Throught this web site we've used a number of technical terms relating to specialist products that you might not have heard of before - here we have given a more detailed explaination of some of the more important ones.
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.
HRV
When creating an airtight house it is vital to control the ventilation by installing a Heat Recovery Ventilation unit. These are designed to remove stale air from kitchens / bathrooms, and replace it with fresh air from outside, which is preheated by the stale air. This results in the air being fresh without losing the heat within the air. Of course in the summer the windows could be left open to provide fresh air, but in the cold winter months this method would lose too much heat / energy from the building. Please see technology page for full details.
"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.
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.
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 detailsdetails and solar gain.
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 draughts going right through the building fabric. Small breaks in the external air tight layer means cold air can pass through making 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 ineffective 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 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.
Solar gain
Gaining heat into the building through the glazed areas is a vital component to a passivhaus. The amount of glazing present on the south facade has to be calculated so that there is enough to provide sufficient heat gain in the winter months without the problem of overheating in the summer.
The diagram shows how the house is designed to bring as much heat in as possible during winter when the sun is low, whilst in summer when the sun is high, large overhangs shade the glass to reduce the heating effect. In a passivhaus where insulation and airtightness are so good, the effect of heat gained from the sun is critical to achieve the desired passivhaus low heating demand of 15kWh/m2/yr.
Thermal store
A thermal store works in a different, much more efficient way than a conventional hot tank. For a hot tank, the tank is filled with water, which is then heated. When a hot tap is turned on this water then arrives at the tap, with cold water replacing it in the tank.
The alternative thermal store is filled with water (plus chemicals) upon install. This water then never leaves the tank. Instead when a hot tap is turned on, cold water is fed directly from the cold main through a loop (coil) within the tank. When this cold passes through it picks up heat via conduction within the pipe then arrives at the tap.
This has substantial advantages over a hot tank - please see technology page for full details
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
| Standard UK Wall building regs | 0.30 |
| Standard UK 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 |
(Touchwood roof build up is the same as walls)
Windows
| Single glazed window | 5.70 |
| Double glazed window | 2.80 |
| Passivhaus Touchwood window | 0.79 |
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. Due to the high pressure installation method of Warmcel it is vital plasterboard fixings are increased in density to our specification to avoid the board being blown off.
This highly effective result cannot be achieved with glass fibre manual installation methods since it is pushed into the cavity prior to plaster boarding - there will always be gaps around the edges acting as cold bridges. The high density pumped installation method of Warmcel ensures a very dense insulation – this cannot be achieved by manually pushing a material into the cavity – a process which will result in low density insulation, suffering from closed loop air movements.
The picture 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.
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. Passivhaus design principles are the ones Touchwood adhere to.