Thetford Roofers carries out commercial roofing work in Lakenheath and across the surrounding area, from initial inspection through to finished installation and site clearance.
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Most business owners asking about a commercial roof replacement or major repair have never been through the process before. Knowing what to expect at each stage helps you plan around the work, ask the right questions, and judge whether a contractor is doing the job properly. This page walks through a commercial roofing project from the first look at the building to the day we leave site.
A commercial roof survey is not a five-minute look from a ladder. On a flat roof, the surveyor needs to walk the entire surface, check every outlet, inspect all upstands and parapet flashings, probe any areas of suspected deck weakness, and assess the condition of roof lights and penetrations. On a profile steel or box profile roof, the same process involves checking lap sealants, fastener condition, and the state of ridge and eaves flashings.
Access equipment matters here. A thorough flat roof survey on a single-storey commercial building often requires nothing more than a safe ladder and roof boards to protect the surface while walking it. Taller or more complex buildings may need a scaffold lift or mobile elevated work platform. The survey should generate a written report, not just a verbal summary from the car park, and it should distinguish between defects that need immediate attention and those that can be planned for.
At this stage, the surveyor should also assess the deck condition - not just the surface. A roof that looks reasonable from above can have a deck that has softened, delaminated, or corroded underneath. Tapping a timber deck with a mallet and probing suspect areas tells you far more than a visual inspection alone.
Once the survey is complete, a written specification sets out exactly what work will be done and what materials will be used. This should include the system type, the number of layers or thickness of membrane, the insulation specification and the resulting U-value, the flashing details, and how existing material will be stripped and disposed of.
A written spec protects you as much as it protects the contractor. It makes comparisons between quotes meaningful - if one quote is significantly cheaper, you can check whether it specifies the same materials and scope. Price differences between contractors often come down to what has been left out rather than what has been included.
For commercial roofing, typical costs vary depending on the system chosen. A flat roof replacement using torch-on felt runs from around £60 to £100 per square metre; EPDM is broadly similar; steel re-sheeting starts from around £30 to £70 per square metre for the sheeting work. These figures are for the roofing work itself and exclude scaffold, skip hire, and any structural repairs to the deck.
Before roofing work begins, the site needs to be set up safely and practically. For a commercial building, this typically involves agreeing a working area with the business occupant, arranging skip or disposal for stripped material, and erecting any scaffold or staging required for access and edge protection.
Edge protection on a flat commercial roof is a legal requirement for working at height, not an optional extra. If a contractor proposes to work on a flat commercial roof without edge protection or a formal method of preventing falls, that is a serious red flag. Ask specifically what access and fall protection arrangements will be in place before work starts.
For a business that needs to stay open during roofing work, the access arrangements also need to accommodate staff, customers, and deliveries safely. A good contractor agrees the working area boundaries and daily start and finish times before work begins, and sticks to them.
On a flat roof replacement, the existing felt or membrane is stripped back to the deck. This is when the true deck condition becomes clear. What looked like minor soft spots in the survey can reveal themselves as larger areas of delaminated or wet plywood or OSB decking once the covering is removed. On a concrete deck, spalled or crumbling sections need to be cut out and made good before the new waterproofing goes on.
Stripped material is bagged or rolled and removed from the roof as the work progresses. Leaving loose stripped felt on a roof deck creates a slip hazard and a trip risk - material should come off the roof and into the skip the same day it is removed. Ask the contractor how stripped material will be managed during the project.
If sections of the deck need replacing, this adds time and cost. Timber deck repairs using new plywood or OSB of the correct thickness, fixed to the correct centres and in the correct direction of run, are straightforward but should be done properly - an underspecified repair in the deck creates a weak point that will cause the new membrane to fail prematurely.
Once the deck is sound, insulation boards go down before the waterproofing membrane. On a warm roof (the most common flat roof construction on commercial buildings), the insulation sits above the deck and below the waterproofing layer. Boards need to be butted tightly with no gaps, laid in a broken bond pattern, and fully bonded or mechanically fixed depending on the system specification.
Any penetrations through the deck - pipes, conduit, plant fixings - need to be detailed at this stage before the membrane goes on top of them. Pipe penetrations in particular need to be upstanded correctly so the membrane can be taken up and over the collar. This is a stage that is easy to rush and where poor detailing causes early failures.
For a torch-on felt system, the base layer goes down first - typically a vented base layer on a new or replacement deck to allow any residual moisture to escape - followed by the intermediate and cap sheet layers, each torched and lapped to the specified lap width. The lap width matters: a 75mm lap on torch-on felt is not the same as a 150mm lap, and a contractor cutting corners here is cutting the life expectancy of the roof.
For an EPDM system, the sheet is rolled out, trimmed to size, and either fully adhered using water-based adhesive or mechanically fixed at the perimeter and seams. Seam tapes and termination bars need to be pressed and rolled properly for the seam to hold long term. On a large roof, the installer should be working methodically across the deck in planned passes, not cutting irregular patches and joining them.
For profile steel sheeting, sheets are fixed to purlins at specified centres with the correct length and gauge of self-drilling screw, with laps sealed using compatible lap sealant before the upper sheet is fixed. Ridge and eaves flashings go on last, with all laps correctly overlapped in the direction of water run.
Flashings seal the junction between the roof waterproofing and any wall, parapet, or penetration. This is statistically where most commercial roof leaks start, so the detailing here deserves as much care as the main field of the roof. Lead, aluminium, or purpose-made sheet metal flashings should be properly dressed to the wall, turned into a raked chase or fixed under a cover flashing, and not just sealed against the face of the brickwork with mastic.
Roof light kerbs need the membrane taken up and over the kerb and a separate weathering detail at the top. A roof light that is simply set into the membrane without a proper upstand and weather detail will leak - it is a question of when, not whether.
Before leaving site, the finished roof should be walked and checked: all outlets clear, all laps inspected, flashings dressed and secure, any debris removed from the roof surface. Gutters and downpipes should be cleared and checked for flow. The site below the building should be cleared of all material, packaging, and equipment.
You should receive a written record of what was done, what materials were used, and any recommendations for maintenance. Ask specifically whether the outlet positions and gutter fall were checked, as blocked or poorly falling gutters are one of the most common causes of premature flat roof failure.
We serve Lakenheath and the wider area including Thetford, Attleborough, Mundford, Brandon, Mildenhall, Methwold, Feltwell, and Watton. Call us to arrange a survey and written specification for your commercial building.
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Call any time. Calls are answered day and night and passed straight to our roofers.
