Nov 14, 2014

Cut your pattern according to your fabric

How to maximise the cost effectiveness and performance of any build, by John Smith - Head of Technical at Stewart Milne Timber Systems.

As we in the construction industry continue to enjoy a rise in demand for our services, maintaining profitability while complying with increasingly ambitious energy and carbon performance targets is critical. 

Taking a fabric first approach to your building projects is the first step in ensuring that you can achieve the highest energy performance possible.  

Fabric first is a design approach to building which emphasises in-built energy efficiency through maximising the thermal performance of the building envelope and ensuring the building elements work together to be as energy efficient as possible.  

It is a great way to maximise cost effectiveness, because energy efficiency is incorporated into the building fabric over its lifetime, and doesn’t need to rely on mechanical or expensive micro renewable bolt-on technologies to achieve higher performance standards.

Although the term indicates otherwise, a fabric first approach is not just about the material used. Instead, the way the building is designed must combine contributing factors of its energy performance for best effect.

Defining the elements of energy efficiency

A building’s energy efficiency is influenced by the three dynamics of U-values, air tightness and thermal bridging – explained below. These elements must all work together to produce a tight, thermally-efficient structure which will last forever, with little maintenance and no moving parts.

The U-value refers to the amount of heat lost through a building element such as a wall, floor or roof; the lower the U-value, the lower the heat loss. In general terms this relates to the amount of insulation used in the fabric. In timber frame construction insulation is placed between the timber studs on the warm side of the home, saving space and maximising the insulation performance, in a dry environment.

Whereas 0.25 is the U-value required for most buildings, we have designed and developed our products to achieve U-values as low as 0.10.

Simply put, air tightness is the measure of how little a building ‘leaks’ air  which leads to heat loss and cold air infiltration from inward  to outward and vice versa. Lower values mean less heat lost, fewer drafts, and less cold air being gained within the building.  ‘Building tight’ requires ventilating correctly to ensure moisture control is appropriately managed and controlled. Stewart Milne Timber Systems’ research and development has developed products which deliver many projects with low levels of air tightness, some as low 0.6 to meet passive-haus standards, providing exceptional performance.

Thermal bridging can be defined as heat loss through a component or junction. This often occurs at junctions such as corners, floors levels, and around apertures and roofs. The lower you can make your thermal bridging, the less heat loss will occur, ensuring there are fewer ‘cold spots’ in the building fabric. Our timber systems take this into account and have been specifically engineered to reduce heat loss where it matters most.

As an example, our closed panel Sigma II Build System can help achieve a thermal bridging value as low as 0.02, due to its unique C-stud framework, which reduces heat loss through the stud by approximately 70%.

Building material

In addition to the above elements, the material you actually use to build with can affect performance as well. Timber, for instance, can reduce a building’s energy impact by 33 %, bringing down its overall heating costs. As an entirely sustainable and renewable building fabric, timber also has the lowest embodied carbon level of any commercially available material.

Combining these benefits with the advanced technology of our build systems, timber frame can also provide reduced costs and improved return on investment. This is because of the increased speed of build and reduced onsite labour requirements which timber systems allow.

In addition, timber frame and prefabrication simplifies the construction processes on site, reducing the likelihood of defects and poor fabric performance arising. There is less site supervision and interfaces between trades, which means quality and confidence in the building performance is built in as you go, and not reliant on supervision and disparate trades. This is an important consideration, as regulation is now considering design versus as-built performance to ensure there is no room for a performance gap to arise from the design intention.

In fact, the offsite construction element of our products means that entire building projects can be designed, manufactured and erected onsite within a matter of weeks.  For example, we have erected 140 homes within 12 months for Miller Homes in Edinburgh; and achieved BREEAM Excellent status to very tight deadlines for a 232 bed, bespoke student accommodation project for Plymouth University.

Benefits of high performance

A fabric first approach using timber frame will take the above elements into account to produce, as energy efficient a building as possible. As outlined above, this methodology and outcome will help you maintain cost effectiveness while still achieving exceptionally high quality and built in confidence in the fabric performance of your building.

Buildings designed with a fabric first approach don’t require additional mechanical technologies or systems which are expensive and need to be maintained or replaced, to enhance their energy performance, and don’t rely on the eventual occupants’ behaviour or habits to delivery energy efficiency. They are future-proof and green in perpetuity over the lifetime of the building, omitting less carbon throughout both the build programme and the building’s lifecycle, whilst saving energy in use. This can provide an attractive incentive to potential home and building owners.

By completing your developments faster, while building a reputation for quality and confidence in delivering energy efficient buildings, you will likely be able to improve cash flow, reduce  costs and develop your brand.  All this will help you to maintain profitability while complying with building regulations – a real win-win in anyone’s book.

Homes For Scotland Home Builders Federation National House-Building Council Royal Institute of British Architects Structural Timber Association Constructionline British Board of Agrement Wood Campus Build Off Site Building Research Establishment WOOD FOR GOOD

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