To move or improve is a common dilemma pondered by homeowners. There has long been a strong stimulus to renovate and add value to homes rather than hunt for a dream property. Money is often the most influential factor, particularly in areas where stamp duty and moving costs can be as high as the cost of an extension.
Sometimes, external forces persuade our thinking, the Brexit-induced stagnation in the property market for example, made many people stay put. It may also be the case that you own a period home which has oodles of character and history that you fell in love with when you bought the property and have no intention of leaving behind. For this group of dwellers, adding value can prove to be a tricky business. Loft conversions and extensions undergo intense planning scrutiny before permission is granted (if at all) with likely compromises to be had on the original plans submitted.
Luckily, adding value is not always about adding space, there are plenty of ways to invest in, and improve your period home without the need for costly and disruptive loft conversions and extensions. In this article, we focus specifically on cost effective ways of adding value to your period property via your sash windows.

Add new double glazed sash windows

One of the most frequent questions we are asked is

“Can you double glaze sash windows?”

The answer is yes, modern timber sash windows are certainly able to accommodate thicker double-glazing. Any estate agent will tell you that double glazed sash windows will not only add value it will also make a property more ‘sellable’. Buyers of period homes prefer wooden window frames over uPVC sash windows to match the property aesthetics.
Plus, plastic is a big ‘no no’ in conservation areas and listed buildings.

London-based Estate Agent, Mr McConville adds:

Installing new, double glazed windows in a period property is a great thing for potential vendors to do.
It increases the kerb appeal of a property, showing off the beautiful features to would-be buyers that drive past. It can also increase your property value, often by more than it costs to do. We recently sold a property in Streatham that a vendor had valued before and after having their windows replaced. She spent £12k on replacing her windows, and her property was valued (and sold for) £35k more than it was valued at originally.

The thermal efficiency, greater soundproofing capabilities and security benefits of double-glazed units allow homeowners to bring traditional wooden sash windows bang up to date without losing their charm and character.

A sound test from a balcony
on a busy London street showed:

This demonstrates how well double-glazed sashes reduce sound.

How to achieve
double glazed sashes

We offer three distinct services to achieve double glazed sashes that will add value to your property:


Sash window replacement
– this is where we can install new double-glazed sashes into the existing box frames.
Replacement sash windows are popular among customers, particularly owners of period properties, as there is not so much work involved and the original box frames can remain, along with their novel charm. When fitting new sashes into your existing box frames, our carpenters will fully draught seal your windows, hang the window on new cords and fit a complete set of ironmongery. We can even repaint the existing timber in a variety of colours, if requested, without detracting from the look of the property.


Complete renewal
– this is where we can install a completely new box frame and double-glazed sashes.
Renewing sash windows includes us removing the old window, and fit a completely new one – architraves, window boards, the whole works. Our professional installers have worked in period properties for many years and are fully aware how to work with and around the challenges sometimes unearthed by older buildings.


Sash window repairs
– if you already have double glazed sash windows, regular maintenance and repair is key to ensure the existing sashes and frames not only look like new but are as efficient as possible.
A regular service overhaul of your sashes will highlight and damage, broken locks, rotten timbers, or poor insulation so you are able to get them resolved quickly and retain the quality of the windows, and therefore the value added to your property.

All our windows (from the frames to the glass) are handmade in our UK-based workshop using British joining techniques and supplied and fitted by our team. These are different to the techniques used within the rest of Europe and will ensure your windows not only look perfect but, are in keeping with the character of your period property. In fact, our understanding of character preservation in period properties and listed buildings in particular, means we can offer owners of listed buildings the chance to benefit from double glazed sashes too without the hassle of applying for planning.

Double glazed sash
windows in listed buildings

Planning officers are super vigilant when it comes to preserving character and originality in conservation properties and listed buildings which has historically seen window and door requests with double glazing declined.

However, we are approved installers of a type of vacuum insulated glass technology that offers ultra slim, energy efficient, glazing that is the width of single glazing but offers the warmth of triple glazing and because it can be retrofitted into all windows and doors (allowing the original, historical frames to be maintained), it is the perfect window for listed buildings. What’s more, as the original aesthetics of the home are maintained in line with local authority guidelines, you won’t even need planning approval to install them.

Vacuum insulated glass windows provide substantial improvements to energy efficiently. In fact, a double-glazed vacuum insulated glass unit is more thermally efficient than a traditional 36mm triple glazed unit.  The long-term return on your investment will not only see you save in energy costs but will add value to your heritage home.  Here’s what some of our customers have to say:

Mr Carn, Blackheath, SE3.

“We live in a flat in a conservation and are not allowed to change our current window frames, which were designed for single glazed 4mm panels. Fineo’s vacuum insulated glass was the only product we could find which would allow us to double glaze without modifying the frames. We had the glass fitted into the windows in our Master Bedroom and have noticed the bedroom is warmer with the ambient air temperature higher throughout the day.
There is no condensation on the windows in the morning and no downdraft. It is noticeably quieter when planes fly overhead too. The glass was quick and easy to install and enabled us to improve thermal efficiency of our glazing within the constraints of our leasehold and conservation area requirements.”

Mr S, London.

“We love the period features of our property, including the windows and French doors, and we were very keen to keep them, but wanted to improve the insulation. We found Fineo vacuum insulated glass online and it sounded great. We used it to glaze all the windows in our entire flat. We have noticed a considerable improvement in the amount of heat kept in the property. It was installed in early spring, but we could certainly notice that we had to put the heating on much less. We are looking forward to the winter and how much we can save on our bills! We live on a busy road and the noise was constant. There has been a noticeable reduction in the noise levels. Keeping the original windows has been great. We’re very pleased with the installation and efficiency.”

Double glazed sash window cost

Obviously, cost of double-glazed sash windows will depend on the specific requirements, number of windows etc. However, here are some examples of recent projects we have completed to give you some of idea regarding budget.

Birkbeck Road project, SW19

We overhauled two windows, installed new sashes to six windows into the existing frame and fitted one completely new window.

Total order value was £11k + VAT.

Cranbrook Road project, SE8

We installed three new sash windows including box frames and a large set of French doors with glazing bars.

Total order value £8.8k + VAT.

Add stained glass to your double-glazed sashes

Stained glass windows have a varied history and their origins date way back to medieval times. The concept is simple; lead is soldered together that holds a series of mosaic coloured glass, usually forming a picture of some kind.
If you are thinking of investing in stained glass (or repairing some that has been broken for years) it is advisable to go for something understated and traditional in terms of pattern and design that will complement your property. A startingly contemporary, personal piece will limit its appeal to those who share your taste. On the other hand, a standard, reproduced image – a classic tulip, for example, won’t conjure the value add you’re after either. Striking the right design is important to ensure you add extra value if you come to sell your home further down the line.

This beautiful new specialist designed coloured glass French Door project in Crofton Road, SE5 is the perfect example of value adding, stained glass design – complementary to the property and timeless.

Can you install new, double glazed sash windows and doors complete with the original stained glass?

Yes, stained glass windows can be double glazed. When deciding on stained glass for your windows, there are two choices:


If you have existing stained glass in your windows, we can remove it, clean, restore it and reglaze it. This encapsulation process involves sealing the stained-glass panel inside a double-glazed unit to form three layers of glass.

A recent stained glass sash replacement project completed at Ritherdon Road, Balham, required us to restore nine original stained-glass windows and then encapsulate them within new double-glazed units. London-based Estate Agent, Mr McConville estimated that the replacement windows, including the repaired stained glass, would add around £75 in value to the property in question.


Alternatively, we can copy an original or bespoke pattern and replicate it into your new double glazed windows. Colours in the new coloured glass will exactly match the original windows to give you the most authentic look possible.

Make your double-glazed sash windows even safer

Double glazed units offer security to your home in themselves.  Not only is double glazing much thickener, but the insulated glass units also fit into windows, so they cannot be removed.  The panes of glass are also much tougher, and intruder will have a hard job trying to smash through two or three layers of glass.

There are also a number of ways that you can secure your sash windows further.  The most common option is sash stops.  These are fitted to the top window and lock in place allowing you to open the window a little to provide ventilation while securing it in place.  This is an excellent option for the heat of the summer, and also gives you an added layer of security when you close and lock the window before heading out.  Sash stops are easy to fit and also make sash windows safe for children, keeping their fingers from getting accidentally caught by the dropping window, and opening it when they shouldn’t.  Sash screws offer an alternative option.  You simply screw them into the top and bottom rails, locking everything together.

You may even consider adding lockable plantation shutters for yet another layer of security if they would be befitting to your property.  Shutters not only add a little extra security but, are practical and insulating too.  They complement any interior décor, regulate light and privacy simultaneously to accommodate modern living and because they are custom made, will remain with the property even if you leave.

According to the National Office of Statistics – Crime Survey for England and Wales more than three quarters of Burglars gain entry via a door and 1 in 5 enter through a window.  Therefore, double glazing, along with these simple security measures, especially on ground floor windows will give buyers the guarantee that your home is worth the asking price: they represent an outlook that means your home has been well cared for.  A demonstrable measure of home security will always add value to your home.

With so many ways to value add at home with double glazed sashes, what are you waiting for?! The Wandsworth Sash Window team would love to help turn your dreams to reality.

Contact us for an online quote whenever you’re ready.

Contact the Wandsworth Sash Windows team

Talk to us – we can help with your bespoke window, door and joinery requirements. Call 02079247303 or email