Energy Plus Sliding Sash Windows

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Quick Overview

For a truly traditional look, whether it's replacing double glazing, restoring a period property or a new build project, our wooden sash windows are thermally efficient, offer long wear and come with lengthy guarantees. 

Our modern sash windows are faithfully replicated in true Victorian and Georgian designs and very different from the original sash windows installed in houses built in Victorian Britain, still full of character and with slim frames and sashes but with all the latest glass, timber and insulation manufacture.

So our windows not only look as elegant as original sashes, their performance rivals and surpasses many modern windows. Highly insulating, rattle-free and with a smooth easy opening action that offers excellent security; these sash windows are not just replacements they are improvements with all the warmth and recognisable style of the originals.

Astragals, or Glazing Bars, can be added to recreate the looks of original windows being restored or updated or to bring a unique style to the property, the links on the right provide more information on the hardware for windows, such as sash catches and handles.

The  sash window comes in two variations, Hidden Spring Sash Window and Traditional Box Sash Window.

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Energy Plus window features 

 1. Multi-layered, 'engineered' timber - a wood stronger than the sum of its parts

When wood absorbs moisture it swells and bends and twists in the direction of the grain - by layering wood with the grain of its neighbour lying in the opposite direction, the forces are cancelled out and no resultant movement occurs. This means warp free and twist free timber, strong windows and doors that are impervious to the movement that causes sticking and jamming. 

2. Impressive optical clarity
We use the best and most up to date glazing and construction techniques ensuring consistent use of superior high quality materials in our performance double glazing - stopping heat transferring across the unit without interfering too much in the natural light allowed into the home. Our glass has a light transmittance of 77% with is getting close to the value of 81% that of plain glass

3. Almost twice as effective as ordinary double glazing
We make sure that every aspect of our double glazing performs as well as it can with the very best components, Our standard double glazed units feature top performance glass along with warm edge spacer bars and argon gas for superb insulation they boast a 1.1 W/m2K centre pane u-value which equates to 45% more energy saved than with ordinary double glazing, 80% more than single glazing

4. Simple security with internal beads
A common way to gain entry to a house is by removing the glass from a window - we fit ours room side, very simple, very effective security measure that actually looks smarter and cleaner than the glass fitted externally.

5. Easy re-glazing
Simple replacement of glass if necessary, the surrounding window is unaffected and will not even require re-painting.

6. Matching colour seals
With specially designed channels to accommodate the sealant, a close and effective seal is created preventing any moisture from sitting in the joints of the timber windows. The coloured sealant ensures a continuous high quality appearance.

7. Warm edge spacer bars
Made from a modern material chosen for its exceptional low conductivity - heat transfer is minimised at a weak point in the construction of a double glazed unit - by increasing the insulation properties of the glazing at this point the overall heat loss is greatly reduced

8. Clean finish with a rebated beading 
On standard timber window and frame construction a crack appears between the bead and the frame. Our rebated bead avoids this whilst creating a clean, professional finish.

9. Preventing mist with drainage and ventilation channels
These important additions ensure that any moisture is allowed to drain away from the windows so avoiding any build up that can lead to misting on the windows.

10. Fully draught stripped

11. Minimal maintenance and a long life come from our factory applied micro-porous coatings
A thorough system that includes a base coat of preservative and two of top coat, micro-porous paint or wood stain, all spray applied in our factory before assembly for a watertight barrier with a durable and consistent finish. 



Using engineered timber and modern paints and stains we offer excellent guarantees on all aspects of our products and with minimal maintenance our timber doors and windows will last for many many years.

  • 30 Years - Rot & fungal infection - The engineered timber is finished with a chamfered profile and sanded. This is then sprayed with an anti-fungus and rot prevention treatment.
  •  10 Years - Double glazed units
  • 10 Years - Hardware - Handles, peg stays, hinges, knobs and knockers
  • 8 Years - Paint finishes - solvent free water-based, micro-porous paint, sprayed for a complete and thorough protective layer with no redecoration for 8 years
  • 5 Years - Stain finishes - solvent free water-based, micro-porous stain -  applied with a spray for thorough coverage.

In normal conditions it will be 8 years before the paint will require redecoration, for the wood stain it is 5 years. 

With such a beautifully smooth finish sanding is not required when the time has come to redecorate, in fact it should only take around 30 minutes per window, a thorough clean and one coat of paint and the protection is renewed for a further 8 years. Exposed areas and properties near the sea will reduce the time before reapplication is needed

Less waste

Multi-layered timber is produced by joining wood sections together to create one piece of timber which is strong and very durable. This use of wood sections means that just the knots can be cut out whilst the remainder of the wood is used. The knot free multi-layered timber that is left is a fantastically strong material, more of the wood is used and waste is reduced even further. 

Protective measures

Our paint or woodstain is used to protect the wood from contact from any moisture. Our environmentally friendly water-based paints and stains contain no solvents and are spray applied before assembly. This delivers the most thorough protection for a low maintenance lifetime. 


Our timber windows are a great choice for people who want to help lessen their environmental impact, we only use sustainable European Redwood timber as standard in all our windows and doors.

The use of European Redwood fulfils several requirements, it is easily grown and grows with few knots,  the wood itself is naturally water resistant and the tree grows beautifully straight - making it easy to process with little waste.  It provides a steady supply of wood for all uses - it has been used for construction purposes for many years.  

Energy Plus Windows endorses FSC, the Forestry Stewardship Council, a not-for-profit non-government organization created to  promote responsible management of the world’s forests.  They actively seek to make all wood fully traceable and change is happening. Their promotion explains why there is a need for full chain of custody - to safeguard the forests of our planet, with wood only sold from sustainable forests, rare species might be saved and deforestation slowed.


U values are only part of the story; sealed glazing units provide the lowest component U values within a window, so the most efficient windows will be those with the most glazing and least frame. Introducing frames and opening sashes reduces the overall window U Value and provides an opportunity for cold to ‘bridge’ the structure or allow air (hot or cold) leakage. For this reason the quality of the components, the quality of construction and attention to detail when fitting can have a significant impact on the lifetime performance – and so contribution to the long term thermal efficiency of the building. This is why there are often significant variations in price when comparing - apparently similar- window quotations.

Choosing a window solely based on lowest U values at the lowest price should  not be the absolute deciding factor, after all there are many inexpensive UPVC windows that are independently assessed with ultra-low U values, but there are often environmental or aesthetic reasons why people do not choose them, more importantly is the maintenance of lifetime  performance. Various studies show that over the lifetime of a window engineered timber will provide a cost effective solution when the maintenance of lifetime performance is taken into account. In fact the Herriot Watt study (which you can download from the ‘TECHNICAL INFO’ tab) clearly shows that quality timber windows last twice as long as UPVC windows and are more cost effective over their lifetime

A note on types of U value Uf, Ug, Uw and Ud-Values

As a householder, you will probably be most interested in the U-value for the whole window or whole door, known as the Uw value and Ud value respectively. In each case these are calculated by combining the U-values for the window or door frame (known as the Uf value) and the U-value of the glass (known either as the Ug value or the ‘centre pane U-value’).

U-values describe the insulation ability of a given construction. The lower the u-value is, the better it insulates, thus reducing heat loss through windows. In a window context, it is the window's total insulation ability, including frame and sash, which is relevant. This value is called Uw and is measured in W/m2K.

By using the construction's aggregated insulation ability, all components and materials are taken into account.

Uw is dependent on window size, pane and sash/frame type and dimension. In the UK manufacturer declared U values are typically given for a standard sized window (1.23 m x 1.48 m), but there is also an obligation to provide the Uw-value for the actual window sizes at the customer's request. The exact U-value is crucial information in energy framework calculations.

On facades, where there is only a little chance of solar heat contribution (i.e. north-facing facades or facades in shadow), the best result will most likely be achieved by primarily focusing on the window's U-value.

The total insulation value for the window or door, Uw, is used in calculating the energy frame for buildings, which are typically made by consulting engineers.

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