Asbestos Roof Encapsulation – Dove Lane, Bristol

Four layers, applied externally, each doing one job. No layer is decorative and none can be left out — the foam without the membrane has no weather protection, and the membrane without the top coat has no UV protection.

1. Sollac Hipolava — biocidal clean. A full biocidal wash to kill the moss, lichen and algae and take the roof back to a sound, dry substrate. This is the step that decides whether the rest of the system lasts twenty years or two — nothing bonds reliably to a living surface, and organic growth left in place simply carries on growing underneath.
2. Purios HR closed-cell roofing foam — 25 mm. Spray-applied across both roofs, self-bonding to the corrugated profile with no mechanical fixings — which matters here, because a fixing means penetrating the very material being contained. The foam follows every contour, encapsulating the sheets and splinting them at the same time.
3. Impermax R3000 ST — liquid membrane. A single-component polyurethane membrane applied over the cured foam, forming a seamless waterproof surface with no laps, welds or joints to fail. Applied in two differently coloured coats so that full coverage is visible rather than assumed.
4. Colodur top coat — aliphatic, grey. An aliphatic polyurethane finish, pigmented on site. Aliphatic chemistry is what makes it UV-stable: it shields the membrane beneath from sunlight rather than degrading in it, and gives the roof its finished grey appearance.

• Thermal conductivity (λ): 0.0233 W/mK
• Density in finished product: min 50 kg/m³
• Closed-cell content: min 90%
• Compressive strength at 10% strain: ≥300 kPa
• Water vapour resistance factor (μ): ≥54
• Water absorption: ≤0.14 kg/m²
• Applied layer thickness: 10–20 mm per pass, to EN 14315-1:2013

Carried out externally by Duratite approved installer McKee Insulations Limited, working off the roof itself — no full scaffold, and no internal works.

The flat roof was treated as part of the same surface rather than as a separate system, so the two roofs were sequenced together and the junction between them was bridged by the same continuous build-up rather than detailed as a joint. Rooflights, vents and roof penetrations were masked before spraying and cut back afterwards, which is why they read as clean openings in the finished roof rather than as coated-over lumps.

The foam was applied in passes of 10–20 mm to a 25 mm finished build. Spraying to a set thickness on a corrugated profile means working to the crown, not the trough — the trough inevitably carries more material, which is what gives the finished roof its even profile. Once cured, the Impermax membrane went on in two coats and the Colodur top coat followed, taking the roof from bare cream foam to the finished grey surface.

Closed-cell foam is unforgiving about conditions. Purios HR requires a substrate and ambient temperature of at least 15 °C and relative humidity no higher than 60%, on a substrate that is genuinely clean and dry — not merely dry to the touch. That is why the biocidal clean and the spray are separated in the programme, and why work of this kind is placed in settled summer weather rather than fitted around it.

Encapsulation is not the answer to every asbestos roof. Where sheets are broken, holed or delaminating, or the structure beneath is failing, removal is the correct route and no coating changes that.

It is the right answer where the sheets are structurally sound but the surface has weathered — which describes a great many of the industrial and commercial asbestos cement roofs still in service across Ireland and Northern Ireland. Dove Lane is a textbook example: a roof with decades of life left in it, held back by a surface that had stopped protecting itself.