The Passivhaus Definition
Passivhaus is a standard for housing design developed by Professor Wolfgang Feist of the Passivhaus Institute in Germany. The passivhaus standard sets out a way to reduce energy use for space heating and cooling by 90% compared to a traditional build house.
To meet Passivhaus standard we use software called the Passivhaus Planning Package (PHPP) to enter data specific to the project in question, such as U-values of walls, cold bridging detail and solar gain. Our own PHPP expert, working with our structural designers, can then model the design and give a figure for the energy demand. If this figure is too high to meet the standard, then various scenarios will be suggested to alter the design which would bring it to the standard - for clients wishing for a certified building.
Formally the principle is defined as the total energy demand for space heating and cooling must be less than 15kWh/m2/yr of treated floor area. A standard house uses around 110kWh/m2/yr. As well as this, the total primary energy use for all appliances, domestic hot water and space heating and cooling is less than 120 kWh/m2/yr.
Read More: The ways in which the passivhaus principle minimises heat loss
- Super air-tight envelope (<0.6ach)
- 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.
The advantages living in a Touchwood Homes’ air tight construction
- No conventional central heating system needed, saving substantial construction costs, and of course running costs.
- Minimal heating demand so very low heating bills – it is common for the MVHR system to supply all required heating via 2kW heater
- Stable internal air temperature from heavy weight insulation (typically 6-8 tons of insulation / house).
- Foundation slab inside the thermal envelope so is all used as thermal mass
- Excellent air quality from MVHR unit supplying house with constant filtered fresh air
- No cold draughts inside the home due to air-tight construction
- Very quiet, calm internal space from super dense Cellulose insulation and triple glazed windows
We currently waste a huge amount of energy in the home through poor structural design. The energy demands of heating a new home is seldom given the design priority deserved, meaning that the majority of "new-builds" are thermally inefficient and expensive to run homes. With increasing fuel costs, and concerns over climate change converging, it is time for building design to change.
Read More:Areas of heat loss in a conventional home
Areas of Heat loss
There are three main routes via which heat is lost from the average traditionally built home, which Touchwood Homes recognise must be minimised:
- Poor insulation: there is no point having the heat you pay for conducting straight through the building fabric to heat the sky.
- Draughts: controlling ventilation in the home is vital. Having hot air escaping through draughts in the building fabric, windows and doors looses an enormous amount of heat.
- Cold bridging: Having structural elements passing through the thermal envelope provides a path for heat to be transmitted to outside. Our I beams only have an 8mm web which passes through the external walls, spaced at 400mm, so over the wall area there is minimal cold bridging.
Touchwood Homes are built differently, we design and pre-cut super-efficient structural frames, which our own dedicated build team diligently erect to ensure that they meet the Passivhaus criteria.
Touchwood Passivhaus Homes | Our structural solutions
Our structural solutions
Our timber frames are all made from factory pre-cut "I beams", which allow for any shape of building, and a fast build time. These are then externally sheathed with an air tight, solid TG fibre board over the entire structure, to provide a completely robust, long term air tight solution – much more efficient than the traditional use of sticky tapes and membrane!
|Foundation diagram||Insulation diagram||Eaves diagram|
Cellulose fibre insulation is pumped into the walls. I beams are the only successful way to achieve this – cheaper twin wall systems are impossible to install with cellulose fibre to the required density
We cover the entire external surface of the build with our TG board, mastic sealed at all joints to form a long term robust air tight layer. We do not use cheap tapes and membranes.
Combating cold bridging
I beams have only the 9mm web passing through the structure, so minimal cold bridging occurs.