USEFUL DEFINITIONS
Like many industries, the construction and property industries have a wealth of strange terms that are used by builders, surveyors and engineers, which can lead the Client wondering what on earth they're talking about. What becomes even more confusing is when local tradesmen use a different term in their part of the country! Hopefully these definitions help to remove some of the mystery from site meetings here in the south-east of England.
Joists, Studs & Bits of Wood:
Sadly we're still in an age where pieces of timber are bought by the metre, but are sized in inches. It is not uncommon to ask for "three metres of four-by-two" at the local timber merchants, although many of the DIY-leaning suppliers will have bar-coded lengths of "100mm x 50mm softwood".
Another important consideration is the strength of the timber, and for most softwood the choice is C16 or C24, with C24 being the stronger, and the most commonly-available these days. The timber is graded by a specialist, depending on the number of knots and other imperfections, and is stamped to show its grading. Stronger timber can have a higher strength class still.
So what's the difference between a beam and joist, and a rafter and a hip?
Most domestic first floors in the UK are timber, and are formed with parallel horizontal timbers called (floor) joists, with floor boards (or flooring sheets) laid across.
In the roof, whether a flat roof of a pitched roof, the horizontal pieces of wood are (ceiling) joists. The sloping roof timbers are (generally) rafters (see photograph), which meet at the ridge board. Where two roof slopes meet, there will usually be a hip rafter (in an external corner) or a valley rafter (in an internal corner), depending on which direction the two roof slopes meet. If one roof slope was built before the other, the two roofs will be joined by lay boards laid across the existing rafters.
Ceiling joists are supported along their span by binders running across the top, which in turn are supported by hangers, which run vertically up to the rafters or ridge. There may also be collars or ties, which help to stop the roof from spreading outwards.
The rafters are supported by a horizontal piece of timber mid-way up the slope called a purlin (again, see photograph). This is often supported midway along its length by one or more struts, which are missing from the photograph - this is why the purlin has a bend in it! The vertical timbers are studs, and are part of the wall at the edge of the room.
The ceiling joists and rafters sit on (and are fixed to) a piece of timber strapped to the top of the masonry called a wall plate. There are many types of timber plate in a building, and that term is given to any piece of timber fixed along its length. The studs in the photograph are sitting on a sole plate (also known as a sill plate). In a typical studwork partition, there is a head plate running along the top, to secure the top of the studs.
When joists are cut around an opening (such as a staircase), the cut joists are referred to as trimmed joists. The cut ends are supported on a short trimmer joist, which itself is supported at the ends by heavier trimming joists. On site, these are usually referred to as "trimmers", although each technically has a different name. The same terms describe rafters which have been cut for roof openings.
Between joists and rafters, studs and plates, you can also have small pieces of timber cut in to support light fittings and shelf brackets, and for other purposes. These are known on site as "noggins" (or "noggings"), although may have a more technical name depending on what they are doing. Fun fact: in Scotland, they are traditionally known as dwangs.
A single piece of horizontal timber is usually a beam, unless it already has a specific name. A large piece of timber (such as over a fireplace or shop window) in an old building is a bressummer.
Roofs on modern houses are often manufactured off-site and brought on a lorry and craned into place. These large triangles of timber construction are called trussed rafters or roof trusses, and use much thinner pieces of timber to achieve the same job.
Stairs & Staircases:
Another forest of confusing building terms arise (no pun intended) in the area of stairs. Let's have a look at the terms commonly used:
The staircase was originally the term used to describe the space into which stairs were built. Nowadays, the terms staircase and stair(s) are synonymous. A stair is a set of steps from one floor to another. It may be divided into two or more flights, from one flat intermediate landing to another. Intermediate landings usually either turn left or right through 90° (known as quarter landings), or turn back on themselves, through 180° (known as half landings), and they help to split the stair up into the space available.
The most efficient stair is a single flight of rectangular flier steps from one floor to another. However, it is often necessary to turn the stair, using either landings, or tapered steps called winders (also known as: kite winders, reflecting their shape). A set of winders in a single flight is also known as a spiral stair. Spiral stairs can appear space-efficient, but in many cases the floor area taken up with headroom (and the lack of storage below) can make them impractical.
The photograph shows the first few steps in a timber stair. The foot goes on the horizontal piece of timber (the tread), which is fixed to the upright riser. This forms a closed stair, with no space between treads. An open stair has spaces between individual treads. Each tread overlaps the riser below slightly, and this overlap is known as the nosing.
The treads and risers are set into the sloping piece of timber on either side, called the string. This carries the weight of the stair from one floor to the next. The underside of the flight is usually encased in plasterboard, or can be enclosed with a decorative triangular panel called a spandrel, which provides a space for storage.
Each stair has a handrail on at least one side, with some kind of infill (known as balusters or banisters) between it and the string. Modern domestic stairs have vertical spindles, but metal or safety glass can also be used. The handrails are supported between heavy newel posts. The whole handrail and infill is known as the balustrade.
When designing a stair, we have to think about the distance from one floor to the next (the total rise), and the space available to fit these steps in. Depending on whether the stair is in a private residential building, is used by the general public, or is an access in a building such as a theatre, the Building Regulations give us different parameters for the maximum pitch (the angle of the stairs), the minimum going per tread (the horizontal distance from one nosing to the next), and the maximum rise per tread (the vertical distance from one tread to the next. There is a minimum headroom over the pitch line (a line through all the nosings), and minimum heights for handrails.