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Part O (Approved Document O) overheating assessments across Bristol & the South West — Bristol City, Bath & North East Somerset, South Gloucestershire and North Somerset. CIBSE TM59 dynamic thermal modelling for high-risk dwellings. 5 day turnaround for planning and Building Control submission.
Part O specialists · TM59 dynamic modelling · 5 day turnaround
Thanks — we'll confirm pricing and timeline within one working day.
Bristol & the South West presents a varied overheating risk profile — south-facing harbourside apartments with high solar exposure, Bath stone-faced flats with limited window options, conservation constraints on external shading, and dense urban infill across the city centre. Approved Document O came into force in June 2022 and applies to all new residential developments and material changes of use that create new dwellings — including conversions, HMOs, student accommodation, and care homes.
A Part O Overheating Assessment is required at design stage to demonstrate the dwelling has been designed to limit solar and internal heat gains. The assessment is mandatory for Building Control sign-off and increasingly required at planning submission for major residential schemes across the South West.
We deliver both the Simplified Method (suitable for lower-risk locations with standard mitigation) and the more rigorous Dynamic Thermal Modelling (CIBSE TM59) for higher-risk dwellings — particularly south- or west-facing apartments, single-aspect units, or schemes in dense urban settings. Most the South West planning conditions accept either route provided the methodology is correctly applied.
The Bristol One City Plan, the Climate Emergency commitments, and BNES heritage policies increasingly references Part O risk evidence at validation stage. We deliver a full Part O Overheating Assessment package in 5 working days, suitable for both planning and Building Control submission.
SAP is desk-based, so we can work in parallel with your design team from anywhere. Most projects are turned around in 3-5 working days from receipt of drawings.
The fastest Part O turnarounds happen when we receive the full information pack up front: floor plans showing orientation, glazing schedule (frame and glass), shading details (any external shutters, brise-soleil, deep reveals), and the proposed ventilation / cooling strategy.
If the scheme is at outline planning, send what you have. We can run an initial risk screen using sensible assumptions to flag high-risk dwellings early — that's the cheapest stage to redesign overheating issues out of the scheme.
Major residential planning conditions in the South West increasingly require Part O evidence at validation. Get in touch early and we'll work back from your submission date.
Local knowledge of overheating risk profiles, conservation constraints, and planning condition wording for each the South West LPA.
Outside the South West? See our Part O pages for Birmingham, Gloucestershire, Warwickshire, Worcestershire.
Part O is Approved Document O, the part of the Building Regulations covering overheating in new residential dwellings.
It came into force in June 2022 and applies to new builds, conversions, HMOs, student accommodation and care homes.
Yes for any new residential dwelling or material change of use creating a dwelling. This includes single-plot self-builds, multi-unit developments, apartment blocks, HMOs and conversions.
The Simplified Method uses fixed limits on glazing-to-floor area ratios and minimum openable areas, suitable for low-risk locations.
TM59 dynamic modelling simulates the dwelling hour by hour against CIBSE TM59 criteria — required for high-risk dwellings and recommended where the Simplified Method is too restrictive.
We recommend the lowest-cost mitigation — external shading (brise-soleil, shutters, deep reveals), reduced glazing g-value, increased openable area, MVHR with summer bypass, or in extreme cases mechanical cooling.
We re-run the model at no extra cost during the same project.
Part O does not generally apply to extensions to existing dwellings — only to new dwellings or material changes of use creating new dwellings.
Over-glazed extensions are covered separately under Part L.
Heritage settings often restrict external shading (shutters, brise-soleil). We work within those constraints by focusing on glazing specification, internal mitigation, ventilation strategy and dwelling orientation to achieve TM59 compliance without visible external interventions.
Yes. We deliver Part O Overheating Assessments across all 4 LPAs in the South West.
Part O is desk-based using CIBSE weather files, so location within the South West makes no difference to turnaround.
5 day turnaround for the Simplified Method, 7-8 days for TM59 dynamic modelling. Send us your plans, glazing schedule and ventilation strategy — we'll quote within one working day.