For the commonly selected casement and Sliding Sash ranges we have provided information to guide you through the measuring process for square and splay bays, but there are other methods you can apply.
Installation and Building Regulations
Bay windows need careful consideration when planning building detail and installation. Approved Document L of the Building Regulations for England and Wales requires the thermal performance around openings to achieve levels that some traditional methods of bay window installation cannot meet.
Traditionally the various types of bays were set against plain brickwork with the joints made by butting the jambs or corner posts up to the brickwork. Most of these details create a cold bridge at this joint which is unacceptable under current regulations. Scottish Building Regulations may vary so please check for information.
Square bays – returned cavities
We recommend brickwork is brought up to the edge of the window using angled or cut brick to replicate the joint between a flat window and the wall. This provides good thermal detail and an attractive finish.
The insulation of the horizontal roof and underside details of bay windows also require careful attention to ensure compliance, particularly where the bay projects beyond the structure.