More Offsite ... Less Energy

Pressure on the construction industry to improve the energy performance of the new built environment is immense and growing; government measures now being  implemented will only increase the need for reduced energy consumptions and lower environmental impact.  Martin Goss, MD of Offsite specialists Mtech Consult, assesses the role of Offsite in the delivery of an energy-efficient building programme.

 

Whilst the housing sector is still coming terms with the Code for Sustainable Homes, the wider construction community is bracing itself for the forthcoming consultation on new Part L of the Building Regulations and the Code for Sustainable Buildings.  At the same time, more clients, both public and private, are demanding buildings that use less energy.  New Part L is likely to impose a further 25% reduction in energy consumption compared with current regulations and the criteria for air tightness may also be increased.

 

For a sector that historically finds it difficult to respond to rapid change of the type we’re now experiencing, it’s hardly surprising that there’s a lack of certainty about how we should adapt our traditional building methods to meet these new requirements.

 

This is exactly where factory produced building elements can really make a difference.  Change within the factory environment is intrinsically easier to implement and control, where the whole process invariably takes place under the one roof.  For instance, we recently worked on a building element that needed to exhibit reduced air infiltration; it was much easier to reinforce this message across the entire delivery process with the short, in-house communication channels and the immediate ability to inspect and assess progress.

 

In a factory environment, where in-process procedures are established to ensure that production is right first time, every time, it’s possible to eliminate post completion testing and costly remedial works on finished buildings that fail to meet the requirements of the codes...because good quality control will ensure they won’t!

 

Sounds too good to be true?  Well, you do have to get Offsite right, but in our experience, once you do, it delivers genuine benefits for both manufacturers and constructors.  Better performing components and systems are increasingly in demand; their ability to improve the environmental performance of finished buildings is proven fact. 

 

Take insulation for instance.  In traditional construction, where many different activities take place simultaneously across the site, it’s difficult to identify whether all the insulation has been fitted and is in full compliance with the design specification.  Typically it will be covered with finishes that prevent inspection other than with sophisticated forensic techniques.  However, with Offsite factory manufacture, fitting insulation is an integral stage in the production process; standard procedures and quality control systems ensure that the product does not move to the next stage until the insulation is correctly fitted. 

 

Offsite really can achieve 100% compliance.  Mtech recently supported a client through its first ever volumetric module project, achieving zero defects at handover and zero call backs throughout the 12 month defect liability period – a total first for that particular client.

 

Cold bridging is another issue that arises in finished buildings, though obviously not by design.  However, we all know that what appears on architects’ drawings is not always what gets built, particularly where details are awkward or tolerances have not been properly considered.  Before we know it, onsite remedial measures have introduced a cold bridge.

 

But Offsite is a way of building that avoids cold bridging.  In the factory environment, assembly teams are not allowed the ‘luxury’ of a quick fix; if components don’t fit together in the agreed manner, the production process stops until the design or specification issue is resolved and the product can be properly assembled.   

 

Delivering the right level of air tightness is perhaps the most difficult requirement to achieve on site, and yet it can have the greatest impact on energy consumption.  Good air tightness is about the detailing of joints and interfaces within the construction.  It’s possible to control the exact fitting gaps between, say, the window frame and the wall fabric when these two elements are brought together in a factory environment.  When these joints have to be made onsite the opportunity for errors and incomplete details grows considerably; whilst the mastic gun is a saviour for site teams trying to achieve the minimum air tightness test result prior to occupation, this approach is unlikely to deliver a long term air tight building.  Through-life energy consumption is the ultimate aim, not just a temporary “good score” at handover.

 

We’ve helped clients develop well-detailed, factory-produced building envelope systems, ranging from volumetric modular through closed panel systems such as SIPs to advanced timber frame solutions, that can readily achieve air tightness of 1.0m3/m2/hr @ 50 pascals.

 

But possibly the most exciting prospect that factory manufacture of large elements of the final building presents, is the opportunity to consider the building as a whole.  Optimising the complete building as a holistic design offers a far greater chance of achieving required energy consumptions at the lowest cost.

 

And we shouldn’t look at energy consumption without a passing thought on the energy required to produce and install a building.  As we continue to drive down lifetime energy consumption, the embodied energy starts to become more significant.  Offsite can really score here, with reduced waste, fewer transport miles and material substitution to reduce reliance on high energy materials, all very feasible. 

 

Interestingly, this flies in the face of the general perception that somehow Offsite creates lots of CO2 emissions.  Modern factory manufacture is the de-facto lowest cost and energy balance for producing main stream products in all other sectors, so why not construction?