Construction Verification Surveys

Construction Verification Surveys

Area Measurement and Referencing Surveys & Reports


Gross External Area in broad terms means the whole are of the building taking each floor into account. This will include:

  • Perimeter wall thickness and external projections
  • Areas occupied by internal walls (whether structural or not) and partitions
  • Columns, piers, chimney breasts, stairwells, lift wells etc
  • Lift rooms, plant rooms, tank rooms, fuel stores, whether or not above roof level
  • Open-sided covered areas (should be stated separately)

GEA will exclude:

  • Open balconies
  • Open fire escapes
  • Open sided covered ways
  • Open vehicle parking areas, terraces and the like
  • Minor canopies
  • Any area with a headroom of less than 1.5m (except under stairways)
  • Any area under the control of service or other external authorities

Note that:

  • Party walls are to be measured to their centre lines
  • The areas of items excluded from GEA should be calculated and shown separately

GEA is used for Town Planning, rating of residential property, council tax and building cost estimation including insurance.

In a bid to create greater consistency and confidence in the global property market, the IPMS (International Property Measurement Standards) Coalition was formed in 2013 and in 2014 IPMS for Office Buildings was published. Following the release of IPMS: Offices, the RICS have redrafted the Code of Measuring Practice (CoMP-6) and have re-published this as the Professional Statement for Property Measurement. This document is mandatory for all RICS members from 1 January 2016.


There are three levels of IPMS which stands for International Property Measurement Standards: Office Buildings.


Used for measuring the area of a building including the external walls. This will calculate the sum of areas of each floor of a building, measured to the outer perimeter of eternal construction features and reported on a floor by floor basis.


Used for measuring the internal area and categorising the use of space in an office building. It can be used by asset managers, facility managers, valuers and cost consultants to provide data on the effective use of space by the tenant.


Used for measuring the occupation of floor areas in exclusive use, but excluding standard facilities and shared circulation areas. This is calculated on an occupier by occupier or floor by floor basis for each building.

Further Information can be found here on the RICS website.


Broadly speaking it’s the whole enclosed area of a building within the external walls taking each floor into account and excluding the thickness of the external walls. GIA is used for building cost estimation, estate agency and valuation, rating industrial buildings, warehouses, retail warehouses, department stores and many specialised buildings, property management for service charges, new homes valuation and marketing new residential developments.

GIA will include:

  • Areas occupied by internal walls (whether structural or not) and partitions
  • Service accommodation such as WCs, showers, changing rooms and the like
  • Columns, piers, whether free standing or projecting inwards from an external wall, chimney breasts, lift wells, stairwells etc
  • Lift rooms, plant rooms, tank rooms, fuel stores, whether or not above roof level
  • Open-sided covered areas (should be stated separately)

GIA will exclude:

  • Open balconies
  • Open fire escapes
  • Open-sided covered ways
  • Open vehicle parking areas, terraces and the like
  • Minor canopies
  • Any area with ceiling height of less than 1.5m (except under stairways)
  • Any area under the control of service or other external authorities

Note that the areas excluded from GIA should be calculated and shown separately.


Broadly speaking, the usable area within a building measured to the face of the internal finish of perimeter or party walls, ignoring skirting boards and taking each floor into account. NIA is used for estate agency and valuation, rating of shops, shop rents, supermarkets, offices, etc, property management service charge.

NIA will include:

  • Perimeter skirting, moulding, or trunking
  • Kitchens
  • Any built-in units or cupboards occupying useable areas (subject to height exclusion below)
  • Partition walls or similar dividing elements
  • Open circulation areas and entrance halls, corridors and atria

NIA will exclude:

  • Toilets and associated lobbies (but extra measurements may be required for shops where they are either in excess of normal staff requirements, considering the type and size of shop) or it is apparent additional toilets have been installed
  • Cleaner’s cupboards
  • Lift rooms, boiler rooms, tank rooms, fuel stores and plant rooms other than those of a trade process nature
  • Stairwells, lift wells, those parts of entrance halls, atria, landings and balconies used in common or for the purpose of essential access
  • Corridors and other circulation areas where used in common with other occupiers or of a permanent essential nature
  • Areas under the control of service or other external authorities
  • Internal structural walls, walls (whether structural or not) enclosing excluded areas, columns, piers, chimney breasts, other projections, vertical ducts etc
  • The space occupied by permanent air conditioning, heating or cooling apparatus and ducting which renders the space substantially unusable having regard to the purpose for which it is intended
  • Areas with headroom of less than 1.5m (this area should be shown separately but excluded)
  • Car parking areas (this area should be shown separately and the number of spaces noted)


Zoning is a standard method of measuring retail premises to calculate and compare their value. It is used by both public and private sector surveyors and has been a method that has been applied in the UK to the analysis of shop rents and properties for rating purposes since the 1950s.

Shop or retail premises are divided into a number of zones each of a depth of 6.1 metres – or 20 feet.

Zone A closest to the window is most valuable, with the value decreasing with distance from the frontage: Zone B is the next 6.1 metres, then Zone C, until the entire depth of the retail area is allocated to a zone – anything after Zone C is usually defined as the remainder.

Volumetric Surveys & Reports

Castle Surveys are able to undertake stockpile surveys and volumetric calculations for either regular updates, asset management and auditing or one-off site visits to quarries, stock yards and construction sites. Using the latest Leica GPS equipment and drones (UAV, SUA), we can safely and accurately carry out these types of surveys and provide the data required.


This type of survey is undertaken to determine if the poured floor slab is level and within tolerance. For example, Castle Surveys was asked to undertake a level survey to establish where imperfections were in the existing floor slab in a large warehouse. Utilising our FARO 3D Laser scanner and LSS Survey Software we accurately surveyed the area and produced a Digital Terrain Model to show the client where the uneven areas were so they could be levelled in order to erect the racking in the warehouse. This was essential as the racking may have caused a health and safety issue for the company if it had collapsed due to the inconsistent floor level of the slab.


Using the very latest in total station technology our regularly updated fleet of structural monitoring instruments allows operatives to employ a diverse range of techniques to monitor movement across the broad spectrum of construction and engineering.

For when large numbers of measurements need to be taken within a short period of time it is often possible (and more practical) to install an automated total station structural monitoring system.

Structural Monitoring

Monitoring surveys are a precise method of surveying in which structures or features which are thought to be moving or have the possibility of moving are repeatedly checked to determine the amount of movement or deflection. The amount of movement, if any, can be quantified and reported.

The movement can be due to adjacent site ground works, such as excavations or drilling works, or due to natural ground movement and settlement over a long period of time. Monitoring of deflection or deformation of structures due to load is another common application of this surveying technique, where the movement of a structure under load is observed, such as a bridge or supporting beam for example.

GPR Concrete & Rebar Scanning

Our comprehensive range of survey services has recently expanded to include concrete and reinforcement bar scanning solutions.

Suitable across a broad range of projects and sectors, the latest ground penetrating radar (GPR) technology can locate and measure the layout of structural reinforcement within elements of the building structure including floor slabs, concrete beams and walls. It is also capable of detecting areas of voids within more unusual types of structure including sea wall defences and promenades.

By no means an exhaustive list, GPR concrete scanning can help identify the following…

  • Voids
  • Cracks
  • Reinforcing bars (position, spacing and layout across one or a number of layers)
  • Non-ferrous services (pipes, conduits, ductwork etc.)
  • Changes in surface
  • Underfloor heating pipework
  • Chimney Stack & wall voids