1 Welcome

1.2 What’s changed

What’s changed in NHBC Standards 2025?

We have a new Part 11 for NHBC Standards 2025 plus new or updated technical information affecting around 5% of the total clauses. In addition, we’ve made improvements to clause and sub-clause numbering which will make recording of Reportable Items and claims information more accurate. There are no changes to Technical Requirements R1 to R5.

Here are the most significant technical changes:

Part 11 — new section on Modern Methods of Construction incorporating three new chapters: general requirements, closed panel systems and volumetric systems
Chapter 3.3 — updates to durability and the requirements for free draining post bases and service life expectations for non-structural timber components for porches and canopies
Chapter 4.4 — enhanced guidance on compressible materials
Chapter 5.3 — introduction of clause on drainage under buildings
Chapter 5.4 — general update and introduction of commentary concerning free lime/mineral salt leaching and use of anti-lime solutions
Chapter 6.1 — improved guidance on check reveals, full fill insulation and further clarification on complex junctions
Chapter 7.2 — additional guidance on underlay, sarking board and sheets
Chapter 8.1 — clarification on the position of cable securing for access and egress routes, update to the provision of UVHWSS discharge pipe terminations
Chapter 8.6 — updated guidance in relation to pipe insulation requirements for heating and hot water systems
Chapter 9.2 — updated requirements for moisture resistant plasterboard to ceilings.

As well as minor changes to chapters 3.1, 4.1, 4.2, 4.5, 4.6, 5.1, 5.2, 6.2, 6.3, 6.4, 6.7, 6.8, 6.10, 6.11, 8.6, 9.2

Change tracker

The table below contains a list, in chapter order, of all the technical changes made to NHBC Standards 2025 which apply to every NHBC registered home whose foundations are begun on or after 1 January 2025, applying throughout the UK, unless otherwise stated.

Chapter	Summary of significant changes
Chapter 3.1	3.1.10 — Additional guidance given relating to lapping mesh reinforcement. 3.1.14 — Additional text detailing requirements around concrete transportation and site mix concrete placed within 30 minutes. 3.1.15 — Additional text included around concrete curing during warm weather.
Chapter 3.3	3.3 — An additional definition of ‘solid external wall’ has been included following questions about timber requiring treatment when built into solid external walls. 3.3.2 — Compliance — external timber for uncoated porches and canopies service life reduced to 30 years. External timber components integral to the structure require a 60-year desired service life. 3.3.2 — Durability — new wording around 150mm from finished ground level or wall finish of piers and free draining post base. Open porch/canopy should not form part of the structure of the home. Where it does, it would require 60-year service life (as per compliance above).
Chapter 4.1	4.1.7 — Where ground gases are present and cavities need to be sealed, downward moving moisture within the cavity still needs to be removed.
Chapter 4.2	4.2.10.6 — New guidance added for seasonal events and desiccated soils.
Chapter 4.4	4.4.9 — Compressible materials — depending on the type of material adopted the thickness should take into account the minimum void required and the residual thickness of the material when compressed.
Chapter 4.5	4.5.2 — New section on provision of information and NHBC requirements.
Chapter 4.6	4.6.4 & 4.6.5.2 — Future building foundations should be assessed for effects of ‘hardspots’. 4.6.6.1 — Suitable sources of engineered fill materials — changes and appropriate testing and technical reports to be provided to NHBC. 4.6.7 Design and specification of earthworks figure 2 amended to be in line with figure 3.
Chapter 5.1	5.1.4 — Ground conditions — new section on desiccated ground.
Chapter 5.2	5.2.10 — Improved guidance for ventilators for timber floors.
Chapter 5.3	5.3.7 — Change in pipe size from 1,200mm to 1,350mm on table 4. 5.3.17 — Drainage under buildings —Included into NHBC Standards 2025 from Technical Extra 23.
Chapter 5.4	5.4.5 — Structural stability — movement — movement joints within the superstructure should be continued into the sub-structure. 5.4.7 — Waterproofing systems — Type C — new guidance detailing access points for servicing are considered as well as mineral salt leach effects.
Chapter 6.1	6.1.6 — Exposure — severe or very severe locations where building with timber frame require check reveals. 6.1.7 — Thermal insulation — guidance enhanced to cover the use of full fill. 6.1.11 — Construction of masonry walls — construction — new paragraph on bed and perpend joints detailing between 6-15mm in line with tolerances. 6.1.12 — Lintels — placing lintels — should be bedded on both leaves to ensure even distribution of loads. 6.1.17 — Provision of DPCs and cavity tray — high load DPC over 3 storeys. 6.1.17 — Additional guidance for complicated junctions providing that internal and external corners can be site folded where the quality of the fold is of the highest standards.
Chapter 6.2	6.2.9 — Fire resistance — text has been moved from section 6.2.4 with additional guidance relating to cavity barriers and design.
Chapter 6.3	6.3.9 — Minor revision to deflection head details.
Chapter 6.4	6.4.15 — Strutting — performance standard updated to include that strutting shall be provided and where required in accordance with the design. 6.4.15 Strutting should be provided along the length of joists at intervals recommended in table 4 and 5.
Chapter 6.7	6.7.3 — Clearer guidance relating to checked reveals and removal of 40-year durability requirement.
Chapter 6.8	6.8.1 — Compliance clause amended to include a broader term prefabricated chimneys.
Chapter 6.10	6.10.4 — Structural design of load-bearing floors and walls — additional support for heavy attachments may be required (boilers, kitchen units, etc).
Chapter 6.11	6.11.7 — Detailing diagram amended to show 40mm requirement to drip throat of the coping stone.
Chapter 7.2	7.2.14 — Underlay and sarking board and sheets — drape between trusses but not excessive. No drape = counter batten or proprietary spacers for drainage. Penetrations in underlay to be neatly cut or follow manufacturer’s guidance. 7.2.15 — Ventilation, vapour control and insulation — where BS 5250 cannot be incorporated then a specialist design should be included.
Chapter 8.1	8.1.4.5 — Boarded walkways and platforms should have a minimum 50mm clearance between insulation and underside of walkway to ensure ventilation. 8.1.6.1 — Cables to be secured where hanging across access and egress routes to not collapse in the event of a fire. 8.1.9.3 — Low level discharge arrangements clarified.
Chapter 8.2	8.2.1.1. — Clarification of MCS certified products and operative competency. 8.2.1.3.6 — Reference to additional requirement in PAS 63100 for the prevention of fire where battery energy storage systems are used.
Chapter 8.6	8.6.3 — Updated guidance for pipe insulation to space heating and hot water.
Chapter 9.2	9.2.4 — Updated requirements for moisture resistant plasterboard to walls and ceilings in bathrooms and ensuites. 9.2.5 — Ceramic wall tiling — change from 3mm for thin bed adhesives and 6mm for thick bed adhesives to +/- 3mm using 2m straight edge. 9.2.5 — Ceramic wall tiling, table 11 — changes to the row names for clarity and revised references for guidance relating to the provision of waterproofing systems to bath and shower enclosures.
Chapter 9.3	9.3.4 — Included guidance from TGN 9.3/01 relating to fibre reinforced screed needing to have necessary technical assessment for the fibres. 9.3.5 — Ceramic, concrete and terrazzo and similar tile finishes — standards relevant to floor finishes include — table 3 — slight wording change to fibre reinforced gypsum tile backer boards subject to assessment.
Part 11	Complete new Part.

Last updated: 2nd January 2025