Large Commercial Building — Flat Roof Overlay

Project Context

A large multi-storey commercial office building (approx. 3,500–5,000m² roof area) with an existing felt and asphalt flat roof system. The roof is experiencing widespread deterioration — leakage at joints, seams and penetrations, with localised moss growth and surface cracks. The building is fully occupied; refurbishment must proceed with minimal disruption.

The building owners and FM team require a long-life overlay solution that eliminates strip-out costs, reduces programme time and provides a clear performance warranty. A traditional felt/asphalt replacement would mean 4–6 weeks of access restrictions, contractor presence and noise.

System Selection: SprayGrade

SprayGrade cold-spray liquid rubber is selected for this project because:

• Overlay capability: no strip-out required. Applied directly over existing roof structure.
• High-output spray: 600m²+ per day means the entire roof can be completed in 5–8 days.
• Cold application: no heat, no flames, no hot-work permits required. Safe for occupied buildings.
• Seamless membrane: creates a fully bonded, waterproof barrier across the entire roof with no seams.
• Proven on felt and asphalt: standard substrate preparation (cleaning, minor repairs) is all that is required.
• 15–25 year warranty: manufacturer-backed performance warranty with clear maintenance terms.

Substrate Assessment & Programme

Pre-application survey confirms:

• • Felt roof in reasonable condition — no structural failure, asphalt surface largely sound.
• • Isolated wet patches in two areas — substrate dried and isolated before application.
• • Moss and surface debris cleaned off; minor cracked asphalt areas patched with specialist repair compound.
• • All penetrations (soil stacks, pipework, roof hatches) inspected and minor sealant failures repaired.

The roof is then power-cleaned and left to dry. SprayGrade is then applied in two coats: base coat + top coat, achieving a 3mm nominal thickness. At 600m²+ per day, the 4,000m² roof is completed in 6–7 working days. The building can be re-occupied the same day application is complete; no post-cure time is required before foot traffic.

Warranty & Maintenance

Following successful completion and inspection, a 20-year manufacturer warranty is issued covering material and application. Warranty conditions include:

• • Annual visual inspection and minor debris clearing.
• • Prompt repair of any isolated damage (e.g., punctures, cuts) using SprayGrade patch compound.
• • Drainage system inspection to ensure no standing water accumulates.