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Inside the hangar sound stage after the work: the whole corrugated roof and its steel trusses under a continuous pale open-cell layer, the stage floor cleared below.
Project recordThe finished roof

Project record · Aircraft hangar · Hybrid build-up

Black Hangar Studios: a 4000 m² hangar roof made quiet enough to film under.

An aircraft hangar in Alton, Hampshire, working as a film sound stage under a corrugated asbestos-cement roof that drummed in wind and rain. In April 2021 the roof was sealed from below with 25 mm of NexSeal LE closed-cell and built up with 150 to 200 mm of SucraSeal open-cell. Three weeks on site; the sheet never touched from above.

4000m²
Hangar roof treated
2 foams
25 mm closed-cell base, 150 to 200 mm open-cell over it
3 weeks
On site
2021
April

01The building

A sound stage under a roof that made its own soundtrack.

A hangar is a good sound stage: huge, column-free, dark when you want it. This one had the wrong roof for the job. Corrugated asbestos-cement sheet, fragile and uninsulated, drummed and resonated in every gust and every shower, vibrated on its fixings, and let the heat go.

The noise. Rain on 4000 m² of thin cement sheet is not background. It stops a take. Wind set the sheets humming on their hooks. For a studio, that was the whole problem in one sentence.

The sheet. Asbestos-cement is not walked on, drilled or removed if there is any way to avoid it. Stripping a roof this size means licensed work, scaffold, downtime and a great deal of regulated waste. The roof had to stay, and it had to stop moving.

The brief. Bond and seal the fragile sheets in place, take the drumming out, bring the thermal performance up, answer the fire requirement for the space, and do it without closing the studio for longer than necessary.

Building
Aircraft hangar used as a film sound stage
Client
Black Hangar Studios
Location
Alton, Hampshire
Roof
Corrugated asbestos-cement sheetKept in place; nothing cut or removed
Area
4000 m²
Application
25 mm NexSeal LE closed-cell base150 to 200 mm SucraSeal open-cell over it
Date
April 2021
On site
Three weeks

02What we specified, and why

A closed-cell skin to hold the sheet, and open-cell depth to swallow the sound.

Two foams in two roles. The closed-cell went on first, thin and rigid, to bond the sheets and seal them. The open-cell went over it, deep and soft, to give the thermal depth and the mass that stops a roof ringing.

  • The base: Enverge NexSeal LE closed-cell, at 25 mm. Sprayed directly to the underside of the asbestos-cement, it bonds to every sheet, lap and fixing and sets rigid, so the sheets stop vibrating on their hooks and the fibres are sealed in. At 25 mm it is a seal and a condensation-control layer; the depth comes from the next layer. Fibre-cement encapsulation.
  • The depth: Enverge SucraSeal open-cell, 150 to 200 mm. Soft, vapour-open and fast to build in multiple passes, it filled the roof to depth around the purlins and trusses. Open-cell absorbs airborne sound within the layer: in laboratory tests to BS EN ISO 10140, 150 to 300 mm of SucraSeal improved the sound reduction index of a blockwork wall by about 3 to 5 dB, mainly at mid and high frequencies. Here its job was to take the drumming out, and the studio reported that it did. Open-cell system data.
  • Why not one foam. Closed-cell alone at this depth would have been a heavy, costly rigid layer; open-cell alone would not have bonded and sealed the fragile sheet. The hybrid gave each layer the job it is good at.
  • What we do not claim. The foam does not add structural strength to the roof. It bonds and seals the sheets and stops them moving; the structure is the hangar's own.
Base layer
Enverge NexSeal LE closed-cell, 25 mm
Build-up
Enverge SucraSeal open-cell, 150 to 200 mm
Substrate
Corrugated asbestos-cement sheet, underside
Access
Scissor lifts across the stage floor
Detail of the finished hangar roof: the pale open-cell build-up over the closed-cell base, following the corrugations and wrapping the steelwork.

The two layers in place. The closed-cell base against the sheet, the open-cell depth over it, the steel wrapped where it passes through. Project record.

Photographs · Project record

Before, during and after, on the stage floor.

The bare sheet, the closed-cell base going on, the open-cell build-up over it, and the finished roof. Taken as the work ran, over three weeks in April 2021.

Before: the underside of the corrugated asbestos-cement roof inside the hangar, grey sheet on steel purlins and trusses.
Project recordBefore: the sheet
Before: the hangar interior prepared for the work, the stage floor cleared and the roof bare above.
Project recordBefore: stage cleared
During: the first closed-cell layer on the corrugated sheets, a thin rigid skin bonding and sealing them.
Project recordDuring: closed-cell base
During: open-cell foam being built up in passes over the closed-cell base, the depth growing across the bays.
Project recordDuring: open-cell build-up
After: the completed roof under a continuous pale layer from eaves to ridge.
Project recordAfter: completed
After: the finished build-up in detail, both layers following the profile and the steel.
Project recordAfter: detail

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

03How the work ran

Three weeks on the stage floor.

Scissor lifts across a cleared stage, the base layer first across the whole roof, then the open-cell built up in passes, then a full inspection for uniform coverage before the studio took the floor back.

  1. Survey

    The sheet, the steel and the schedule.

    Sheet condition and fixings, the truss and purlin geometry the layers would follow, and the studio's own programme, so the three weeks landed where they hurt least.

  2. Base layer

    Closed-cell to every sheet.

    NexSeal LE sprayed from scissor lifts to the underside of the asbestos-cement across the full 4000 m², bonding and sealing the sheets before any depth went on.

  3. Build-up

    Open-cell in passes to 150 to 200 mm.

    SucraSeal applied over the cured base in multiple passes, filling around purlins and trusses, the depth read as it grew.

  4. Inspection

    Uniform coverage, then hand-back.

    The whole roof inspected for coverage and depth, the floor cleared and the stage returned to the studio.

04The outcome

The drumming gone, the sheets still, the roof kept.

Reported by the studio in its own terms, immediately after the work. The acoustic result is a report, not a measurement; the stability of the sheets is what bonding does.

Rain and wind on the roof

Virtually goneas reported

The studio reported an immediate acoustic improvement: drumming and resonance from rain and wind virtually eliminated.

The sheets

Bonded and stillsealed in place

Every sheet, lap and fixing enclosed in the closed-cell base; nothing cut, lifted or removed.

Thermal depth

150 to 200mmopen-cell

A deep vapour-open layer over the sealed sheet, across the full roof.

Time on site

3 weeksApril 2021

Across 4000 m² from scissor lifts, with a full inspection before hand-back.

Where this record comes from

Reported, not measured by us. No sound-level readings were published for this roof; the acoustic result is the studio's account, and the laboratory figure above is the product's, on a different construction.

No structural claim. The foam bonds and seals the sheets. It is not a structural repair and we do not describe it as one.

05Where this record leads

If this looks like your building.

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

Your next step

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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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