Thermal bridge analysis.
Every junction inside-to-outside is a potential thermal bridge. We model each to BS EN ISO 10211, build the PHPP-ready catalogue, and detail every fix for the contractor.
What thermal bridge analysis delivers.
What it isA thermal bridge is any junction in the building envelope where heat flows faster than through the surrounding construction: a wall-to-floor connection, a balcony slab, a lintel, a window reveal, a column embedded in a facade. In a Passivhaus building, where wall and roof U-values are already very low, thermal bridges can account for 20 to 40 percent of the remaining transmission heat loss. The PHI standard requires every linear thermal bridge to be calculated to BS EN ISO 10211 and entered into the PHPP model. Estimated or assumed values are not acceptable for certification.
Our analysis gives you three things: the psi-value for each junction (in W/mK, for PHPP input), the temperature factor for condensation-risk assessment, and a drawn and annotated junction detail that the contractor can work from on site.
The PHI recommends keeping each individual linear thermal transmittance below 0.01 W/mK. Above this threshold the junction must be explicitly modelled and entered into PHPP. A well-designed wall-floor junction can achieve 0.001 to 0.005 W/mK. An unbroken concrete balcony slab can reach 0.50 W/mK or more.
All models are built to BS EN ISO 10211 boundary conditions and validated against the standard’s benchmarks. Where the geometry requires 3D analysis, we use validated three-dimensional FEA. Every model is reviewed by a PHI-accredited Passivhaus certifier before it leaves the office.
Method: how we work.
MethodWe review the architectural and structural drawings and identify every distinct junction type: wall-floor, wall-roof, wall-wall corner, balcony, opening reveals, pipe and duct penetrations. We agree the junction list with the design team before modelling begins, so there are no surprises at the end.
Each junction is modelled in 2D finite-element analysis software validated to BS EN ISO 10211. Where geometry demands it, we run 3D models: corner columns, balcony ties, point fixings. Boundary conditions follow the standard: internal surface resistance, external surface resistance and declared material conductivities from product data or BS EN ISO 10456 tabulated values.
The linear thermal transmittance (psi-value, W/mK) is extracted from each model for PHPP entry. The temperature factor fRsi is calculated for condensation-risk assessment to BS EN ISO 13788. Where the temperature factor falls below the threshold for the project’s climate and internal conditions, we flag the junction for redesign.
Results are compiled into a junction catalogue: each junction shown as a cross-section, with the psi-value, the fRsi, a description of the assembly, and notes for the contractor. The PHPP model is updated with the calculated values in place of the assumed defaults. If a junction fails the condensation check or the psi-value is higher than the target, we advise on redesign options before the catalogue is issued.
Estimate your thermal bridge scope.
Use our thermal bridge estimator to size the job in 30 seconds. Real Mosart rates, indicative scope and fee, confirmed by a certifier before it becomes a quote.
Common questions.
FAQWhat is a thermal bridge and why does it matter for Passivhaus?
A thermal bridge is any junction in the building envelope where heat flows faster than through the surrounding fabric: a wall-to-floor connection, a balcony slab, a lintel, a window reveal. In a standard building the heat loss through thermal bridges is a modest fraction of the total. In a Passivhaus, where wall and roof U-values are already very low, thermal bridges become a large proportion of the remaining heat loss. The PHI Passivhaus standard requires every linear thermal bridge to be calculated to BS EN ISO 10211 and entered into the PHPP model: estimated values are not acceptable for certification.
What is the difference between 2D and 3D thermal bridge modelling?
Most building junctions can be accurately modelled in two dimensions: a wall-floor junction, a parapet, a window head or cill. The 2D cross-section captures the heat flow path completely. Three-dimensional modelling is needed where geometry in a third direction significantly affects the result: a corner column embedded in an insulated wall, a balcony tie through insulation, a point fixing. We use validated 2D FEA tools for standard junctions and 3D analysis where the geometry demands it.
How many thermal bridges does a typical Passivhaus project require?
A typical single dwelling has 15 to 30 distinct junction types once repetition is factored in. A multi-unit residential scheme might have 40 to 60 distinct junctions: more if there are balconies, transfer structures or complex facade systems. We produce a junction catalogue that covers every type, and the contractor draws on the same catalogue for on-site guidance. Use our thermal bridge estimator to get an indicative scope and fee in 30 seconds.
Can thermal bridge analysis reduce a building’s PHPP space-heating demand?
Yes, significantly. On a building with a high-performance envelope, thermal bridges can account for 20 to 40 percent of the remaining transmission heat loss. Redesigning a wall-to-floor junction to route insulation continuously, or replacing a concrete balcony slab penetration with a proprietary thermal break element, can cut the psi-value for that junction by 80 to 90 percent. When we model thermal bridges early in the design, the architect and structural engineer still have full freedom to change the detail. Modelling late, after the structure is fixed, leaves only expensive proprietary solutions or a failed certification.
Start with the estimator.
Use the thermal bridge estimator for a 30-second indicative scope and fee. Or contact us directly if you want to talk through the junction list.