Area Calculations for Measured Building Surveys: GIA, NIA, IPMS & RICS Code of Measuring Practice

The three measurement standards

UK 2026 measured building surveys produce area calculations in one of three standards, depending on the project:

1. GIA (Gross Internal Area) — UK industry standard for cost estimation
2. NIA (Net Internal Area) — UK standard for office / industrial letting
3. IPMS (International Property Measurement Standards) — the international standard, increasingly used for cross-border portfolios

All three are defined in the RICS Code of Measuring Practice 6th edition and IPMS 3.0.

GIA — Gross Internal Area

GIA is the area of a building measured to the internal face of the external walls at every floor level. It includes:

• Internal partitions and columns
• Service accommodation (plant rooms, stairwells, lift wells)
• Common areas (reception, toilets, common corridors)

GIA excludes:

• External walls
• Balconies (unless enclosed)
• Open light wells
• Sub-surface voids

GIA is the standard for building cost estimation (e.g. £2,000/m² GIA for a new build). It is also the basis for many professional fees and ratings.

NIA — Net Internal Area

NIA is the usable area within the building, measured to the internal dominant face of walls. It includes:

• Office areas, workstations, meeting rooms
• Storage, kitchenettes, internal corridors (within a demise)

NIA excludes:

• Common areas (reception, shared toilets, common corridors)
• Internal partitions between occupiable units
• Service accommodation (plant rooms, lift wells, stairwells)
• Restricted headroom (less than 1.5m)

NIA is the standard for commercial letting, especially office and industrial property. Most UK commercial leases use NIA for rent calculation.

IPMS 1, 2, 3 — International Property Measurement Standards

IPMS is the international standard, developed by the International Property Measurement Standards Coalition (IPMSC). It is increasingly used in the UK for cross-border portfolios.

IPMS 1 — IPMS External: the external footprint of the building at every storey. No exclusions. IPMS 2 — IPMS Internal: all internal area, excluding restricted headroom and vertical service penetrations. IPMS 3 — IPMS Building Use: occupiable area by use class (3A: occupiable area; 3B: shared areas; 3C: external covered areas). IPMS 4 — IPMS Tenant Use: tenant-exclusive area (for office leasing). IPMS 5 — IPMS Tenant Use: tenant-exclusive area on occupied floors only (for office leasing).

For most UK 2026 projects, IPMS 1 + IPMS 2 are sufficient. IPMS 3-5 are used for portfolio benchmarking and cross-border leasing.

How to choose the right standard

The choice depends on the project:

For most 2026 UK projects, GIA + NIA is the minimum. For international portfolios, add IPMS 1 + IPMS 2.

The RICS Code of Measuring Practice 6th edition

The RICS CoMP 6th edition (current in 2026) sets out the detailed rules for GIA, NIA, and IPMS calculations. The key changes from the 5th edition:

• IPMS 1-5 fully integrated (the 5th edition only mentioned IPMS in passing)
• NIA redefined to align with IPMS 2 (where possible)
• GIA measurement clarified for buildings with complex geometries
• New guidance on basement and mezzanine areas
• RICS member firms must use the 6th edition for all measurements from 2024 onwards

The Icelabz standard for 2026 measurements is the RICS CoMP 6th edition throughout.

Download

Next steps

• See our Measured Building Survey service page
• See Asset 1: The Complete Guide
• Book a 15-minute clarity call

References

Frequently asked questions

What is the difference between 2D CAD and 3D Revit deliverables? 2D CAD (.DWG/.DXF) is flat line drawings showing geometry only. 3D Revit (.RVT) is an intelligent model where each element (wall, door, window, beam) carries physical and functional data. 2D is cheaper; 3D is required for BIM projects and FM handover.

What is the difference between RICS Band A and Band B? Band A: ±15-25mm (1:50/1:100 scale). Band B: ±50mm (1:200 scale). Most UK measured building surveys are Band B; heritage and tight-clearance work is Band A.

What is LOD 200 vs LOD 500? LOD 200: approximate geometry for early design. LOD 300: precise geometry for design and construction. LOD 400: fabrication-level detail. LOD 500: verified as-built for FM handover and digital twin.

Do I need a measured building survey for a building regulations submission? Yes — building control bodies require accurate existing-drawings to verify the proposal. The measured survey provides the baseline against which the proposed extension or alteration is checked.

Can a measured building survey be done with the occupants present? Yes, with some caveats. Occupants are usually asked to leave for a few hours while the surveyor sets up the scanner. Laser scanning is non-contact and quiet; the main disruption is the surveyor walking through the space.

What is the difference between a laser scan and a measured survey? A laser scan is the data-capture method. A measured survey is the deliverable. Most 2026 measured building surveys use laser scanning as the data-capture method and produce 2D plans, 3D models, and point clouds as deliverables.

How long does a measured building survey take? A typical 3-bed house takes 2-4 hours on site for a 2-person scanner team, plus 1-2 days for processing and drafting. Larger or more complex projects take proportionally longer.

Can the measured survey be done from the outside? Partially. External elevations can be captured from outside, but internal floor plans, sections, and ceiling heights require internal access.

What is the Icelabz standard deliverable? 2D DWG + PDF + E57 point cloud, with a Revit LOD 300 model as optional add-on. For heritage projects, additional HDR photographs and detailed ornamental record drawings.

How do I commission a measured building survey? The standard process: send a brief, receive a fixed-fee quote, verify surveyor credentials, arrange site access, site visit, CAD/BIM drafting, QA check, delivery. Most 2026 quotes are returned within 48 hours.

How to commission

Book a 15-minute clarity call with an Icelabz measured building surveyor. We'll review your situation and give you a fixed fee in 24 hours. Or read the complete measured building survey guide and see the measured building survey service page and 3D laser scanning service page for the full service descriptions.