Building type
Plant, product, people and process moisture under a cold steel sheet. Closed-cell foam applied from below, one zone at a time, with the rest of the floor running.
01What is happening
A factory puts more moisture into the air than a store does: wash-down, drying, curing, cooking, breathing people and open doors. On a cold morning the roof sheet sits below the dew point of that air. Water forms across the underside and drips onto machinery, finished goods and electrical gear. It looks like a leak. It is condensation.
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 sheet.
It is not always condensation. Water at a lap, a fixing or a rooflight during rain is ingress, repaired first, by someone else.
02Recent projects
Installation footage and photographs from HOLVEM's own industrial projects: roof undersides and walls sprayed in continuous passes, an MOT bay, a piled wall, and an interior finished for year-round use. Every item is labelled Project record.
03What is applied
The existing sheet stays as the weather line. The layer is applied from below in passes, closes the side laps and wraps fixings and purlin flanges. Metal-clad walls take the same layer from inside. The purlin continues through and remains a thermal bridge; the calculation accounts for it.
Schematic / not to scaleKeyed 1 to 5 below
The weather line, and it stays. We do not replace it and we do not make it watertight.
Loose coating, corrosion product and process residue removed. Adhesion is decided here.
Follows the profile and closes the side lap. λ 0.027 W/mK is the NexSeal LE product figure.
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. Uncoated, that classification does not carry.
Applications on this building
The problems it answers: Roof condensation Heat loss and thermal performance Corrosion of metal roofs Rain noise and acoustics
04Working around the building
Only the area under the work is released. Plant is sheeted or moved, the spray zone is contained, the layer goes on from below and the zone is handed back. On a busy floor the clearing is the real constraint, not the spraying.
Nights, weekends and shutdowns where the process allows. Zones are agreed with your production manager before anyone arrives.
Machines, panels and product under the spray zone are sheeted or moved. Extraction and containment keep overspray inside the zone.
Masking down, floor cleared, zone returned before the next shift. The roof above was never opened.
Re-entry time for the treated zone, and any ventilation needed during cure, are set out in the method statement for your unit.
05Enverge 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 for different objectives: hybrid build-ups, sound absorption, or where the layer has to breathe. It is not what goes onto a cold sheet or a cold soffit. Open-cell system data · Closed-cell system data
06How we check
A factory's moisture load is the input, not an afterthought. The condensation risk analysis runs with your process in it; the U-value calculation carries the purlin bridge; the fire strategy decides whether the coated system is specified.
The roof build-up is checked against the temperature and humidity your process actually produces, to BS EN ISO 13788 and, where the case warrants it, a transient WUFI analysis. The depth that keeps the sheet above the dew point comes out of this, not off a rate card.
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 rather than ignored.
U-values and Approved Document LOccupied industrial space often carries a reaction-to-fire requirement. The coated NexSeal LE and DC315 system achieves B-s2,d0 in the build-up tested; whether your unit needs it is the fire strategy's question.
Fire performance and coatings07The objective sets the depth
What does the roof need to do? Pick one below and you will see the depth that does it, and just as plainly what it won’t do. Nothing is left to come out later: the survey confirms the right depth for your building.
Four depths, drawn to one scale and measured from the sheet underside. The objective and the calculation set the thickness on your building.
Condensation stops forming on the underside, so nothing lands on what is beneath it. A direction for the survey to confirm, not a specification for your building.
Controls condensation and holds useful heat overnight, so it takes less to bring the building back up in the morning. Confirmed at survey against the building's use and heating.
For heated, chilled or temperature-controlled areas where a figure has to be proved. The target sets the depth: a contract-specified 0.18 W/m²K has needed 135 to 140 mm on a concrete deck and on live retail soffits.
Where the specification requires a reaction-to-fire classification, the DC315 intumescent coating is applied to the cured layer. The foam depth under it depends on the scope and what the building has to achieve. B-s2,d0 to BS EN 13501-1 belongs to the coated NexSeal LE and DC315 system as tested: 35 to 40 mm of NexSeal LE on 9 mm plasterboard with DC315 at 0.7 mm wet film thickness (BTTG report 27/06638/12/24), confirmed for each project against the fire strategy. Uncoated, the layer carries Class 1 surface spread of flame to BS 476-7, which is not a Euroclass.
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