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Inside the TJW Grab Hire warehouse after the work: the box-profile steel roof and purlins under a continuous cream closed-cell layer, the polycarbonate rooflights left clear, vehicles parked below.
Project recordThe roof, after

Project record · Metal roof underside

TJW Grab Hire, Bournemouth: a 505 m² metal roof that stopped dripping on the lorries.

A box-profile steel roof in good condition over a grab-hire business's warehouse. Uninsulated, it ran with condensation, swung with the weather and dripped onto the vehicles and equipment beneath it. We sprayed 50 mm of NexSeal LE closed-cell to the underside, left the polycarbonate rooflights clear, and handed the building back after two working days.

≈505m²
Roof treated
50mm
Closed-cell, from below
2 days
On site
Clear
Rooflights left uncoated

01The building

A good roof doing one thing badly.

The roof was not the problem. The sheet was sound, the fixings were tight, and nothing was leaking. What it did badly was keep the inside of the building apart from the weather: bare steel above lorries, plant and a working yard, running wet every cold morning.

Condensation, not a leak. Vehicles come in wet and warm. Overnight the air inside cools, meets a sheet that is colder still, and the moisture lands on it. In the morning it drips: onto cab roofs, onto equipment, onto the floor. It looks like a leak and is not one.

Temperature swings. With nothing between the inside and a metal skin, the building was as warm as the weather and no warmer. Heat put in overnight was gone by morning.

The brief. Stop the drips, hold some warmth, keep the daylight from the rooflights, and do it in the shortest window a working yard could give up.

Building
Warehouse and vehicle store, grab-hire business
Client
TJW Grab Hire
Location
Bournemouth, Dorset
Roof
Metal box-profile sheet, in good conditionKept as the weather line
Area
About 505 m²
Application
50 mm Enverge NexSeal LE closed-cell
Rooflights
Polycarbonate, left uncoated
On site
Two working days

02What we specified, and why

50 mm closed-cell to the sheet: condensation stopped, heat held, daylight kept.

Condensation control alone is a 25 mm job. This building also wanted to hold warmth overnight, so the layer went to 50 mm, the band that does both. The rooflights were the customer's call, and the call was daylight.

  • The system: Enverge NexSeal LE closed-cell, at 50 mm. Sprayed directly to the underside of the box-profile sheet, following the profile into every trough and over every purlin. At 50 mm the layer controls condensation and holds useful heat overnight. How thickness follows the objective.
  • Why closed-cell on metal. It bonds to the steel and sets rigid, so the sheet is no longer the surface the inside air meets. NexSeal LE declares a water vapour resistance factor (μ) of 62 to BS EN 12086, which we use in condensation-risk analysis to BS EN ISO 13788.
  • The rooflights, left clear. Where a client prefers rooflights sprayed, we prime them first. Here the polycarbonate rooflights were masked and left uncoated, so the yard keeps its daylight and the layer stops cleanly at each one.
  • Why from below, in two days. The roof is sound, so there was nothing to do from above. Working from inside, from a scissor lift, with the vehicles sheeted, the whole roof was done in two working days.
Product
Enverge NexSeal LE, closed-cell
Depth
50 mm
Substrate
Metal box-profile sheet, underside
Rooflights
Polycarbonate, masked and left clear
Thermal
λ 0.027 W/mK aged, BS EN 14315-1 (product figure)
An installer in full protective equipment on a scissor lift spraying closed-cell foam onto the underside of the box-profile roof, the cream layer growing across the sheet.

The layer going on. From the scissor lift, in passes, the sheet disappearing under a continuous cream layer. Project record.

Photographs · Project record

Before, during and after, in two days.

The bare sheet, the layer going on from the scissor lift, and the finished underside with the rooflights left clear.

Before: the underside of the bare box-profile steel roof, purlins and fixings exposed, rooflights along the slope.
Project recordBefore: bare sheet
Before: the unit interior with vehicles and equipment beneath the uninsulated roof.
Project recordBefore: the floor
During: closed-cell foam being sprayed to the roof underside from a scissor lift, polythene over the equipment below.
Project recordDuring: from the lift
After: the roof underside in a continuous cream closed-cell layer, the polycarbonate rooflights left clear.
Project recordAfter: rooflights clear

Photographs from the job, as it ran. Labelled Project record because they are.All project records

03How the work ran

Sheet the lorries, lift, spray, hand back.

A two-day job because the building let it be one: sound roof, clear floor once the vehicles were sheeted, and a single scissor lift reaching every bay.

  1. Survey

    The sheet read from inside.

    Profile, purlin spacing, rooflight positions and the places water was landing. The 50 mm depth set against the objective: condensation plus overnight warmth.

  2. Protection

    Polythene over everything that stayed.

    Vehicles and equipment sheeted in heavy polythene, the rooflights masked, lighting and services covered.

  3. Application

    From the scissor lift, in passes.

    NexSeal LE sprayed directly to the metal to 50 mm, bay by bay, wrapping purlins and stopping cleanly at each rooflight. An electric lift, so no fumes in a closed building.

  4. Hand-back

    Day two, finished.

    Sheeting down, floor swept, building back in use. What was applied, where and at what depth, recorded.

04The outcome

Dry lorries, a warmer building, daylight kept. Two days.

Reported by the customer after the work, in their own terms. No figures were metered and none are published.

Condensation

Stoppedas reported

The customer reported the condensation eliminated: nothing forms on the layer, so nothing drips.

The building

Warmer, drieras reported

A steadier interior that holds some of the warmth put into it.

Daylight

Keptrooflights clear

The polycarbonate rooflights left uncoated, the layer stopped cleanly at each.

Time on site

2 daysworking days

About 505 m² from a single electric scissor lift, vehicles sheeted beneath.

Where this record comes from

Reported, not metered by us. No temperature or energy readings were published for this building; the result is the customer's report.

Yours will differ. A different sheet, use or depth gives a different result. How we run a condensation risk analysis.

05Where this record leads

If this looks like your roof.

The building type, the method this roof was treated under, and the problem it started from.

Your next step

Your building.
Your brief.
A specialist.

If you already know the U-value or thickness you need, tell us and we price to it. If you do not, tell us what you know about the building and the problem, and we work it out with you. Someone who does this every day reads it and comes back to you.

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Or pick up the phone

Telephone . Before 3pm on a working day, you are contacted the same day. After 3pm, the next working day. A commitment to contact, not a quotation.

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