Project Overview
Project Type
The project was a private residential conservation and renovation project in a two hundred years old, stone-built house with Victorian brick extension, replacing the original single glazed timber sash windows with new bespoke double-glazed sash windows in new sash boxes on a like-for-like basis. This project was completed in February 2024.
Project Scope
When the present owners took up their ownership of the property in 2008, it had suffered an extended period of neglect under previous owners. They commenced a long-term programme of extensive and sympathetic renovation, restoration, conservation and landscaping under several separately approved listed building consents, planning permissions and tree work approvals, taking every care to enhance the contribution of the property to the visual amenity of the local street scene and local heritage within the Oakham Conservation Area. This refurbishment continues to be an ongoing labour of love.
The window project aimed to replace the single-glazed windows and window frames in the stone-built part of the property with new wooden, bespoke frames and double-glazed units which as far as possible would replicate the appearance of the windows replaced. The requirement was to replace the windows but leave them apparently unchanged to a casual passer-by. Neither change of use nor alteration to the fabric of the building were proposed. Specifically, Listed Building Consent was obtained for the replacement of the fourteen windows in the stone-built part of the property.
In addition to simply replacing the windows, the project aimed to
- Upgrade the property while maintaining its heritage value and having no adverse effect on the appearance and aesthetics of the building, both in its immediate setting and within the street scene, or on other environmental and highway interests, or important features, such as trees. The aesthetics of the overall property were maintained for the overall site and buildings, and enhanced for the publicly visible South, West and North elevations of the stone-built part of the house, thereby visually contributing to the Oakham built environment.
- Preserve and enhance the long-term integrity and security of the building by having windows that operate effectively, provide more secure closures, and have a reduced requirement for maintenance, afforded by modern timber treatments and paint systems.
- Improve the thermal efficiency of the building by eliminating heat loss and draughts through the use of slim double-glazed panes and more effective window seals, thereby reducing its heating costs and carbon footprint and eliminating problems of condensation.
- Reduce pollutants (traffic fumes, dust, and noise) entering the property.
- Secure the long-term future of the building. In a world where energy costs are rapidly rising and reducing carbon footprint is now a national and global priority, increasing the thermal efficiency of all buildings will be high on the political agenda. Potential future buyers of the property will insist on double-glazed windows as a sine qua non for their purchase. Its absence will seriously impact the value and marketability of the property thereby putting its long-term future at risk.
In summary, the property has been extensively restored and refurbished in a careful and sympathetic programme over a long period and has been transformed from a dilapidated, uncared-for, and near-uninhabitable condition to become a genuine heritage asset in the Oakham Conservation Area.
The project was intended to be deliberately neither prominent nor intrusive. It has not detracted from the asset’s historic significance but is entirely beneficial to its long-term preservation within the landscape.
Clients Requirements and Challenges
Conservation
Historically, obtaining consent to installing primary double-glazing in listed buildings has been very difficult and the conservation authorities have favoured the repair of existing windows over installing new ones. If double glazing were to be permitted, internal secondary double-glazing was likely to be the approved solution, even if not the best looking one. Concern about the possible aesthetic impact on reflections in windows with modern glass (particularly double-glazed) compared to those with “old” glass can be a reason for refusing consent. Another potential pitfall is that the profiles of the timber components, particularly items like glazing bars are slimmer in old single-glazed windows than is possible in heavier modern double-glazed units. Repairing old frames with wood fillers or cutting out rot and splicing new wood back in does not last as the wood moves, often preventing the repaired windows from working properly. It was fundamental in the LBC application that all these issues were addressed and alternative solutions put forward to ensure that approval would be obtained
Design Issues
Of the fourteen windows that were replaced, ten were traditional vertical sashes and four were horizontal Yorkshire sliders with entirely different designs. Whilst all the sash windows appeared to be of the same size, they were all different and each new one needed to be made to measure. All the pointing (in lime mortar) around the new windows in the original apertures needed to be replaced and it was necessary to appoint a specialist builder to carry out this work. Whilst Simplicity Timber Solutions made good any damage around window apertures internally, separate arrangements had to be made for repainting walls and woodwork.
Simplicity’s involvement from the beginning in producing drawings and technical information and working very closely with the owners was an essential part of gaining planning consent.
We replicated the traditional joinery sections without compromise but designing them to include modern weatherproofing seals, Simplicity ensured that weather seals were designed into the windows, even in period joinery especially where double- glazed units have been specified. Any external cold air that could be blown into the property could then again add to a condensation issue, and our design prevents this.
There were several bespoke design features. The genetically modified timber of accoya was specified for its stability in service. Accoya is a high-performance wood made from sustainably sourced timber. The Georgian bar design is a very delicate section when machined and we also crafted traditional one-piece scarf joints on all the meeting rails like the original window design that we had been commissioned to replicate. Having the accoya’s stability will help to bring years of a trouble-free service life with these delicate and intricate sections.
All the windows were factory finished with a waterborne micro-porous coating system. All the exterior was colour matched to Gardenia BS 10B15 and some of the windows were supplied in a split colour finish for the interior and these were colour matched to a Farrow & Ball All White colour. The windows were offered to the spray room in as many component parts as possible, so that as many surfaces as possible are fully finished. This even included the internal faces of the weight boxes as well as the counter-balanced weights, which had a specialist anti rust coating applied
A 12mm Heritage type double glazed unit with U value of 1.9 W/m2.K was specified and included a warm edge spacer bar that creates the cavity to help reduce any further risk of condensation that can be associated with generic aluminium spacers. The heritage double-glazed units were manufactured to include a high-performance low e coating on the glass, and the cavity was filled with krypton gas. Also, as part of the Listed Building Consent application, we were able to include a Goethe heritage restoration glass for some of the units, glazed into specific openings within the Georgian bar design as described in the Consent application. The glazing apertures were designed for the heritage double glazed units to be installed into a fully bedded putty system and then capped with a very delicate timber bead.
Preparation for Installation
One concern was that as the original windows were taken from their place in the window apertures, there was a possibility that, unsupported, an aperture might partially collapse. We consulted a structural engineer who was unable to recommend any precautionary measures but suggested that a one at a time approach be adopted with a builder on hand to deal with any problems but otherwise suggested keeping our fingers crossed.
Thankfully, the problem did not arise. It is also an issue that works on old buildings often give rise to entirely unanticipated problems. Again, the presence of a highly skilled stone mason on site provided the necessary reassurance.
Building and Conservation Regulations Compliance
Simplicity use local authorities for all our inspections and never use any self-certification schemes as we see this as a two-way protection for both the homeowner and us in that they are directly and independently inspecting our work. On this project, we had a few conversations with the Building Control Officer and then we requested a site meeting because of a particular 2nd floor window. This was a large Yorkshire sash style window, and the concerns arose because it was situated considerably lower than 800mm from the floor. This meant that all glass needed to be safety type as it would be acting as a barrier to prevent anyone accidently falling. Also, because this was a 2nd floor window that opened, it needed to be restricted with an acceptable product again to stop anyone accidentally falling while it could be a means of escape in a fire, which we felt needed professional guidance and clarification from the Building Inspector who agreed with the glass safety specification and the use of restrictors.
Project Summary
Key Results
This was a complex project involving a great deal of collaboration to conclude a successful LBC application. The client worked closely with Simplicity to obtain the technical knowledge to be able to argue the case in the application for Listed Building Consent. In addition, Simplicity had experience of having worked on other projects requiring consent and played a guiding role. In addition, Simplicity gave the client an education in windows and joinery technicalities to enable the right decisions to be made to achieve a seamless integration between the latest technology in wooden window design with the heritage property.
The project has achieved about a 30% increase in window heat loss efficiency with a corresponding reduction in energy costs. The installed windows look beautiful, operate beautifully and are delivering the advantages of the timber and paint technologies.