Single-envelope construction revolutionlising UK warehouse construction

A recent advance, called ‘single-envelope construction’, is set to revolutionise UK warehouse construction, especially for temperature-controlled spaces

Composite panel construction has been around for some time now, and has proven itself as a durable and lightweight alternative to older concrete and masonry construction techniques, all the while offering the UK warehouse construction market much improved insulative and thermal protection properties. A new advance in composite panel construction, called single-envelope technology, now promises to UK warehouseprovide further improved performance and much faster build times. As lengthy construction time can be one of the greatest areas of expense in UK warehouse construction, and substantial reduction in build time can mean an impressive reduction in costs. Maintenance is also said to be easier, and the new technique offers a greatly reduced carbon footprint as well.

Composite panels, sometimes called ‘structural integrated panels’ are made in layers. They include at least one insulating sheet of polymer (plastic) foam enclosed by at least two layers of sheet metal, cement, or wood called ‘structural board’.

They find use in UK warehouse construction as exterior roof and wall cladding and for interior divisions, especially in temperature controlled or ‘clean room’ spaces. A polystyrene and plywood panel type has been in constant use since 1967. The last twenty years has seen a concerted movement to find an alternative that performs at least as well, but offers improved protection from fire and surface fatigue.

Older composite panel technology presents a fire risk for UK warehouses

Polystyrene foam is a wonderful insulator, but is extremely flammable. As a result, these older composite panels chief flaw is their poor resistance to fire. Somewhat ironically, the panels constructed of aluminium or other metals can sometimes be more dangerous than those whose structural boards are wood. If there is any damage or cracking to the metal cladding, the fire can spread to the internal insulating layer where traditional fire extinguishing methods, usually the spraying of water or fire retardant foam, cannot reach the polystyrene core. The result was all too often the destruction of large sections of composite panelling, and occasionally the destruction of entire warehouses or other facilities.

The fact that these panels have been incorporated into so many structures over the last twenty years has not gone unnoticed by safety organisations or insurance assessors, fuelling the search for alternative technologies.

What actual benefits does single-envelope construction offer for the UK warehouse market?

Now, even very large facilities can be skinned with a single later of adhered membrane (the single-envelope), over a steel frame.

This means the entire facility is insulated, and can potentially be air-tight. The facility need no longer contain a separate ‘box in box’ cold storage facility, reducing design and construction costs. Traditionally, a UK warehouse featured a separate cold storage facility which was essentially one building constructed inside another. That requires separate insulation and a fire-prone roof void (which in turn often required its own sprinkler systems). This set up is time consuming and costly to build, and was never terribly thermally efficient.

As a great deal less construction material is needed for a facility of this type, construction costs are greatly reduced. The panels themselves are significantly stronger, and require less secondary steel support. As a result, a few recent examples have reported up to a 20% in construction costs.

Total build time is reduced by a similar proportion. The total programme length is usually only 80% of the build time for a traditional warehouse. Better still, there are fewer individual sub-contractors required, making the programme easier to manage.

A single-envelope warehouse can have a smaller footprint, and less total height, without sacrificing internal volume. You will also experience a great deal more flexibility in placing HVAC equipment. This not only means potentially larger facilities on existing plots, but can make all the difference in getting planning permission.

Overall fire risk is reduced by doing away with the voids in roofs and walls, and easier maintenance of a single skin reduces risk of insulation fires. Nonetheless, the design offers improved thermal performance. In fact, due to the increased thermal efficiency and air tight construction of these facilities, a cold-storage equipped UK warehouse can expect to see reduced operating costs, on the order of 5% for a 50/50 chilled/ambient facility (which can add up to nearly £1million per year for a large UK warehouse), and as much as 14% for a 100% chilled warehouse.

Beyond incremental improvements, single-envelope technology gives the UK warehouse market a few entirely new options

Especially interesting is the fact that these facilities can be made effectively airtight. This allows a few new tricks, including new levels of environmental control. An airtight warehouse can be operated with an oxygen depleted internal atmosphere.

Normal atmospheric oxygen levels are around 20%. What does it mean to run a warehouse or other facility at 15% oxygen? The first good news is that no special equipment is needed. The effect is likened to working at a high altitude. That means your employees can still breathe normally. It does make it a lot more difficult for fires to start, take hold, and spread, though. That means you can spend less on fore control and sprinkler systems, and still get lower insurance rates for improved safely.

There are similar advantages when it comes to protecting against frost and moisture. Let’s face it, this is a pretty soggy place. An airtight building can be kept a great deal drier than one which merely has a good solid roof. The maintenance repercussions are clear, and a drier facility is less expensive to cool.

This is a young technology, but several large UK warehouses have already been constructed using the technique, and if their performance lives up to predictions, we’ll be seeing a lot more in the next few years.


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