Why Are the Beams on the Outside? Wood Was Cheap and Carpenters Were Not

The structure is a frame of substantial timbers, posts standing on a horizontal sill beam, tied by further horizontals and stiffened by diagonal braces, and that frame carries every load from the roof to the ground. The material between the timbers carries nothing and exists only to keep out weather, which is why it can be a light and cheap infill rather than masonry. That distinction is the whole logic of the method, and it is the same principle as a modern steel-framed building with glass panels between the members, arrived at several centuries earlier.

The infill varied with what was locally available:

• •Woven hazel or willow panels plastered with clay, dung and straw
• •Brick laid in decorative patterns, common where clay was good
• •Stone rubble set in mortar, where stone was to hand
• •Clay mixed with straw and pressed around a stake framework
• •Later, plain lath and plaster or render over the whole wall
• •The frame was frequently covered over entirely in later centuries

The frames were assembled without nails or bolts, using joints cut so that the timbers hold each other, and the skill in that is what made carpenters valuable. A mortise and tenon joint secured by a tapered peg is the basic unit, and the peg holes were deliberately offset so that driving the peg pulled the joint closed permanently. Frames were laid out and cut flat on the ground, test-assembled, and marked with numbered symbols so each joint could be reunited with its partner during the raising, and those marks are still visible in surviving buildings. Raising a frame needed many people at once, which is why it was a communal event.

Old examples are conspicuously out of true and the reasons are worth separating, since not all of them are decay. Green timber was frequently used because seasoning large sections takes years, and it shrinks as it dries, which pulls a frame out of square permanently within a decade of building. Foundations were shallow and settle unevenly. Upper floors were deliberately built to project outward over the street, which gains floor area and throws rainwater clear of the wall below, and a row of such projections leaning at slightly different angles produces the familiar effect. The frames tolerate all of this because the pegged joints flex slightly rather than cracking, which is why the buildings survive at all.

The method declined for practical reasons rather than aesthetic ones. Large straight timber became scarce and expensive as woodland was cleared. Brick became cheap enough to build whole walls with once industrial production arrived. Fire regulations after urban fires restricted exposed timber in cities. And fashion turned against visible framing, so existing buildings were rendered or refronted to look like brick. The exposed frame returned in the nineteenth and twentieth centuries as decoration, with boards nailed to the outside of ordinary walls in a pattern imitating structure that is not there, which is now so common that most people's mental image of the style is of the imitation rather than the real thing.

A frame of jointed timbers carries the entire building and the material between the members carries nothing, which is why the infill can be woven hazel and clay or brick. Joints were cut so timbers hold each other, with offset peg holes pulling them permanently tight, and frames were test-assembled flat and marked before raising. Scarce timber, cheap brick and fire regulations ended the method, and painted boards imitate it now.