Description

Retrofitting insulation into external timber-framed walls with no underlay brings the risk of water transfer from the back of the cladding to the insulation and/or framing.

BRANZ investigated this in direct-fixed weatherboard walls. Using drainage plane mesh together with underlay was found to be the best method of reducing moisture transfer. It also allows for thicker insulation than some other options.

Scope

This Research Now includes:

• Test procedure and analysis
• Results 
  • Insulation without underlay or separation (no mitigation)
  • Insulation without separation and with retrofitted underlay (a method in NZS 4246:2016)
  • Insulation with 20 mm separation and without underlay (a method in NZS 4246:2016)
  • Insulation with separation via drainage plane mesh and underlay (an alternative method)
  • Insulation with separation via drainage plane mesh and underlay taping underlay to framing or tucking strip of underlay behind framing
  • Inspecting the framing before retrofitting
• Conclusion