Bay window shutters: choosing the right style for a splay, box or curved bay

Stand outside and look at the corners. If the side windows angle back towards the house at roughly 30 or 45 degrees, you have a splay bay, the standard on inter-war semis across Warrington. If the sides meet the front at a right angle, that is a box or square bay, common on Edwardian villas and some new builds. If there are five or more narrow faces in a gentle arc, it is a curved or cant bay. Each one asks for a different shutter answer.

The splay bay is the easiest to dress well. Three sections, one panel each, joined by two mitred posts cut to the splay angle. We normally add a mid-rail at roughly the height of the transom or handle so the lower louvres can be closed to the pavement while the upper louvres stay open. Café style is the budget alternative on a splay bay and looks right on terraced streets where the window sits close to the footpath.

Tier on tier is possible on a splay bay but the shallow angle means the upper panels of the side sections can catch the front section when folded back, so it needs careful planning at survey.

A box bay has deep side returns, which gives the upper tier of a tier on tier shutter somewhere to fold flat against without meeting the neighbouring panel. Those bays also tend to be tall, so the horizontal split between tiers falls at a natural point. If the box bay is on a first-floor bedroom, plain full height is usually enough because privacy is less of an issue up there.

A curve cannot be dressed with three wide panels; the frame would stand off the glass at each end. Instead the arc is broken into five, six or seven narrow sections, each with its own slim panel, and the frames are mitred at a small angle at every join. It is more work and more posts, and it is priced per section like any bay, but the finished effect follows the curve closely and looks intentional from both sides of the glass.

Because a bay is seen as one wide composition, louvre size should stay consistent across all sections and ideally match the other front windows. On most bays 64mm or 89mm looks right; 47mm can appear busy across three faces. Frame choice matters more in a bay than on a flat window because the eye tracks the vertical posts; a slimmer L frame keeps them light, while a deeper Z frame hides an out-of-square reveal but adds visual weight at every corner.

Three things we see on bays fitted by others, and how to avoid them.

• Assuming the angles. Bays are surveyed with an angle finder at every join because settlement means the two sides are rarely identical.
• Ignoring the cill. Bay cills are often stepped or sloped, and the frame has to be packed and scribed rather than just screwed down.
• Fitting a radiator cover too close. Full height panels need room to swing; if a radiator shelf sits proud of the reveal, plan for it at survey.