Building type
Retail sheds, high street units and the soffits above them. Condensation, cold floors and energy bills, treated from inside out of hours, with the doors open again in the morning.
01What is happening
A retail unit is heated for people all day, with doors that open every minute and a stock room that is barely heated at all. The roof sheet or the soffit above is the coldest surface in the building. On a cold morning water forms on it and lands on stock, ceilings and the shop floor. In a shopping centre it lands on the units below.
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.
02Recent projects
HOLVEM's own record from a regional shopping centre: 3800 m² of soffit above trading units, closed-cell foam at 140 mm in three passes, condensation above the units eliminated and the centre trading throughout. Labelled as it should be: Project record.
Project record
Condensation above trading units eliminated, engineered to 0.18 W/m²K, with the centre trading throughout.
03What is applied
On a retail shed the existing sheet stays as the weather line and the layer is applied from below, closing the side laps and wrapping the purlins. On a centre or an undercroft the layer goes onto the concrete soffit above the unit. Either way it is one continuous bonded layer with nowhere for condensation to start.
Schematic / not to scaleKeyed 1 to 5 below
Profiled sheet or concrete. It stays, and we do not make it watertight.
Dust, loose coating and contamination removed. Adhesion is decided here.
Follows the profile or the soffit. 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 Energy costs EPC, MEES and compliance Damp and mould
04Working around the building
Trading does not stop. The work is phased by unit or by zone, after close, with stock and fittings under the spray zone sheeted or moved, and the area cleaned and handed back before the doors open. A centre is treated the same way, one soffit zone at a time.
Nights and closed days where the unit allows. The programme is agreed with the store manager and, in a centre, with centre management.
Shelving, tills, fittings and stock under the spray zone are sheeted or moved. Containment keeps overspray inside the zone.
Masking down, floor cleaned, zone returned before trading. Ventilation during cure and re-entry time are set out in the method statement.
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 shop's moisture load comes through the door with the customers. The condensation risk analysis runs with the trading pattern in it; the U-value calculation is done for this roof or soffit; the EPC position is checked with the assessor before anyone promises a band.
The roof or soffit build-up is checked against the temperature and humidity the unit actually runs at, 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 purlins or beams included. A contract-specified 0.18 W/m²K on live retail soffits needed 140 mm; that is a record, not a promise for your unit.
U-values and Approved Document LInsulating the roof usually improves the rating; by how much depends on the whole building, and the assessor holds that position. HOLVEM supplies the calculation and the evidence pack the assessor needs.
EPC, MEES and compliance07The 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 deck. 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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