Lean-to roofs

Duo-pitched roof with a central division wall

Care and attention to detail are required in this type of lean-to construction when fixing the head of the rafters in order to ensure rigidity while still ensuring the party wall contains sufficient fire-stopping and sound insulation. The sketches opposite show the approach recommended for such details. The rafters and ceiling joists are omitted from the sketches for clarity.

Diagram D57 - Duo pitched roof with party wall detail with fire stoppingg

Diagram D57 - Duo pitched roof with party wall detail with fire stopping

Diagram illustrating typical “back-to-back” dwellings.

Diagram D58 - Duo pitched roof with party wall strapping detail

Diagram D58 - Duo pitched roof with party wall strapping detail

Detail – Shows positive fixing of rafters to prevent horizontal thrust at eaves.

Diagram D59 - Duo pitched monotruss

Diagram D59 - Duo pitched monotruss

Diagram D60 - Duo pitched roof with party wall

Diagram D60 - Duo pitched roof with party wall

Prefabricated mono trusses as shown above can be used as an alternative to “cut timber” back-to-back lean-to construction.

Diagram illustrating a typical “back-to-back” detail where prefabricated mono trusses are used.

Lean-to roofs

Diagram D61 - Lean to abutment detail

Diagram D61 - Lean to abutment detail

Abutment detail

The diagram above shows the flashings detail for abutments of porch and lean-to roofs. Flashings should be built into the cavity tray as shown and ventilation should be provided to the roof as explained previously.