Timber frames

Timber-framed infill construction was well established between 1400 and 1600, with close frame and box frame grids being most competently built. Frames are usually made up of whole panels set at regular intervals to form bays, which are then held together with floor beams and ridges. The whole frame sits on a cill beam, which has a major structural function of distributing the final load evenly to the stone plinth. All of the major posts of a genuine frame must therefore sit on a firm cill plate.

Members of a timber-frame construction are all interconnected. Theoretically, it would be possible to pick up a timber-framed house and put it down again without damaging it. Its interconnectivity is the frame's strength, but the loss of a beam, rafter or joist can have serious consequences on the frame's ability to carry load. This is because the frames were not designed by engineers, and many of the elements are sized and placed as a result of the experience of the builder, rather than through any determination by calculation.

• Often the main or primary beams are undersized and secondary beams are oversized.
• Floor joists may be laid flat, with the smallest dimension forming the depth of the member, and this is structurally compensated for by thick plank floor joists and closely set primary beams.

Timbers were often reused from other buildings, which makes timber-framed buildings difficult to date accurately (references to ship timber can be historically misleading). Despite being made of wood, timber frames perform remarkably well in fire, as the beams tend to merely scorch, rather than burn. Soot-blackened roof timbers may not be evidence of a previous fire, but could indicate a very early house, constructed before the advent of chimneys.

Such houses are of immense historical importance. If such beams are discovered, they are almost certainly the original beams at the heart of the original plan layout. Infill panels may be the original wattle and daub or later addition brick panels. These brick panels (mainly from the 1600s) sometimes stress the frame, as they do not expand as evenly as wattle and daub. Note that there are great regional variations in the construction methods of timber frames and roofs. Surveyors should investigate the types and styles locally to form a better picture of how they may perform.