Timber Sash & Casement Window Guide

We have put together a simple guide to take you through the process of replacing your traditional timber sash and casement windows.

Material – Always use timber for the construction of your replacement windows. For durabiliry ensure you choose timber windows which are factory spray finished. Painting any Hardwood is a debatable subject due to the effects on the enviroment. Types of timber used in construction should be from a sustainable source for painted windows an Engineered Scandinavian Redwood works very well. Engineered meaning all the best bits are finger jointed back together – this eliminates any movement within the timber it also ensures there are no nasty knots and splits on the facings of the timber. In turn it paints and finishes extremely well and provides a cost effective, durable and perfectly finished end product. In most cases a hardwood such as Sapele would be use as an integral sill which adds durability to the most effected part of the window.

Additional Treatment can also be added to the timber prior to painting such as Protim Vac Vac Preservative.

Construction – Choose 'Like for Like' section and construction details – it's extremely important that the new timber frame and sash section sizes are as close to the existing original details as possible. Traditionally the timber sash frame would sit behind the brickwork into a brick reveal or brick rebate hiding half of the sash box frame ( where the couter weights are ) this provides pleasing views from the outside with narrow delicate frame lines.

Original Box sash window frames would typically have a depth of 5 ¼ Iches ( imperial ) which in (mm) converts to 135mm ( metric ) the width of the sash box typically being 88mm ( including the internal staff beading ) these are the magic sizes when considering replacement timber box sash windows. This will allow the new window to fit into the exact same space as the original old window. Be careful of chunkier box frame sections this as you can imagine causes issues with internal reveals, plaster lines and architrive mouldings.

Replacement Bespoke Sash Windows London

Glazing Bar Details – Glazing bars should replicate the original narrow bars, usually between 16mm and 20mm with traditional designs of Ovalo and Lambs toungue on the inside of the glass / window with a tapered or chamfered bead on the outside of the glass which would replicate the original method of glazing putty.
Modern Timber Sash Windows London
Opening / Sliding Sash System – The opening mechanism on a sash window traditionally uses a time proven pulley cord and counter weight action, there's no doubt that this is still the best method. However there are new systems such as spiral spring balancers typically used in new builds where external walls dont have the required depth to sit the complete window behind the brickwork. Spiral spring balancers would have a debated life span due to the amount of tension required to operate the sash windows as it should for such a period of time before it would need 're tensioning'.

Draught Seals – Original box sash windows had minimal draught seals. Most originals may have been tampered with after years of repair and refurbishment. In these cases they probably had inadequate brush or feather seals which have gathered and clogged up with grime and dust and simply become useless at stopping draughts and weathering.

A new system has stepped up over recent years, an ultra modern memory foam seal called 'Q-lon' fitted to the moving sashes, and in some cases doubled up for additional draught proofing and weathering. These in turn will improve u values , energy rating and noise reduction. The Q-lon gasket is also a very easy material to keep clean and doesn't allow for any build up of grime and dust.

Glass – Many conservation areas have many stipulations on which glass should be used. The glazing in original box sash windows would make extremley in-effiiciant single glazing. If in your situation single glazing is the only option use a thicker 6mm toughened unit. This with modern techiques is much better than any original glass.

Where possible you must consider a double glazed version which in most cases will be completely acceptable using either a standard 28mm Double glazed unit or double glazed units as thin as 12mm with a filling of GAS can achieve very good U values and sound proofing.

Finally - Use a company who will tailor to your exact requirements. Keeping the windows as close to the originals as possible should be your main goal when it comes to replacing your timber sash windows.