More than any other topic, the subject of self build timber frame kit houses attracts the most comments and requests for information on this web site. Particularly the Walter Segalrefers to a simple self build timber frame form of construction pioneered by the architect Walter Segal. see details of the systemThe architect who devised a simple timber frame self build system (often simply known as 'Segal self build'). see more on the Segal method system which has featured on Grand Designs a number of times has been seen as a possible way forward.
Until recently the difficulty with making such construction sufficiently airtight has meant that no ready made solution was available. A relative newcomer is the company Passivhaus Homes with their timber kit houses. It looks like they are providing a design service and kit “to full 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 (15kWh/m².a) or our PH30 ‘near Passivhaus’ specification to 30kWh/m².a.”
Timber frame construction is particularly suitable for incorporating high levels of insulation, especially if an external rain screenthis is a (usually thin) outer cladding on a wall which prevents rain, snow, etc getting at the structure of the wall behind. see more on rain screen is used, rather than a masonry outer skin. This way you can have most of the depth of the wall carrying insulation (say 300mm) without the whole wall becoming excessively thick. See the page on Insulation and wall thickness
The problems that can arise with kit houses are mainly about sealing the gaps between panels and framework, especially when there are complicated three or four way junctions. This is where a well designed kit has its benefits as all this is well thought through beforehand. The other big advantage is of course more certainty around costs.