How to Modify Timber Frame Houses

Plan any modification carefully, with detailed plans of every wall or element that will be changed or added. Detailed design is crucial with timber framed houses. Every joint must be exact. Work with an architect or engineer, especially if any of the original timbers will be modified. Draw a rough floor plan of the modification for use by the professional. Include any electrical or plumbing modifications.

Remove exterior siding with a pry bar from any area that will be modified. Most timber framed houses are covered in structural insulated panels (SIP), thick foam insulation sheathed on both sides with oriented strand board (OSB). Take these off to expose the original timber frame.

Cut new mortises in the original timbers with a reciprocal saw and chisel or install metal brackets where new walls will connect. Build new timber frame wall and roof sections and erect them with a crane, fastening tenons to mortises in the original timbers. Drill holes through timbers and drive in wood pegs with a hammer or mallet to connect timbers or use metal brackets. Cover outside walls, new and old, with SIPs, fastened to timber frames with long lag bolts. Deck the roof with OSB and install roofing.

Use conventional framing for an addition by designing and building 2-by-4 lumber walls with base plates, top plates and vertical studs. Set these in place and fasten to original timbers with nails or metal brackets. Frame and install roof sections with trusses or rafters. Connect these to beams in the original timber frame. A single-slope shed roof will be easiest to tie into original framing. It will connect easily to a timber beam.