Accurate Ψ-value and psi calculations for Part L compliance
At Barlings KWA, we provide professional thermal bridging detail calculations to support SAP, SBEM, and Building Regulations compliance.
Thermal bridges occur at junctions where building elements meet, such as:
- wall to floor junctions
- wall to roof junctions
- window jambs, heads and sills
- lintels
- corners
These junctions can significantly increase heat loss and condensation risk if not properly assessed.
Our detailed psi value calculations help demonstrate compliance with Building Regulations Part L while improving overall fabric performance.
What Are Thermal Bridging Calculations?
A thermal bridging calculation measures the additional heat loss at junctions in the building envelope.
This is expressed as a Ψ-value (psi value) in W/mK.
Unlike a U-value, which measures heat loss through an area, a psi value measures heat loss along a junction line.
Typical examples include:
- where the external wall meets the ground floor
- roof eaves details
- window and door openings
- steel beam penetrations
- junctions around flat roof upstands
These values are then entered into SAP or SBEM calculations to improve the overall Y-value and energy performance result.
Why Are They Important?
Even when wall, roof, and floor U-values are good, poor junction details can create significant additional heat loss.
Thermal bridges may contribute a substantial proportion of total fabric heat loss and can also increase the risk of:
- surface condensation
- mould growth
- cold spots
- occupant discomfort
By calculating the junctions accurately, we can often improve the SAP result compared with default assumptions.
When Do You Need Them?
You may need thermal bridge calculations for:
- new dwellings
- extension details
- commercial Part L projects
- bespoke junction details
- steel frame interfaces
- retrofit insulation projects
- SAP and SBEM compliance
- condensation risk checks
This is especially useful where standard manufacturer details are not available.
Our Service Includes
At Barlings KWA, we provide:
- bespoke junction psi calculations
- linear thermal transmittance (Ψ) values
- condensation temperature factor checks
- SAP and SBEM compatible outputs
- BR 497 compliant calculations
- practical junction improvement advice
- fast turnaround
Calculations are undertaken in accordance with BRE BR 497
Request a Quote
Need thermal bridging calculations for your project?
Contact Barlings KWA for a fast quotation and expert advice.
Email:william@barlingskwa.co.uk
Call: 01522 797344