Sash Windows Part and Full Replacement

Bespoke Wooden Sash Windows Supplied with Building Control Certification

Specify complete renewal only where necessary and save money, time and remedial works…

In this case the southerly aspect had caused damage beyond reasonable repair so the box frames had to be stripped out to the masonry.

Period houses are valued higher on the market when original features are intact simply because they look right. It wasn’t always that way but since the mid 1990’s wooden sash windows have been undergoing a major revival and due to environmental pressures a bit of a rethink. State of the art box sash windows now overtake ‘modern’ plastic window installations in certain areas providing higher insulation values via wooden framing anda new type of double glazing.

We consider each sash window project a chance to show off our honed skills. From Transport For London’s Victoria HQ to various country piles and from the RAF Club Mayfair’s  20 foot tall sash windows  to Holland Park’s Debenham House with Dulwich Estate properties and a wealth of charming period housing stock in London, and the Home Counties in between.

…and so were replaced with high performance timber sash windows.

It’s worth mentioning that wooden sash window refurbishment covers an aspect defined as ‘part renewal’ in Building Control speak and no PartL rules apply, so unless a window has been thoroughly neglected most box frames (sub-frames) are usually in fair to good order. Renewing a good box frame can be an issue with structural and cosmetic remedial works. The sliding sashes within existing frames are invariably worn out though and wouldn’t accommodate sealed unit double glazing anyway so they are normally renewed and when fitted to a refurbished box frame you now have a sash window set that looks new. There is information aplenty on this website to guide you; from the type of timber you should be using to Building Regulations to the trade terms explained in our PDF guide on the homepage.

Each project we undertake, be it new sashes to existing  box sash window frames or complete renewal, we make all our windows and sundry items in our joinery in South London which not only means better fitting items but speedy problem solving. We also adhere to the same traditional hand made joinery standards that ensure absolute authenticity. That, coupled with state of the art double glazing and our own in-house designed weather- proofing system, produces unbeatable customer satisfaction.


Beaverwood School Chiselhurst during an extensive refurbishment to the box frames. The sashes were renewed.

…and after. Just in time for school!

We ensure our wooden sash windows are as energy and acoustically efficient as possible meeting Part L Building Regulations when complete renewal is the order of the day. Over the years we’ve innovated and introduced various solutions that make producing exact copy-of-original period sash windows that conform to today’s environmental demands not only possible but the norm. For example – we fit our own in-house designed weather proofing system that has stood the test of time (it’s not brush-pile but a more durable solution) and we don’t use lead weights when installing double glazed sash windows which are far too toxic for anyone’s liking, we have our own unique system called the Sashpro Balance that offers an assisted lift and a smoother action.

All in all we aim to be as helpful, open and honest to you as possible and like most show-offs simply love sharing our knowledge gained over the last couple of decades. We even have an open information policy and will assist you in choosing the right materials for the right aspect of a given project – you can download our courtesy information PDF from our homepage and throughout this site you can glean other information vital to your project’s success for example; on wood selection and correct usage please click here

The ‘railway cottages’ in Clapham


Call: 020 8819 3264 for a quick quote


Double glazed sealed units produced in house keep all our costs down

Since 2004 Building Regulations have had to be extended to include period properties. Even back as far as the early nineties Sashpro (not a Ltd company then) was coming up with ways to improve the weather performance of period windows. Sash windows have gone further with major changes in order to provide for the demanding environmental challenges that must be met.

As one of the first ‘modern’ firms to address the preservation of sash windows in general, Sashpro has helped to develop a number of innovations that make it possible for the period sash window

Sashpro durable weather-proofing

to remain in existence and be accountable ecologically. We developed a weather proofing system that not only addressed the traditional synonymous combination of the words draughty and sash window, now thankfully rendered apart but we did it completely invisibly. In other words it’s one of those clever devices you’ll never see, so sash windows remain unaffected aesthetically. All good so far but not good enough for building regs.

Sashpro glass stillage



Double glazing and traditional sash windows were never terms that sat happily together on the purists tongue however looking at the combination from the perspective that it was inevitable and thanks to a great Scottish inventor (whose needs might perhaps be considered greater up north!) Sashpro took a leap of faith and started to use the innovative Slim Sealed Unit. A low emissivity glass and the dense inert gas krypton, used instead of argon, along with ‘warm edge technology’ all allowed for the manufacture of super slim double glazing for sash windows, traditional timber casement windows and of course timber doors. We no produce our own sealed units which keeps costs considerably lower than most of our competitors. Great savings you can pass onto your customers to win the contract. We’ll provide help all along the way from product information, detailed specifications of works to final data sheets for your Building Control needs.

Sashpro slim sealed units

Sashpro slim sealed units





Allow these photos to explain

Here we can see that the sealed unit is virtually undetectable though it provides a U value of 1.5 meeting PartL Building Regs 2014 to current


Complicated sashes can be double glazed (and yes, that’s a lot of sawdust)

…and installed looking exactly like the original

Re-made to look exactly like the original below, double glazed and draught proofed

…and how the old one looked when we brought it back to the workshop





Click here to get in touch and find out more about our  double glazed sash windows in London, Surrey, Sussex and Kent.