Garden Survey – how to measure my garden

Doing a proper survey on garden can be one of the most difficult parts of the design process. While many people may feel they may have the confidence to ‘have a go’ at creating the design, actually measuring the land to get the plan to scale can prove a daunting task. Below is a detailed guide to the various things you will need to do to produce an accurate and useful plan of your existing garden on to which you will be able to draw your new design. We will try to keep it as simple as possible. However, be realistic about what you are confident in achieving. Some of the methods we describe will work best with fairly basic square or rectangular suburban gardens. If your plot exceeds an acre and has many levels, boundaries or is a very odd shape, you may need to employ the services of a professional surveyor instead.

Measuring the space:

You will ideally need a long tape reel – a 30 metre surveyors tape, available from most DIY stores for around £10 – £15, should be sufficient unless you have a very large garden – and a 5 metre metal tape measure. Roughly draw out the layout of your garden so you have a template on which to mark your measurements, include the house and any side returns.

Start with the house. Mark all windows, doors, down pipes and drains on your plan. If your house does not have a flat facade you will also need to mark any returns, alcoves, posts, etc. Once you have done this, start measuring the back of the house. You will probably find that the metal tape measure is the easiest for this part.

Measure from one boundary where it joins the house to the first feature (door, window, return etc) and mark this measurement on your plan. Always draw measurements in mm to avoid confusion. Next measure and mark length of the feature itself, not forgetting for doors and windows to mark which way they open and in what direction. Repeat the process for each feature, measuring and marking the distance between each feature and the length of the feature itself. For accuracy, you should also measure the total width of the house façade, the width of any gap between the house and the boundary, and the width of the entire garden along the house (from boundary to boundary). Once you have taken these measurements, measure the length of both side boundaries from the house to the bottom of the garden using the surveyors tape.

Finally, measure the width of the garden along the back boundary and mark on your plan. If your house has a flat façade and the lengths of your side boundaries or the widths of the garden at either end are different then it may mean that one or more of your boundaries has a slant to it. It can be difficult for someone inexperienced in surveying to determine the exact line of a boundary that is not square to the house. There are methods, such as triangulation, which can be used to work out the angle of the line, but this can be tricky to get right if you have not done it before. If you can determine, using a builders square, that one of the side boundaries is perpendicular to the house, then it should be fairly easy to work out the angle of the other boundary. Simply draw the perpendicular boundary on your plan and then mark the width of the garden at both ends as measured from the perpendicular boundary. Draw a line between the two points to give the approximate position of the other boundary. While this is not foolproof, it should give a good to-scale approximation of the shape of your garden, which for the purposes of your re-design will be adequate – you are not building a house or other project that would require millimetre accurate precision, so there is a reasonable margin of error.

Once you have plotted the basic layout of your garden, you can start to mark existing features on your plan. Usually, it is only necessary to mark things that will be retained in the redesign, such as manholes or trees and other large plants. If you do not intend to keep the feature and it will be removed during clearance, then do not waste your time marking it on the plan – you will just end up in a cluttered and confusing mess. To accurately mark an item on your basic layout, you will always need a measurement from two different fixed points at 90 degree angles to each other– ideally one from a straight side boundary and one from the back of the house. Try to avoid using one feature as a measuring point for another feature, as this can lead to confusion.

Levels:

If your garden has a noticeable slope or existing terraced levels then you will need to mark these on your plan to ensure that they are taken into account in your re-design. For existing terraces, measure along one side of the garden from the back of the house to the edge of your terrace, and make a note of the position of the edge of the terrace at this point. Do the same along the other side of the garden. Draw a dotted line between the two points and this will give you the profile of the terrace edge. Measure from the top of the terrace wall to the floor on the level below to give you the height of the terrace.

There are a few ways to work out the gradient of a slope, with varying degrees of accuracy. However, for all but the most complicated slopes and designs, you will not need pinpoint accuracy – simply knowing the rough difference in height between one end of the garden and the other should be sufficient. For some of the methods you will need a helper.

The simplest, and least accurate, way of determining the gradient of a garden is to follow the line of the boundary fences or walls. In most cases if there is more than a very slight fall to the garden, the boundaries are likely to be stepped to take the slope into account. This means that the fence panels or walls will have been installed so that they are level for a distance and then at a certain point there is a step down so that the next run of level boundary is lower than the previous. If the slope is distinct, or it is a long garden, there are likely to be more than one step along the boundary. Simply measure the height of each step down along the entire boundary – that is the distance between the top of the lower fence panel or wall to the top of the one above – and add them all together. This will give you a rough indication of the height difference between the top and bottom of your garden. However, this will only work if each section of boundary is level. If there is a gradient to the fence or wall itself, then using this method will be wildly inaccurate .

Another, more accurate method is to use a line level. This is simply a long piece of string onto which a spirit bubble is hung. Attach one end of string to a fixed point at the highest end of the garden – a post or the back of the house for example – and measure the distance between this point and the floor. Run the string to the other, lower end of the space and pull it tight, with the spirit bubble hanging somewhere in the middle of the string. Keeping the string tight, move the string up or down until the bubble is in the centre of the body of the line level (this is where you need a helper to read the bubble while you adjust the line) and measure the distance between the end of the string at the lowest point of the garden and the floor. Now simply subtract the distance between line and floor at the highest point from the distance between line and floor at the lowest point to give you the height difference between the two ends of the garden.

The most accurate way to determine the height difference between points in a garden is to use a site level. In simple terms this is a telescopic lens set on a tripod, through which the user looks at a marker rod held vertically at a certain point in the space (for our purposes this would be the lowest point) and reads the height markings (in metres and centimetres) on the rod against sight lines on the lens itself. This reading is then compared against a datum or benchmark reading, which will usually be one taken at floor level against the house, to give the height difference between the two points. While this is the most accurate method of taking a level measurement, it is also the one that requires the most skill. While it is not difficult to obtain accurate readings using a site level, a certain amount of practice will be needed. Site levels can be hired quite cheaply, and the hirer will usually be happy to give a quick lesson in their use.

Aspect:

This is the direction your garden is facing. The most favourable aspect is the ‘south facing garden’. It is important you know your aspect as this will determine the best placement of specific plants as well as preferred locations for patios.

The simplest way to find your aspect is with a compass. If you don’t own a compass many smart phones now have apps with a compass feature. To find your aspect using a compass stand with your back to the house and find north. Draw the direction of north in relation to the back of your house on your plan. Whatever direction the compass needle is pointing at directly away from the house is your garden’s aspect.

Another less accurate way of determining the aspect is to type your postcode into Google maps. North always points to the top of the screen, therefore you should be able to see which way your garden is facing in relation to north and work out your aspect accordingly. This is particularly useful if you are unable to physically get to the site, for example if you are considering buying a property and want to know which way the garden faces.

If you are unable or unwilling to try and determine the aspect of your garden, you should still take time to try and work out which are its sunniest, and shadiest, parts. You don’t want to find that the sundeck on which you have placed your expensive handmade loungers only gets 15 minutes of direct sun at around 4.30 in the afternoon. Bear in mind that the relative positions of the sun, and therefore the parts of the garden which get the most sunshine, will be different in the summer and winter months.

Soil analysis:

Many plants like certain soil conditions. The RHS has a particularly detailed library of plants and their preferred conditions. This information is useful when selecting plants to ensure their survival. There are two ways of detecting what type of soil you have:

1)    Look at what is currently growing in your and your neighbours’ gardens. If shrubs such as rhododendron, azalea and pierces are thriving the chances are you have acidic soil. Most woodland soil is acidic and these plants are prevalent in woody areas. If you know anything about the history of the land, for instance it was once an orchard for a country estate, this can also help you to guess at the most likely soil type.

2)    By far the most accurate way of determining your soil type is to do a chemical PH test. These can be obtained very cheaply from most DIY or garden centres, are very easy to carry out and you will have the results in a matter of moments. It is worth doing a test at least a couple of places in the garden as sites can vary from one end to another and you could have a mixture of alkaline in one area and acidic. Once you have determined what type of soil you have, check on the RHS website or speak to your local garden centre about the most suitable plants for that particular ph level

Damp Course

If you intend to install a new hard surface, such as paving or decking, against a house you must always take the property’s damp course into account to avoid potential problems caused by rainwater ingress into the property. As a rule, the finished level of any hard surface against a building should be a minimum 150mm below the level of the building’s damp course, to prevent rainwater splash back from seeping through the wall above the damp course into the building interior. If it is not feasible to install the hard surface at this level, then a protective barrier such as waterproof render, flashing or a cladding material, should be installed along all affected parts of the wall to at least 150mm above the finished level of the flooring surface. However, this should be avoided wherever possible.