In housebuilders’ offices across the country, the Code for Sustainable Homes (CSH) is a daily conversation. The need to achieve Code levels 3 or 4 is already a reality for any developer working in the social housing sector, and the political drive towards all homes reaching Code level 6 by 2016 – currently defined as ‘zero carbon’ – remains strong.
But get a group of constructors together to discuss how best to reach the higher levels of the Code, and there will be little agreement. The housebuilding industry is crying out for direction and guidance: anything that can help them find low risk solutions that will notch up the necessary Code credits without breaking the bank.
Timber frame designers and manufacturers are asked for their help on this every day. Now their advice and guidance has been published in a new report commissioned by the UK Timber Frame Association (UKTFA) and wood for good.
The Comfort and Cost report is based on the latest technical research for the timber frame industry by ESD and Buro Happold. It explains how credits can be gained in relevant sections of the Code (timber frame scores particularly well when it comes to heat loss parameters and materials credits). It contains information on how to deal with airtightness and thermal bridging, both critical issues for low and zero carbon buildings, and it measures the typical carbon emissions associated with various building methods, including the embodied carbon.
Most important of all in these recessionary times, the report measures the financial costs of compliance, comparing timber frame with traditional construction.
“It’s inevitable that achieving higher Code levels is going to be more expensive, whichever way you build,” said Steven Streets, technical manager at the UKTFA. “You’re paying for a thermally enhanced fabric and a new suite of energy generation and water saving technologies.
“Our research suggests that you should budget for a cost increase of between 8-24% to deliver a Code level 5 timber frame house instead of one that complies with current standards. But if you choose to build in masonry, the additional cost is from 10-30%. And this cost differential between timber frame and traditional construction occurs at all higher levels of the Code, so it really does matter what build method you choose. The percentage cost uplifts to achieve Code compliance for a masonry building are always higher than for a timber frame building.”
Comfort and Cost details the aspects to be considered to achieve thermal efficiency including insulation, thermal bridging, airtightness, solar gain, ventilation, orientation, house type and shape, and new technologies. Success requires a combination of passive and active strategies.
Streets also points to the performance details for an indicative range of timber frame open and closed panel systems in the report which show some potential model specifications for walls, floors and roofs to reach the various heat loss parameters of Code level 3, 4 or 6.
“An efficient fabric is definitely the best place to start,” he said. “Fabric energy efficiency measures can reduce energy consumption in large detached houses by a third, and up to 20% for apartments. The key is knowing how to maximise that opportunity. It is simple to build highly insulated and airtight timber frame homes. This is still the best option of cutting energy use over the annual cycle for the foreseeable future.”
One of the most striking conclusions of the research also tackles the issue of thermal mass. Buro Happold showed that the difference in this area between timber frame and standard masonry will never be a significant factor affecting the occupant’s thermal comfort or the home’s energy consumption, now or within the lifetime of the building. Some element of thermal mass could be useful, but its importance should not be over-exaggerated.
“There are several things that affect home comfort, including external air temperature, thermal insulation, air tightness, solar gain and ventilation, as well as thermal mass, but no one aspect is the killer issue,” said Streets. “In fact, the researchers found that in the comfort or energy consumption of a building, the difference in thermal mass between masonry and timber frame does not matter, even assuming a 60-plus year lifetime of the home and temperature changes likely in that time.”
He added that the UK’s need for well insulated, airtight, thermally efficient and sustainable homes which are responsive to occupants’ lifestyles will outstrip the need for heavyweight buildings with loads of thermal mass.
“It would be a mistake to create a generation of homes with such high embodied carbon and such a heavy need for winter-time heating,” he said.
