Touchwood Fact Finder

Fact Finder

Code for Sustainable Homes (CSH)

To push forward the efficiency of new build houses in the UK the government introduced the Code for Sustainable Homes which became a mandatory rating for new homes from May 1st 2008. The code measures the sustainability of a new home using 9 categories such as energy efficiency, use of materials and water efficiency. All houses can then have a 1-6 star rating to express the overall sustainability of a new home, with code level 6 being the best rating. The Code replaces the previous eco-homes rating system.

The CSH has been criticised by some eco-home designers and builders, with some arguing that the Passivhaus approach holds up better as a framework guide to constructing a low energy building.

The passivhaus approach is fundamentally about minimizing energy losses within the building fabric through insulation and air-tight construction. The CSH is wider ranging, covering building design, water usage, garden space and renewable energy devices such as wind turbines and PV. Ultimately, priority one is to make the building consume as little energy as possible (by building to passivhaus principles), then PVs and wind turbines can be added to produce the small amount of energy required on site. Simply bolting renewable energy products onto a poor building is the wrong approach. The AECB carbonlite standard is based around the Passivhaus principles, and passivhaus is also endorsed by the Green Building Store. Passivhaus design principles are the ones Touchwood adhere to.

If you would like to know more about this, why not call us on 01279 506189
or email us on sales@touchwoodhomes.co.uk

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Glulam beams
Glulam, also known as glue laminated timber is an engineered product using structurally graded timber laminations. These may be in Redwood, Larch, Douglas Fir or more usually Scandinavian Whitewood.

Each lamination is end jointed to allow production of beams to any length and size – subject to your structural loadings. Glulam beams create an excellent visual feature in any building, we often have exposed Glulam posts in our builds to create a great feature that shows off the structure of the house.

If you would like to know more about this, why not call us on 01279 506189
or email us on sales@touchwoodhomes.co.uk

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"I" Beams
Instead of using conventional solid timber, we use “I” beams, so called due to their profile in the shape of the letter I. The beams consist of two 50mm x 50mm flanges connected by a web made from fibre board.

‘I’ beams have many advantages over simple solid timber:

lightweight minimal timber use

web made from wood waste and water

Static -will not twist and warp like solid timber

thick walls and roofs are possible -essential to achieve super insulation

web provides minimal thermal bridging.

We have worked with ‘I’ beam construction houses for 16 years and have developed the skills and design experience to utilise them to full effect. Using our pre-cut frame method, a complete ‘I’ beam structure can be supplied to site with all structural timber pre-cut and numbered ready for efficient on-site build time. This technique avoids the need for carpenters to spend time on site deciphering architects’ drawings -we have done that already. Simply nail each item in place as indicated on the simple instructions for a trouble-free construction.

If you would like to know more about this, why not call us on 01279 506189
or email us on sales@touchwoodhomes.co.uk

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Micro generation
Micro generation refers to devices such as PV and wind energy system that can produce electricity on site. These are most commonly grid connected devices where excess power is exported and sold to the national grid. Touchwood are local dealers for Segen, performing site surveys for PV and wind installations.

As a company we would normally recommend PV in a built up environment where the wind speed is too low for wind energy to be effective. In rural areas though on a good site, wind energy can be very good. We would recommend installing a system no smaller than the Skystream 1.8kW (with a 3.7m diameter blade) – since due to the non linear relationship between blade diameter and energy capture, any turbine with blades smaller than this we feel would not make a significant contribution to a household’s energy use.

If you would like to know more about this, why not call us on 01279 506189
or email us on sales@touchwoodhomes.co.uk

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Passivhaus

Passivhaus is a standard for housing design developed by Professor Wolfgang Feist of the Passivhaus institute in Germany. The overall ambition to the standard was to set out a way to reduce energy use for space heating and cooling by 90% compared to a standard house. The standard formally sets out the criterion for this so that a dwelling can be certified as being Passivhaus.

To meet the standard, software called the Passivhaus Planning Package (PHPP) is used to enter full details of the project in question – such as U values of walls, cold bridging details, solar gain etc. Touchwood Homes have our own PHPP expert who working with our designers ensures our projects meet the criteria.

The principle minimises heat loss in these main ways;

Excellent levels of insulation

Minimal cold bridging in the external frame

Excellent levels of air tightness

Controlled internal air quality by mechanical ventilation system

Clever design of solar gain and summer shading to maximise winter heat gain from the sun.

Use of low energy household appliances and lighting.

Formally the principle is defined as the total energy demand for space heating and cooling is less than 15kWh/m2/yr of treated floor area - a standard house uses around 110kWh/m2/yr. The total primary energy use for all appliances, domestic hot water and space heating and cooling is less than 120 kWh/m2/yr

Construction Issues

A particularly important aspect to meeting the standard is extreme attention to detail on site during construction. For example to achieve the air tightness specification demands no worker on site cuts corners – inspection of work and attention to detail are critical to avoid breaks in the air-tight layer. Good detailing around windows and doors is also vital to avoid drafts going right through the building fabric. Small breaks in the external air tight layer means cold air can pass straight through. This also makes the insulation ineffective.

Recent research published in the green building magazine has shown how important an external air tight layer is - a 300mm thick wall packed with insulation exposed to a 2.5m/s wind speed (very low) would make the insulation 35% less effective. The key to making insulation work effectively is to stop any air movement through the insulation, which can occur in two forms, ‘open loop’ and ‘closed loop’.

Open loop air movement occurs when air from outside can travel straight through the insulation – a movement type successfully stopped through the use of an air tight layer. Closed loop air movement is when the air moves within the insulation through convection currents. This also makes the insulation in-effective since the air movement transports heat through the insulation. Our solution to closed loop convection currents is to insulate with Warmcel insulation, installed to a density of 50kg/m3. At this density air movement no longer occurs within the insulation layer – a solution which is impossible to achieve with conventional Rockwool type insulation.

Cold bridging is another aspect that has to be on the mind of anyone working on the timber frame during construction – otherwise mistakes will be made such as using metal brackets which could conduct heat straight through the building fabric. It is practical solutions such as these that make our houses perform well – everything has to be installed with attention to detail.

Tests on our houses have shown the success of our approach – our recent project in Essex achieved ecohome achieving an air tightness figure of 0.47 m3/m2.hr @50Pa (passivhaus stipulates a figure less than 1.0). When this level is achieved along with super insulation, there is no longer a need for a conventional heating system - the minimal heating demand can be met by a system integrated into the house ventilation unit.

If you would like to know more about this, why not call us on 01279 506189
or email us on sales@touchwoodhomes.co.uk

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U values
A U value is a measure of the rate of heat loss through a material. The smaller the number, the greater the insulating properties of the material. Each element of the build is given a U value, such as walls, roofs, glass, and the whole window element. Care has to be taken here to ensure the U value quoted for a window is that of the whole unit, not just the glass since complete windows with low U values are harder to build and require thermally broken frames. Some example U value figures are given here:

Walls

Wall building regs. 0.30

Pitched roof – building regs. 0.16

250mm touchwood I beam wall 0.16

300mm touchwood I beam wall 0.14

350mm touchwood I beam wall 0.12

400mm touchwood I beam wall 0.10

(TW roof build up is the same as walls)

windows

Single glazed window 5.70

Double glazed window 2.80

Passivhaus Touchwood window 0.79

If you would like to know more about this, why not call us on 01279 506189
or email us on sales@touchwoodhomes.co.uk

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Warmcel Insulation
This impressive insulation is produced from recycled newspaper resulting in minimal embodied energy - unlike glass fibre insulation. The material is processed into a fine grey fibre after being mixed with Boron fire retardant and is then compressed into 12kg bags at the factory. On site, after plaster boarding, these bags are then fed into our machine which fluffs the material up and pumps it densely into the wall cavity resulting in a solid mass of insulation completely filling the space.

This highly effective result cannot be achieved with glass fibre since it is stuffed into the cavity before plaster boarding - there will always be gaps around the edges acting as a cold bridge. The picture below shows Warmcel installed in a timber frame wall with a conventional looking brick skin. Warmcel also provides a great deal of thermal mass to the structure, stabilising the internal temperature.

If you would like to know more about this, why not call us on 01279 506189
or email us on sales@touchwoodhomes.co.uk

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