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.
One thing follows from that and it is worth stating plainly, because it is the difference you are buying. We do not fix anything through the waterproofing. The structure that carries the boards stands on the waterproof layer and is held by its own weight and its own geometry, so when we hand the terrace over, the membrane below it is exactly as continuous as it was on the day it was inspected. Screwing a frame down through the membrane is quicker, it is what a decking contractor will normally do, and every one of those screws is a hole in the only thing keeping the room below dry. Those holes are sealed on the day. They are also the most common reason a terrace that was fine for two winters starts marking a ceiling in the third, and by then the deck has to come up to find out which one of them it was.
The obvious next question is what the deck stands on instead, and the honest answer is that it depends on the roof. There is no one method that suits every terrace, and choosing one before looking is how a terrace ends up sitting badly on a roof it does not fit. What the deck bears on is matched to what is underneath it: the type of waterproofing it will sit against, the falls already in the roof, what the structure will carry, and how much height there is to play with before the deck reaches the bottom of the door threshold. That last one closes off options faster than anything else. We settle it at the survey, on your roof, and tell you what we are proposing and why before you have a price in front of you.
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
We never fix through the waterproofing
The deck stands on the waterproof layer rather than being screwed to it. We put no fixings through the membrane at all on a terrace over a room, because every fastener through it is a permanent hole in the only thing keeping that room dry.
The support is chosen at the survey
What the deck bears on is matched to the roof it is going on: the waterproofing it sits against, the falls, what the structure will carry and the height left under the door threshold. No terrace is specified from a catalogue before anyone has been up there.
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.
Boards, in whichever material you want
We lay every type of decking board rather than working in one material, so the surface is your choice rather than something you inherit from the contractor. The trade-off worth understanding before you make it is maintenance: composite is largely left alone once it is down, while timber needs treating on a cycle for as long as you have it and goes grey and tired quickly if that stops. Whichever you pick, the setting out has to let the boards move, because decking materials expand and contract and none of them should be pinned tight to an edge.
Balustrades and edge protection
Most terraces need an edge protection of some kind, and what it is gets agreed with you at survey. We have fitted a glass balustrade, and we will take one on where a job calls for it, but it is arranged per project rather than being something we hold as a standard product. What matters on any of them is the same: 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 put right first
Where the roof is not moving water towards its outlet, the falls are corrected before the membrane goes on. Sealing over a dip only guarantees the water sits somewhere out of sight for longer. What the drainage itself needs is established at the survey and set out in the quote.
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 on the waterproofing, with nothing fixed through it, then the boards are laid with the movement allowance the material needs and the edges, steps and any edge protection 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.
What our 10-year workmanship guarantee covers, how it differs from a manufacturer product guarantee, and what falls outside it.
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 the quote shows the waterproofing and the terrace as separate lines, so you can see what each part costs before deciding anything.
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.
No. On a terrace over a room we put no fixings through the waterproof layer at all. The structure that carries the boards stands on the membrane and is held by its own weight and its own setting out, so the layer underneath stays as continuous when we leave as it was when it was inspected. This is the opposite of the normal decking approach, which screws a frame down because it is faster, and it is worth understanding what that costs you: each of those screws is a penetration through the one thing protecting the room below, sealed on the day and relied on for the next twenty years. A terrace with no penetrations has nothing to rely 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.
Tell us the building height at first contact, because it decides the material before anything else does. Under regulation 7 of the Building Regulations 2010 in England, materials in the external walls and the specified attachments of a residential building with a storey at least 11 metres above ground level have to achieve European reaction to fire classification A2-s1,d0 or A1, and a balcony counts as a specified attachment. Composite and timber boards do not generally reach that classification, so on a building of that height the deck is normally a non-combustible specification rather than the boards used everywhere else. We are open to these jobs and have not yet carried one out, so we would establish the requirement with you and with the building before quoting rather than after. The height rule is about the building, not about any contractor, and it applies whoever does the work.
Both, and the honest way to choose between them is on maintenance rather than on looks. We lay every type of board, so this is your decision and not ours. Composite costs more at the outset and then asks almost nothing of you: no oiling, no annual treatment, and it holds its colour. Timber costs less to buy and needs treating on a cycle for as long as you have it, which is fine if you will actually do it and disappointing if you will not. 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 have to be corrected that is roof work before either. Area, access, whether a crane or a hoist is needed, the board choice and any edge protection 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 the decking boards, and on any balustrade components where we have supplied them, 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