Beware Roof Upstands Causing Dwelling Condensation

Increasing numbers of upstands are required on rooftops for placing mechanical plant, such as heat pumps, leading to hygrothermal risks. The risk impacts compliance with Part C and Part L of the Building Regulations.

Though the roof is insulated, the upstands are typically not and penetrate above the insultation line.  Upstands that are not adequately thermally broken act as a lightning rod for the cold outside getting into the dwelling below.

This leads to a risk of:

• Lower average roof U values impacting fabric compliance requirements;
• Cold spot on the underside of the warm dwelling creating the condensation risk.

There are several steps that can be considered to minimise the risk including using thermally broken upstands or insulating the upstand walls.