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Interior of a large aircraft hangar at first light, the wide profiled steel roof and deep trusses seen from the apron door, pale daylight across the floor.

Building type

Aircraft hangars: a huge cold roof, and an airframe under every drip.

A hangar is the largest single volume most operators own, heated a little and roofed in thin steel. On a still, cold morning the sheet is below dew point and water lands on wings, avionics and floors. A sprayed layer under the sheet stops that, keeps the clear height, and is specified from a calculation, not a guess.

  • Wide-span steel or asbestos-cement roofs
  • Applied from below, aircraft moved bay by bay
  • 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?

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

Takes about 30 seconds. No contact details yet.

01Why this building

Warm air, thin steel, and an aircraft where the water lands.

A hangar puts open doors, vehicles, a few people and a great deal of air under one steel skin. When the sheet cools below the dew point of that air, condensation forms across the whole underside and drips under the valleys. On an aircraft that means corrosion, paint damage and water in places electrics should never see it. It looks like a leak, and it is not one.

Looking up inside an unheated hangar on a cold morning: fine condensation across the underside of the profiled steel roof between the trusses, a drip line forming under a valley.
The roofBelow the dew point
  • Cold, still mornings. The steel is colder than the dew point of the air beneath it.
  • The whole field of the sheet. Truss to truss, not at one spot.
  • Drips fall under the valleys. Onto whatever is parked there.
Roof condensation: what is happening on the sheet Why it forms, when, and what stops it.

02Recent projects

Wide steel roofs sprayed from beneath: HOLVEM's own footage.

HOLVEM's record on wide-span steel roofs, sprayed from below in continuous passes. Every item here is HOLVEM's own work and carries the label Project record.

Looking up at a pitched steel truss roof sprayed from beneath in a continuous cream closed-cell layer, fluorescent battens hung below the trusses.
Project recordSteel truss roof
Pitched steel truss roof sealed from beneathClosed cell over the sheet, trusses left exposed.
Project recordCoverage check
Metal roof underside, coverage checkedThe applied layer inspected bay by bay.

All HOLVEM project records

03What is applied

Closed-cell foam to the underside, truss to truss, with the height kept.

The existing sheet stays as the weather line. The layer is applied from below in passes, closes the side laps and wraps the fixings. Trusses stay exposed; the layer runs over the purlins between them. Tall access is part of the job: MEWPs and towers, one bay at a time, with aircraft moved out of the bay in hand and back afterwards.

Schematic / not to scaleKeyed 1 to 4 below

The same hangar roof after treatment: a continuous cream closed-cell layer following the sheet between the trusses, the steel trusses left exposed.
AppliedTreated bay
The layer follows the sheet between the trusses. The next bay, still bare steel, is the next week's work.
1 / Existing roof sheet

Profiled steel, or asbestos-cement where it passes a condition survey. It stays, and it is not made watertight by us.

2 / Closed-cell layer, in passes

Follows the profile and closes the side laps. At 25 to 50 mm it takes almost nothing from the clear height.

3 / Trusses and fixings

Purlins are wrapped; the deep trusses stay exposed and remain thermal bridges the calculation accounts for.

4 / The aircraft

Moved out of the bay in hand, never sprayed over. Containment beneath the spray zone.

The build-up in sequence, step by step

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 hangar puts in front of us, and the problems they bring.

Most hangars are profiled steel; older ones on airfields are often asbestos-cement, and some have concrete-framed annexes. Each is its own application page. The problems below are the ones hangar operators usually 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 mmStops the drips onto aircraft and floors; the sheet stays dry.
Retain heat50 mmHolds heat in the volume overnight so there is less to bring back each morning.
Reach a calculated U-value75 mm and aboveA figure to meet for a heated maintenance hangar, calculated with the trusses in it.
Achieve Euroclass BDepth to suit + DC315 coatingWhere the fire strategy asks for a reaction-to-fire classification on the exposed face.

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, from the hangar floor, fitted around aircraft movements. Nothing comes off the roof and nothing stops. It gives us the five things a specification for this hangar has to stand on.

  1. Condensation, or a leak

    Where the water shows, when it shows and what your photographs say. Condensation and ingress look alike from the floor and need different answers.

  2. The sheet, from below

    Profile, condition, fixings and coating. Asbestos-cement passes a condition gate first.

  3. Trusses, cranes and door tracks

    The truss and purlin layout, and the rooflights, door tracks, cranes and services the layer has to stop at.

  4. How the hangar runs

    Doors, heating, aircraft movements and washing down. Together they set the moisture load.

  5. Tall access

    MEWP or tower reach, the bays that can be released, and how aircraft move out of the bay in hand.

What you get after the survey

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

  • A specificationWritten for this roof, 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 roof, in writing. What moves it is explained in the cost guide.

Survey, or photographs?Send photographs of the roof

A firm figure starts with the building. Yours takes a minute to describe.Building, roof, 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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Project records

Work we have done on buildings like this.

All project records
Project recordBlack Hangar Studios, AltonA 4000 m² hangar roof made quiet enough to film under.Read the record Project recordA Nissen hut for Rolls-Royce Motor Cars50 mm of closed-cell to the curve, finished with DC315 coating.Read the record

08Straight answers

Ask us the hard ones.

The questions hangar operators and airfield estate 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 hangar insulation cost?
It depends on the depth, and the depth depends on what you are trying to fix. 25 mm is the condensation control specification and 50 mm retains useful heat as well. The rate falls as the area rises, and a hangar roof is usually a large area. Above 75 mm the depth is set by a U-value target and calculated first. Tall access is priced in, not added later. The cost guide sets out the rates.
Will the layer reduce our clear height?
By its own thickness only: 25 to 50 mm under the sheet, between the trusses. Nothing is hung below the trusses, so door heights and tail clearances are unchanged.
Our hangar is asbestos-cement. Can you still do it?
Often, yes. The sheet passes a condition survey gate first. Where it passes, 50 mm closed-cell encapsulates it in place from below and the roof is retained. Where it fails, we tell you before anything is priced.
Does spray foam help with noise from engine runs?
Closed-cell foam is a thermal and condensation specification. Where sound is the objective, open-cell foam is the different product; HOLVEM installs it and it has its own data sheet. Open-cell system data.
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. You hold the evidence, not our word.

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 hangar, the roof and what is landing on the aircraft; 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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