Balancing Performance, Character and Conservation with New Sash Windows

• 23 April 2026|
• News

Georgian townhouses to Victorian terraces, the vertical sliding sash has stood the test of time as a hallmark of traditional design. But when older sash windows begin to fail, architects, developers and housebuilders face a critical decision: repair, or replace with new sash windows?

This blog explores when replacement is the right choice, how new timber sash windows can deliver modern performance without compromising a home’s character, and how an architect-led approach helps balance conservation with thermal efficiency.

At a glance:

• Repair works well for sash windows with sound frames and minor decay.
• Replacement with new sash windows is appropriate when frames are beyond economical repair or when performance upgrades are required.
• Modern timber sash windows can deliver U-values as low as 1.1 W/m²K while preserving period charm.
• Lomax + Wood supplies made-to-order wooden sash windows suitable for conservation areas, listed buildings, new builds and contemporary homes

Repair or replace? An architect-led approach

The first question on any renovation project is whether existing sash windows can be repaired. Original joinery often has real value, both historically and structurally. Skilled joiners can splice in new timber, replace sash cords, and introduce draught proofing to extend the life of period windows by decades.

Replacement becomes the better option when:

• Frames show widespread rot or structural failure
• Single glazing is driving up energy bills and heat loss
• Building regulations require improved thermal efficiency (for example, in extensions or change-of-use projects)
• The property needs improved acoustic performance due to noise pollution
• Previous uPVC sash windows have been installed and the client wants to return to authentic timber

An architect-led decision weighs heritage value against long-term performance. For a listed property, a sensitive repair may be mandated. For a Victorian terrace with previously replaced uPVC frames, new timber sash windows can restore the home’s character while delivering modern performance.

How new sash windows can improve thermal and acoustic performance

Modern wooden sash windows are engineered to perform very differently from older sash windows. Our box sash window range achieves U-values as low as 1.1 W/m²K with double glazing, with the option to upgrade further. Acoustic glass options deliver noise reduction up to 42dB, a significant improvement for homes in busy urban areas.

Key performance features include:

• Factory double glazing with argon fill and low-E coatings to meet Part L
• Full weather-stripping for thermal and acoustic insulation
• Warm air retention, reducing reliance on heating systems
• PAS 24 (2016) security testing for Part Q compliance
• Weather testing to BS6375: Air Class 4, Wind Class C5, Water Class 7A

For heritage projects where double glazing is not permitted, vacuum sealed units within slim single glazed sash windows offer a compelling alternative. These units meet strict conservation officer requirements while delivering thermal efficiency close to that of standard double glazing.

Preserving character without compromise

New sash windows installed on a heritage property should never look like new sash windows. The detailing matters: decorative sash horns, traditional ovolo glazing bars, correct sight lines, and putty glazed options for the most authentic finish.

Our timber sash windows are designed to replicate the proportions and detailing of original period windows. This matters enormously in conservation areas, where planning officers scrutinise every profile. Unlike uPVC frames, which struggle to replicate traditional joinery, made-to-order timber windows deliver timeless elegance alongside modern performance.

For new build and contemporary homes, the same craftsmanship applies. Whether specifying anthracite grey finishes on a modern sash window, or matching bay windows on a Georgian-style development, the flexibility of timber allows architects to meet any brief.

The Lomax + Wood sash window range

We offer three distinct ranges of new sash windows, each suited to different project requirements.

Traditional box sash windows

Our flagship wooden sash windows, with weights and pulleys faithful to the original design. Ideal for period property restoration, listed buildings and high-specification new builds. U-value as low as 1.1 W/m²K.

Spring balance sash windows

A more economical made-to-order option for developers and housebuilders who need historically accurate sash window installations without the weights-and-pulleys cost. Factory double glazed, fully weather-stripped, and often specified for new build projects where flush reveals have been detailed by the architect.

Single glazed sash windows

Designed specifically for listed buildings and conservation areas where double glazing is prohibited. Putty glazed with authentic sight lines. Can be upgraded with vacuum sealed units where permitted.

Timber casement windows

For projects that mix vertical sliding sash with casement windows, we supply matching timber casement windows and French doors, ensuring consistent detailing across the entire fenestration package.

Sustainability and sourcing

At Lomax + Wood, environmental responsibility is central to our manufacturing philosophy. We source all timber used in our bespoke windows and doors with full Chain of Custody certification (FSC® or PEFC), ensuring complete traceability throughout the entire supply chain, from the forest to the finished product.

This matters for architects working to BREEAM or similar standards, and for developers looking to reduce the carbon footprint of their projects. Timber is a naturally low-carbon material, and specifying responsibly sourced wooden sash windows over uPVC sash windows supports lower carbon emissions across the building’s lifecycle.

Why specify Lomax + Wood

• Over 30 years of sash window manufacturing experience (established 1994)
• Full design, supply and fit service with one point of contact
• Made-to-order to exact architectural specifications
• Comprehensive technical data for specification and planning submissions
• UK-wide supply to architects, developers, housebuilders and homeowners

Our customer service team supports specifiers throughout the project, from initial design through to installation. Whether you need further information on glazing options, sash window prices, or detailed sections for planning submissions, we provide the technical backup professional projects require.

Frequently asked question

How do new timber sash windows compare to uPVC or aluminium sash windows?

Timber offers superior aesthetic appeal, better longevity and a lower carbon footprint than vinyl, uPVC or aluminium alternatives. Timber window frames can be manufactured to any width and specification, allowing us to match the original window detailing of period properties. uPVC and aluminium frames cannot replicate the proportions, sight lines or traditional style of authentic joinery to the same high standards.

When should I choose repair over full window replacement?

If your existing window frames are in good condition with only minor decay, repair with new weatherstripping, draught proofing and a sash replacement kit may be sufficient. If the old sashes are warped, rotten or single glazed with poor energy efficiency, window sash replacement or full window replacement with a new window is usually the better long-term investment.

Can new sash windows be installed in conservation areas?

Yes. Our timber sash windows are designed to meet conservation officer and listed building requirements, with authentic detailing, putty glazing and traditional craftsmanship available.

How do new timber sash windows compare to uPVC sash windows?

Timber offers superior aesthetic appeal, better longevity, lower carbon footprint and full conservation area approval. uPVC frames cannot replicate traditional joinery to the same high standards.

Do new sash windows add value to a period property?

Yes. Authentic wooden sash windows preserve a home’s character and typically increase the value of your home compared to uPVC replacements.

What is the lead time?

Typically 6 to 8 weeks from order confirmation, depending on specification.

Get a free quote on new sash windows with Lomax + Wood

Planning a renovation, conservation project or new build? The Lomax + Wood team is here to help you specify the right new sash windows for your project.

Contact us today for a free quote or to discuss your requirements with our specification team. You can use our online contact form or call 01277 353857.