Cambridge Roofers installs and repairs flat roofs in Milton, and this page walks through exactly how the job unfolds from the first inspection to the final clear-up.
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Most homeowners have no idea what a flat roofing job actually involves until it is happening on their property. Knowing the sequence helps you ask the right questions, understand what you are paying for, and spot whether a contractor is cutting corners. Below is an honest account of how a properly executed flat roof installation or full re-cover should run.
Before any price is agreed, the roof needs to be seen properly. A survey means getting on the roof, not just looking at it from below or through a window. The roofer should walk the surface checking for soft or spongy areas, probe any suspect zones, check the condition of outlets and overflows, measure the falls, and look at every upstand, flashing, and penetration.
From inside the building, damp patches on the ceiling or any signs of staining should be noted. The location of those stains relative to the roof above is useful information, though water often tracks sideways before it shows at ceiling level. A good survey takes 20 to 40 minutes on a typical domestic flat roof and produces a clear picture of what is failing and why, not just where the wet patch is.
At this stage, the roofer should be able to tell you whether a repair is viable or whether a full re-cover is the right course. A roof where the deck is soft and wet, where the falls are wrong, and where the membrane is more than 20 years old is not a repair candidate, however localised the visible damage appears to be.
Once the survey is done, a quote should set out what system is being installed, what build-up is involved, whether the existing surface is being stripped, what happens if the deck is found to be damaged once the old material is removed, and what the drainage and upstand details will look like. A quote that simply says "supply and fit new flat roof" tells you almost nothing.
Ask specifically whether the price includes stripping the old membrane, replacing any rotten decking found once the surface is off, making good the falls, and installing new outlets and flashings. These items can add significantly to the cost if they appear as extras mid-job, and they are almost always necessary on a roof that has been failing for some time.
On the day work starts, the first task is stripping the old membrane back to the deck. On a felt roof, this means removing the old cap sheet and base felt, any chippings if they were used, and any old adhesive or surface dressing. The deck is then exposed for proper inspection. Even if the pre-start survey identified soft areas, it is common to find more once the old felt is off. Any section of decking that is wet, spongy, or cracked needs to be cut out and replaced at this stage, not covered over.
Where the existing deck is sound OSB or plywood, it can often be retained. Where it is the older tongue-and-groove timber boarding, it may need partial or full replacement depending on condition. This is the point in the job where unforeseen costs most commonly arise, and a good roofer will be transparent about what they have found before ordering additional materials.
With a clean deck exposed, the falls can be checked against the minimum standard of 1 in 80 (approximately 12mm per metre of run). If the existing structure does not achieve this - which is common on older extensions - falls can be created using tapered insulation boards, which build up the slope without altering the structure below. This is standard practice and adds relatively little to the overall cost compared with the damage ponding water causes if the falls are left inadequate.
Outlets are checked and, where necessary, repositioned or replaced. The outlet should sit flush with the lowest point of the fall, not raised above the deck surface. A raised outlet is a common installation error that guarantees standing water regardless of how good the membrane above it is.
On a warm roof installation - currently the recommended build-up for domestic flat roofs - rigid insulation boards are fixed to the deck surface before the membrane goes down. The boards need to be butt-jointed tightly with no gaps, as any air path through the insulation layer allows warm moist air to reach the cold deck surface and condense. The insulation thickness should comply with current building regulations for thermal performance, which typically means at least 100mm of good-quality rigid insulation board in a new installation.
If the roof is being re-covered as a like-for-like repair rather than a full upgrade, insulation is sometimes retained below the deck, but the condition of any existing insulation should still be checked, as wet insulation loses its thermal value entirely and adds weight and moisture to the structure.
For an EPDM installation, the rubber sheet is cut to size on the ground, positioned on the roof, folded back, and the adhesive applied to both the deck and the underside of the membrane. The sheet is then carefully rolled out into contact with the deck, working from one edge to avoid trapping air. Corners and internal angles are detailed with pre-formed EPDM trim pieces or hand-formed patches bonded with the same adhesive. Every join and termination point is pressed out thoroughly to ensure full contact.
For torch-on felt, the base layer is mechanically fixed or hot-bonded to the deck, laps are torched and pressed, and the cap sheet is torched over the top with laps staggered from the base layer. Edge trims, drip edges, and upstand details are worked in as the membrane is laid.
In both cases, the membrane at the walls should turn up at least 150mm above the finished roof surface and be mechanically fixed and sealed at the top edge. This is the most commonly under-specified detail and the first place a rushed job fails.
Where the roof meets a wall, chimney, or parapet, lead or aluminium flashing is dressed over the top of the upstand membrane and into a chase or under the coping. This two-part detail - membrane upstand below, flashing above - is what keeps wind-driven rain out at the junction. Flashing without a proper upstand beneath it, or an upstand without flashing above it, is not a complete detail.
Drip edges at the exposed perimeter of the roof are fitted to carry water cleanly off the membrane surface into the gutter, rather than letting it run back under the edge and rot the fascia board.
Before the roofer leaves, the surface should be walked again and every outlet, upstand, join, and edge detail checked. Outlets should be cleared of any debris from the installation. All old membrane, chippings, and off-cuts should be removed from the site. The gutters below the roof should be checked and cleared if they have collected material from the stripping operation.
A job on a typical home - single garage or small extension - will usually take one to two days from start to finished clean-up for an EPDM installation. A larger extension roof of 30 to 40 square metres might take two to three days. These timings assume dry weather; torch-on felt and EPDM adhesive both require dry conditions to bond correctly.
A full strip and relay on a domestic flat roof in the Milton area typically costs between £70 and £120 per square metre installed, including stripping the old surface, any straightforward deck repairs, insulation, the new membrane, and edge details. A garage roof of 15 to 20 square metres would usually be in the range of £1,200 to £2,400. A 30-square-metre extension roof would typically run from £2,500 to £4,000. Costs rise where the deck needs significant structural repair, where access is difficult, or where the specification includes upgraded insulation to current thermal standards.
If you have a flat roof in Milton or nearby Cambridge that needs inspection, call us to arrange a proper survey and a clear price before anything is agreed.
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