U-Value &
Condensation Risk
Calculations.
Thermal performance and condensation risk calculations for proposed construction build-ups. EBSNI supports architects, specifiers and project teams across the UK and Ireland with documented assessments of walls, roofs and floors.
Walls, roofs and floors
Calculated U-values for the stated construction
Assessment method matched to the build-up
Project-specific scope and requirements
Understand the
Construction Build-Up.
A U-value describes the rate of heat transfer through a building element, expressed in W/(m²·K). A lower value means less heat passes through that element for the same area and temperature difference. The result depends on the construction layers and relevant detailing.
Condensation risk analysis considers moisture behaviour under stated conditions. Surface condensation occurs at a surface; interstitial condensation occurs within a construction. A thermal calculation alone does not establish that a build-up is moisture-safe.
EBSNI reviews the specified materials, layer order and supporting product data before confirming the appropriate calculation scope. Results document the assessed construction, inputs and assumptions so designers can review the proposed detail.
Fabric Performance Requirements
Across the UK & Ireland.
Thermal targets and moisture provisions depend on the jurisdiction, building type and work proposed. We agree the calculation purpose and applicable assessment route before reviewing the construction.
Northern Ireland
In Northern Ireland, Technical Booklets F1 and F2 address energy requirements for dwellings and non-domestic buildings respectively. Fabric calculations can support the relevant assessment.
The required performance depends on the work and applicable provisions. Moisture resistance and the suitability of the construction detail need separate consideration.
England & Wales
England and Wales have separate Approved Document L guidance. U-value calculations can support fabric specification and the relevant building energy assessment.
The project’s location and regulatory edition determine the applicable requirements. A U-value result does not, by itself, establish compliance with every energy or moisture provision.
Scotland
Section 6 of the Scottish Technical Handbooks addresses energy performance. Calculated fabric properties may form part of the relevant design and warrant information.
The proposed construction also needs to satisfy the applicable moisture provisions. We confirm the calculation scope with the project team.
Republic of Ireland
In the Republic of Ireland, Technical Guidance Document L addresses energy performance for dwellings and buildings other than dwellings. Fabric inputs support the appropriate Irish assessment route.
The building type, proposed work and applicable guidance determine the requirements. Moisture performance must be considered alongside thermal performance.
Calculation methods are selected for the construction and purpose. Relevant references include EN ISO 6946 for suitable building elements, EN ISO 13370 for heat transfer via the ground, and EN ISO 13788 for simplified condensation assessment where appropriate. UK moisture design should also consider BS 5250. The report states the method and limitations used.
Review the Layers
Before the Detail Is Fixed.
Send the full construction from inside to outside, including finishes, membranes, cavities and repeated structural members. Insulation thickness alone is not enough to establish the performance of an assembly.
A simplified condensation calculation is not suitable for every construction or exposure. Where its assumptions do not match the proposed detail, the need for a different moisture assessment must be identified before relying on the result.
From Construction Detail
to Calculation Report.
We confirm the purpose and suitability of the assessment first, then review the information and complete the agreed calculations. Product substitutions or later detail changes may require the results to be revised.
Confirm the Element
Send the location, project stage, construction type and assessment purpose. We agree the scope and required outputs.
→Review the Build-Up
We check the layer sequence, dimensions and thermal or vapour data, identifying missing information and assumptions.
→Assess the Detail
We apply the appropriate method within the agreed scope and discuss the implications of the proposed specification.
→Document the Result
The report records the assessed construction, calculation basis, results and limitations for the project team’s review.
✓Preparing Your
Construction Details.
Provide product-specific information where possible. Tell us which materials are confirmed and identify any provisional selections so the basis of the report is clear.
Common Questions.
What is a U-value?
A U-value expresses thermal transmittance in W/(m²·K). It describes heat flow through a building element per unit area and temperature difference. Lower values indicate less heat transfer through the assessed element under the stated calculation conditions.
What information is needed for a calculation?
We need the construction layers in order, their thicknesses and relevant material properties, together with details such as framing, cavities and fixings. Product datasheets and membrane information help establish a traceable basis. Floor calculations may require additional geometry and ground information.
Does a low U-value mean there is no condensation risk?
No. Thermal performance and moisture behaviour are different matters. The layer sequence, vapour properties, environmental conditions and detailing affect condensation risk. A low U-value does not establish that the construction is suitable in every moisture condition.
Is a simplified condensation calculation suitable for every build-up?
No. The appropriate method depends on the construction, exposure and moisture mechanisms involved. A simplified assessment under EN ISO 13788 has limitations and cannot represent every situation. Some details need a different or more detailed moisture assessment, whose scope must be agreed separately.
What happens if the proposed build-up needs changing?
We explain the assessed result and discuss agreed specification revisions with the design team. Any revised calculation must use the updated layers and product data. A calculation does not replace the designer’s responsibility to coordinate construction, moisture management and workmanship requirements.
Does this include thermal bridging calculations or a site survey?
This service assesses the agreed element build-up from the supplied information. Junction psi-value calculations are not included. An inspection of an existing building, investigation of concealed construction or diagnosis of damp is a separate scope and should not be assumed to form part of the calculation report.
One Build-Up.
A Traceable Assessment.
For a proposed wall or roof, the team supplies the layer sequence, dimensions and product data. The agreed assessment records the thermal performance and condensation findings within the method’s scope, giving the designer a documented basis for reviewing the detail before construction.
Discuss Your ProjectDiscuss Your Construction Build-Up
Send the location, section detail, product information and programme. We will confirm the appropriate calculation scope. Part of the Newell Group.
