Contextual Surveys:
Where to get relevant information?
Detailed site surveys are key to the beginning of any project. There are many digital tools and professionals which can assist in building a very detailed picture of a site and its surrounding context. However, what you decide to choose can depend greatly on the type of project, site and output you require. In this article, we will explore some of the survey options and how to gain a better understanding of your site.
Scroll to the end to download this article as a handy PDF guide!
OS maps can be downloaded as a pdf or in a more useful and editable DWG or DWF. Once you have paid and downloaded the required area, you will have a number of layers with information such as plot boundaries, building outlines, roads, pavements, vehicle crossovers, ground height above sea level, railways, waterways and power lines.
Some of the most popular companies that provide downloads of these maps are the following:
Most websites also allow you to download further information which is overlaid onto the OS map. Such as:
1m contours – These contours are usually based on the LiDAR survey from the Environmental Agency. They will not 100% accurate compared to what is on site, but do give you a deeper understanding of the ground on very sloped sites.
Building Heights – Points overlaid onto the map showing indicative building heights to gain a better understanding of the local context.
National Tree Map – This overlay gives you the location, height and canopy extents of trees greater than 3m in height. As with the contours, this is not 100% accurate information, but it can be used as a starting point for a more thorough onsite survey.
Freehold Boundaries – Based on the Land Registry information, this can help when ownership of land in the area.
Most university’s will also be signed up to Digimap® where OS mapping information, along with historical maps, can be downloaded for free following your universities log in information.
For initial viewing purposes, the ordnance survey maps can be viewed at 1:50k and 1:25k using the Bing search engine – the scale changes dynamically as you zoom in.
https://www.bing.com/maps?FORM=Z9LH2
Defra Magic
A database for information relating to ecology that may have a potential impact on a site/development. There are lots of designations that can be turned on/off independently; things like SSSI, AONBs, and lots more. Any ecologist preparing a survey report or desktop assessment of a site will use this as a starting point.
Also, it very usefully has a good measuring tool which can record an area or linear measurement, and in multiple steps.
Radon Maps:
Not usually something that affects planning but is relevant for construction and detailing. It is worth noting that in December 2022 the British Geological Society updated their radon map database which has changed the potential levels in a few places.
Geology Maps:
The British Geological Survey have a couple of online map resources, the basic version of which is the BGS Geology Viewer – this is a ‘lightweight viewer designed to provide geology enthusiasts and the general public with bedrock and superficial geology maps of Great Britain’
https://www.bgs.ac.uk/map-viewers/bgs-geology-viewer/
Again, less relevant for planning stage but useful to get a handle on what the construction stage might involve.
ARCHITECTURAL MEASURED SURVEY
On small residential projects, most architects will complete their own site surveys of a property to produce plans, sections and elevations. This will involve taking pictures and measuring the building. For more information on this type survey, please see a previous post Measure Survey 101. Whilst measuring the plans and sections can be straight forward, measuring the elevation can be very tricky.
A way of measuring and then drawing the elevation can be to measure the ground floor windows, cills and general building façade as well as a few bricks on site. Then from the elevation photographs, the brickwork can be counted and drawn up along with the previous information. It is always worth bearing in mind that the brick coursing or pattern may vary and that this should be taken into account when producing elevations. If the house does not have a visible bricks elevation, you can use the local council’s planning application viewing tool to see other examples of similar buildings on the street and their elevations.
For architectural detailing which is hard to measure both at height or not, many people try and take a picture as face on as possible. It can be further flattened on programmes such as Photoshop and then imported into your chosen CAD software. Here, you can then scale the image to fit into the size required and trace over.
SURVEY COMPANIES
For complicated sites, where further context is required, for listed buildings or to gain more accuracy and save time, a laser survey may be the prefect option. A survey company will use the OS information described at the beginning as a starting point. With a laser scanner on a tripod, they can create more detailed plans, sections and elevations through using triangulation from the survey station base point. These surveys will usually show heights of window cills and opening but may not show further details such as the window design, mullion, brickwork or detailed architectural features. These will usually be added in afterward by the architect.
Many companies can now also offer drone survey’s. This may be required if the roof is not easily accessible or if the site access is restricted by neighbouring buildings.
(http://www.drainage-surveys.co.uk/SurveyingServices/TopographicalAndMeasuredSurveys)
(https://terrainsurveys.co.uk/surveying-services/topographical-surveys)
3D SURVEYS
With the advance of technology, there are more and more survey options to give a detailed picture of a site.
Point cloud surveys have become a very popular option for very complex sites. This is a very detailed survey based on millions of geo-located points to create a 3D object or surface. This type of survey can give you the exact shapes of tree trunks if you need to design within a forest or historical layers of plasterwork and crumbling walls if working within a historic building. However, due to the complexity of these surveys, the geometry is usually simplified so it can be used in editable CAD software. This import will sometimes need to be further simplified to make the information easier to work with.
In areas such as London, there are also a number of companies that have produced accurate, regularly updated 3d massing models of the city. These will usually have all the roads and buildings massed with correct roof pitches and building heights. These can be great when showing your design within context or needing to see the proposal from important views. Some even offer information on windows sizes and locations which are key for drawing elevations, rights to light and daylight and sunlight issues.
Companies such as the ones listed below provide these services:
Google maps provides a less accurate version as well as the use of Street View which can be a useful tool is seeing the surround context of a site.
OTHER SITE SURVEYS & CONTEXTUAL INFORMATION
Once you have a contextual survey of your site and necessary surround area, these can be used by other people to build an even more accurate picture of the site. Every site is different and may require a long list of surveys to gain the best understanding of the area prior to planning, design, demolition or construction.
Some of these surveys include:
Drainage survey – There are a number of ways of conducting this survey depending on the project requirements. For small residential projects a CCTV camera and dyes will be used to see the condition and direction of existing drains. This along with site measurements of inspection chamber location and depth, combined with public drain information can help to build a better picture of drain location and depth. This information is necessary if an existing inspection chamber needs moving and extending or if new drains are being added to an existing system.
More detailed surveys use a type of sonar to work out the exact locations existing ductwork so pipes like gas mains are not damaged during demolition or ground works.
Habitat survey – These will need to be conducted be a suitably qualified professional if it is deemed that there is wildlife in the surrounding area that may be affected by construction work. Your planning office will normally detail the requirements. If your existing building is abandoned, a bat and bird survey may be required as they may have nested within the empty building. If you building is located within the countryside, other animals such as badgers may need to be considered.
Ecological survey – Usually called a tree survey, this may be required if there are existing trees near or on your site. A suitably qualified surveyor with use an OS map, National Tree Map data and a site visit to detail each tree on site, its height, canopy area, trunk location and thickness, root protection areas, health of the tree, etc. to produce a report.
Soil / contamination survey – This may also be a survey required by the local authority. There are a number of levels of information depending on the site requirements. First a desktop survey is carried out to ascertain any historical contamination. If this is deemed to be the case, one of several trial holes will be dug to take soil samples. There are then tested in a laboratory. If contaminants are found, further holes may be needed or a soil remediation plan may be needed prior to commencement on site. Foundation and ground floor design may also be affected greatly by the findings of these surveys.
Flood Risk – With the increased of Global Warming and more extreme weather events, flood risk can be a key factor in deciding whether to build on a site or how to build if there is a risk. This information is free to access via the gov.uk website. The map feature can show a number of different forms of flooding including surface water, risk from rivers or the sea and risk from reservoirs. If there is a high risk of flooding, a flood risk assessment may be required.
The Local Authorities Policies Map – Each council will have a policies map of an area. Looking at this can help give you a clearer picture of what the local authority is envisioning for the future of the area your site is in. This map will also usually contain any areas where architectural character is protected such as Conservation Areas or if there are any Article 4 Direction.
Listed Building – To check if a building is listed within England, you can use the Historic England website. If your site has a listed building on it, it may require a Listed Building Planning Application as well as possible extra reports.
Noise maps – If your site is near a busy road or railways, Extrium can be a useful tool in seeing how this will affect your project. If you are in an area with high exposure, you may choose to upgrade the sound absorption of your glazing or specify vents which are acoustically rated. If your site is near a London airport you may want to refer to the Airport Noise Mapping provided by gov.uk.
Ptal Map – Another London specific map is the WebCAT Ptal map, provided by Transport for London (TFL). This give a Ptal rating to your site which is a measure of distance from frequent public transport. It rates a point from 0 (worst) – 6b (best), 0 meaning there is very bad access to public transport and 6 meaning there are many public transport options. This map may help the designer and the council agree on parking requirements for a site.
If the site has very good connection to public transport you will usually be recommended against the provision of parking. If the rating is very low, you will have to provide parking according to the council’s requirements.
CONCLUSION
There can be many options when trying to build a better picture of your site. What you choose to do will depend on site specific constraints and budget. For example, a house survey for an extension will not require a point cloud survey. However, it is always helpful to know what the options available are, to best inform your client.
Download the Guide!
Download this helpful article as a pdf to keep for reference later.
Author
Written by Aida Rodriguez-Vega, architect and researcher. Aida keeps busy by carrying out technical research and drawing new details for the ever-growing library and construction detailing books.
0 Comments