Cambridge Roofers covers flat roofing repairs and installations in Potton, and this page walks you through exactly what happens at each stage of the job - so you know what to expect and what to ask.
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A flat roof replacement is not a small job. It usually takes one to three days, involves stripping back to the deck, and touches parts of the building that are not always visible from the ground. Homeowners who understand the process are better placed to spot if something is being skipped, and to have a useful conversation with any contractor they are comparing.
Cambridge Roofers installs and repairs flat roofs on extensions, garages, bay window roofs, and outbuildings in Potton and across the Cambridge area. We use EPDM rubber and torch-on felt systems depending on the roof. Here is how a typical flat roofing job runs from start to finish.
A flat roofing job should always start with a proper inspection before any quote is given. This is not just a look from the ground. A roofer needs to get on the roof to check the membrane surface, probe for soft spots in the decking, inspect every flashing and upstand detail, and look at how the roof drains.
What the survey is checking for:
After the survey, a straightforward job will result in a quote that itemises the work - membrane system, deck replacement if needed, flashing details, and any access requirements. If a contractor quotes without going on the roof, treat that as a warning sign.
Before work starts, the access to the roof needs to be sorted. On a single-storey extension or garage roof, scaffolding is rarely needed - a good set of roof ladders and a ladder standoff to protect the gutters is usually sufficient. On two-storey structures or where a parapet is involved, scaffolding may be required for safe working at height.
Tools, materials, and a skip or waste bags are organised before stripping starts. If the job is torch-on felt, a propane torch will be on site - combustibles near the work area (garden furniture, stored wood, plastic fascias) are moved clear or protected before any torching begins.
The old membrane, chippings, and any failed flashing material are stripped back to the deck. This stage often reveals the true condition of the decking and is where the scope of a job can change. If, for example, a survey suggested one or two rotten boards but strip-out reveals that half the deck is saturated, the quote will need to be adjusted to cover the additional decking.
This is why a thorough survey matters - it reduces the chance of surprises. But a genuine roofer will always tell you what strip-out has revealed before proceeding, rather than covering it up with new membrane and sending the bill later.
All waste material is cleared as work progresses. The roof should not be left stripped overnight unless the weather forecast is confirmed clear. If a delay occurs - a material delivery, for example - the deck is protected with a temporary cover.
With the old membrane off, the deck is checked board by board. Any section that is soft, delaminating, or visibly rotten is cut out and replaced with matching OSB or plywood. The replacement boards are fixed securely to the joists beneath.
If the deck has inadequate fall, this is the stage at which tapered insulation can be added to correct it. Tapered insulation boards build up a gradient across the flat surface so that water naturally runs toward the outlet. This adds cost but is worth doing if ponding has been a persistent problem, since no membrane - however good - benefits from sitting in standing water.
The deck surface is swept and checked to be clean and dry before any membrane goes down. Even small amounts of moisture trapped beneath a bonded membrane cause adhesion to fail and blisters to form.
For an EPDM installation, the rubber sheet is cut slightly oversized and allowed to relax before adhesive is applied to both the deck and the underside of the membrane. The sheet is carefully folded back, adhesive applied, then rolled out progressively to avoid air bubbles. The edges are trimmed and the membrane is turned up all upstands by a minimum of 150mm and bonded securely with appropriate adhesive and termination bar.
For torch-on felt, a base layer - typically a polyester-reinforced bitumen sheet - is torched to the deck first. The cap sheet, mineral-faced, is then torched over the top, with all laps torched and rolled to ensure a complete bond. The cap sheet is also dressed up all upstands and trimmed neatly at all edges.
Seams and laps - whether EPDM tape or torch-bonded felt - are inspected carefully before moving to detailing. This is a point where cutting corners is easy and where failures originate.
Every junction between the roof and the building needs a proper flashing. Lead is the standard material for most residential details. On a parapet, the membrane is turned up the inside face and lead-dressed over the top. Where the roof meets a wall, soakers or stepped flashings are let into the mortar course above and lapped down over the membrane upstand.
Outlets are dressed individually - the membrane is cut to the outlet collar and bonded or clamped to form a watertight seal. If the outlet or its pipe is blocked or damaged, this is the point to replace it.
Once the membrane and all flashings are in place, the roof is checked for any exposed deck edges, unfixed terminations, or areas of membrane that have not bonded fully. Gutters are cleared of any debris from the job. The ground around the property is cleared of all waste material, old felt, chippings, and fixings. A good roofer leaves the site as they found it.
After the job, it is worth running a hosepipe over the roof and checking inside for any signs of water penetration before signing off. This simple check catches any detailing issues while the crew is still on site.
A straightforward single-garage roof replacement typically takes one full day. An extension roof of 30-40 square metres with standard detailing usually takes one to two days. Larger or more complex roofs with multiple upstands, penetrations, or significant decking replacement can take three days or more. Access requirements and weather also affect the programme.
Flat roofing in and around Potton typically runs from £70-£120 per square metre for torch-on felt and £90-£150 per square metre for EPDM rubber, including stripping and deck replacement where needed. If you would like a survey and written quote for a flat roof in Potton, call Cambridge Roofers and we can arrange to come and take a proper look.
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