Building type
A container is a steel box that heats and cools with the day. Bare, it runs with condensation. Closed-cell foam sprayed straight to the corrugated steel gives a dry, sealed shell for the office, workshop, store or home going inside it.
01What is happening
Steel has no insulation and no mass to speak of. A container skin follows the outside temperature within minutes, so on a cold night it falls below the dew point of the air inside and every wall and the roof run with condensation. Fit a board lining and the same water forms behind it, in the corrugations, where nobody sees it until the rust does.
It is not a leak. Water across the whole underside of the roof on a dry cold morning is condensation.
It is not solved by a heater. Warmer air holds more moisture and finds the same cold steel.
It is not solved by ventilation alone. Vents help; only insulation changes the temperature of the steel.
02Recent projects
Installation footage and photographs from HOLVEM's own container projects: conversions and units sprayed to the corrugation before fit-out, walls and ceilings in one continuous layer. Every item is labelled Project record.
03What is applied
The layer is sprayed onto the prepared inside face of the walls and roof, following every corrugation and sealing the seams, corner posts and floor edge. It bonds without primer or fixings and needs no cutting or jointing. The battens for the lining go on after, and the lining sits on a dry, sealed shell.
Schematic / not to scaleKeyed 1 to 5 below
Wall or roof. It stays as the weather line, and its paint and seams are checked first.
Loose paint, rust and residue removed. Adhesion is decided here.
Follows the corrugation and seals the seams. λ 0.027 W/mK is the NexSeal LE product figure.
Wrapped by the application; the lining fixes to battens set after the layer.
Left exposed, coated, or lined for fit-out. Where a fire classification is required the coated system carries B-s2,d0, as tested.
Applications on this building
The problems it answers: Roof condensation Damp and mould Corrosion of metal roofs Summer overheating
04Working around the building
A standard container is a small area and a simple shape. It is prepared, masked and sprayed in one visit, ready for battens and lining. Several containers are done in a run. Where the container is already converted, the work is planned around what is inside.
The box is emptied, loose paint and rust are removed, doors, vents and fittings are masked.
Walls, roof and, where access allows, the floor underside in continuous passes. A standard 20 ft or 40 ft container is usually a single day, confirmed in your specification.
Battens, lining and services go on after cure. Re-entry time and any ventilation needed 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 container is simple, which is why it is worth getting right. The use decides the objective: a dry store needs the steel kept above the dew point; an office or a home needs a U-value and probably a fire classification. The reading is written to the use, and the depth follows.
The steel shell is checked against the temperature and humidity the container will hold in use, to BS EN ISO 13788. For a storage or welfare unit that sets the depth; for a habitable conversion it is the start.
How the analysis worksA container becoming an office, classroom or home carries a target. The calculation is done for this shell to BS EN ISO 6946 with the corner posts and floor edge in it.
U-values and Approved Document LAn occupied conversion often needs a reaction-to-fire classification. The coated NexSeal LE and DC315 system achieves B-s2,d0 in the build-up tested; the lining specification decides what else is needed.
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 container wall. 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.
Want a figure for your building? It takes about a minute.Shell, use, reading, details. A real figure for your container the same working day; nothing sent to anyone else.
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