Why single envelope construction is driving the design of new warehouses and cold stores

A pioneering, single envelope construction technique using insulated composite panels as the construction medium is changing conventional warehouse design and bringing with it significant savings. Tony Wall, managing director of ISD Solutions comments.

It is important for architects to think beyond insulation for optimal building performance and to look holistically at warehouse or cold store projects.  By bringing together smart design, experience, expert delivery and proven know-how, a cost reduction of up to 20 per cent1 can be achieved whilst delivering virtually airtight, high-performing buildings with low lifetime running costs.

Architects’ design skills are needed to calculate the correct level and type of insulation to achieve optimal thermal efficiency and fire protection (if required).  Other challenges for architects are to ensure that buildings remain virtually airtight while accommodating up to 40mm shrinkage and expansion, with air leakage levels below the guidelines set by the International Association for Cold Storage Construction.

At a time when utility costs are rising, inefficient facilities will need to be replaced or upgraded.  For cold stores, supermarket distribution and logistics companies the energy-saving characteristics and reduced construction costs of insulation have never been so important.

Traditional cold storage warehouses effectively involve the construction of two buildings, one inside the other.  The resulting void between the envelope and the internal cold store roof may require fire prevention, heating/cooling and air-handling, all of which will add to the capital investment.

A traditional build can be time consuming to construct and not particularly sustainable or thermally efficient.

A pioneering, single envelope construction technique using cold store specification insulated composite panels as the construction medium is completely changing conventional warehouse design and bringing with it significant savings to developers and operators alike.

Design efficiency

Careful attention to detail at the design stage ensures optimal performance of the building in the longer term.  A careful assessment of location, wind loadings and temperature cycles is required to ensure warehouse design can safely accommodate normal shrinkage and expansion of up to 40mm and still remain virtually airtight.  It is essential to minimise the effects of ‘thermal bowing’, the physical distortion of wall panels as the exterior metal skin heats up in the sun, while the cold interior face contracts.

With a potential temperature difference of 60 degrees on a hot summer’s day, how the composite panels are fixed in place and the design of junctions, connections and fixings are critical.  A fully-automated high-bay frozen warehouse, operated by Partner Logistics in Cambridgeshire, was designed to operate down to temperatures of – 25 degrees Centigrade.  Containing a staggering 77,000 pallets of frozen food the warehouse, combined with the loading and picking building, required over 36,000m² of composite panels.

Build efficiency

Single envelope warehouses and cold stores can be constructed around 20 per cent faster than traditional builds when using cold store specification composite roof and wall panels.

The inherent strength and spanning characteristics of these modern composite panels significantly reduce the requirement for secondary steel-work, representing a real cost saving.

The panels themselves are made from a low-carbon material.  Another aspect of build efficiency is a high bay design resulting in a much smaller footprint which can reduce land requirements by 4-5 times.

 Significant savings in build cost and maintenance

Apart from requiring lower capital investment at the outset, a single envelope cold storage facility requires an estimated 30 per cent fewer raw materials.  It can also deliver significantly lower long-term running costs than  a traditional build.  This is due to increased thermal efficiency and air tightness of the single envelope, which minimises the need to run duplicate services for a ‘building within a building’.

Fire and safety

The airtightness of a building enables reduced levels of oxygen to be maintained within the envelope, down from 21 per cent to 15 per cent.  This means that personnel can work as normal – but fire cannot sustain momentum, so expensive fire prevention sprinkler systems are not needed.

Where required, steel-faced composite panels can be used in fire wall applications.  Fire separation, between chambers of a warehouse with excellent fire resistance, can be achieved from 60 to 240 minutes.

Good for the environment

Aside from the environmental benefits of a smaller physical footprint, fewer raw materials used in construction, and higher levels of thermal efficiency, the cold store spec single envelope design achieves WRAP and BREEAM targets by using low carbon composite panels with a reduced ‘global warming

potential’ (GWP).  The thermal qualities of these metal-faced composite panels keep temperatures constant and virtually airtight, regulating heat loss and gains to reduce a building’s energy consumption.  Solar PV systems can be incorporated to improve energy efficiency even further, as was the case with Aldi’s new 52,000m2 distribution centre at Goldthorpe, designed to operate 24/7, 365 days a year.

With air leakage regularly achieved at below 0.1m3 per hour per m2 at a pressure of 50 pascals, the building far exceeds 0.5m3 design guidelines set by the International Association for Cold Storage Construction.  These environmental factors significantly improve carbon reporting.

In conclusion, with more cold store specification single envelope projects already underway, there is growing interest across the warehousing, cold storage and retail distribution sectors in these innovative and sophisticated, thermally-efficient, low-carbon storage solutions.