Chewton Mendip
A very interesting terrace of three houses, on a curved road junction, has recently been completed in this Somerset village.
Some of the main features of the design are as follows:
- Very high insulation levels provided by insulated concrete forms (ICF) with added exterior face insulation
- Structural insulated panel (SIP) roofs
- Eco-slab ground floors and upper floors of expanded polystyrene rib and slab formwork with cast reinforced concrete covering
- Mechanical ventilation heat recovery (MVHR)
- Good level of air tightness
- Triple glazed timber windows facing west and south west
- Rain water harvesting for toilet flushing and washing machines
houses from the rear
Although these houses were built by a professional builder the use of ICFs for self builders is very attractive for several reasons
- Masonry and carpentry skills are not so important. Assembling the forms is more like building with lego - and very fast. Some of the suppliers do short courses
- In-situ concrete creates almost perfect air tightness - always something difficult to achieve with timber frame, especially if the building shape is complicated.
- In situ-concrete is good on acoustic insulation. There are frequent complaints with timber houses on this score.
- Concrete is good for fire separation and this begins to matter with more than two storeys or where it may be advantagious to design flexibility into a building so that certain areas can be isolated from others at a future date. See flexible design.
- Concrete can help with thermal mass and the inner layer of insulation afforded by ICFs means that a higher internal surface area temperature can be achieved more quickly when the heating is swithched on. See Decrement delay
The problem with all this concrete and polystyrene is one of embodied energy. Both of the materials rate badly in this respect. Of course the longer a building exists, the less of a problem this is. The pouring of concrete is also a job which requires some experience and expertise.
Using SIPs for roofs is also a very fast way of achieving weather tightness and is good for air tightness. The development was intended to aim for Passivhaus standards and may well have achieved them although they have not been certified as such. (to date - September 2009 - only one house in the UK has actually been certified to the standard although several others have probably achieved it)
These houses were clad in local stone on the front and end elevations to satisfy the planners.
There is an excellent downloadable article from the Green Building Press on this development
