Technical Booklet F1 Conservation of Fuel and Power in Dwellings·Page 19·1.5, 1.6
Service openings in walls and roofs
Openings in walls and roofs for building services such as waste pipes, ventilators, flue pipes or passive stack ventilators should be treated as part of the wall or roof fabric and assigned the same U-value as that element.
An opening in a wall to accommodate building services, such as a waste pipe or ventilator, should be regarded as part of the wall and assumed to have the same U-value as the wall.
An opening in a roof to accommodate building services, such as a flue pipe or passive stack ventilator, should be regarded as part of the roof and assumed to have the same U-value as the roof.
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