Timber Sash Windows
Timber sash windows are the defining architectural feature of London's period housing stock, and they remain the best material choice for anyone who wants a window that looks right, lasts well and can be repaired rather than replaced when the time comes. AMB Joinery manufactures made-to-measure timber sash windows in our London workshop, using traditional joinery methods and modern timber species selected for stability and longevity. Every window is designed to your exact aperture, with moulding profiles, glazing bar arrangements and glazing specifications chosen to suit your property and your local authority's requirements.
Whether you are replacing failed windows in a Victorian terrace, upgrading the performance of draughty originals in an Edwardian semi or specifying new windows for a heritage-sensitive new build, we can produce timber sash windows that meet the brief. All installations are carried out by our own team and registered with FENSA, with a 10-year guarantee on every window we fit.
Why Timber for
Sash Windows?
The debate between timber and uPVC for sash windows is largely settled among anyone who has studied the subject carefully. Timber wins on almost every criterion that matters for London period properties.
Aesthetics
Timber can be machined to replicate the slim, crisp profiles of original Georgian, Victorian and Edwardian sash windows. The meeting rail, the parting bead, the glazing bars — all of these can be made to match surviving originals exactly. uPVC sections are inherently thicker because the hollow chambered profile requires more material, and the result is a window that reads differently on the façade, regardless of what colour it is painted or foiled.
Repairability
A timber sash window can be repaired section by section. If a corner joint fails, a sill decays or a glazing bar is damaged, a skilled joiner can cut out the affected section and splice in new timber. The window does not need to be replaced in its entirety. A uPVC window that fails — whether the sealed unit mists, the hardware breaks or the profile degrades — usually requires full replacement, because the material cannot be jointed or spliced effectively on site.
Planning compliance
In conservation areas and for listed buildings, uPVC windows are almost universally unacceptable to local planning authorities. Timber is the standard material specified in conservation area character appraisals and listed building consent decisions. Choosing timber from the outset avoids planning refusals and the cost of a second installation.
Lifespan
A quality timber sash window, correctly finished and maintained, will last 50–100 years. uPVC manufacturers typically quote a design life of 20–25 years before the profile becomes brittle, the seals fail and the colour yellows. In terms of whole-life cost, timber is frequently the more economical choice even before accounting for its repairability.
Paint colour flexibility
Timber can be painted in any RAL or BS colour and repainted when you want to change the finish. uPVC is foiled or co-extruded in a limited range of colours, and changing the colour in the future requires either painting (with adhesion risks) or full replacement.
Timber Species and Materials
Accoya
Accoya is acetylated radiata pine — a softwood that has been chemically modified at a molecular level to make it dimensionally stable, highly durable and resistant to rot and insect attack. The acetylation process replaces the free hydroxyl groups in the wood cell structure with acetyl groups, drastically reducing the timber's ability to absorb or release moisture.
For London properties, where windows are exposed to significant rainfall and temperature fluctuation, Accoya is our premium recommendation. It is dimensionally stable to a degree that conventional softwoods cannot match, which means the window will not swell and stick in wet weather or develop gaps in dry conditions. Accoya carries a 50-year above-ground durability guarantee from the manufacturer, and it accepts paint finishes exceptionally well, giving a long-lasting decorative finish.
Accoya is ideal for exposed elevations, south-facing windows that absorb solar heat, and any situation where low maintenance is a priority. It is also acceptable to many conservation officers as a modern material that performs within a traditional timber window.
Accoya is acetylated radiata pine — a softwood that has been chemically modified at a molecular level to make it dimensionally stable, highly durable and resistant to rot and insect attack. The acetylation process replaces the free hydroxyl groups in the wood cell structure with acetyl groups, drastically reducing the timber's ability to absorb or release moisture.
For London properties, where windows are exposed to significant rainfall and temperature fluctuation, Accoya is our premium recommendation. It is dimensionally stable to a degree that conventional softwoods cannot match, which means the window will not swell and stick in wet weather or develop gaps in dry conditions. Accoya carries a 50-year above-ground durability guarantee from the manufacturer, and it accepts paint finishes exceptionally well, giving a long-lasting decorative finish.
Accoya is ideal for exposed elevations, south-facing windows that absorb solar heat, and any situation where low maintenance is a priority. It is also acceptable to many conservation officers as a modern material that performs within a traditional timber window.
European Redwood
European redwood (Pinus sylvestris) is the traditional material for joinery-grade sash windows and remains a cost-effective, well-proven choice. It is a sustainable, widely available softwood that machines cleanly, takes paint and primer well, and has a long track record in historic window applications.
We use slow-grown, kiln-dried redwood with a moisture content suited to the internal environment of the finished window. For larger sections, finger-jointed redwood is available, which reduces the risk of cupping or bowing in wider boards. European redwood is the right choice for projects where budget is a significant consideration and where the windows will be well maintained over their lifetime.
European redwood (Pinus sylvestris) is the traditional material for joinery-grade sash windows and remains a cost-effective, well-proven choice. It is a sustainable, widely available softwood that machines cleanly, takes paint and primer well, and has a long track record in historic window applications.
We use slow-grown, kiln-dried redwood with a moisture content suited to the internal environment of the finished window. For larger sections, finger-jointed redwood is available, which reduces the risk of cupping or bowing in wider boards. European redwood is the right choice for projects where budget is a significant consideration and where the windows will be well maintained over their lifetime.
Hardwoods
For specific applications, AMB can manufacture sash windows in hardwood species including European oak and meranti. Oak is occasionally specified for ground-floor windows where security and robustness are priorities, for external doors with sash-style glazed panels, or for projects where an unpainted natural finish is intended. Meranti is a medium-density hardwood with good stability and paint adhesion, sometimes specified for conservation projects where a hardwood is preferred by the heritage authority. We will advise on the most appropriate species for your project at the design stage.
For specific applications, AMB can manufacture sash windows in hardwood species including European oak and meranti. Oak is occasionally specified for ground-floor windows where security and robustness are priorities, for external doors with sash-style glazed panels, or for projects where an unpainted natural finish is intended. Meranti is a medium-density hardwood with good stability and paint adhesion, sometimes specified for conservation projects where a hardwood is preferred by the heritage authority. We will advise on the most appropriate species for your project at the design stage.
Construction and Details
AMB sash windows are made using traditional joinery methods that reflect the way the best sash windows have always been built.
The sashes themselves are constructed with mortice and tenon joints at the corners — the same method used in original Victorian and Georgian windows, and significantly stronger than the dowel-jointed or mechanically fastened construction used in some manufactured windows. The joint is glued and, where appropriate, wedged for additional rigidity.
The operating mechanism is specified according to the window type. For box sash windows, we use traditional cast iron counterbalance weights on waxed cotton cord or stainless steel chain, routed over pulleys in the stile. This is the most authentic and most repairable mechanism available. For spring-balanced sash windows, we use high-quality stainless steel spring balances that can be replaced independently of the frame.
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Moulding profiles are a defining detail of any sash window. AMB can produce windows with ovolo, ogee and bar moulding profiles on the glazing bars and the sash rails, matching the profile of surviving original windows in your property or replicating profiles specified in your local authority's design guidance. If you have a fragment of original timber or a measured drawing, we can match it.
We can produce any glazing bar configuration: 2-pane over 2-pane (common in late Victorian and Edwardian properties), 6-pane over 6-pane (Georgian), 8-pane over 12-pane, or any bespoke arrangement required by your property or planning authority.
Moulding profiles are a defining detail of any sash window. AMB can produce windows with ovolo, ogee and bar moulding profiles on the glazing bars and the sash rails, matching the profile of surviving original windows in your property or replicating profiles specified in your local authority's design guidance. If you have a fragment of original timber or a measured drawing, we can match it.
We can produce any glazing bar configuration: 2-pane over 2-pane (common in late Victorian and Edwardian properties), 6-pane over 6-pane (Georgian), 8-pane over 12-pane, or any bespoke arrangement required by your property or planning authority.
Our Timber Window Range
The glazing specification for a timber sash window affects thermal performance, acoustic performance and — particularly in conservation areas — planning acceptability.
Single pane
The traditional specification; slimmest sight lines; suitable for listed buildings, conservation areas and projects where authenticity is the priority; performance can be significantly improved by adding draught-proofing.
Slim double glazed sealed units
Units from 12 mm total thickness that fit within traditional timber sash profiles without requiring oversized rebates; warm-edge spacer bars to reduce cold bridging at the edge of the unit; suitable for most domestic replacement projects.
Acoustic glazing
Sealed units with asymmetric pane thicknesses (for example, 6.4 mm laminated glass on the outer leaf) that reduce sound transmission more effectively than standard double glazing; recommended for properties close to busy roads, railways or flight paths; available as slim units for use in sash windows.
Fineo vacuum glazing
A sealed vacuum unit just 6 mm thick with thermal performance equivalent to conventional triple glazing; the slimmest double-glazing option available and therefore the most appropriate for conservation areas and listed buildings where the conservation officer requires minimal visual impact; see our double glazing upgrade service for more information.
Finishing and Colour
Every AMB timber sash window leaves our workshop with a factory-applied primer coat as standard. This seals the timber on all faces — including the rebates, the bottom rail end grain and the back of the sashes — before the window reaches site, which is important for long-term durability. Moisture ingress through unpainted surfaces is the most common cause of premature failure in timber windows.
We can supply windows with a full factory finish: primer, undercoat and gloss or satin top coat in your chosen colour. Factory finishing is applied in controlled conditions and typically gives a better, more durable result than site painting.
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Colour options are unrestricted. We can match any RAL or British Standard colour, replicate an existing colour from a colour reference, or produce windows in standard white (RAL 9010 or BS 10 B 15). Popular choices for period London properties include Farrow and Ball Pitch Black (off-black) and various shades of grey and stone, though we are happy to match any colour you specify.
If you prefer to have the windows painted on site — for example, to ensure a perfect match with existing joinery — we supply the windows primed and ready for the decorator.
Colour options are unrestricted. We can match any RAL or British Standard colour, replicate an existing colour from a colour reference, or produce windows in standard white (RAL 9010 or BS 10 B 15). Popular choices for period London properties include Farrow and Ball Pitch Black (off-black) and various shades of grey and stone, though we are happy to match any colour you specify.
If you prefer to have the windows painted on site — for example, to ensure a perfect match with existing joinery — we supply the windows primed and ready for the decorator.
Frequently Asked Questions
What is the difference between timber sash and timber box sash?
A timber sash window is the general term for any vertically sliding timber window. A box sash window is a specific type where the frame is hollow — "boxed" — to conceal cast iron counterbalance weights on cords or chains. The box frame gives a deeper, more traditional profile and is the authentic construction for Georgian, Victorian and Edwardian properties. A non-box sash uses a spring balance mechanism and has a slimmer frame. Both types are available from AMB; we will advise on the most appropriate construction for your property.
A timber sash window is the general term for any vertically sliding timber window. A box sash window is a specific type where the frame is hollow — "boxed" — to conceal cast iron counterbalance weights on cords or chains. The box frame gives a deeper, more traditional profile and is the authentic construction for Georgian, Victorian and Edwardian properties. A non-box sash uses a spring balance mechanism and has a slimmer frame. Both types are available from AMB; we will advise on the most appropriate construction for your property.
How do I maintain timber sash windows?
The most important maintenance task is keeping the paint finish intact. Check the windows annually for any areas where the paint has cracked, flaked or failed, and make good promptly to prevent moisture reaching the bare timber. A full repaint every 7–10 years is a reasonable expectation for quality factory-finished windows. Keep the drainage holes in the bottom rail clear, and apply a dry wax lubricant to the sliding channels if the window becomes stiff. Avoid over-painting the parting beads and staff beads, as this is the most common cause of windows becoming stuck.
The most important maintenance task is keeping the paint finish intact. Check the windows annually for any areas where the paint has cracked, flaked or failed, and make good promptly to prevent moisture reaching the bare timber. A full repaint every 7–10 years is a reasonable expectation for quality factory-finished windows. Keep the drainage holes in the bottom rail clear, and apply a dry wax lubricant to the sliding channels if the window becomes stiff. Avoid over-painting the parting beads and staff beads, as this is the most common cause of windows becoming stuck.
Can timber sash windows be fitted with security hardware?
Yes. We fit a range of security hardware as standard, including dual screws at the meeting rail — a simple and very effective device that locks the upper and lower sashes together and prevents the window from being pushed open from outside. Sash locks with key operation are available for additional security, as are night vent positions that allow the window to be opened slightly for ventilation without becoming a security risk. All hardware is selected to be sympathetic to the period character of the window.
Yes. We fit a range of security hardware as standard, including dual screws at the meeting rail — a simple and very effective device that locks the upper and lower sashes together and prevents the window from being pushed open from outside. Sash locks with key operation are available for additional security, as are night vent positions that allow the window to be opened slightly for ventilation without becoming a security risk. All hardware is selected to be sympathetic to the period character of the window.
What moulding profiles can you replicate?
We can replicate any moulding profile given sufficient reference information. The most common profiles in London period properties are ovolo (a quarter-round with a small step), ogee (an S-curve with a flat) and bar moulding (a flat glazing bar with a chamfered edge, common in late Victorian and Edwardian windows). If you bring us a fragment of original timber, a measured drawing or a clear photograph, we will produce a matching profile. We can also produce windows to profiles specified in conservation area design guides or listed building consent conditions.
We can replicate any moulding profile given sufficient reference information. The most common profiles in London period properties are ovolo (a quarter-round with a small step), ogee (an S-curve with a flat) and bar moulding (a flat glazing bar with a chamfered edge, common in late Victorian and Edwardian windows). If you bring us a fragment of original timber, a measured drawing or a clear photograph, we will produce a matching profile. We can also produce windows to profiles specified in conservation area design guides or listed building consent conditions.
What is the lead time for made-to-measure timber sash windows?
Our typical lead time from survey to installation is 8–12 weeks. This covers the survey appointment, production of drawings for your approval, manufacturing in our workshop and scheduling of the installation. Lead times can vary depending on order volume and the complexity of the specification. We will confirm the expected programme at the quotation stage.
Our typical lead time from survey to installation is 8–12 weeks. This covers the survey appointment, production of drawings for your approval, manufacturing in our workshop and scheduling of the installation. Lead times can vary depending on order volume and the complexity of the specification. We will confirm the expected programme at the quotation stage.
Get a Quote for Timber Sash Windows
AMB Joinery offers a free, no-obligation survey for all timber sash window projects across London. Our surveyor will visit your property, measure every opening, discuss your options and provide a fixed-price quotation. We are FENSA registered and back every installation with a 10-year guarantee.
