To discuss all the glazing package configurations available to you would be a bewildering and frustrating exercise, so, to get things started, let's tell you what your window will be fitted with as standard:

4mm low 'E' glass – 12mm Argon filled cavity with Thermix © spacers – 4mm float glass

This system confers a thermal transmission coefficient (Ug) of approximately 1.24 W/m2K

This is a solidly performing package designed to fit discreetly into the sash joinery and retain the inherent elegance of this window form: specifying slim joinery sections also positively affects the weight of the sashes meaning they require less lead (or steel) to counterbalance them; this in turn has a positive effect on the price you pay.


    This is a straightforward addition to the joinery to accurately simulate traditional 'Georgian' bars from inside and out. We apply solid timber bars to the interior and exterior of the glass and include an internal spacer to the glass package so the bar appears to travel through the depth of the sash. We are also charged by our glaziers for each crossing point of the bars and this will be passed on in the final price. To select bars for your windows, merely tell us how many bars run vertically and horizontally in each sash and the calculator will do the rest, if you have asymmetrical bar arrangements, this is fine, just send us a photo; we might ask you to provide some sizes but this is easily done.
    Part N1 of the Building Regulations dictates that if a piece of glass is located within 800mm of the finished level of the room's floor it must be toughened, as well as in other areas of risk, including staircases, etc.: this means that if the underside of the cill is within 650mm of the floor (that's 25½ inches in 'old money') we would urge you to have the lower sash toughened. We can also toughen the top sash but remember, tempering glass is a time consuming and relatively pricey business. Select only the windows which require toughening by ticking the appropriate boxes.
    You might well need this for bathrooms, loos and anywhere you require a bit of privacy. We can offer a variety of patterns and, once again, this form of glass is charged at a premium. Select the windows which require obscuring by ticking the appropriate boxes.
    Our single intention in this section is to not in any way to 'blind you with science' or sell you something that you do not need: specialist glass is expensive and we make our money from working wood, not selling glass! Consider the anatomy of a box frame window, there is a minute passage of cooled air around the sashes, this is unavoidable and many people, me included, consider this to be healthy. If you are committed to a higher specification, we are definitely able to help... Selecting one of the following will convert the entire order to the chosen specification.


    This is the same depth as our astandard package (20mm) but, instead of 'low E' glass, the inner pane is 'GN 1.0', lowering the Ug Value to approximately 1.14 W/m2K.
    Once again, the same depth as the standard package except with Krypton gas replacing the Argon within the cavity, the Ug Value consequently drops to an impressive 0.95 W/m2K.


The list of non-standard options is comprehensive and, at the rate at which glass technology is evolving, quite possibly endless. Here is a selection of some of the common glass types for which we can cater...


Prices change on these products quite regularly and in some cases, due to glass weight, we must re-design the joinery to accommodate it, but feel free to send an email with your ideal package and we will see what we can do and what it will cost to achieve it.

Finally we should mention that we also have a long-standing relationship with a traditional lead-worker who has an impressive portfolio of designs that she can be commissioned for; this must be considered a luxury purchase but it's unbeatable if you are looking for something truly unique!

Timber Windows

Butler & Bowler windows maintain the aesthetic of a traditional window manufacture with the benefits of innovative design and incorporating modern technology. Maintenance is a breeze.

Wooden Doors

Timber Doors

Butler & Bowler uses the latest door manufacturing technology that allows our products design versatility and optimum performance.


Bespoke Joinery

This section is still under construction. Content will be added soon.