Commercial Roof Waterproofing
Understanding which waterproofing system is appropriate for a commercial roof depends on several factors: the roof type, its current condition, the project objective and the required programme. This page is a decision framework — not a product catalogue.
Understanding Commercial Roof Waterproofing Systems
Commercial roof waterproofing is the application of a membrane or coating system to a commercial building's roof to prevent water ingress, protect the building structure and extend the service life of the roof.
It covers a range of scenarios: a new building requiring a primary waterproof layer, an ageing roof that can be refurbished in place, localised failures that need targeted repair, and roofs that have deteriorated beyond refurbishment and require replacement of the membrane.
Refurbishment and replacement are not the same decision. Refurbishment applies a new waterproofing system over or alongside the existing roof without full strip-out. Replacement removes the existing membrane and installs a new system from the deck up. Whether a roof is a candidate for refurbishment depends on a survey of the substrate, drainage, existing system condition and structural integrity — not on the age of the roof alone.
Different waterproofing technologies — sheet membranes, liquid-applied coatings, spray-applied coatings and polyurea systems — have different appropriate applications. The sections below set out a framework for identifying which approach may be relevant to a specific roof.
Commercial Roof Types
Different commercial roof types present different waterproofing challenges and have different system compatibility requirements. Identifying the roof type is the first step in determining an appropriate approach.
Metal Roofs
Corrugated steel, standing seam and profile metal roofing. Subject to cut-edge corrosion at laps and penetrations. Typically suited to polyurethane coating systems (e.g. TopSpray35) for refurbishment, or full replacement with new metal and a waterproof system. Not all liquid rubber systems are designed for metal substrates — check compatibility.
Concrete Roofs
Common on industrial and commercial buildings. Can accept liquid waterproofing systems and spray-applied coatings. Substrate preparation — including crack treatment, primer selection and moisture assessment — is critical to system performance.
Asphalt Roofs
Mastic asphalt and bitumen-based systems. Ageing asphalt can crack, blister and oxidise. Can be overcoated with compatible liquid systems in some conditions — substrate assessment essential. Delamination, ponding water and structural movement must be considered before any overlay.
Existing Liquid Systems
Roofs with an existing liquid waterproofing membrane, whether fully or partially failed. Compatibility with a new system must be assessed. Partial failures may be locally repaired; widespread adhesion failure may require removal.
EPDM Roofs
Rubber sheet membranes. Where the sheet has failed or reached end of life, it is typically removed and replaced. Localised failures at seams and penetrations can often be repaired. Not typically overcoated with liquid systems.
Felt Roofs
Traditional built-up felt roofing. Where deteriorated, felt is usually removed before a new system is installed. Overlay refurbishment may be feasible in limited circumstances subject to survey.
What Condition Is the Roof In?
The condition of the existing roof is a primary determinant of which approach is appropriate. These categories are a framework — a survey is required before any system recommendation can be made.
Sound but ageing
The roof is watertight but the existing membrane is showing signs of weathering, UV degradation or minor cracking. The deck and drainage are sound. This is typically a strong candidate for planned refurbishment before failure occurs.
→ Proactive refurbishment. System overlay may be viable subject to survey.
Localised failure
The roof has isolated leak points — failed joints, split flashings, blocked outlets or damage around penetrations — but the majority of the membrane is intact and performing. The underlying structure is sound.
→ Targeted repair. The failure points can often be addressed without a full re-waterproofing programme.
Widespread deterioration
Multiple areas of failure across the roof surface. The existing membrane is extensively cracked, blistered or delaminated. Drainage may be compromised. Repairs are failing repeatedly.
→ Full re-waterproofing is likely necessary. Whether this is an overlay or strip-and-replace depends on deck condition.
Active leaks
Water is entering the building. The immediate priority is identifying the ingress point and preventing further damage. Emergency repair may be appropriate as a temporary measure while a specification is developed.
→ Emergency repair to stop active water ingress. Full survey required to determine the permanent solution.
End of service life
The roof membrane and potentially the deck structure have reached the end of their serviceable life. The roof cannot be economically or safely refurbished — full replacement of the membrane (and potentially the deck) is required.
→ Roof replacement. Not a refurbishment candidate.
Refurbishment or Replacement?
This is a project-level decision that cannot be made without a survey. These are the factors that inform it.
Refurbishment may be appropriate when:
- The roof deck is structurally sound and dry
- The existing membrane has failed but the deck is intact
- Drainage falls are adequate and outlets are functional
- The building requires waterproofing without operational shutdown
- The objective is extending the roof life rather than full renewal
- An overlay-compatible system can be specified for the substrate
Replacement is likely necessary when:
- The deck has sustained water damage and is structurally compromised
- Ponding water has been retained within the roof build-up
- The falls are insufficient and drainage cannot be improved by overlay
- The existing membrane is delaminated across the majority of the surface
- Repeat repairs are consistently failing within short timeframes
- The deck material is incompatible with any available overlay system
The decision between refurbishment and replacement must be based on a physical survey — not on the age of the roof or visual inspection alone. Forti Nova can provide technical guidance once survey information is available.
Commercial Waterproofing Systems
Each system has specific appropriate applications and specific situations where it is not the right choice. No system is universally suitable.
EPDM Roofing
Suitable for
- New flat roof construction
- Full roof replacement
- Garden rooms and small extensions
- Roofs up to approximately 300m² as single sheet
- Projects where a long-term membrane system is the objective
Not appropriate when
- Roofs with complex detailing where the sheet cannot conform
- Overlay refurbishment where the deck is structurally compromised
- Very large commercial roofs where seaming multiple sheets is undesirable
Liquid Rubber HBS200
Suitable for
- Localised waterproofing repairs
- Complex detailing — upstands, penetrations, gutters, parapets
- Refurbishment of smaller roof areas
- Overlay applications onto stable substrates
- Preparation and detailing work alongside spray systems
Not appropriate when
- Large commercial roof areas where spray application would be faster
- Substrates with significant structural or drainage defects
- Projects requiring very rapid programme completion
SprayGrade
Suitable for
- Large commercial and industrial flat roofs
- Warehouses, distribution centres and factory buildings
- Refurbishment projects where output speed is a priority
- Asbestos cement roof encapsulation (subject to survey and compliance)
- Roofs where a seamless high-build membrane is required at scale
Not appropriate when
- Small residential roofs where mobilisation cost is disproportionate
- Metal roofs requiring a polyurethane coating system
- Balconies and terraces requiring a trafficable surface
- Projects where spray equipment access is not feasible
Prokol MonoSeal
Suitable for
- Balconies, terraces, walkways and podium decks
- Trafficable waterproof surfaces
- Complex flat roof detailing requiring a pure polyurea membrane
- Refurbishment projects on balconies and accessible decks
- Gutters and drainage details
Not appropriate when
- Very large areas where spray application is more efficient
- Metal roofs requiring a polyurethane topcoat system
- Substrates that have not been correctly prepared and primed
Rocathaan HotSpray
Suitable for
- Large commercial roofs requiring spray-applied polyurea
- Projects where faster cure than liquid rubber is required
- High-specification commercial and industrial waterproofing
- Extensive roof areas where a high-build seamless membrane is specified
Not appropriate when
- Residential or small-scale projects where mobilisation cost is disproportionate
- Metal roofs where a polyurethane coating is specified
- Projects without access to specialist polyurea spray equipment and trained operatives
How Commercial Roof Projects Are Assessed
A meaningful system recommendation requires information from a physical survey. These are the factors that are typically assessed.
Roof Condition
Visual inspection of the existing membrane, laps, joints, penetrations and flashings. Identification of failure points, water ingress locations and areas of blistering, cracking or delamination.
Substrate
Assessment of the deck material — concrete, metal, timber or composite — and its structural integrity. Moisture content where relevant. Compatibility with candidate overlay systems.
Drainage
Assessment of falls, outlets, gutters and drainage capacity. Ponding water indicates falls insufficiency which may need to be addressed before or during the waterproofing programme.
Access
How the roof is accessed for survey and for application. Equipment positioning, working at height constraints, scaffold requirements and logistics for spray or manual application.
Detail Complexity
Number and type of penetrations, upstands, parapets, outlets and special details. High detail complexity may favour liquid or hand-applied systems over spray for those areas.
Project Objectives
Whether the objective is emergency repair, planned refurbishment extending the roof life, or full replacement. The programme requirement and budget framework also influence system selection.
Related Applications
If you are looking for guidance on a specific application type, these pages may be more relevant.
Flat Roof Waterproofing
System comparison for residential and commercial flat roofs
Read more →Commercial Roof Refurbishment
Refurbishment vs. replacement decision framework for commercial and industrial roofs
Read more →Metal Roof Refurbishment
Specialist polyurethane systems for metal roof structures
Read more →Waterproofing Systems Hub
Overview of all waterproofing systems supplied by Forti Nova
Read more →Prokol MonoSeal — Balconies
Hand-applied polyurea for balconies, terraces and podium decks
Read more →Rocathaan HotSpray
Spray-applied polyurea for large commercial roof areas
Read more →Related Problems
If you have arrived here because of a specific problem, these routes may be more directly relevant.
Leaking Flat Roof
Emergency waterproofing repair for active leaks
Read more →Emergency Roof Repair
ProFix — waterproof repair sealant for immediate action
Read more →Roof Repairs Repeatedly Failing
Why commercial roof repairs keep failing — and when to escalate
Read more →Roof Refurbishment vs Replacement
Decision framework for ageing commercial roofs
Read more →Support Pathways
Depending on your role and requirement, these routes provide direct access to the appropriate level of support.
Approved Contractor Route
Project scoping and approved-contractor introductions across the North West
View Contractor Route →Training Courses
Professional installer training for EPDM, Liquid Rubber, SprayGrade and more
View Courses →Approved Applicator Programme
Find or become an approved contractor for Prokol systems
Learn More →Frequently Asked Questions
Discuss Your Commercial Roof Project
If you have survey information and need help identifying the appropriate waterproofing system, or need technical support to specify for a project, call the Forti Nova team.
01254 433987 · Mon–Fri 7:30am–4:30pm · Blackburn, BB1 3DL