What am I likely to pay to replace a flat roof on a commercial building near Ely?

The cost of commercial flat roof replacement depends on the system used, the condition of the existing deck and the complexity of the roof layout. Torch-on felt and EPDM rubber are the two main options, and the price difference between them is often less significant than the deck condition - a rotten or waterlogged deck adds to the cost regardless of the membrane chosen. A site visit is the only reliable way to give you an accurate figure.

How do I know whether my commercial roof needs repairing or replacing?

The main indicators that point towards replacement rather than repair are widespread blistering or delamination across the membrane, a saturated or soft deck beneath, multiple previous repair patches that have not held, and water damage appearing in several different locations inside the building. Isolated damage to flashings, outlets or a single section of membrane can often be repaired cost-effectively if the rest of the roof is sound. We can inspect the roof and give you an honest assessment before you commit to anything.

Can you work on a commercial roof while the building is still in use?

Yes, in most cases. Work can be phased so that only one section of the building is affected at a time, and the exposed area should be made weathertight at the end of each day. For sensitive premises such as food units or schools, we discuss the programme and any specific requirements at the survey stage. Scaffolding, access and noise all need to be planned around the building's normal operation.

Flat Roofing in Bar Hill

Flat Roofing · Bar Hill

Expert Flat Roofing
in Bar Hill

Choosing the Right Flat Roofing System

There is no single best flat roofing material. The right choice depends on the size of the roof, its current deck condition, how accessible it is for maintenance, and your budget. What follows is a plain account of the systems we install, what they are good at, and where each one has limitations. We would rather give you this information upfront than have you discover a mismatch after the work is done.

Mineral Felt (Built-Up Felt)

Traditional three-layer mineral felt has been used on British flat roofs for decades. It consists of multiple layers of bitumen-impregnated felt bonded together with hot bitumen or torch-on heat, finished with a mineral surface layer that reflects some solar heat and resists minor abrasion.

Honest pros:

Lower upfront cost than EPDM - a felt re-roof on a typical single garage or extension is often the most budget-friendly option at the point of installation.
Widely available and straightforward to repair if a split or blister develops.
Suitable for most deck types and can be installed in sections without specialist joining equipment.

Honest cons:

Shorter lifespan than EPDM. A properly installed three-layer felt system typically lasts around 10-15 years in ordinary UK conditions.
Susceptible to blistering when moisture is trapped between layers during installation or when an old roof is overlaid without fully drying the substrate.
Bitumen becomes brittle as it ages, and cracking at upstands and edges is a frequent failure point.
Over its lifetime, felt can cost more than EPDM because it needs replacing sooner.

Felt is a sensible choice when budget is the primary constraint and the deck is in good condition. It is less suitable as a long-term solution for a roof that is difficult to access for periodic inspection.

EPDM Rubber Membrane

EPDM (ethylene propylene diene monomer) is a single-ply rubber membrane that has become the preferred flat roofing material on residential properties over the past two decades. It is supplied in large sheets that can cover many roofs with just one or two joins, which significantly reduces the number of potential leak points.

Honest pros:

Long manufacturer-stated lifespans. EPDM membrane manufacturers typically quote 25-50 years for the material itself, though installation quality and maintenance affect real-world performance.
Highly flexible. It handles the thermal expansion and contraction of a roof without cracking or splitting in the way bitumen products can.
Fewer seams mean fewer potential leak points. Large sheets bond directly to the deck with adhesive, and joins are made with specialist bonding tape.
Resistant to UV degradation. Unlike felt, EPDM does not dry out or become brittle in the sun.
Lightweight and low-maintenance. Once installed correctly it needs little attention beyond keeping the drainage clear.

Honest cons:

Higher upfront cost than felt. For a typical flat roof on an extension or garage, EPDM installation generally costs more to begin with, though the longer service life often makes it better value over time.
Requires careful installation around penetrations, upstands and drains. Poorly executed details are where EPDM roofs fail, so the quality of the roofer matters as much as the material.
If punctured mechanically (tools dropped on it, foot traffic over sharp objects), it needs prompt repair. Small punctures can be patched with compatible bonding tape.
Dark colour can make the roof surface hot in summer, though this is rarely a practical problem on a garage or single-storey extension.

EPDM suits residential extensions and garages where the homeowner wants a long-term solution and is not looking to re-roof again in ten years.

Typical Flat Roofing Costs

Flat roof installation costs generally fall in the following ranges for a straightforward re-roof on a sound deck:

Three-layer mineral felt: approximately £40-£70 per square metre installed, depending on specification and access.
EPDM rubber: approximately £60-£100 per square metre installed.

These figures are for the roofing work only. If the existing deck is rotten and needs partial or full replacement, the total cost rises. Deck timber is typically quoted separately once the old covering has been removed and the extent of the damage is clear.

A single garage flat roof (say, 15-20 square metres) might typically cost £700-£1,500 for felt or £1,000-£2,000 for EPDM, depending on condition. A larger kitchen extension roof at 25-35 square metres would sit proportionally higher. These are indicative ranges - actual prices depend on the specific job.

Which Material Suits Which Situation?

A budget-conscious repair on a young roof in otherwise good condition might be best served by a felt patch or torch-on repair. A full re-roof on an extension you plan to keep for the long term is almost always better served by EPDM. If the roof has complex detailing - multiple penetrations, a parapet wall, a rooflight - the single-seam nature of EPDM reduces the number of vulnerable joints.

What About the Deck?

The material you put on top of a flat roof is only as good as what it sits on. Flat roof decks are usually constructed from exterior-grade plywood or OSB (oriented strand board). Both absorb water when a roof leaks and both rot. When we strip a flat roof, we assess every board. Soft, spongy or delaminated sections need to come out and be replaced before the new membrane goes down. A new membrane on a wet or rotten deck will fail early regardless of which material is used.