1 · Existing roof exposed

Tiles stripped. Existing breather membrane and battens removed. Rafter condition inspected and made good where needed — rot at eaves, woodworm damage, sagging or sprung rafters. Any structural repair happens before insulation goes up. Existing between-rafter insulation kept or replaced depending on its condition and the project's U-value target.

2 · Vapour-control layer

Intelligent vapour-control layer (membrane that lets vapour pass outward but blocks airflow) sits directly on top of the rafters. Tied at eaves, ridge, and verges with airtight tape. The vapour-control layer plus the Pavatex above forms the assembly's airtight envelope — critical for EnerPHit retrofit targeting blower-door performance.

3 · Pavatex Isolair Multi

Boards laid in a staggered pattern across the roof slope, T&G joints engaged. Cut to length at hips and valleys with a fine-tooth saw. Boards held in place by their own weight and the tile-batten fixings — no separate adhesive needed in standard installs. Boards are walkable for tile-battening above.

4 · Counter-battens

Vertical counter-battens fixed through the Pavatex into the rafters below using long stainless steel screws — typical fixing length is the Pavatex thickness plus 80 mm into the rafter. The counter-battens create the drainage and ventilation cavity between the insulation and the tiles, and provide the mechanical fixing path.

5 · Breather membrane & tile battens

Reinforced breather membrane laid over the counter-battens — secondary weatherproofing for storm-driven rain past the tiles. Horizontal tile battens fixed to the counter-battens at the standard tile-gauge spacing. The assembly is now ready for tiling.

6 · Tiles re-laid

Tiles re-laid on the standard battens — concrete tiles, clay tiles, slate, or new replacement covering depending on the project. The visible roof appearance is unchanged from before; the thermal upgrade is invisible from the street. Eaves, ridge, hips, and verges detailed per the standard tile manufacturer's specification.

FSC-certified Swiss softwood

Sourced from European managed forests under Forest Stewardship Council certification. Spruce and fir from Swiss and Alpine softwood programmes. Pavatex manufactures at Cham, Switzerland — short transport from forest to factory.

Wet-process wood fibre

Wood fibres refined into a slurry, formed into a continuous mat, pressed under heat. The lignin in the wood acts as the natural binder — no formaldehyde or PU resin needed at standard board density. Same wet-process chemistry as Gutex Thermowall on the wall side.

160 kg/m³ density

Density that delivers the summer decrement performance. Higher than EPS (~30 kg/m³) or PIR (~35 kg/m³) — the mass is what shifts the daily temperature peak from midday to midnight. The reason Pavatex is the specified roof insulation on Victorian top-floor retrofits and Passivhaus new-build alike.

Carbon-negative balance

Each m³ of Pavatex stores roughly 200 kg of atmospheric CO₂ in the wood substrate. After accounting for the manufacturing energy (mostly biofuel heat from sawmill residue at Pavatex's plant), the net embodied carbon is negative — the roof is a carbon sink, not a carbon cost.

Fire class: E (system Bs2-d0)

Wood fibre is combustible Euroclass E as a board. Under tiles in a standard pitched-roof assembly, the system tests Bs2-d0 — tiles are the external fire-exposed face, Pavatex sits below. Suitable for buildings under 11 m external wall height (the wall regulation extends to roof slope in the height calculation).

PHI Passivhaus listed

Listed in the Passivhaus Institut component database with verified thermal performance data. Specifiable into PHPP energy models for Passivhaus-certified new-build and EnerPHit retrofit with audit-ready confidence. The PHI listing is what separates "wood fibre" generally from products that can be cited in a certified Passivhaus model.

50+ year fabric design life

Properly detailed wood-fibre roof assemblies have track record back to 1980s European retrofit programmes. With a sound substrate, weather-tight detailing, and a maintained tile finish, Pavatex stays in service for 50+ years. The tile covering is the maintenance variable, not the wood fibre below.

No annual service required

No moving part, no electrical component, no consumable. The wood fibre sits between tile and rafter doing its job. Standard tile inspection cadence applies — every 5–10 years on weather-exposed elevations, slate inspection annually in coastal locations.

Roof-tile lifecycle aligned

UK pitched roofs typically need re-tiling every 40–60 years (concrete) or 60–100 years (clay or slate). The Pavatex install's design life is matched to or longer than the tile covering it sits under — when the tiles need replacing decades from now, the boards can stay in place or be re-used.

Eaves, ridge, and verge details

Eaves, ridge, and verge details are where wood-fibre roof systems can fail. Water ingress at a failed verge tile or a poorly-detailed eave tracks into the board edge — and unlike rigid foam, wood fibre will eventually rot if kept persistently wet. Every Pavatex scope from CleverBloom uses manufacturer-specified eave and verge details with a 6-month inspection visit included.

Warmcel between rafters

The breathable warm-roof assembly is Pavatex over-rafter plus Warmcel dense-pack between rafters. The pairing is what hits typical Part L and EnerPHit U-values; Pavatex alone at 140 mm needs supporting between-rafter insulation to reach the target without excessive over-rafter thickness. CleverBloom includes the between-rafter scope on most Pavatex projects.

Roof ventilation strategy

A warm-roof assembly with vapour-open materials still needs ventilation above the breather membrane — the cavity between the breather membrane and the tiles vents at eaves and ridge to manage any moisture that passes through the assembly. Tile manufacturer's ventilation specification is followed precisely; eaves and ridge vents installed as part of the scope.