The Architectural Grid

As part of my update for Mitchells Construction, I thought I would add a section within Structures on the Use of the Architectural Grid, with a passing mention in Strucrures, Site layout, and possibly Surveying.

All buildings, from the simple shed to complex skyscrapers, need to stand up under its own weight, the weather and occupants and Dead loads . It is importand to understand the path of the load though the building, in relation to both the internal layout and their use. A grid helps to both coordinate these loads, and define and control the location of the structure floor by floor, and its here we start to define the grid as not just a single one layer floor, but for all floors controlled by a vertical grid.

Distributing the Load

The masons of old, soon found out that ignoring the load created by the structure on the ground will inevitably lead to the buildings collapse, and that cutting or excavating the top soil and any unstable layers below was essential to supporting the new building.

To understand the path of loads passing down through a building we first must understand the relationship of each floor with the floor above and below. This is done by overlaying the drawn floor plans to align walls and columns.

To aid this method of understanding the path of all loads we use a grid to locate the walls. 

Most building regulations will have some sections that outlines this complex area of construction. The UK which has four sets of regulations:

• England (The building regulations Part A)

• Scotland

• Wales

• Nothern Ireland

All set ot the requirements of passing load down through the building safely distributing it to a firm footing.

The Architectural Grid

Its a complex and often related subject that we need to revisit in many areas of design, where we looked briefly at the use of a grid to aid the design process, detailing, and set out on site, working with the structural Engineer, the grid defines the material selection, given loads expected, the 3D concept where loads travel down through the building and distribute into the surrounding substructure.

The grid starts its life very early on in any design some times its used to define spans, and on larger schemes to locate certain areas of the building, but its main role is to define the path of loads verticaly through the structure.

The size of the grid is often defines the materials being used to span from suport to suport 

• Steel 

• Concrete 

• Timber 

• Stone 

• Composite

I mention earlier, the need to see the grid not just as a single control but with each floor having its own grid controled and coordinated by the ground or lowest floor. 

Originaly we used 2D drawing on paper and ink, overlaying tracing paper plans to check each floor plan on the lower floor plan to make sure each column or wall passes load directly down through the building, a time consuming exercise often utilising a light box or a large enough window to highlight the grid and structure, floor by floor. The move to 2D cad eased this process considerably.

But the move 3D Cad and digital drawings, we can now view the grid in 3D following lines of load easily, and now seeing room relationships verticaly, together with services and their ducts.

The Main Grid

It can be seen therefore, that establishing this grid over any layout for almost any building allows the designer, and engineer, to locate and control the structure following loads down through walls, and columns. But the grid can also be used to coordinate the use of standard materials.

Walter Segal in the design of his self build houses used a Tartan grin, to both organise his use of materials and ensure loads and spans were controlled.

This is not a new idea, just take a look at the cathedrals built at the turn of the century, their layout, is very controlled by an elaborate grid, aligning columns, and the space between columns. Built around the turn of the first century, these catheredrials show a layout defined by the use of a grid, often using multiple grids with circular or orthoganal shaps, linking parts of the stucture that were obviously built at a later date, and no relationship to the layout of the original design, but a grid may well have benn the only way they were linkd and understood by the Masons who designed them.

Grids also establish the size of spanning materials, steel, concrete, timber, stone, Laminates. The larger the span the limitation on the material choice. Grids also helped to design buildings with columns that had none parallel sides to give a optical allusions, a fascinating thought for buildings so old.

Sub Grids

Grids withing grids are often used to define the position of columns not located on a main grid, together with other elements like curtain walling.

Shape and design of the grid

Most grids are square, or Orthoganal ie at right angles to each other, however some designs are anything but square, being circular, or flowing like a river bed. 

This appears complicated at first, but is supprisingly simple once a defined relationship between the main elements can be found and easily reproduced on site.

There is no rule on a grids shape and orientation, its can be circular, square, oblong, rectangular, or a combination of all above, as long as the grid can be set out acuratly, and reproduced verticaly.

The grid can be seen in so many cultures, the streets of New York are a classic example against the small area once owned by the British, a Rampling pattern of streets and land ownership. The Romans, with their organisation and straight roads, used grids to set out forts and dwellings along their roads, But the classic example is the cathedrals built at the turn of the First Century, often a mix of square, rectangle and circular grids, and bear in mind these grids were laid out by line of sight, no computers or even basic theodolite machines, just a man looking along a line of poles, a technique I taught many students to use.

Who Owns the grid

There is always the question when designing a grid for a new building, who owns it, the designer, Engineer, or the Contractor. 

The simple andswer is the designers should get agreement with the engineer at an early point in the design, and control the grid, adjusting and moving the grid to suite the evolving design, but at some stage a block should be made to any other alterations. 

Contractors may want to completly redesign the grid, but unless they were part of the initial design team, they will have to live with the layout, and comply.

Surveying Grids

The use of Grids is not limited to the design of a building, land surveyors often set out a site using a grid to locate boundaries and main features of a site, 

Old fashioned Vs Digital

Although modern day digital total stations can locate any point and accuratly locate it to any digital ordanance Survey map. It is always benefitial to understand how to do it manualy with a simple dumpy level and a set of raging poles and steel tapes, utilising line of site to arrange the first line og poles and the remaining Grid utilising the Three Four Five Triangle, and the operation of line of sight, are age old skills that should be learned. Relying of a total digital knowledge base, is fine but there are times when it will not work, but the traditional older methods will always work.

Earlier in this article I start to examine this relationship between span, and material choice, Students should define a chart showing general materials and their spans to help to understand this relationship, they might want to look at early Egyptian buildings before arch’s were used, to see how stone limited the span between columns. 

Do not forget, the grid is not just the horizontal spacing of columns and walls, it should also be viewed vertically, the room height, the space for each floor’s services, and the thickness of each slab, which as you will now see, is a direct relation to the span and material choice.

Profile Boards

The profile board, is perhaps one of the most important tools used to locate and set out the buildings grid, This involves nothing more simple than a pair of timber stakes with a horizontal timber bar, with nails to mark the grid, and external line of the brickwork, edge of slab and foundation, laid out with a line of string stretched between the profile boards, and marked on the ground with a spray can, ready for the JCB digger to excavate, with firm warnings from the site manager about damaging his profile boards is any way.

Set out is a question I so often received, in the early days, it was, “give me all the line lengths, and diagonals”, but in modern times with Theodolites, or now Total stations it’s the spreadsheet with all lat and long or grid ref of the grid intersections.

But again I still want you, the reader to look at Grids and see the structure, and above all, still think of me on a cold wintes day setting out a grid to teach students the basic but age old way of seeing out a building, tapes Rod, poles and those aluminium stands because the ground was to hard to push in a pole.

Happy days.

Bibliography

Frog up or Down web site

• Setting out a grid

• Using a grid