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A row of modular site accommodation units on a UK construction site at dawn, pale grey steel skins and a stair tower, soft daylight.

Building type

Modular and portable buildings: a shallow wall zone that has to do everything.

A modular unit has 60 to 100 mm of wall to insulate, seal and keep dry, on a skin of steel, GRP or plywood that moves with the weather. Board leaves gaps at every stud and every joint. A sprayed closed-cell layer fills the zone to its full depth, bonds to the skin, and gives the module its airtightness in the same pass.

  • Steel, GRP, aluminium or timber skins
  • Applied in the factory or on site
  • From £16/m² + VAT at 25 mm

Same-day estimator

About a minute · no obligation

Step 1 of 4: your building.

Which building is it?

Modular is pre-selected. Change it if yours is different.

Takes about 30 seconds. No contact details yet.

01Why this building

Every stud is a cold bridge, every joint is a leak, and the space is already small.

Modular units live or die on airtightness. A thin skin on a light frame follows the outside temperature, so any warm air that reaches it through a gap in the board condenses there, behind the lining, where nobody sees it until the lining stains. Making the wall thicker is not an option: the floor area is the product.

Inside a stripped modular unit: a thin steel skin on a light steel frame, condensation streaking down the inside of the skin, a bare shallow wall zone.
The skinCold behind the lining
  • A thin skin is at outside temperature within minutes.
  • Board leaves gaps at studs, corners, service holes and every joint.
  • Condensation forms behind the lining, out of sight.
Air leakage and draughts: where the warm air goes Why airtightness is the whole game in a small volume.

02Recent projects

How the work looks: HOLVEM's own footage of walls sealed from inside.

HOLVEM's own installation footage of walls filled and sealed with closed-cell foam. Every item here is HOLVEM's own work and carries the label Project record.

Project recordWalls sealed
Walls sprayed in continuous passesClosed cell, from inside, between the frame members.
Project recordSteel skin
Corrugated steel skin filled from insideThe same method on a container conversion.

All HOLVEM project records

03What is applied

The zone filled to its full depth, bonded to the skin, sealed in one pass.

Closed-cell foam is sprayed into the wall and roof zone from inside, filling it to the frame depth so there is no cavity behind it. It bonds to steel, GRP or timber, seals the sheet joints and service penetrations, and needs no fixings. The lining goes on afterwards. In a factory the sequence is a production step; on site it is a day or two per unit.

Schematic / not to scaleKeyed 1 to 4 below

The same wall zone filled to its full depth with a cream closed-cell layer, the frame members just visible in the surface, ready for the internal lining.
AppliedFull-depth fill
The frame zone filled and trimmed flush, ready for the lining. No cavity, no void, no fixings.
1 / Outer skin

Steel, aluminium, GRP or plywood. Prepared and dry before spraying; adhesion checked on a test area.

2 / Full-depth layer

Fills the frame zone with nothing left behind it. At 0.027 W/mK, 60 to 100 mm does real work in a small zone.

3 / Frame members

The only bridges left. They stay in the calculation and, where a U-value is targeted, they set what the zone can achieve.

4 / Lining

Plasterboard, ply or panel over the cured layer. Where a classification is required on an exposed face, the DC315 coating is applied instead.

Walls: metal-clad, stud and masonry

04Enverge NexSeal LE

The material we spray, and why it matters.

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.

0.027 W/mKThermal conductivity · aged · BS EN 14315-1
Class 1Surface spread of flame · BS 476-7 · uncoated
B-s2,d0Coated with DC315, as tested · BS EN 13501-1
25 yearsWorkmanship warranty, plus the manufacturer’s

HOLVEM also installs open-cell foam. It is a different product with its own data sheet, specified for different objectives: hybrid build-ups, sound, and where the layer has to breathe. Open-cell system data · Closed-cell system data

HOLVEM spray rig van with Enverge NexSeal LE A and B component drums plumbed into the proportioner.
HOLVEM rigA and B on board
The HOLVEM rig · Enverge NexSeal LE A and B components on board. HOLVEM's own photograph.

05Applications and problems

The elements a modular building puts in front of us, and the problems they bring.

A module is walls, a roof and a floor in one small building. The three elements have their own application pages, and the problems below are the ones hirers, fleet owners and modular manufacturers ring about.

The elements

The problems

06Depth

Four objectives. Each one sets the depth.

Start with what the building has to do; that decides the depth. Below is what each depth is for on this building. The survey confirms the right one, and the price follows from your area and access, never the other way round.

ObjectiveDepthWhat that depth is for here
Control condensation25 mmKeeps the skin's inner face above the dew point behind the lining.
Retain heat50 mmHolds heat in a small volume so the heater cycles instead of running.
Reach a calculated U-value75 mm and aboveA figure to meet for a module sold or hired against a specification, calculated with the frame in it.
Achieve Euroclass BDepth to suit + DC315 coatingWhere the exposed face needs a reaction-to-fire classification instead of a lining.

Prices are in the cost guide. A firm figure needs your building, and a coated system is always priced for the project. · Thickness and objective

Want a figure for your building? It takes about a minute.Building, structure, reading, details. A real figure for your building the same working day; nothing sent to anyone else.

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07The survey

Five things we check before anyone talks about depth.

A survey is one visit, in your factory or on site, fitted around production. Nothing is opened up that is not already open. It gives us the five things a specification for these units has to stand on.

  1. Skin material and condition

    Steel, GRP, aluminium or timber, and whether it is dry.

  2. Frame depth and spacing

    They set the zone the layer can fill and the bridges left in it.

  3. Services in the zone

    Cables, pipes and boxes that have to be fixed and sleeved before spraying.

  4. The unit’s use

    Sleeping, office, welfare or plant. Occupancy sets the moisture load.

  5. Where the work happens

    In your factory as a production step, or on site, unit by unit.

What you get after the survey

Five things in writing, whether or not you go ahead.

  • A specificationWritten for this unit, from what we found, with its assumptions named.
  • The depth, and whySet by the objective and confirmed by calculation for the element as built, bridges included.
  • The condensation-risk positionWhether anything will condense inside the build-up, to BS EN ISO 13788 with the BS 5250 climate.
  • The fire positionWhether your fire strategy calls for a classified surface, and the coated or uncoated build-up that answers it. Confirmed against the strategy, never assumed.
  • A firm priceFor your unit, in writing. What moves it is explained in the cost guide.

Survey, or photographs?Send photographs of the units

A firm figure starts with the building. Yours takes a minute to describe.Building, unit, what you are seeing, and how to reach you. A real figure for your building the same working day; nothing sent to anyone else.

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08Straight answers

Ask us the hard ones.

The questions modular manufacturers, hire fleets and site managers actually ask on the call, answered the way the specialist answers them. A question we have not answered? Ask it on the call. No obligation.

How much does modular building insulation cost?
It depends on the depth the zone allows and what the module has to achieve. The rate falls as the total area rises, and for a fleet or a production run that is what moves the number. Where a U-value has to be met the depth is calculated and priced per project. Send the unit and we ring you the same working day.
Will the foam add weight to a unit that is craned?
Closed-cell foam is light, and the weight for the depth specified is taken from the product data sheet. It is usually lighter than the board and membrane it replaces, and it is bonded, so nothing shifts in transit.
Does it move with the skin when the unit is lifted and towed?
The cured layer is rigid but bonded across the whole skin, so it shares load with it rather than fighting it. Adhesion is proved on a test area before the run starts.
Do we still need a vapour control layer?
Closed-cell foam at the depths used in a module is its own vapour control; that is the point of it. Whether any additional membrane is needed is answered by the condensation risk analysis for your build-up, not assumed.
How do you prove it was installed correctly?
Applied thickness checked and recorded, coverage logged, all compiled into a QA evidence pack handed over at completion. For a production run, per unit.

The next step

Your building.
Your brief.
A specialist.

If you already know the thickness or U-value you need, we price to it and confirm it is right; if not, we work it out with you. Tell us the skin, the frame depth and how many units; the estimator takes about a minute. “Not sure” is a useful starting point.

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Or call . Enquiries received before 3pm on a working day are contacted the same day. After 3pm, the next working day. A commitment to contact, not a quotation, a survey or a price.

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