Creating construction build-ups in IES VE can be time-consuming, particularly when working with multiple walls, roofs and floors with different U-values.
To make this easier, BPEX has developed two Python scripts that automatically create Part L 2026 construction build-ups in your IES VE project.
The scripts are provided as .txt (Text Document) files. Before using them in IES VE, simply rename the downloaded files by changing the file extension from .txt to .py. Step-by-step instructions are provided below.
The scripts cover dwellings and non-domestic buildings in England, using representative materials and layer thicknesses to achieve the relevant limiting U-values.
Both scripts are available to download below.
1. Part L 2026: Dwellings
19 ready-made constructions: Based on Approved Document L, Volume 1: Dwellings (2026 edition).
The script creates constructions for roofs, external walls, floors, party walls, doors, windows and rooflights.
It includes examples for new dwellings, extensions and existing building upgrades.
Download:
2. Part L 2026: Non-domestic buildings
15 ready-made constructions: Based on Approved Document L, Volume 2: Buildings Other Than Dwellings (2026 edition).
The script creates constructions for walls, roofs, floors, windows, rooflights and different door types.
It includes examples for new buildings, extensions, replacement elements and existing building upgrades.
Download:
3. Construction reference workbook
We have also included an Excel workbook containing the construction names, intended applications, U-values, thermal mass values, representative build-ups and regulatory references.
This makes it easier to understand the assumptions used and document them in your modelling reports.
Download:
How to import the scripts into IES VE
You do not need to build the constructions manually. Follow these steps:
- Download the relevant text files and save it in a folder on your computer
- Convert the relevant .txt files into .py files (see instructions below)
- Open IES VE and save a backup of your project
- Open the Python editor by selecting
Tools > VEScripts - Add your script folder by right-clicking in the file list and selecting
Add script folder - Select the BPEX script from the file list and click
Run - Check the results in the output window, then open your project’s construction database to review the new constructions
Part L 2026 and Part L 2021
Many of the headline limiting U-values introduced in Part L 2021 have been retained in the 2026 edition.
However, some requirements for existing elements differ. Always check which edition and requirements apply to your project.
The 2026 edition takes effect in England from 24 March 2027, or 24 September 2027 for higher-risk building work, subject to transitional arrangements.
Coming soon: Historical Part L construction scripts
We are working on further scripts to support modelling and assessment of existing buildings against earlier Building Regulations.
| Part L edition | Availability |
|---|---|
| Part L 2013 | Coming soon |
| Part L 2010 | Coming soon |
| Part L 2006 | Coming soon |
| Part L 2002 | Coming soon |
These will help users quickly create representative building fabric constructions associated with earlier regulatory standards.
Important:
The BPEX scripts use representative construction build-ups for energy modelling. They do not represent specific products or verified as-built constructions.
Users should check U-values, glazing properties, thermal mass and other assumptions against their project requirements. Meeting a limiting U-value alone does not demonstrate Building Regulations compliance.
References: Approved Document L 2026, GOV.UK.
BPEX is an independent educational resource and is not affiliated with or endorsed by Integrated Environmental Solutions Ltd. IES VE is a software product of Integrated Environmental Solutions Ltd.