Metek sustainability statement

Sustainability in the context of construction is presented in terms of various 'metrics' of environmental, social and economic performance. In the UK, BREEAM is widely used for offices, and the Government's Code for Sustainable Homes (CfSH) now replaces EcoHomes that has become the environmental standard for use in the residential sector.
Although voluntary at present, the CfSH will become mandatory in the future. An EcoHomes 'Excellent' rating broadly corresponds to a 3* CfSH rating, which will become the preferred standard for most housing and residential projects.

LIGHT STEEL FRAMING TECHNOLOGY

The technology of light steel framing by Metek uses pre-fabricated 2D panels, and fl oor joists that are produced 'just in time' and delivered to site as required, leading to minimum storage on site. They are light enough to be manhandled into place and the panels are screw-fi xed to each other using simple hand operated power tools.
The accuracy of the manufacture is guaranteed by the FrameCAD design and detailing package, which is linked to the industry-standard detailing system, X-Steel, that contains the whole building model. Therefore, detailing and manufacturing errors are eliminated and all components fit together with minimum tolerances.
The sustainability assessment of this technology is presented below in terms of various key performance indicators that link to environmental criteria in the Code for Sustainable Homes.

ENERGY AND CO2

The primary use of energy over the building's life is its operational energy due to heating (and in some cases cooling). Low U-values of less than 0.2 W/m2°C can be achieved by 'warm frame' construction in which the majority of the insulation is placed externally to the light steel frame and is supplemented by mineral wool placed between the light steel members.
Steel framed buildings can be designed to be very air-tight, with a leakage rate of less than 2m3/m2/hr, which would otherwise be a source of unwanted heat loss.
The operational energy of a house is 10-15 times more than the embodied energy in its materials over a 50-year design life span.
However, light steel framing compares well with concrete or brick/blockwork construction in terms of low embodied energy (see Table 1).
The embodied energy of a light steel frame is estimated to be 26% less and the carbon footprint 57% less than that of a concrete frame with blockwork walls (excluding the cladding and fi nishes which are common to both). Where required for higher-rise applications, a composite fl oor supporting light steel infi ll walls is estimated to contain 2% less embodied energy and 24% less in terms of carbon footprint than a concrete frame.

MATERIALS

Light steel framing is by its nature lightweight, and the light steel structure of a medium-rise residential building can weigh less than 20% of that of an equivalent concrete frame (see table on back page), and is even lighter than a timber frame. Other lightweight materials used in this technology include various types of boards and insulation.
Savings in foundation sizes can be significant when the low weight of the light steel framework is taken into account, which is very important on 'brown-fi eld' sites and poor ground, where concrete in foundations can be reduced by up to 50% relative to brick and blockwork.

WATER

The construction technology is essentially 'dry' and minimal water is required in manufacture.
Where a thin Gyvlon self-levelling screed is used, its water content is about 10%, which is held in the matrix of the material.

WASTE

Waste in traditional construction arises from various sources:

• Over-ordering to allow for site variations
• Damage and breakage and losses on site
• Re-work due to errors and inaccuracies
  

According to BRE, the construction industry average for material wastage on site is 13%.
In comparison, waste is essentially eliminated by light steel framing manufacture and installation. All off-cuts and drill swarfs are fully recycled in the factory and site wastage is recycled. Nationally, 98% of all steel is recycled after use and 50% of current steel manufacture in Europe comes from recycled steel (scrap). No steel is sent to landfill.

POLLUTION

Pollution on site is eliminated when using light steel technology, and all steel can be recycled efficiently after dismantling. Transportation of materials to site is reduced by 70% in comparison to brick and block construction, with a consequent reduction in traffic pollution.

Comparison of the embodied energy and carbon footprint of a typical 4-storey apartment building based on 4.5 m span and 2.8 m floor-floor height, excluding the cladding and finishes.

*200 mm flat slab

The embodied energy and CO₂ data are taken from published sources and include appropriate recycling rates for the various materials. Account may also be taken of the energy used in vehicle movements and in equipment used on site, which will further benefit the use of pre-fabricated construction technologies.