EXPOSED TIMBER beams have a particular place in the British heart, despite their timeless propensity to leave dents in the British head. Estate agents' particulars and holiday cottage brochures always draw attention to the presence of beams, because of their ability to evoke sentiments of cosiness and tradition. The use of the word "beam" in these publications often errs on the side of generous, however, as the woodwork in question usually turns out to be ceiling joists, partition wall studwork or even lintels above doorways, none of which was ever intended by the original builders to be left on display. Their current public exhumation is part of a sentimental historical analysis of working-class housing in which every bit of naked timber, however small, is a vestige from some imaginary romantic rural past of haystacks, meadows and rosy-cheeked milkmaids. Not to mention a dab bit of trowel work by the modern-day plasterer who is asked to leave them on show.

Exposed ceiling joists can certainly impart a quaint olde worlde feel to a building, but since they are also the floor joists for the rooms above, the shrinkage gaps between the floorboards will allow heat to pass upwards, dust to fall downwards, and noise and smells to pass in both directions. No wonder our forebears preferred to cover them up.

Timber studwork in partition walls is also better covered over with lath- and-plaster. The only time it would have been left on display would have been in very poor housing, where the stud walls were plastered only on one side; the occupants of these were usually so embarrassed at the unfinished look that they covered the exposed studwork themselves with flowery wallpaper. Many examples remain, but you won't find them featured in the conservation journals.

In real construction terms, a beam is a horizontal member spanning across two columns in a framed building, and as such, it will usually be hidden within a wall, so on the rare occasions when an estate agent does correctly identify an exposed beam, it will usually be a secondary beam, supported by either columns or main beams, and designed to reduce the span of the floor joists above. In many cases it will have been put in to pick up the joists during alterations, taking the place of an earlier partition wall.

Timber secondary beams in old pubs often sag in the middle. This is not a sign of imminent collapse, but because of a phenomenon known as "creep", which occurs when fibrous materials such as wood gradually distort under load. This is what gives old timber-framed buildings much of their character. If you see a beam in an old pub which is not sagging, then it is probably not a timber beam at all, but an RSJ (Rolled Steel Joist) cunningly disguised with timber or PVC boards.

A friend of mine has recently made an involuntary close study of exposed secondary beams in a Suffolk country pub. Intoxicated by the atmosphere of the late-night revelry, and driven by the foot-tapping rhythms emanating from the jukebox, he started to dance. But, as all country dwellers know, people under beams shouldn't pogo. Lucky for him that the "beam" was a fibreglass fake, or the blood loss could have been even greater.