Understanding what a professional commercial roofing job looks like from start to finish helps you ask the right questions and spot when corners are being cut.
A commercial roofing job carried out correctly takes time and follows a clear sequence. Each stage informs the next. If a contractor skips the survey, the spec will be wrong. If the deck is not properly prepared, the new membrane will fail early. Knowing what a proper job involves means you can have an informed conversation with any contractor before you agree to anything.
We carry out commercial roofing across Girton, Newmarket, Cambridge and the surrounding area, working on flat roofs, pitched commercial roofs, agricultural buildings and retail premises. Here is how a job should unfold from the first phone call to the final clean-up.
Before any quotation is put together, the roof needs to be looked at properly. A good survey is not a five-minute walk around the yard - it involves getting onto the roof, checking the membrane or covering in detail, and looking at the condition of the deck, the drainage outlets, the upstands, the flashings and any penetrations (soil pipes, flues, ventilation units, rooflights).
On a flat roof, we check for blistering, ponding, cracked or open seams, failed upstands and blocked outlets. On a pitched commercial roof, we look at the condition of the tiles or sheets, the state of the battens and any visible timbers, the gutters and the leadwork. We also look at how the roof is accessed and note anything that will affect how the job is delivered - for instance, whether scaffolding will be needed, whether a hoist is required for materials, and where waste skips can be positioned without blocking the business.
If the deck condition is uncertain - particularly on older felt roofs where the insulation may have absorbed water over years - a moisture survey using a conductance meter or by taking core samples gives a much clearer picture before the work is priced.
Once the survey is done, the quotation should set out exactly what is being done and to what specification. For a flat roof replacement this means: what system is being used, what thickness of insulation is being laid, how the outlets will be dealt with, and how the edges and upstands will be finished. Vague quotes that say only "flat roof replacement" without specifying the system or the insulation value should be queried before signing anything.
At this stage, access arrangements need to be confirmed. Commercial premises in Girton and nearby towns including Cambridge and Histon may have staff, customers or deliveries to consider. We discuss in advance whether we start early, work in sections, or schedule the noisiest or most disruptive work at quieter times. Overnight security - how the building will be left watertight each evening if the job spans multiple days - should also be agreed before work begins.
Most commercial roofing jobs require some form of access equipment. Flat-roofed buildings with a low parapet can sometimes be accessed safely by ladder and roof ladder, but larger buildings, pitched roofs and anything with significant height will need scaffold. The scaffold needs to be sufficient not just for the workers but for the materials - bundles of tiles, rolls of membrane, insulation boards and so on.
Protection of the building below matters from the first day. Any openings in the roof deck during a strip-out need to be covered if rain is forecast. On occupied buildings, internal areas should be sheeted where debris could fall. Plant and rooflights should be protected during work in the immediate area.
On a flat roof replacement, the existing covering is stripped back to the deck. This is the stage where the real condition of the roof becomes clear. Saturated insulation shows up as discoloured, compressed or friable material. Deck boards may have softened or show signs of rot. Any damaged deck sections need to be cut out and replaced with new material of matching thickness before any new system is laid.
This stage cannot be properly assessed from the ground or from a photo. It is one of the main reasons a proper on-roof survey before the job is so important - a contractor who has seen the deck in person can price the job more accurately and is less likely to come back mid-job with significant additional costs. That said, strip-out can still reveal unexpected problems, and a good contractor will show you what they have found and explain what needs to happen before continuing.
On a pitched commercial roof, the equivalent stage is stripping the tiles, slates or sheets and checking the battens, underlay and rafter or purlin condition. Battens on older commercial roofs are frequently corroded or decayed at the fixings even when the surface covering looks passable.
Flat roofs need to drain. Any flat roof that ponds water after rain is not draining as it should. The causes are a combination of inadequate falls (the roof is too flat or has settled over time), blocked outlets, or outlets that are positioned too high relative to the surrounding surface.
When a flat roof is being replaced, the drainage system should be reviewed as part of the job. Outlets may need to be repositioned or added. Tapered insulation boards can be used to create or improve the falls across the roof without raising the overall height of the build-up. Installing a new membrane over a roof that still ponds water is a false economy - the ponding will continue and the new membrane will deteriorate faster as a result.
For flat roofs, the new build-up is laid in a defined sequence: vapour control layer, insulation boards, and then the waterproof membrane. The membrane - whether torch-on felt, EPDM rubber or another system - needs to be taken up and over all upstands to a minimum height, typically at least 150mm above the finished roof level. All outlets need to be properly collared. Any penetrations through the membrane (pipes, fixings, supports for plant) need individual detailing.
The quality of the edge and upstand detailing is where most flat roof failures begin. A membrane that terminates short of the required height at a parapet wall, or that is not adequately secured at its perimeter, will lift and allow water ingress long before the main field of the membrane has deteriorated.
For pitched roofs with tiles or slates, new battens are fixed to a consistent gauge matched to the tile specification, new underlay is draped and lapped correctly, and tiles are fixed with the correct number and type of fixings per square metre - not just at the verges and ridge. Ridges and hips are bedded and pointed, or dry-fixed using a manufacturer ridge system, depending on the tile type.
For profiled metal sheet roofing on agricultural or industrial buildings, sheets are fixed with the correct type and spacing of fixings, with sealing washers in good condition. Laps between sheets are of the specified minimum and sealed where required. Ridge and barge flashings are fitted to close off the profile at the top and sides.
A new roof covering is only effective if the drainage system functions properly. Commercial gutters need to be checked, cleared and repaired or replaced as needed. Downpipes should be checked for blockages and correct fixing. Box gutters built into the roof structure are particularly important to inspect - a blocked box gutter on a commercial building can back up and flood a large internal area very quickly.
Lead flashings at abutments, chimneys, rooflights and parapet walls are part of the roof system, not an afterthought. New or re-dressed flashings should be pointed into the masonry with an appropriate sealant or mortar and stepped or cover flashings should be checked to ensure they are correctly lapped and secured.
Before leaving site, the roof should be walked to check that all outlets are clear, all upstand detailing is correct, and there are no obvious areas where the membrane or covering has not been properly finished. Gutters should be cleared of any debris from the job.
The site should be left clean. Waste from a commercial roofing job - old felt, insulation, broken tiles, metal offcuts - is significant in volume and should be removed by the contractor. Confirm before the job starts how and when waste will be removed and who arranges the skip or disposal.
We cover Girton, Newmarket, Cambridge, Histon and the wider area. If you have a commercial roof that needs attention, call us to arrange a proper on-roof survey before any decisions are made.
No obligation · We usually respond within 2 hours
Storm damage, active leak, damaged ridge - we aim to be on-site within 24 hours.
