Cambridge Roofers carries out flat roof replacements and repairs in Saffron Walden, and here is exactly what happens from the first survey through to clearing up and walking away.
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A flat roofing job involves more stages than most homeowners expect. Understanding what each stage involves - and why it matters - helps you know what to ask for, what to check, and whether the work is being done properly. This page walks through a typical flat roof replacement from first contact to finished job.
Cambridge Roofers covers Saffron Walden and the surrounding area, including Cambridge, Newmarket, Royston, and St Ives. We install EPDM rubber and torch-on felt systems on extensions, garages, outbuildings, and larger flat-roofed sections of residential properties.
The process starts with a proper hands-on survey, not an estimate based on a photograph or a look from the ground. A roofer needs to get onto the roof to assess it accurately.
During the survey we check the following:
Once the survey is complete, we can give a realistic quotation. Any quote issued without a proper survey cannot account for deck condition and is likely to change once work starts - which is a situation worth avoiding.
Before work starts, the scope should be clearly agreed. This means knowing which system is being installed (EPDM or torch-on felt), what specification of membrane and insulation, whether any decking replacement is included, what happens with flashings, and how drainage is being handled.
If the survey identified falls that are too shallow, this is the point to decide how to correct them. Tapered insulation boards installed above the deck are the most common solution - they create the fall without rebuilding the structure. Agree this in advance rather than discovering mid-job that the roof will not drain properly under the new membrane.
A warm roof specification (insulation above the deck) performs better thermally and avoids the condensation risk of older cold roof designs. It adds cost and raises the finished roof height slightly, but it is worth asking about when doing a full replacement.
On a replacement job, the old membrane is stripped back to the deck. This is not always done in the industry - some installers lay new felt over old - but laying over an existing membrane hides deck condition and can trap moisture between layers. Stripping to the deck allows a proper assessment and gives the new membrane the best possible base.
Stripping generates a reasonable amount of waste material. Old felt, damaged decking, and any removed flashings all need to be taken away. Ask how waste disposal is being handled when you agree the job.
Once stripped, the deck is inspected again. What seemed like an isolated soft spot from above can turn out to be more extensive once the membrane is off. Any rotten, delaminated, or structurally compromised decking boards must be cut out and replaced before the new membrane goes on.
On a timber deck, new boards are cut to fit and fixed to the joists. The deck must be smooth, with no protruding fixings, gaps between boards, or level changes that would telegraph through the membrane and create stress points. On a concrete or screed deck, any crumbling or hollow sections are made good before the membrane is applied.
A common problem on older extensions is decking that has been repaired piecemeal over the years, leaving a surface with varying board thicknesses and fixings at different heights. This needs levelling before a membrane is applied - EPDM in particular will follow the profile of the deck beneath it.
If falls are being corrected or a warm roof is being installed, insulation boards go on after the deck is prepared. Tapered boards are cut to a pattern calculated to create the correct drainage falls across the roof. They are bonded or mechanically fixed to the deck before the membrane is applied on top.
This stage adds time and material cost but it is the right way to correct inadequate falls rather than relying on the membrane to cope with pooling water.
This is the stage most people picture when they think of flat roofing, but by this point the preparation work described above will have taken up most of the time on a well-run job.
For EPDM: The rubber sheet is cut to size, then laid out across the deck and allowed to relax before bonding begins. Bonding adhesive is applied to both the deck and the membrane, left to become tacky, and then the sheet is carefully folded down onto the deck and rolled out. The perimeter and any seams are bonded with lap adhesive and seam tape. Upstands are wrapped and bonded, with corners carefully formed.
For torch-on felt: A base layer is mechanically fixed or partially bonded to the deck first, giving the cap sheet something stable to bond to. The cap sheet is then torch-applied, the roofer working steadily across the surface, ensuring consistent bond and overlapping joints. Laps must be a minimum of 75mm and fully bonded throughout.
In both cases, the membrane must be turned up at all edges and upstands, not simply terminated at the edge of the deck. Water must never be able to get behind the membrane at any point.
Flashings at walls and parapets are normally lead, bonded felt, or a combination. Lead is cut and dressed into the wall chase or fixed under the pointing, then overlapped onto the membrane. On a properly detailed job, the flashing and membrane together form a continuous waterproof layer with no exposed gap.
Drip edges and trims at the roof perimeter should be fitted before the membrane reaches the edge, so the membrane can lap over the trim and direct water away from the fascia. This detail is often missed on cheaper jobs, allowing water to track back under the edge and rot the fascia board.
Roof outlets are either set into the membrane using a compatible collar that bonds to the membrane, or they drain over the edge via a straight run to a gutter. Either way, the outlet must be at the lowest point of the roof and properly integrated with the membrane so no water can bypass it and sit against the edge detail.
Once the membrane and all details are complete, the roof should be walked and checked. Every lap, every upstand, every flashing, every outlet collar needs to be confirmed as fully bonded and dressed correctly. Any loose debris is cleared from the roof surface and gutters before packing up.
All waste material - old felt, timber offcuts, packaging - should leave the site with the roofer. Ask about this in advance. A skip arranged by the homeowner for general building waste is one approach; the roofer taking waste away in their vehicle is another. Either is fine but it should be agreed beforehand.
A straightforward garage roof replacement in the Saffron Walden area typically takes one to two days for the membrane installation itself, assuming the deck is sound. If decking replacement is needed, add a day. An extension roof of 30-40 square metres with standard detailing usually takes two to three days. Larger or more complex jobs take longer, and weather affects programme - membrane bonding should not take place on a wet or very cold day.
For context, EPDM flat roof installation in this part of the country typically costs £75-£120 per square metre fully installed. Torch-on felt usually comes in at £60-£100 per square metre. Deck replacement, where needed, adds roughly £30-£60 per square metre on top. These are working figures to help you sense-check quotes - actual prices depend on your specific roof, access, and specification.
If you are planning a flat roof replacement or repair in Saffron Walden and want to understand exactly what the job involves before committing, call Cambridge Roofers. We will carry out a proper survey, explain what we find, and give you a clear picture of the work required at each stage.
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Call any time. Calls are answered day and night and passed straight to our roofers.
