There are several systems on the market which allow you to cast concrete using clip together poystyrene forms. The two leafs of insulation are connected together by plastic ties and the units are clipped together and then filled with concrete, usually by pumping, so the whole process is very fast. Reinforcing bar can be inserted in the concrete though this is seldom necessary for domestic work. The concrete can be vibrated. It is also possible to create curves. There is a variety of external finishes possible including render, timber and sheet cladding and brick and stone slips. Internal lining is necessary with concrete render, plasterboard or clay based boards.
First the bad news. Both concrete and expanded poystyrene are high in embodied energythe total amount of energy it takes to make a material (or a building). See more on embodied energy and they both have associated pollution during manufacture. However in terms of the embodied energy needed to provide thermal massthis is about how much heat something can absorb - so it involves its specific heat capacity and its volume. It can be useful for levelling out the peaks and troughs of temperature within a house. See the page on thermal mass, concrete is one of the better choices.
Having said that, there can be some excellent in-use energy saving benefits to this type of system provided the external layer of insulation is substantially increased. As they are supplied, the inner and outer leaf of insulation are usually each about 70mm thick with the concrete layer being about 125mm although these dimensions can be varied.
It seems that the manufacturers have still not generally caught up with the sort of insulation required for PassivhausSee more on the Passivhaus standard. The PassivHaus Institute has pioneered a standard for low energy buildings. It includes very low energy usage and ways of achieving this. The word is derived from the idea of buildings which are fundamentally low energy and passive solar heated rather than using extra gadgets to heat them. See Passivhaus for the UK branch of the organisation. standard so the occasional examples in the UK where this has been attempted have relied on adding extra EPexpanded polystyrene insulation insulation to the outer skin to bring the total up to about 300mm. Concrete can be foamed to increase its insulation value but with resulting loss of strength. The thermal mass of the concrete can help retain heat and contribute to decrement delayThis relates to the lag time that insulation itself takes to heat up or cool down. It introduces a delay into the effect of the insulation. This can help level out peaks and troughs of temperature. See the section on Decrement Delay. However the calculation of the effects of decrement delay are complex and require expert advice.
The fact that concrete is poured into the wall means that there is a continuous air-tight layer so there should be no problems with air tightness, in the walls themselves at least. Concrete is a good sound insulator and has excellent fire resistance[for the purposes of part B of the Approved Documents] - The ability of a component or construction of a building to satisfy, for a stated period of time, some or all of the appropriate criteria specified in the relevant part of BSBritish Standard 476.. The combination of clip together formwork and poured concrete tends to significantly reduce waste and offcuts on site.
An interesting example of ICF walls are the three recently completed houses at Chewton Mendip
The Building Regulations part A covers the structure of a building. The Approved DocumentsThese are a part of the Building RegulationsThese are the legal regulations which govern how a house is constructed. (not to be confused with Planning Permission which is about whether you are allowed to build the house at all or what it might look like) see Building Regulations) which ensure, if you follow them, that your plans will be automatically approved. The full set of the documents is available here part Apart A of the Building Regulations Approved Documents relates to Structure. See an abridged version which covers house building go into a lot of detail for traditional masonry buildings but almost none for timber frame, steel frame, earth building SIPsStructural Insulated Panels - prefabricated (usually in a factory) timber panels often forming part of an integrated building system and aimed at fast site erection. see more on SIPs etc. For these you will need to consult a structural engineer (while SIPs structures are usually handled by the manufacturer)
With most forms of construction there will be implications concerning fire safety. These are covered in the Building Regulations and you can see examples of how to conform with these in the Approved Documents Part B (Fire Safety)
The regulations include a section called “Part C – Site preparation and resistance to contaminants and moisture” which covers site remediation along with protection from nasties which might affect the construction and occupants such as damp, rain, radon etc. There is an abridged version of the Approved DocumentThese are a part of the Building Regulations which ensure, if you follow them, that your plans will be automatically approved. The full set of the documents is available here specially for houses.