Thetford Roofers provides commercial roofing services across Bury St Edmunds and the surrounding area, working on flat roofs, sheeted roofs, cladding and guttering for industrial, retail and agricultural premises.
When a commercial roof reaches the end of its life, or needs replacing after storm or water damage, the choice of system matters more than most property owners realise. The wrong material for the building type, the roof pitch or the local conditions will cost more in the long run. This page sets out the main options honestly, with the practical pros and cons of each.
Most commercial flat roofs are covered by one of three main system types: built-up felt, torch-on modified bitumen, or single-ply membrane. Each has its place depending on the building, the deck condition and the budget available.
Built-up felt consists of multiple layers of bitumen-impregnated felt bonded together with hot bitumen or cold adhesive. It has been used on commercial buildings for decades and is well understood. The main advantage is that multiple layers mean a single puncture or split is less immediately catastrophic than on a single-layer system. The disadvantages are weight, the need for hot works on site, and a shorter lifespan than modern alternatives. On a well-prepared deck, a quality built-up felt system typically lasts 15 to 20 years before it needs significant attention.
Torch-on felt is a modified bitumen sheet applied with a gas torch. The modification process (either APP or SBS polymer) gives the sheet greater flexibility and resistance to cracking than traditional felt. It is quicker to apply than a multi-layer built-up system and gives a reliable waterproof finish when installed correctly. A two-layer torch-on system on a sound deck can be expected to perform for 20 years or more. The downside is that torch-on work requires careful fire risk management, particularly on buildings with combustible deck materials or insulation.
EPDM (ethylene propylene diene monomer) is a synthetic rubber membrane that has become the material of choice for many commercial flat roof applications. It is applied in large sheets with very few joins, which reduces the number of potential weak points. It performs well in both cold and heat, does not become brittle with UV exposure the way older felts do, and is lighter than a built-up felt system. EPDM flat roofs in commercial use typically last 30 years or more when correctly installed and maintained. The main consideration is that detailing around penetrations, upstands and kerbs needs to be carried out carefully - poorly detailed joins are the most common source of failure in an otherwise sound membrane.
Industrial units, warehouses and agricultural buildings are often roofed with steel box profile sheeting or fibre cement (formerly asbestos-cement) sheets. The choice between them is largely determined by what is already on the building.
Steel box profile is the standard choice for new-build commercial and agricultural roofs. It is lightweight, fast to install and available with a range of polyester or plastisol coatings that carry manufacturer colour guarantees of 25 to 40 years depending on the specification chosen. The practical weaknesses are fixing corrosion over time (the neoprene washer on each screw compresses and cracks), and the need to insulate separately if the building requires it - a single-skin steel sheet provides negligible thermal performance. Insulated composite panel systems (a steel outer face, a foam core and a steel inner face) solve the insulation problem but cost significantly more per square metre.
Typical installed costs for steel box profile re-roofing in the current UK market run from around £20 to £35 per square metre for single-skin sheeting, depending on sheet profile, coating specification, access difficulty and the amount of supporting structure work required.
Many older commercial and farm buildings carry fibre cement (non-asbestos) sheets that replaced asbestos cement in the 1980s and 1990s. Fibre cement is durable and relatively low-maintenance, but sheets become brittle and porous with age. Walking on old fibre cement sheets without proper support boards is dangerous. When fibre cement sheets need replacing, the realistic choice is between like-for-like replacement (where the purlin spacing is suitable) or over-sheeting with steel box profile laid over the existing sheets. Over-sheeting avoids the cost and disruption of removing the old sheets and is a practical option where the existing structure is sound.
Note: If any existing sheets on your building were installed before 1999, arrange for a sample to be tested before any work involving drilling or cutting takes place. Asbestos cement and non-asbestos fibre cement look similar but must be handled differently.
Roof lights in box profile or fibre cement roofs are typically polycarbonate or multiwall polycarbonate sheets profiled to match the roof sheet. They degrade and discolour with UV exposure, and the seals at the laps fail. Replacing roof lights at the same time as re-sheeting is far more cost-effective than returning to the building separately. Where additional natural light is needed, new roof light bays can be incorporated into a re-roofing scheme.
Box profile steel is also widely used for wall cladding on commercial and agricultural buildings. If the roof sheeting is being replaced, it is worth inspecting the wall cladding at the same time. Failed cladding at the eaves and base of panels allows water and wind ingress and can undermine the insulation performance of the whole building envelope.
Box gutters, pressed aluminium and UPVC systems all have a place on commercial buildings. Box gutters built into the roof structure are effective but must be maintained - blocked box gutters overflow internally, and the damage to the building fabric can be severe. External gutters on sheeted roofs are easier to inspect and clear, but the gutter to fascia bracket fixing corrodes on older buildings and the gutter runs can sag, creating standing water. When a re-roofing project is being specified, the gutter system should be part of the scope.
Thetford Roofers covers Bury St Edmunds and the surrounding area, working on commercial buildings of all types. Call us to arrange a survey and get a written price before any work starts.
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