1 · Pre-fill prep

Loft cleared of stored items, hatch widened if needed, ventilation paths at the eaves protected with vent baffles. Downlights inspected for fire-rated covers (open downlights need fire hoods before cellulose goes around them). Recessed light fittings, pipework, and cable runs photographed for the homeowner pack.

2 · Eaves and hatch detailing

Vent baffles fitted at every eave to maintain the air gap above the wall plate — critical for roof ventilation and to prevent fibre blocking the cold roof air path. Loft hatch surround insulated and weather-stripped. These details account for ~40% of the heat loss the loft scope is trying to fix.

3 · Hose and blower setup

Trailer-mounted blowing rig on the kerb outside; hose runs through a hatch or open window to the installer in the loft. Fibre bales fed continuously into the rig hopper. The rig handles the air mixing and fibre feed automatically — the installer controls the nozzle.

4 · Open-blow application (lofts)

For horizontal lofts, the installer works from the far corner back to the hatch, building up the fibre evenly to the design depth (typically 400 mm for a standard ECO4 scope). Depth markers fixed to joists or rafters before fill so the installer can verify visually as they go.

5 · Dense-pack application (walls/rafters)

For vertical or sloped cavities, the installer fits a temporary membrane (mesh or intelligent membrane), inserts the nozzle through a small access hole, and packs the cavity to the design density. Pressure gauge on the rig confirms the cavity is full. Access hole sealed with the same membrane and tape after fill.

6 · Verify and photo-evidence

Final depth measured at sample points across the loft. Photos taken of depth markers, vent baffles, hatch detailing, and the finished loft surface. Evidence pack issued — ECO4 grant claims and CleverBloom guarantee documentation both reference the photo log.

85% recycled newspaper

The fibre stream is post-consumer newsprint and office paper, sorted at UK paper recycling facilities. Each tonne of Warmcel diverts roughly a tonne of paper from landfill or paper-pulp re-processing. UK supply chain — Welsh manufacturing site, UK feedstock, mainland UK delivery routes.

Borate fire treatment

Boric acid and sodium tetraborate (borax) blended through the fibre mass at manufacture. Borate suppresses flame propagation — fire moves through Warmcel as a slow char rather than a flame front. Same borate chemistry has been used in cellulose insulation since the 1970s; well-understood, no off-gassing in service.

Density: depends on the application

The same Warmcel 500 is installed at 30–50 kg/m³ for horizontal lofts (gravity-stable), 50–55 kg/m³ for rafter dense-pack, 55–65 kg/m³ for wall cavity dense-pack, and 60+ kg/m³ for acoustic studwork. Density is what controls settling resistance and acoustic damping; thermal conductivity is constant across the range.

Hygroscopic, not vapour-blocking

Cellulose can hold ~20% of its own weight in water without losing thermal performance — unlike fibreglass, which collapses when wet. The fibre acts as a moisture buffer in vapour-open assemblies, absorbing peaks and releasing them back when the air dries. Compatible with intelligent membranes; not specified with vapour-tight foils.

Pest deterrence

Borate makes the cellulose unappetising to rodents, insects, and microbial life. Loft cellulose installs from the 1980s show no rodent burrowing into the fibre mass — pests will tunnel around it but not through it. Long-term passive protection without ongoing pest-control intervention.

Fire class: E (system Bs2-d0)

Cellulose is combustible (Euroclass E) as bulk fibre. In standard build-ups — behind plasterboard for stud walls and rafters, exposed in horizontal lofts where no flame source exists — the borate treatment plus the build-up containment delivers safe service. Loft installation in occupied dwellings is BBA-certified.

60+ year fabric design life

Cellulose loft installations from the 1980s show no significant degradation after 40+ years in service. The fibre is dimensionally stable, the borate treatment doesn't wash out in dry loft conditions, and the carbon stays locked in the wall or loft for the life of the building.

No annual service required

No moving part, no electrical component, no filter, no consumable. The cellulose sits, insulates, and stores carbon. Standard loft housekeeping — keep stored items off the fibre, don't compress the depth — is all the maintenance needed.

Top-up rather than replace

If a future renovation needs a deeper loft (because Part L thresholds keep tightening), Warmcel tops up cleanly over the existing fibre — no need to remove what's there. Same product, same chemistry, blown over the existing mass to the new design depth.

Loft hatch insulation

An uninsulated loft hatch in a properly fluffed loft becomes the single biggest residual heat-loss path — the equivalent of a small permanently-open window. We fit an insulated hatch surround and a weather-stripped door panel as part of every Warmcel loft scope. Costs less than £150 and saves 50–80 kWh/year on a typical UK loft.

Eaves vent baffles

Roof ventilation at the eaves prevents condensation in the loft above the insulation line. Without vent baffles, blown cellulose can drift over the eave opening and block the cold roof air path — leading to summer overheating in the loft void and winter condensation on the underside of the felt. Always specified on cellulose loft scopes.

Downlight fire hoods

Open recessed downlights in the ceiling below the loft must have fire-rated hoods before cellulose goes around them — both for fire safety and to prevent the fitting overheating against the fibre. We fit hoods as part of the scope where missing. A loft fill that goes in over un-hooded downlights is a fire hazard and a service-life issue.