How bricks make doors

Lucy Greenslade discovers the uncommon importance of the common brick.

For two hundred years before the middle of the twentieth century, the fired clay brick was the structural material of choice for most of London’s housing stock. The coming of the canal system and then the railways in the nineteenth century meant that large quantities of bricks could be supplied cheaply to London from kilns in Middlesex, Bedfordshire, Cambridgeshire, Suffolk and Essex. The pre-historic Wealden clays of Kent and Sussex – with famous names such as Funton and Chailey – also helped to give London stock bricks their characteristic appearance, blending warm tones of browns and yellows.

Long before a Danish carpenter invented Lego, Londoners were building using a strict modular system, and the module they used was the common brick. Brick dimensions are neither random nor accidental. Before metrication, the typical London brick was about 9 inches long by 4 inches wide by 2½ inches high. The metric equivalent is 215mm long by 102.5mm wide by 65mm high. Metric or imperial, the truly important consideration is that bricks must be the perfect size to fit a human hand.

It starts with the width. Look at the span between your thumb and fingers. Comfortably, it’s likely to be around four inches (that’s 102mm). Bricks have to be suitable for lifting using only one hand – leaving the other one free to wield a trowel laden with mortar. If both hands were needed to manoeuvre the brick, the speed and rhythm of bricklaying would be lost.

Next – for the modular system to work – the length of the brick follows from its width. Two bricks laid side by side with 10mm of mortar between them measure 215mm across. This is important for bonding; in traditional building, alternate bricks laid at right-angles held a wall together. A brick laid with its long side exposed is described as a ‘Stretcher’: showing the short side makes it a ‘Header’.

Solid masonry laid in English Bond: Headers and Stretchers in alternate courses
Solid masonry laid in English Bond: Headers and Stretchers in alternate courses

The height, 65mm, results from two further considerations. One is weight – we are using only one hand, remember – and the other is cutting. If bricks were much thicker than 65mm cutting them by hand (using only a hammer and bolster chisel) would become unreliable and therefore wasteful.

And so to period front doors. To work efficiently, bricklayers avoid cutting bricks and so the heights and widths of the openings into which our doors must fit are multiples of brick dimensions. Horizontal dimensions should be multiples of 215mm and 102.5mm (called a “half” brick) – not forgetting 10mm for each of the vertical joints (called ‘perpends’). Builders use ‘co-ordinating dimensions’ of 225 x 112.5 x 75mm so that the joints are not forgotten.

Co-ordinating size is the brick plus 10mm of mortar
Co-ordinating size is the brick plus 10mm of mortar

The majority of London front doors have always been made to suit frames which had been built directly into the brickwork as it was being raised. The size of the opening naturally determined the size of the frame and consequently also the dimensions of the door.

Typically, the minimum convenient width of an opening around a doorway in an outer wall would be the length of 4½ bricks plus six perpends, say 1022.5mm. Its height should result from multiples of 75mm plus one additional 10mm (for the mortar bed above the top course). For Victorian front doors, the brickwork also has to accommodate a door-sill below and, in most cases, a fanlight above. Therefore the minimum height of the brick opening around a traditional London front door frame is likely to be 2710mm, or 36 brick courses (not forgetting that extra 10mm for the bedding at the top).

The front door itself, required to be more imposing than the internal doors, would be at least 2082mm high and 915mm wide; that’s 82 inches by 3 feet to a Victorian carpenter.

For internal doors, 28 courses of brickwork give a height of 2110mm (from joists to underside of the lintel). This is why, after allowing for floor boards and the head of the frame, the resulting doors are generally around 2032mm (80 inches) in height. Widths are more variable but a width of four bricks allows for a door width of 820mm. That’s 6’ 8” high by 32 inches wide and, ultimately, all because of the size of the bricks!

Bespoke Front Door


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