Replacement Sash Windows & Doors 1

Custom Made Windows

For Over 20 Years We Have Been Replacing Sash Windows, Casement Windows and Period Doors.

Bespoke Sash Windows That Are Built To Last A Lifetime

Replacement  traditional windows To match your existing Period Frames.

  • Energy-efficient (Low-E), double or single glazed   
  • Authentic timber replicas of your existing sash windows.
  • Wide range of timbers and finishes.

When period windows Have Rotten Beyond Economical Repair We Offer Replacement Joinery.  

Our window repair service can restore most traditional sash windows, casement windows and doors but occasionally some frames do need replacing.  By paying close attention to copying the fine detail such as sash horn shapes and moulding profiles we create authentic replicas of your current window frames.

The new glass will let more light into your room, whilst the Low-E coating reflects heat to keep your home warmer in winter and cooler in summer.  

The discreetly hidden draught seals are low friction to improve sliding functionality, but tight enough to stop rattles, ensuring a cosy and energy-efficient period home.

Replacement sash windows are individually made to measure. 


  • An energy efficient home is a comfortable home
  • Double glazing reduces your homes carbon footprint.
  • Double Glazed Units can reduce heating bills by around 20%.
  • Reduced UV prevents furnishings from fading
  • Reduced condensation on glass
  • Air borne noise, dust and other pollutants that are suspended within draughts are also greatly reduced.
  • Low friction draught proofing strips aid smooth window operation and stop annoying rattles


  • Survey of the existing frames
  • Removal of the old windows
  • Replacement replica joinery
  • Architraves, nosing, liners and beading.
  • Optional paint finish
  • All replacement joinery includes draught seals as standard.


Unaltered Appearance

We can replicate any heritage glazing pattern or intricate window shape, to ensure the original charm of your heritage home remains unaltered.

Long Life

Time-proven traditional construction, combined with a 50-year guarantee from Accoya wood, ensures that our double glazed sash windows will last a lifetime. 

Energy Efficient

Save on fuel bills and lower your carbon footprint with Low-E glazing and draught seals.  

Contact Your Local Branch

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Bespoke Timber Windows & Doors | Sash Window Specialist UK & AU

Replacement windows and doors that reflect a bygone era

Our sash window workshops manufacture bespoke timber windows & doors in any style, constructed using traditional mortise & tenon joints.  Suitable for conservation areas and listed buildings.

Unaltered Heritage Appearance


Double Glazed Wooden Sash Window.We carefully reproduce a copy of your original windows, paying close attention to the original horn shape, timber mouldings & sectional details.  Preserving these fine details, that vary by region and era, is important to maintain the architectural significance of your heritage property. 

If the original window frames are missing or replicas are required for building alterations then we can work from old photos or copy the architectural details from a neighbouring property.

Traditional sash window construction

The Edwardian’s and Victorians perfected the construction of wooden windows, structurally we build them just as they did.  Our modern sash windows only differ from the originals by using modern glues, built-in weather seals and improved glass technology. 

Bespoke Timber Windows & Doors | Sash Window Specialist UK & AUGlued and wedged mortise & tenon joints, bonded with modern glues, ensures that our joinery is of the highest quality possible and built to last.  Some other companies do offer cheaper timber windows constructed using cost cutting methods and cheaper grades of wood.  Typically these cheap sash windows only last 15 – 20 years and do not represent good value.  At Sash Window Specialist we only supply traditional period windows that are built to last.

Replacement Sash Windows & Doors 3

Bespoke Timber Windows & Doors | Sash Window Specialist UK & AU

Modern advances blended into heritage homes

Sash Weather & Draft Seals.

Draught seals are machined into the timber components to become an integral, practically invisible part of the windows or door.  Brush draught seals are the best option for a sliding sash window but compression weather seals are better suited to doors.

accoya wood for sash windows

Accoya® wood is the perfect material for most timber window frames and external wooden doors. 50 year anti-rot guarantee

  • Eco friendly
  • Light weight
  • Extreme durability
  • Insect barrier
  • Dimensionally stable

Accoya® wood represents a major development in wood technology. It enables the consistent supply of durable, non-toxic, dimensionally stable wood. This makes it an ideal material for manufacturing high performance, exterior timber products.  Accoya is manufactured through the acetylation of plantation grown softwood. For over 80 years this has been the gold standard in the academic field of wood science. A breakthrough in closed-loop engineering, culminating in 2007, led to the first commercial scale production of the product in the world.

Period windows and doors made with Accoya have a 50 year guarantee, giving complete confidence that Accoya® windows and doors will stand the test of time. An Accoya® wooden window or door is developed to excel in external applications, even in challenging conditions.

Bespoke joinery is also available from a range of other premium timbers.   

Read more : Guide to sash window timber

Redwood pine timber used for wooden sash windows, casement windows and doors. Douglas Fir premium softwood timber used for wooden sash windows, casement windows and doors. Oak hardwood timber used for wooden sash windows, casement windows and doors. Meranti hardwood timber used for wooden sash windows, casement windows and doors. Mahogany hardwood timber used for wooden sash windows, casement windows and doors. Jarrah hardwood timber used for wooden sash windows, casement windows and doors. Accoya modified softwood timber used for wooden sash windows, casement windows and doors. Choose Accoya for long life, durablity and eco friendly.


bespoke French windows / french doors | double glazing & draught seal

Custom made doors.

Glazing Options

Choosing Glass

Replacement windows and doors must comply with local building regulations, unless a legal exemption is in place for heritage conservation.  New windows will require Low-E laminate glass or double glazing to achieve energy efficiency compliance.

UK – FENSA, Document L & The Building Regulations?.

Historic Glass

If your property has intact hand made glass or lead-light then some consideration should be given to reusing the existing heritage glass.  We can not guarantee every single pane intact but it is usually possible to transfer heritage glass.  Transferring glass in this way may necessitate boarding up your existing windows whilst the new windows are in production.  Ideal for conservation areas and listed buildings. 

Read more : Window glass 


Selecting Double Glazed Units

The thickness of your existing sash window frames dictates the room we have to work with in order to include the best energy-efficient double glazing.  

Spacer Bars

The spacer bar inside the glass unit governs the cavity between the two panes.  The wider the cavity the better the energy efficiency will be, but there is a law of diminishing returns.  The first 5mm of the cavity is responsible for the most significant insulation improvement but a 10mm void is not twice as good as 5mm.

12mm is the average thickness of the spacer bar that we use in new sashes, but with thin sashes or if you choose to incorporate a thick laminate or acoustic glass then we may use a thinner spacer bar.  A 16mm spacer bar is reserved for much thicker sashes, typically found in heritage public buildings.

Spacer bars can be either rigid aluminium duplex bars or ‘warm edge’ flexible foam spacer tape.  A warm-edge spacer bar performs slightly better at reducing heat conduction around the unit perimeter.

Double Glazed Timber Sash Windows With Castellated.Style Glazing Bars.
Double glazed unit with warm edge spacer bar. Castellated pattern.

Not all double glazing is created equal.  When double glazed units (dgu) first came to the market they simply comprised 2 panes of glass separated by an air space.  Whilst we can still supply these budget d.g.u. the saving over low-e units is not a sensible cost cutting measure.

Low-e double glazing outperforms those early double glazed units by a large margin.  Firstly the air space is now filled with an inert gas that conducts heat less readily.  Secondly, Low-E coatings baked into the glass surface reflect any heat energy back to its source, resulting in significant improvements to the insulating properties.  

Pilkington K glass is the best-known energy efficient, low-e glazing, but all glass manufacturers offer comparable products.

How Does Low-Emissivity Glass Work?

low e glass for period casement and sash windows

Low-e glass has a special coating that reflects heat back into the room.  In winter heat is reflected back indoors, in the summer heat from the
sun is reflected away keeping the room cooler. 

Because a Low-E coating reflects some wavelengths of the light spectrum it will slightly alter the colour tone of the light passing through the glass.  There are various Low-E coatings offered by different glass manufacturers that each have their own colour signature and performance characteristics.  Ask your local branch representative about the options on offer in your area.  


Argon vs. Other Inert Gas-Filled Units

A gas-filled unit features an inert gas in the cavity between the glass panes.  Using an inert gas that is denser than air stops circulation within the unit, which may lower overall efficiency.  Argon is the most commonly selected gas as it provides the best value.

  • Xenon – Xenon gas offers very high efficiency but does not warrant the cost.
  • Krypton – Krypton gas glazing offers up to 27% increased energy efficiency in comparison to air.
  • Argon – Argon typically reduces the insulating value by about 16% in comparison to air and is the most cost-effective and most widely used option.
Gas fillings should not lose more than 5% of the total gas over a period of 25 years.

slimlite Vs. Single Unit

Single Unit

Double Glazing Traditional Sash Windows. Berkshire UK.Using one glazed unit per sash is the best value. 

Timber beads are bonded to the exterior pane of glass mimicking the interior glazing bars that are mortice and tenon jointed to the outer sash frame.  Sealed inside the glass unit are matching spacer bars to fill the void, creating a solid glazing bar effect.  Internal spacers also brace the panes and reduce any flexing of the glass. 

Our bonded beads are custom made to the same thickness as your original sashes, ensuring the overall charm of the period property is preserved.

  • Bonded using high-performance glazing tapes
  • Shaped to represent the traditional putty lines of single glazing.
  • Intricate glazing patterns can economically be reproduced.
  • Timber beads can be painted in any colour. 

We have been offering this system for over 20 years, it is a very durable solution.  

Glazing this way allows us to recreate more intricate glazing patterns that are prohibitively expensive when using many separate, shaped glazing units.

Slimlite/Slimline Glazed units & Pilkington Spacia Units

Manchester Sash Window Repair SpecialistsFitting many individual glazed units is more expensive, but can add a little more character to the glazing of multi-paned sashes.  As each unit will sit slightly out of level with its neighbour some of the ‘flatness’ that a single unit creates is reduced.  

Energy efficiency is slightly reduced by selecting the slimlite 5mm spacer bar option, but some people prefer the look of a thinner unit with slightly more ‘meat’ left in the timber sash.

The weak spot of all double glazed units is the edge.  If the seal around a glazed unit fails then the inside of the glazed unit can mist up.  The simple fact that this option increases the number of glass edges also increases the potential weak spots.

Slim units can be beneficial for double glazing existing sash frames.

For sashes with no glazing bars, a single unit is used anyway.

Our Double Glazing Options Include

  • A choice of inert gas fills.
  • Acoustic DGU configuration.
  • A choice of low-e, energy efficient glass.
  • Etched or patterned glass.
  • Safety Glass.
  • Slimlite units or duplex spacer bars.
  • 5 – 16 mm air space depending on the sash thickness.
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Window Security & Hardware


We offer a wide range of hardware options, available in a variety of finishes.

Improved Energy Efficiency

Sealing draughts in your home will return significant savings in heating and cooling costs, as up to 25% of heat is lost via air leakage in a typical home.

Bespoke period sash windows can reduce the draughts by almost 90%, therefore significantly reducing the air cooling or heating requirement needed for the room.  Warm or cold draughts make air cooling and heating systems work harder and make occupants feel uncomfortable, often adjusting room thermostats to compensate.  

Wood is a natural insulator

The natural insulating properties of timber make this an extremely energy efficient building material.  Timber window frames are highly energy efficient as they do not conduct heat. 

Timber windows help to lower your carbon foot print. 

Wood is a sustainable building material, derived from a renewable source. Any home owner choosing green living should consider preserving or reinstating timber windows.    


Bespoke period window | sash window specialist berks, london & south

Bespoke period windows & doors, constructed the traditional way. 

50-year anti-rot guarantee if the windows and doors are made from Accoya WoodTM