AutoPSI thermal modelling software
Calculate PSI values for SAP and fRsi values for retrofit in minutes. Quick, precise and simple enough for the whole technical team.
Outside 0 °CInside 20 °C
Change the way you calculate PSI values
Designing to the Building Regulations means balancing a lot of decisions. Traditional thermal modelling software is complex, slow and expensive, while the defaults you're allowed to use instead can drive up the cost of meeting the regulations.
That's a challenge for technical teams, housebuilders, architects and SAP assessors alike. AutoPSI gives you a dedicated PSI value tool, so you can model junctions quickly and pass each assessment with ease.
Why modelled values matter
With Accredited Construction Details withdrawn under Part L 2021, every junction needs its own PSI value or takes a default — and the default can be far worse than how the detail really performs. Modelling it accurately can improve the SAP rating and reduce the need for other energy measures.
Features
- Exceptionally fastPSI values in minutes rather than days.
- IntuitiveDrag and drop layers and bridges to build the junction.
- Fully customisableModel bespoke junctions to match your actual details.
- Reliable and accurateSelf-accredited for 2D calculations to BR 497 conventions.
- Fully onlineAccess your models anywhere, with nothing to install.
- CollaborativeShare designs easily with everyone on the project.
Who it's for
Anyone completing SAP assessments, or assessing mould and condensation risk in renovation work.
- Housebuilders
- Architects
- SAP assessors
- Retrofit assessors and coordinators
- Construction product manufacturers
AutoPSI is used by teams at manufacturers and consultancies including Knauf, Rockwool, Saint-Gobain, Celotex, Recticel, Superglass, SIG, Actis, Proctor and Galaxy Insulation.
Questions about PSI values and AutoPSI
What is a PSI value?
A PSI (ψ) value is the linear thermal transmittance of a junction, measured in W/mK. It captures the extra heat lost along the length of a junction — where a wall meets a floor, roof or window — beyond what the U-values of the plain elements account for.
Why calculate PSI values instead of using defaults?
Since Part L 2021 removed Accredited Construction Details, junctions without a calculated value must use default PSI values in SAP. Defaults are deliberately pessimistic, so a modelled value usually improves the result and avoids paying for extra insulation or renewables elsewhere.
What is an fRsi value?
The temperature factor (fRsi) compares the coldest internal surface temperature at a junction with the inside and outside temperatures. It is used to assess the risk of surface condensation and mould growth; for dwellings, BR 497 guidance uses a critical value of 0.75.
Who can use AutoPSI?
AutoPSI is used by housebuilders, architects, SAP assessors, retrofit assessors and coordinators, and construction product manufacturers.
Can I try AutoPSI before buying?
Yes. You can start a free trial of AutoPSI online with no credit card required.
Model your first junction today
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