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Flat roof renewal. Extend the life of a failing roof and cut the carbon of a full strip-and-replace.

Where an overlay is technically suitable, renewing the waterproofing layer can deliver reliable performance at a fraction of the embodied carbon, cost and waste of tearing the roof off. Model the difference for your roof below.

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Roofing team installing insulation over a profiled metal flat roof during a renewal overlay

/Allbase Renewal Programme

Measure the impact before you commit to the strip. A full strip-and-replace tears off the existing build-up, sending insulation, membrane and deck to landfill and rebuilding the roof in new, carbon-intensive material.

Stripping a roof back to the structure is disruptive and rarely necessary where the existing build-up is sound. The removed material becomes waste, the haulage adds transport emissions, and every new layer carries its own embodied carbon before the roof is even watertight again.

Where an overlay is technically suitable, a reinforced liquid system bonds to the prepared surface and forms a new seamless waterproofing layer over the existing roof. The calculator below compares Allbase overlay systems against a full-replacement baseline, with an optional oversheeting comparison for metal roofs.

Roof carbon comparison. Enter your roof and see the lower-impact options ranked against replacement.

Indicative estimate for general guidance. Figures use generic published material factors and exclude transport, installation and site-specific conditions, so actual savings vary by project.

Full replacement
Strip & replace
27,875 kgCO₂e
Replace steel deck · 150 mm PIR · 5.0 kg/m² membrane · incl. strip-out
89%
24,815 kgCO₂e saved
Lowest-carbon overlay
Overcoat STP
3,060 kgCO₂e
Primer + STP resin · applied over the retained build-up, no strip-out.
1,182 trees / yr
carbon absorbed equivalent
£48,500 saved
vs full replacement
10.8 tonnes
diverted from landfill
Method
Embodied carbon
vs base
Total
Full replacementbaseline
-
27,875 kgCO₂e
Overcoat STPLowestoverlay
89%
3,060 kgCO₂e
Fibrecoat PUoverlay
88%
3,448 kgCO₂e
PMMAoverlay
79%
5,990 kgCO₂e
XR Polyureaoverlay
85%
4,291 kgCO₂e
Across 500 m² · baseline: Replace steel deck · 150 mm PIR · 5.0 kg/m² membrane · incl. strip-out. Lowest-carbon overlay highlighted.
Methodology
Figures are cradle-to-gate estimates built from generic published material factors. The model compares the embodied carbon of a full strip-and-replace build-up against a reinforced liquid overlay applied to the retained roof. It excludes transport, installation and site-specific conditions, and any trapped moisture or structural repair a survey may identify, so the result is indicative guidance rather than a project-specific assessment.

Overlay systems built for renewal. Reinforced liquid-applied systems that bond to a prepared existing surface.

Each system forms a seamless waterproofing layer over a suitable substrate, extending service life without the disruption, waste or cost of a full strip-out. GRP is excluded here as it is not suitable for overlay application.

Overcoat

A specialist STP overlay system that bonds to a wide variety of existing roof coverings, restoring weathered flat roofs without removal.

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Fibrecoat

A reinforced, highly flexible liquid layer applied onto prepared surfaces, ideal for extending the life of an ageing roof.

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PMMA

A fast-curing reactive resin system for rapid return to service and complex detailing, suitable for overlay on sound substrates.

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XR Polyurea

High-performance spray-applied waterproofing for demanding commercial and industrial roofs, available to approved trade contractors.

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Frequently asked questions. Suitability, performance, carbon and long-term results.

Choosing between roof renewal and complete replacement is not always easy. Below are answers to the most common questions we receive about the Allbase Roof Renewal Scheme, to help early decision-making before a full consultation.

What is the roof renewal scheme?
Renewal is an overlay-led alternative to a full strip-and-replace. Where the existing roof is structurally sound, a reinforced liquid system is applied over the prepared surface to form a new seamless waterproofing layer, extending the roof's service life without removing the existing build-up.
How do I know if my roof is suitable for renewal?
Suitability depends on the condition of the existing waterproofing, the deck and insulation, and the level of trapped moisture. A site survey, and where needed core sampling and moisture mapping, confirms whether an overlay is technically appropriate or whether replacement is the safer option.
What types of roof problems can renewal address?
Renewal is well suited to ageing or weathered waterproofing, surface cracking, failed laps and seams, and general loss of performance on otherwise sound roofs. It is not a fix for significant structural failure or saturated insulation, which a survey will identify.
Is renewal cheaper than full roof replacement?
In most suitable cases an overlay costs less than a full strip-and-replace, because it avoids strip-out, disposal and the supply of a complete new build-up. The calculator above gives an indicative comparison; a survey produces a firm figure for your roof.
Does renewing a roof reduce carbon impact?
Retaining the existing build-up avoids the embodied carbon of new insulation, deck and membrane, and removes the transport and landfill emissions associated with strip-out. The calculator above gives an indicative comparison using generic published material factors, so figures are a guide rather than a project-specific assessment.
Will a liquid overlay last as long as a new roof?
When specified correctly and installed on a suitable, well-prepared substrate, a reinforced liquid system provides long-term waterproofing performance comparable to a new covering, and can be covered by a guarantee. Expected service life depends on the system chosen and the condition of the roof beneath.
What happens if my roof is not suitable?
If a survey shows an overlay is not appropriate, we will say so. We can then advise on the most suitable replacement strategy, including which elements need to be removed and rebuilt, so you are not committed to renewal where it would not perform.
Is renewal suitable for commercial buildings?
Yes. Overlay renewal is widely used across commercial, public sector, industrial and residential buildings. Spray-applied systems in particular suit large commercial and industrial roofs where rapid curing and minimal disruption to operations matter.

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