Producing an elevation drawing
Additional survey equipment that might be required for recording an elevation:
• ladders please refer to health and safety section
• spirit line level
• plumb bob
• red laser spirit level and tripod
Creating a scaled elevation drawing is a fairly straightforward way of adding a third, vertical dimension to the drawn record of your site. This process is simplified if a scaled building plan has been created beforehand.
An elevation presented with a plan on the same drawing sheet gives a good, clear representation of a building. While the measurement methods described are more complex, an elevation can be drawn as a field sketch on site with dimensions added, enabling you to draw this up formally and neatly off site.
Measurements taken for creating an elevation drawing are usually taken from a horizontal line – known as a datum line. The datum line may be a recognisable feature in the architecture or, more usually, an artificial line in the form of a string or chalk line set up across the face of the building. If you use a string line it will need to be fixed into position and levelled. A string line is certainly the most effective type of datum line, as it can be set up to intersect the middle of windows and doors, so that tops and bottoms of the features can be measured easily and noted in a clear way. Where the datum string does not touch the building or it is difficult to take a measurement, a builder’s spirit level can be used to transfer the datum onto the structure.
Next, you will need to establish a horizontal zero point on the datum line. In the case of a straight-sided building, you might choose the left edge of the building. If surveying an irregularly shaped building, you might chose a point to the left of any detail that you wish to measure in. (A scale rule is marked from the left, so it is always easier to measure and plot the distances in the same direction.) Measuring an elevation is similar to carrying out a tape and offset survey. Each point that you want to fix requires one measurement along the datum line and one measurement up or down from the datum line.
In certain circumstances it might be easier to collect a series of measurements for the height of a building from the interior, particularly if there are stairways that give access to roof spaces. Recording the elevation of a building exterior that exceeds the height of reasonable safe access at ground level should be avoided. Some alternative methods for establishing heights of structures are covered above.
Examples of a simple elevation of a domestic building – end gable and façade showing form and location of openings. Although there is no scale bar the general proportions can be gauged from the relative size of the doorway.
If a drawn plan exists, your elevation drawing can be started by laying a piece of transparent drawing film over the plan to trace off the positions of the building corners, door and window openings or blockings that will be included in the elevation. From these points, where the distance along the building is known, a semi-rigid steel tape can be used to measure up or down from the datum line to obtain the height. The positions of the datum line and of the points are then plotted onto your elevation drawing.
Once the detail of these known points has been plotted onto your drawing, you will have the bare bones of an elevation. You can now start adding detail for which you need a distance along the datum as well as a height. You might want to record distances and heights onto a sketch survey, or (an easier option) a second person can take measurements and call them out as you draw.
Creating a section
The methodology for creating a section drawing shares many of the shares many of the points covered for elevations and plans and in most cases requires information from both these sources. A successful section drawing should combine aspects of both exterior and interior planes, heights, widths and thicknesses to show heights and vertical angles which are not possible to represent in plan view.
Ideally, free and easy access throughout all parts of a building is required to construct an accurate section, but the reality is that this is rarely an option. For example, buildings may be too high, lines of sight may be obscured, and roof spaces, whole floors or rooms may not be accessible for any number of reasons.
An example of a section drawing through the same building shows wall thicknesses, the configuration of the roof trusses and the location of a ground floor fireplace – all features that cannot be verified from an external viewpoint. The section drawing right was created at the same time as the plan and elevation, and shows the kind of features that can be recorded in such a view plane.
These are common problems and even the most modern digital technology can struggle in the face of such obstacles. On the positive side, it would be unusual not to be able to create some level of section drawing from available resources, measurements, archive material and a bit of informed guesswork.
If you have previously been able to record a plan and/or elevation of the building, you will already have taken most of the key measurements you will need to create a ‘wireframe’. These key measurements will provide points that you can plot onto your drawing, and from which you can take further measurements to build up the level of detail required for your section.