Building regulations in Wales: Part L U-values for commercial buildings

This guide covers non-domestic insulation only. For anything else in the Welsh building regulations, such as extensions, windows, fire safety or making an application, start at gov.wales.

First, establish which table and column fit the work. Your designer or building control body confirms the category and applicable table; HOLVEM calculates the build-up against it. This guide is not legal or design advice.

01Which document applies

Which Part L document applies to a commercial building in Wales?

Before choosing an insulation depth, choose the right document. Wales publishes its own Approved Documents. For non-domestic insulation, use Approved Document L, Volume 2, buildings other than dwellings. Volume 1 concerns dwellings and is outside this guide.

The Welsh 2022 edition took effect on 29 March 2023. Its introductory page allows earlier rules for qualifying notices or applications submitted before that date where work on each building started before 29 March 2024. Circular Letter 005/2022 carries the full transitional arrangements.

As at 14 October 2026, the 2022 edition is the current starting point. Wales has published a 2026 edition for use from 4 March 2027, with its own transition. England's documents do not apply to a Welsh building, even where a figure happens to match.

02New and replacement limits

Limiting U-values for new and replacement elements

With the document settled, identify the element and the building category. Welsh Table 4.1 has three columns: new buildings, existing buildings essentially domestic in character, and all other existing buildings. These are maximum U-values, in W/m²K; a lower number means less heat passes through the element.

Source: Welsh Volume 2, 2022 edition, Table 4.1, printed pp.36 to 37, PDF pp.40 to 41. Roof, wall and floor cells and notes checked against the PDF on 14 October 2026.

The existing-building columns concern new or replacement elements in those buildings. They are not a blanket instruction to give every unchanged existing roof that U-value. Renovation of an existing element has a separate table below.

The figures describe the whole element, including its layers, framing and fixings. A thickness copied from another roof does not establish your result.

03The Wales-only column

“Essentially domestic in character”: the Wales-only column

The building's use decides which existing-building column to read. Note 5 names student accommodation, care homes and similar uses where occupancy and internal heat gains are essentially domestic in character. These remain within Volume 2; they are not ordinary dwellings under Volume 1.

For these existing buildings, the roof figure is 0.15 W/m²K for all three roof types listed, with 0.21 for walls and 0.18 for floors. The all-other column has different wall, floor and roof figures. Calling a building “commercial” is therefore not enough to select the column.

Tell your designer or building control body how the space is used. Once the column is confirmed, we can calculate against its target.

04Renovating an element

Renovating an existing roof, wall or floor

If the work retains and improves an existing element, turn to Table 4.2. It has a threshold column and an improved-value column. Paragraph 4.7 directs renovated elements towards the improved values; the threshold is not a second target to choose simply because it needs less insulation.

All figures are W/m²K. Source: Welsh Volume 2, 2022, Table 4.2, printed p.40, PDF p.44, checked against the PDF on 14 October 2026. The table's notes remain relevant to the particular construction.

When the renovation provisions apply

Regulation 23 addresses renovation of more than 50% of an individual thermal element's surface area, or work constituting a major renovation. Section 11 defines a major renovation as more than 25% of the external building envelope's surface area being renovated. The 50% test is measured on one element; the 25% test on the whole building envelope.

The provisions concern upgrading the whole element so far as technically, functionally and economically feasible. See the regulation extract on printed p.98 and Section 11 on p.102. Confirm the planned work's category with your designer or building control body.

If the improved value is not feasible

Paragraph 4.8 gives the route where the column (b) value is not economically, functionally or technically feasible: upgrade the element as far as is feasible, with column (a) as the reference. Record the construction supporting that decision.

For economic feasibility, the document uses a 15-year simple payback test. It compares the cost of the improvement measure with its annual energy saving. It is not a promise that your project will save a particular amount or recover its cost within that period.

Notes 11 and 12 to Table 4.1 allow a lesser provision where meeting the standard would reduce a room's internal floor area by more than 5% or create significant problems with adjoining floor levels. Keep the reason for a different provision with the specification. See paragraphs 4.7 to 4.8, printed pp.38 to 39.

05Wales against England

How Wales differs from England, and where it is the same

Compare like with like: Wales is tighter in some cells and looser in others. This table compares the current Welsh 2022 Table 4.1 with England's 2021 edition incorporating 2023 amendments, Table 4.1. It concerns new or replacement elements, not the renovation table.

All figures are W/m²K. Wales source: Table 4.1, printed pp.36 to 37, PDF pp.40 to 41. England source: Volume 2, 2021 edition with 2023 amendments, Table 4.1, printed p.25, PDF p.35. Both checked against the PDFs on 14 October 2026.

For an existing building in the all-other Welsh category, a new or replacement pitched roof insulated at ceiling level needs 0.15, against England's 0.16. At rafter level the Welsh figure is 0.18, against England's 0.16. The direction of the difference changes with the construction.

Walls match at 0.26; existing-building flat roofs match at 0.18. Welsh floors in the all-other category use 0.22, compared with England's 0.18. The separate Welsh domestic-character column has no corresponding column in England's Table 4.1.

For renovation, the roof, wall and floor threshold and improved figures in Table 4.2 are the same in both documents. Both also use the 15-year simple payback test. For the English guide, follow building regulations U-values in England.

06Two editions, two dates

2027: two new editions, two dates

If the programme reaches into 2027, put the nation and the notice date beside the specification. A “2026 edition” does not yet apply to work in 2026.

The Welsh 2026 document retains the roof, wall and floor values shown above. The tables become 3.1, printed pp.37 to 38, and 3.2, p.41. Their cells were checked against the 2022 tables on 14 October 2026.

Circular Letter 003/2026 gives Wales's full transition. England's Circular 01/2026 has its own dates, including a separate 24 September 2027 commencement for the specified higher-risk building work. Keep those English arrangements out of a Welsh specification.

Want a ballpark figure for your building?

Send photographs or drawings for a free estimate, no survey needed. We measure your roof from satellite and aerial imagery for a ballpark area first, then confirm every measurement in person.

Send photographs | Start a project brief

07Getting a calculated value

Getting a calculated U-value for a building in Wales

Once the work category, column and target are confirmed, we can turn them into a proposed build-up. Send drawings, photographs, the building's use and the information you have about the existing layers. Include the designer's target and the applicable document edition if these are already agreed.

HOLVEM calculates it for the roof as it will be built, timber and fixings included, and shows the working.

Our roof deliverables include a calculation on the BS EN ISO 6946 method with the bridge correction stated, and the assumptions alongside the figure. They also include a condensation risk analysis, with a WUFI report where the simple method is inconclusive. The thermal figure and the moisture assessment answer different questions about the same construction.

For a calculated U-value for your building, the written specification shows the layers and the result the proposed construction is designed to achieve. A calculated result is not a metered outcome or a promise of an EPC band.

The right photographs & measurements often get you a free, same-day estimate, no survey needed. Drawings can support that estimate too. The virtual survey uses aerial imagery alongside your information.

How it works: Send photographs or drawings → free, same-day estimate with a virtual survey → confirmed on install, or a free survey and firm written quote for larger jobs.

Straightforward jobs are confirmed on installation day before work starts. Larger or complex jobs get a free survey first, then a firm written quote. No obligation either way.

A binding quotation is issued in writing before work starts, from a survey or from the photographs and drawings you send.

08Why HOLVEM

Why HOLVEM

A roof that passes England's table can still miss the Welsh one: on an existing building, a pitched roof insulated at ceiling level needs 0.15 W/m²K in Wales, where England asks for 0.16.

That comparison is for new or replacement elements in Table 4.1's all-other existing-building category.

• The Welsh document follows the building. One team surveys, specifies and installs, across England and Wales from four depots. On Welsh buildings, we work to the Welsh Approved Document L.
• The calculation becomes the specification. We use certified spray foam systems, which we apply as an accredited installer for the manufacturer. The U-value calculation and condensation risk analysis inform the written build-up; the QA pack gives building control and your surveyor the application evidence to review.
• The retained roof stays overhead. Where the construction suits underside insulation, the building avoids a roof strip-out and weeks open to the weather.
• You can compare the methods. Closed-cell foam starts at £16/m² + VAT, against overcladding at £60 to £90/m² and replacement at £100 to £160/m². Typical UK industry figures, 2026. Send photographs or drawings for a free estimate. See the cost guide.
• The warranties come to you. Backed by a 25 year product and workmanship warranty.

Send drawings and the building's use, with the Welsh column confirmed by your designer or building control body, so we can calculate the proposed installation.

Start a project brief

09Which column applies

Three questions point to the table and column.

Answer the three below. The result names the table and column to check; your designer or building control body confirms them.

10Questions, answered

FAQ

Do England's Part L U-values apply in Wales?

No. Wales publishes its own Approved Document L. Use the Welsh Volume 2 tables for non-domestic work and confirm the applicable edition and work category with your designer or building control body.

What U-value does a commercial roof need in Wales?

Table 4.1 gives 0.20 W/m²K for the listed roofs in new buildings. For new or replacement roofs in all-other existing buildings, it gives 0.18 for flat and rafter-level pitched roofs, and 0.15 for ceiling-level pitched roofs. Existing buildings essentially domestic in character use 0.15 for all three. Renovation has Table 4.2.

How is Part L in Wales different from England for commercial buildings?

For new and replacement elements, walls match at 0.26 W/m²K, while several roof and floor figures differ by building category and roof type. Renovation threshold and improved values, and the 15-year simple payback test, match in the current documents.

Does the 2026 Approved Document L apply in Wales?

England's does not. Wales's own 2026 Volume 2 takes effect on 4 March 2027, subject to transitional arrangements. Its listed roof, wall and floor limits remain the same as in the Welsh 2022 edition.

When do I have to upgrade an existing roof, wall or floor?

The planned work and renovation provisions decide that. Where the element is being renovated under those provisions, Table 4.2's improved values apply, with the feasibility route in paragraphs 4.7 to 4.8 where needed. Economic feasibility uses the 15-year simple payback test.

What does “essentially domestic in character” mean?

Note 5 to Table 4.1 gives student accommodation, care homes and similar uses with essentially domestic occupancy and internal heat gains as examples. Confirm the building's category before selecting its existing-building column.

Will insulating the roof improve my EPC?

Insulation improves the building fabric the assessor rates. The resulting EPC depends on the building and assessment; no band is promised. See commercial EPC requirements for the separate assessment and letting questions.