uPVC Lipped Casement Windows: A cost effective Alternative to Timber for your London or Surrey Home

The History of Lipped Casement Windows

The most cost-effective casement window on the market is the uPVC lipped casement window, also known as a storm casement.

Timber lipped casement windows were first introduced to the UK in the 1970’s. Prior to that, timber windows were almost exclusively of the ‘flush casement’ style. When uPVC windows were subsequently introduced in the 1980’s, they followed the 1970’s lipped casement design.


Only after around 2010 were period flush casement windows available in uPVC.


Specialising in London and around Surrey, we can introduce you to our fully vetted network of manufacturers and installers to ensure the right solution for you and your home.
The most cost-effective casement window on the market is the uPVC lipped casement window, also known as a storm casement.

The difference between lipped casement and flush casement windows is this: on a lipped casement window the opening sash protrudes forward of the window frame, while flush casements have no protruding lip, so visually the frame and sashes are level and symmetrical with one another.


On a lipped casement, the protruding sash’s lip extends to 15mm around the entire edge and has a rubber weather seal gasket fixed to it in order to form a storm-proof seal against the frame when shut (hence the name). Flush casements, which have symmetrical openings and frames, have no protruding lip.


This means that the weather seal is out of sight, hidden away internally using a traditional rebated frame and sash.

To economise on manufacturing costs and save on materials, most uPVC storm casement windows (unlike flush timber or flush uPVC windows) don’t have dummy opening sashes fitted as standard in the non-opening panes, so you will need to ask for them if you’d like them.


The term ‘unequal sightlines’ is used because the glass in the opening windows is different in size from the glass in the fixed panes, and causes the ‘glass line’ to step up and down. The opening sashes can also appear to be thicker than the adjacent fixed panes. There is no right or wrong look – any choice you make depends on your
personal preference.


In summary, the advantage of choosing dummy sashes is that they help to retain the period charm of a property by keeping the frame and glass lines symmetrical.


You can, of course, save money and opt for ‘unequal sightlines’ by not paying for the additional dummy sashes. The price difference is approximately an additional £50 per dummy sash fitted to the non-opening fixed panes.


If you’d like to see both options, we can simulate both of these with a photo of your house, so you can make a truly informed final decision.

Many uPVC window frame extruders still make five-metre lengths of frame profile that are designed for external glazing. However, the manufacturers reverse butt weld the frames so that they are all internally glazed. This shortcut presents a new problem in that openings and fixed panes will then possess different putty line finishes.


If you have sculptured beading rather than chamfered putty-line beading, some of the frame will be sculptured while other sections are chamfered, and this ‘asymmetric’ look can appear to be slightly odd.


This can be avoided by choosing a frame that is specifically designed for true internal beading, and where all the chamfered edges and beading are in perfect symmetry.

As with timber, the quality of uPVC casement windows does vary. For long life performance, we recommend choosing a uPVC frame extruded through stainless steel Greiner Die with a high or medium gloss uPVC mix. We also recommend coextruded dual density gaskets, long life high compression hinges and locking. This spec will see your frames looking brand new for decades due to reduced dirt engraining. In addition, the airtight seal will be maintained for a much longer timeframe.


The high quality dyes also help to keep the frame straight over time and place less stress on the sealed units and hardware, which also contribute to an extended life span. So robust is the product that some installers now offer 20-year guarantees on this specification, compared to the standard 10 years.


Surface finishes range from timber effect woodgrain, through to low, medium or high gloss finishes. The medium and high gloss finishes are more expensive but they are more effective at preventing dust, dirt and pollutants from engraining into the uPVC frame surface over time.


In other words, they continue to look new, for longer.

Nowadays, most double glazed windows are premium ‘A’ rated as standard, however there are still around a dozen variations of glass and coatings to choose from. These vary and will depend on whether security, soundproofing, anti-UV, condensation, heat retention or heat rejection are the priorities.


As a rule of thumb, we recommend using ultraclear low-iron glass for the outer pane and a premium low e-soft coat on a standard iron pane for the inner pane. This combination will give the appearance of clear glass from the outside and inside (rather than a distorted cloudy look that some lower cost low e-hard coats on standard iron can create when viewed from certain angles).


Warm edge spacer bars and a gas-filled double glazed cavity (rather than air-filled) will further improve heat retention. The inner pane temperature will increase as the heat can’t escape, while the solar radiation passes through the low-iron clear outer pane and warms up the invisible high performance low e-metallic coating on the inner pane. This specification also further reduces condensation as the inner pane warms up more than standard double glazing options.


Surprisingly, triple glazing doesn’t offer many more heat retention or sound proofing benefits compared to high performance double glazing. The extra weight of triple glass panes can also cause additional stress to the hinges and sashes which, in turn, produces problems when the sashes drop under the excess weight. For extra security and soundproofing, we recommend opting for a 6.8mm low-iron laminated outer pane. This product is about 70% quieter than single glazing (standard double glazing is 20% quieter) and is also hammer-proof.


The low iron content also reduces the green appearance of thicker glass that contains the PVB-reinforced plastic sheeting necessary for enhanced security and sound dampening. PERFORMANCE GLAZING

Lead work was the norm up until the last century because the technology of the time limited the size of individual glass pieces. As a result, multiple smaller pieces would be held together to make up larger panes.


Decorative glazing provides a creative alternative to clear glass, and there are plenty of options to choose from. Choose lead strips in square, diamond or designer patterns; or stain the glass in between the lead patterns themselves.


If you have existing stained glass windows, we can also arrange for them to be refurbished and replaced into triple glazed units, with the refurbished stained glass making up the centre pane.


Alternatively, the same design can be faithfully replicated onto
double glazing.

In the days when glass could only be produced as smaller panes, timber glazing bars provided an alternative to leaded lights. These timber glazing bars, or slimmer astragal bars, held smaller pieces of glass together to make up larger panes.


Astragal bars can run horizontally or vertically across the glass, or they can make squares or patterns. These patterns have changed through the different periods in history.


When producing modern uPVC windows, Georgian bars can either be fitted inside the double glazed unit or they can be fitted as astragal bars onto the external surface of the glass. The former option is easy to clean while the latter creates real squares on both the internal and external glass panes, for a true period look.


Note that astragal bars are always used on timber windows, whereas uPVC windows can have either option depending on your preference.
In the days when glass could only be produced as smaller panes, timber glazing bars provided an alternative to leaded lights.


A ‘no-salesperson’, no-obligation emailed quote

A free home visit, if required (for those in London and Surrey)

CAD drawings with detailed specifications for each quoted product

Realistic before & after photo simulations, if required

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Design your dream conservatory with our interactive visualiser and preview it in Augmented Reality.

Conservatories and orangeries have long been a popular extension style, as they can be designed specifically to complement the design of your property. What’s more, modern performance glazing and next-generation thermal conservatory roofs, pillars and posts allow for optimum temperature control throughout the seasons.

Say goodbye to overheating in the summer, and ice-cold temperatures in
the winter!
Online photo quote service with design advice plus scale drawings
Online photo quote service with design advice plus scale drawings

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