Structural insulated panels (SIPS) for house extension construction.

These are pre-formed composite materials usually of structural timber bonded to insulation board to form ready made thermal building materials ready to span fairly long distances for walls, floors and roofs in particular.

Again, this is an off site construction method that can be cut and adapted within factory conditions and brought to site ready for putting together as a form of kit build.

This building system could be utilised for home extensions but would probably not be cost effective.  They tend not to sit well when abutting the existing properties roof and walls.  They would work well for detached garden buildings rather than extending the main home.