Signs to look out for
- Persistent ponding or outlets that do not drain freely
- Splits, blisters or lifting edges in the roof covering
- Damp patches beneath an extension, garage or dormer roof
What should be inspected?
The covering is only part of the picture. Checking the edges, outlets, slope and accessible deck helps establish whether the problem is a local split, trapped moisture or a wider drainage issue.
Repair or replacement?
A small defect on a sound roof may be repairable. A wet or weakened deck, widespread splits or repeated leaks may need a more extensive renewal. The condition underneath matters before an overlay is considered.
Materials and their trade-offs
The descriptions below explain common coverings you may encounter when comparing quotations. Suitability depends on the roof assessment and the proposed specification; no single material is the best choice for every roof.
The covering and the construction
EPDM rubber
A flexible waterproof membrane supplied in sheets. Large sheets can reduce joins across the main roof, but edges, outlets and any seams still need the correct detailing. Ask how the proposed sheet layout and junctions suit your roof.
GRP fibreglass
A covering formed on the roof using resin and glass-fibre reinforcement. The suitable substrate and treatment of joints and trims depend on the specified system. Ask which system is proposed and what preparation it requires.
Reinforced felt
A bitumen-based membrane system, commonly using an underlayer and finishing sheet. Application methods vary, including flame-free options. The quotation should identify the complete system rather than simply describe it as felt.
What does a warm flat roof mean?
A warm flat roof places the insulation above the supporting deck, beneath the waterproof covering. A conventional cold flat roof places insulation below the deck, with ventilation above the insulation and below the deck. These describe the roof’s construction, not the name of its surface material. When comparing quotations, ask how insulation, moisture control and the existing roof will work together.
Further reading: Elevate’s EPDM overview, Cure It’s GRP system guidance (PDF), Bauder’s flame-free detailing, NFRC CPS roof construction FAQs.
What the quotation should include
- The proposed system and manufacturer’s installation specification
- Deck repairs or replacement and how concealed damage is handled
- Insulation, falls, outlets, upstands and perimeter trims
- Removal of old materials, access and agreed cover terms
Access and disruption
Extensions and garages can have fragile roof surfaces. Access and protection need planning, including how the roof will be kept weatherproof while the work is under way.
What affects price and timing?
The deck, insulation and drainage can make a bigger difference than the covering alone. Roof size, access and junctions with walls or rooflights also affect the price and time needed.
Read the guide to roofing cost factors
Your questions, answered
Which flat roof covering should I choose?
The roof’s construction, drainage and use should guide the choice. Compare the full proposed system, including the deck and edge details, rather than choosing by the covering alone.
Can a new covering go over the old one?
Only if the existing roof is dry, sound and suitable for that system. Trapped moisture, weak decking or poor adhesion can make an overlay unsuitable.
Is standing water a sign of a leak?
Not on its own. Persistent pools or slow drainage still need attention, particularly around blocked outlets or uneven areas of the roof.
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