The door threshold, and how water is kept out of it
- Whether the structure can carry the loading of a terrace in use
- Access for materials, and whether a building requires a permit
How it works
How we build a roof terrace
1
Free survey
We open up enough to see what the existing surface is and what condition the deck below is in, rather than pricing from what is visible. On a terrace this is the step that decides everything after it.
2
Waterproofing specified
The system is chosen from what the survey found, the falls available and whether the space below stays occupied during the work, then quoted as part of the terrace rather than as an extra.
3
Falls and outlets corrected
Where water is not reaching the outlet, that is put right before the membrane goes on. Sealing over a dip only guarantees the water sits somewhere out of sight for longer.
4
Waterproofing installed and checked
The membrane is completed to every edge, upstand and threshold and inspected while it is still fully visible, because this is the last moment anything can be corrected without lifting a deck.
5
Structure and boards
The supporting structure is set out and levelled off the waterproofing, then the boards are laid with the movement allowance the material needs, and edges, steps and balustrade fixings are completed.
6
Handover
You get the terrace, the record of what was found and installed underneath it, and a 10-year workmanship guarantee in writing covering the work as a whole.
Why choose us
Why customers choose K & M Roofing
01
Certified HYDRONYLON applicators, a system most London roofers cannot offer.
02
One team for the whole job, from survey to sign-off.
03
Rated 5.0 by 60 customers on Google.
04
Certified flat roofing contractors building the terrace, so the layer that keeps the room below dry is the part of the job we know best.
05
Transparent pricing with no hidden costs, and a 10-year workmanship guarantee.
Knowledge
Read more before you decide
Common questions
Frequently asked questions
A garden deck has soil under it and a roof terrace has a room under it, and that changes the entire job. On a garden deck water simply passes between the boards into the ground, so the work is about a level, well-ventilated structure that drains away from the house. On a roof terrace the water has to be caught and taken to an outlet by a waterproof layer beneath the boards, and a fault in that layer ends up on a ceiling. The visible deck can look identical. What is underneath is a completely different piece of construction.
Sometimes, and the survey decides it rather than the appearance of the surface. If the existing waterproofing is sound, the deck below is dry and the falls still take water to a working outlet, a terrace can be built over it. If any of those three is wrong, decking over it buries the problem instead of solving it and makes the eventual repair far more expensive, because the deck has to come up first. We tell you which case you are in before quoting, and where the covering is at the end of its life we price the waterproofing and the terrace together.
The leak carries on, and it becomes much harder to find. Water still enters at the defect, but it now travels under a deck you cannot see through, so the stain on the ceiling below can appear a long way from the actual entry point. Fixings driven through the membrane to hold the deck down add new holes to the same problem. By the time it is reported, the repair involves lifting the whole terrace to reach a fault that would have been visible and cheap before the boards went on.
By building the deck so it can be taken up in sections, particularly around the outlet and the perimeter. Every roof terrace will need the layer underneath inspected at some point, whether for a leak, a blocked outlet or simply age, and a deck that has been permanently fixed down turns that into a demolition job. We plan the lifting points at the setting out stage and tell you where they are at handover, so whoever looks at it in ten years is not guessing.
To an outlet, through falls built into the layer beneath the deck, not off the edge of the boards. That is the part most often got wrong, because the deck surface itself is usually laid level for comfort, which means the water is being moved by something you cannot see. Outlets have to be sized for the area, positioned at the low point and reachable for clearing. If an existing terrace ponds after rain or the outlet cannot be found, that is the first thing we look at.
Usually yes. Permitted development rights for roof alterations specifically exclude balconies, verandas and raised platforms, so a roof terrace normally needs a planning application even where a dormer of the same size would not. Overlooking of neighbouring gardens and windows is the issue councils weigh most, and a conservation area or an Article 4 direction removes the argument entirely. On a flat or a managed block you also need the freeholder or the management company to agree, separately from the council. We flag which permissions apply at survey, before drawings are commissioned.
Yes, and it is worth raising early. Building regulations in England restrict the use of combustible materials on balconies attached to relevant buildings above 11 metres in height, which directly affects what a balcony can be decked in. That is a rule about the building rather than about any contractor, and it is checked before a specification is agreed rather than after boards are ordered. If your balcony is on a block of that height, tell us at first contact so the survey covers it properly.
Composite for most roof terraces, timber where the setting is right for it and it will actually be maintained. Composite does not need annual oiling, keeps its colour and stays predictable underfoot in wet weather, which matters on a terrace that is used all year and is awkward to work on. Timber costs less at the outset, looks better to some eyes and needs regular treatment to stay that way. On a terrace over a habitable room the more important decision is not the board at all, it is what supports it and what is underneath it.
It depends far more on the waterproofing than on the decking, which is why we do not publish a rate for it. A terrace built over waterproofing that is already sound is a decking job. The same size terrace over a covering at the end of its life includes a flat roof in the price, and where the falls or the outlet have to be corrected, that is structural work before either. Area, access, whether a crane or a hoist is needed, the balustrade specification and the board choice move the rest. Every quote follows a free survey and is itemised, so you can see what the waterproofing, the structure and the surface each cost.
A 10-year workmanship guarantee on the work, issued in writing at handover, and where the waterproofing beneath the terrace is finished with HYDRONYLON it carries the separate 10-year product guarantee issued by HYDRONYLON LTD as well. Manufacturer warranties on decking boards and balustrade components are separate documents issued by their makers, and we pass those on to you at handover rather than folding them into ours.
Free on-site estimate
Let us talk about your roof
Tell us what is going on and we will arrange a free survey. No pressure, no hard sell, just honest advice and a clear price.
Kamil07593 196505
Mateusz07544 188268