A glossary of terms to ensure you're always in the know.
The Latin geometrical term for 'summit, peak, tip, top, or extreme end'. It is the highest point and is typically used to refer to the vertex opposite some base or lowest point.
A barn roof is known as a gambrel or gambrel roof. The name derives from the Medieval Latin word gamba.
Similar in appearance to a mansard roof (see below), historically we did not distinguish between a gambrel roof and a mansard roof – calling both types a mansard. In contrast to a mansard roof, a gambrel has vertical gable ends and overhangs the facade.
Barn style roof
A mansard or mansard roof (also known as a French roof or curb roof) is a four-sided gambrel-style hip roof. Its classic structure consists of two slopes on each side, the lower slope adorned with dormer windows and angled to be steeper than the upper slope.
Cathedral and Vaulted Ceilings
A cathedral ceiling is any tall ceiling area similar to those in a church or cathedral.
Also refered to as a vaulted ceiling where the space in the room is taken right up to the underside of a steep sloping roof, or rafters.
Strictly speaking, a vaulted ceiling is where the room is formed by an arch below the ceiling or roof.
Cathedral/vaulted ceiling at Stow Minster, Lindsey.
Dropped and Flat Ceilings
A dropped, or flat ceiling is where the finished surface is set any distance - from a few inches or centimetres to several feet or a few metres below the (roof or floor) structure above it.
A collar tie is seen in many pitched roofs where the rafters need to be 'tied' together to stop the roof from 'spreading'. This is often done at the eaves level via ceiling beams or joists set between opposing pairs of rafter feet.
If the rafter feet are not present, e.g. as in a vaulted roof, then ‘collars’ or ‘collar ties’ may be necessary to prevent such ‘spread’. In this case the roof collars are acting in tension to prevent opposing rafters from being pulled apart.
1: Rafter tie 2: Rafter 3: Collar tie
A traditional timber framing term for a post in roof framing which stands centrally on a tie or collar beam. More information about Truss types here
A joist is one of the horizontal supporting members that run between foundations, walls, or beams to support a ceiling or floor. Typically, a joist has the cross section of a plank. Joists are often supported by beams laid out in repetitive patterns.
A king post (king-post, kingpost) is a vertical post usually positioned centrally in architectural or bridge designs. More information about Truss types here
1. King Post 2. Tie Beam 3. Principal Rafters 4. Struts
Purlins are longitudinal or horizontal beams which give support to the rafters.
Purlins can be used to increase roof spans without increasing rafter sizes
A queen post is a tension member in a truss which spans longer openings than a king post truss. More information about Truss types here
1: Queen post 2: tie beam 3: Straining Beam 4: Principal rafters
A traditional roof truss is quite different from ‘Trussed Rafters’, although these are often incorrectly referred to as ‘roof trusses’.
A structural frame in its own right, a roof truss is part of the support for the common rafters to which the roof surface, e.g. tiles or slates, is fixed. Often seen in a triangular ‘A’ frame shape for conventional roofs, it can be altered to suit individual roof types.
Traditional wood frame roof truss with king post
Often seen in post-and-beam construction, a ridge beam is a horizontal timber beam set at the apex of the roof. It is the support for the high ends of the rafters, ensuring that there is no risk of spreading
1: Ridge Beam 2: Purlins 3: Common Rafters
Tie beams and Rafter ties
Are the same thing.
They tie together the feet of opposing roof rafters to prevent ‘spread’ (the outward thrust) at the junction between the house ceiling and walls.
Like collar ties, this helps keep walls from being pushed outwards by roof’s weight and any other load on it (e.g. snow, wind).
Rafter ties are always required unless the roof has a structural (self-supporting) ridge, or is built using engineered trusses. A lack of rafter ties is a serious structural issue in a conventionally framed roof. The wooden beam allocated to this purpose is a tie-beam and when a roof incorporates this design it is known as a tie-beam roof.
15th-century tie-beam roof, St Mary’s Church, Radnage, Bucks
Timber Framing & Post and Beam
Both are methods of building with heavy timbers rather than dimensional lumber such as 2”x4”s.
Traditionally structures are created using timber that is squared off, carefully fitted and joined with large wooden pegs.
It can be clearly seen in wooden buildings from 19th century and earlier and is still a very popular building method today.
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