This guide advises on the selection of gaskets for fixed joints (not opening joints) in the external envelope of buildings. Gaskets are the main alternative to sealants for sealing joints in construction. Gasketted joints can provide effective weathersealing, but this requires appropriately designed joints and gaskets coupled with the use of suitable gasket materials. This Digest covers the physical properties of gaskets that need to be considered, including durability under various conditions. General principles for the design of gasket joints and typical applications are described. 12 pages.