U-values and Condensation Risk

Specification

Thermal performance of a PVC-U window frame; frame detail (top) and thermal bridging through reinforcement and glazing spacer (bottom).

Specifying component U-values does not guarantee that a cladding system will meet the requirements of the Building Regulations: U-values of some components can be calculated or reported to give at least three different figures, each requiring adjacent components to be differently allowed for.

Sandberg provides specialist advice to help Specifiers to:

• Ensure that facades perform as required by the client and by Building Regulations
• Check compliance of proposed solutions with the specification
• Identify technologies that will deliver the specified performance
• Achieve sensible performance requirements with a low risk of condensation

Design Support

Heat flow through cladding systems is a complex three-dimensional process. Sandberg uses advanced computer prediction techniques, fully validated to the latest Standards, to accurately predict heat flow through cladding details and:

• Derive component and facade average U-values
• Identify thermal bridging
• Compare alternative designs to achieve optimum performance
• Establish real temperature distributions through components and predict condensation risk

Investigation

Should a problem be suspected during or after construction, Sandberg offers a number of alternatives.

• Review of specification and design drawings to identify areas of concern
• Site visit and basic measurement to check performance of components or systems
• Computer prediction of performance
• Infra-red thermographic survey of building to locate hot/cold spots

It is recommended that all new buildings be subject to an infra-red survey, which can be used to identify:

• Missing, slumped or wet insulation
• Thermal bridging
• Omitted thermal isolators
• Unexpected air spaces or voids
• Air leakage paths