Timber is best known as a structural material, we use it to form the shape of the building and support the roof. This can be done using a traditional post and beam frame, as shown here, or using smaller sections of timber in a stud-work frame. There are ways of making timber structures more efficient by using engineered timber such as 'glulam'.
There are a number of board materials made from wood; plywood, sterling board, MDF, chipboard etc. These all involve a degree of processing, and some, such as MDF, have a lot of glue in them and are not good for you! Waste sawdust can be turned into insulating woodfibre boards, as seen here.
Further processing turns timber into paper, and paper can be recycled into cellulose insulation, such as 'Warmcel'. Cellulose is also used in 'Fermacel' an alternative to conventional plasterboard that is both stronger and better for the environment.