Technical Booklet C Site Preparation and Resistance to Contaminants and Moisture·Page 26·5.19
Interstitial condensation risk with DPM on cold side of insulation
When the DPM is placed on the cold side of insulation, a vapour control layer (VCL) is required to prevent year-on-year interstitial condensation accumulation, unless condensation analysis software confirms the risk is acceptable with high vapour resistance insulation.
When the DPM is placed on the cold side of the insulation there is a risk of interstitial condensation which may accumulate year-on-year and a VCL will be required. However, with insulation of high vapour resistance, a VCL may not be necessary but designers should use condensation software to determine if there is a risk of a year-on-year build up of interstitial condensation (see paragraph 8.2).
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