Building type
Sports halls that drip, kitchens and changing rooms that steam, classrooms cold under a bare roof and loud under rain. Closed-cell to a cold hall roof or soffit, open-cell within a flat classroom roof, and cavity walls filled where they exist. Applied in the holidays, or in a segregated zone in term time, with fire and safeguarding planned before anyone arrives.
01What is happening
A school puts hundreds of people, showers, a kitchen and a sports hall under roofs that were often built cheaply and are now decades old. The roof sheet or the soffit is the coldest surface in the building. On a cold morning water forms on it and drips onto the hall floor, the dining tables and the classroom desks. Rain on a bare metal roof drowns a lesson.
It is not a roof defect. Repairing the roof will not stop it.
It is not solved by heating harder. Warmer air holds more moisture and finds the same cold surface.
It is not always condensation. Water at a lap, a fixing or a rooflight during rain is ingress, repaired first, by someone else.
02What is applied
Sports halls and dining halls usually carry a profiled steel roof, treated from below with closed-cell and the sheet kept as the weather line. The single-storey classroom blocks that make up most primary estates sit under flat roofs, where 150 mm of open-cell within the roof construction gives the depth a flat roof needs and lets it breathe. Cavity walls are filled in the same visit where they exist.
Schematic / not to scaleKeyed 1 to 5 below
Profiled sheet, flat deck, soffit or corrugated sheet. It stays, and we do not make it watertight.
Dust, loose coating and contamination removed. An asbestos-cement sheet passes a condition survey gate first.
Follows the profile and closes the laps. λ 0.027 W/mK is the NexSeal LE product figure. A flat classroom roof takes open-cell within the construction instead (see the project record below).
Encapsulated by the application, and still a thermal bridge in the calculation.
B-s2,d0 belongs to the coated NexSeal LE and DC315 system, as tested. An occupied school space usually asks for it.
Applications on this building
The problems it answers: Roof condensation Rain noise and acoustics Heat loss and thermal performance Fibre-cement and asbestos-cement roofs
03Working around the building
Most school work sits in the summer, Easter or half-term breaks, when the building is empty. Where term-time work is unavoidable it is done in a zone segregated from pupils and staff, with the arrangements agreed with the school before anyone arrives.
Halls, kitchens and whole blocks are best done empty. The programme is booked to the school calendar, often a year ahead.
A zone closed to pupils and staff, its own access route, no contact with the school day. Safeguarding checks for operatives on site follow the school's own requirements.
The fire strategy decides whether the coated system is specified; the asbestos register is consulted before the survey, and an asbestos-cement roof passes its condition gate first.
Cure time before a space is reoccupied, and any ventilation during cure, are set out in the method statement for your school.
04Enverge NexSeal LE
Enverge NexSeal LE is a two component closed cell polyurethane, spray applied directly onto the prepared substrate. As it cures, it expands and sets into one rigid, continuous layer, bonding into corrugations, laps, fixings and awkward junctions without being cut, jointed or mechanically fixed.
That matters because most insulation problems start at the gaps.
Board systems can leave voids at ribs, laps and junctions, and every gap is a potential cold bridge where warm internal air meets a cold surface and condensation forms, hidden behind the insulation. NexSeal LE is applied as one continuous bonded layer, so there is nowhere for that to start: a sealed, stable building envelope that controls condensation, reduces heat loss and protects the structure underneath.
HOLVEM also installs open-cell foam. It is a different product with its own data sheet, specified where a build-up needs depth that breathes: the flat roofs of 29 primary and junior schools across Hampshire and Berkshire took 150 mm of it. It is not what goes onto a cold sheet or a cold soffit. Open-cell system data · Closed-cell system data
05How we check
A sports hall, a kitchen and a classroom hold very different air. The condensation risk analysis is run for the space, not the school; the U-value calculation carries the purlin bridge; the fire strategy decides the coating. The evidence pack goes to the estates file.
Each roof build-up is checked against the temperature and humidity the space actually produces, to BS EN ISO 13788 and, where the case warrants it, a transient WUFI analysis. The depth that keeps the surface above the dew point comes out of this.
How the analysis worksWhere a figure has to be met, the calculation is done for this build-up to BS EN ISO 6946 with the purlin bridge included. HOLVEM supplies the calculation; the assessor holds the compliance position.
U-values and Approved Document LOccupied school space usually carries a reaction-to-fire requirement. The coated NexSeal LE and DC315 system achieves B-s2,d0 to BS EN 13501-1 in the build-up tested; the school's fire strategy decides where it is specified.
Fire performance and coatingsProject recordSchools programme
Not every school roof is a pitched hall roof. Across Hampshire and Berkshire we treated the flat roofs of more than 29 primary and junior schools with 150 mm of open-cell foam, and filled the cavity walls at several, booked to the school calendar and repeated school by school.
What the record states: a flat roof U-value of 0.20 W/m²K and the surface condensation risk eliminated year-round. No metered energy figure was published for the programme, and none is claimed.
At one of the schools. Stoke Park Junior, Shamblehurst Primary, Marchwood Junior and Brockhurst Primary are among the schools named on the record, with more than twenty-five others across the two counties.
Project records
