Types of Timber Casement Window Explained

What a timber casement is

A casement is any window whose opening sash swings on hinges along one edge. Timber casements have been fitted to British houses for centuries, and they are still common on cottages, inter war houses and many newer homes built to look traditional. The type is defined mainly by how the opening sash sits against the outer frame when it is closed.

Flush casements

On a flush casement the opening sash closes into the frame so its outer face sits level with the frame around it. The result is a clean, flat front with even sightlines between opening and fixed panes. This is the traditional look many period homes were built with, and it is the look that modern flush casement windows in uPVC set out to copy.

Flush timber casements need accurate joinery and well maintained paint or stain, because the closely fitting edges are where water and swelling first show up.

Storm proof casements

The storm proof casement became common in the mid twentieth century. The opening sash has a rebated edge that laps over the outer frame, creating a double barrier against wind driven rain. You can recognise it from the stepped profile: the opening sash stands slightly proud of the frame and the fixed panes.

Storm proof designs are robust and weather well, which is why they were fitted so widely. Their look is chunkier than a flush casement, which matters if you are trying to match a neighbouring window or restore an original appearance.

Lipped and traditional variations

Between those two sits a range of lipped and traditional profiles, where a small lip on the sash overlaps the frame without the full stepped look of a storm proof window. Mouldings on the inside edge, such as ovolo or chamfered profiles, add further variation. Matching these details is what makes a repair or replacement blend in with the rest of the house.

Opening styles

Whatever the construction, each pane in a casement window is either fixed or opening, and opening sashes are hinged at the side or the top.

• Side hung: opens like a door, gives the widest clear opening and can serve as a fire escape window where the size allows
• Top hung: hinged along the top, often used for small vents that can stay open in light rain
• Fixed lights: panes that do not open, used to add glass and keep costs down
• Combinations: most windows mix fixed and opening panes to suit the room

Glazing bars and patterns

Timber casements are often divided by glazing bars into smaller panes, giving cottage or Georgian patterns. Older windows use true bars with individual pieces of glass. With double glazing, bars are usually applied to the faces of a single sealed unit, which keeps the look while improving warmth. The number and width of bars has a big effect on how traditional the window appears.

The timber itself

Timber windows are made from softwoods, hardwoods and engineered timber, where layers are bonded together to resist twisting. As a general rule hardwoods and engineered sections are more stable and durable, while softwoods rely more on good paint and regular maintenance. The finish, and how well it is kept up, matters as much as the species for how long the window lasts.

Restore, replace in timber or change material

We restore timber windows or replace them in full, and we also fit uPVC and aluminium casements, including flush styles, for anyone who wants a traditional look with less upkeep. Small areas of rot can often be cut out and repaired. Widespread soft timber, failing joints or frames that no longer close properly usually point to replacement. Our timber window care guide explains the maintenance side, and a survey will show which option is sensible for your frames.

Questions we get asked on site

What are the different types of timber casement window?

The main constructions are flush casements, storm proof casements and lipped or traditional profiles, each opening as side hung, top hung or fixed panes.

How can I tell a flush casement from a storm proof one?

On a flush casement the opening sash sits level with the frame. On a storm proof casement the sash laps over the frame and stands slightly proud.

Can timber casement windows be repaired?

Often, yes. Limited rot, worn seals and sticking sashes can usually be repaired. We restore timber windows where the frames are sound enough.

Can I get the flush timber look without timber?

Yes. We fit flush casement windows in uPVC, which copy the level sash of a traditional timber window with much less maintenance.

Do glazing bars reduce energy efficiency?

Bars applied to the faces of a single sealed unit have little effect on warmth, which is why they are the usual choice on double glazed timber casements.