Planning – Application Comments

Consultation Date: Wed 26 Jul 2023

Comment Date: Mon 25 Sep 2023

I have read through the window schedule (particularly the notes section,) which provide useful details on the existing condition of the sash windows and the revised Heritage and Planning Statement. The details provided in the notes clearly demonstrate that the windows are in a poor condition and in many cases have been heavily altered through replacement material over the course of their usable life-cycle. As such I am now more content with the proposal to completely replace the windows. Looking through the schedule I would raise two issues.
1. Original glazing bars have been identified therefore we know that the glazing bars should be16mm to retain the historically authentic appearance of the property. The proposed windows have a 22mm glazing bar. I think the increase in width would be very unfortunate and that any replacement should be to the original 16mm dimensions. The difference in width will have a significant visual impact, within a 24 pane sash. The revised heritage statement says 'the profiles and bead sizes to match the existing removed exactly'. This would not be the case if all glazing beads are produced at 22mm width.
2. I would question why 6.5mm insulated glass units are not being used now that they are available, this would be more comparable to modern 4m-6mm single glazed panes whilst offering improved thermal performance.

I am not opposed to the complete replacement and do not object, subject to confirmation on the glazing bead dimension which should match the original 16mm dimension.
As an informative it would be worth noting that within sash windows there is significant thermal bridge through the glazing bar and frame, this is particularly acute in 24 pane sash windows which have more glazing bars within the construction. Reducing the width of the glazing bar would reduce the overall thermal bridging area. I am also mindful that insulated glass units have a projected life-span of 25 years, given the high embodied carbon and issues with recycling, in energy terms IGUs have pay-back periods that can greatly exceed their design life and as such are a false economy. Single glazing however has a much greater longevity (the existing glass is likely 100-200 years old and still functional), it is also recyclable and requires less carbon in the manufacturing process as well as being more historically authentic.

Comment Date: Mon 21 Aug 2023

Trinity House (3 Friars Lane) is a grade II listed mid-18th Century townhouse within the Barbican Conservation Area (Adopted 1967). The property largely retains its 18th C 24-pane hornless sash windows which contribute to the character and significance of the building and the historic streetscape.

The proposal is for the replacement of deteriorating windows with matching Accoya hornless sash windows incorporating double glazing, as well as the re-hanging of slate on the south elevation and render redecoration where required.

I have no in principle objections to the proposed works, and the like for like replacement of the timber sash windows with timber replicas is acceptable where it is shown that historic sash windows have deteriorated to a point where they cannot me repaired. There is a lack of information on the condition of the windows in the submitted documents. There is a general statement that "the repair and maintenance of these existing units is deemed unsuitable due to the
large amount of replacement works that will be required." We would request a full condition survey of the windows carried out by a suitably experience and qualified professional to determine the extent of the fabric decay and inform a decision on the suitability of the proposed works. There are also a number of concerns with the overall approach to improving thermal efficiency.

As well as a condition survey we would like confirmation of the existing glazing bar dimensions, both width and depth. At present the submitted information gives the proposed profile in drawing P1212-01 REV A with a 22mm glazing bar. The Heritage Statement also states "new units shall be produced from Accoya with profiles and bead sizes to match the existing removed exactly". But the drawings and the Heritage Statement do not give the existing window dimensions (profile and bead dimensions) so it is impossible to determine if the proposed 'New timber sash window' drawing an exact match. As a general rule early 18th C glazing bars were quite thick but by the mid-18th Century, glazing bars were commonly 13mm finished width. Therefore confirmation of the existing dimensions is required prior to commencement. Furthermore, given the 18th Century origin of the windows, we would also like confirmation that the existing glass is not handmade cylinder or crown glass. If cylinder or crown glass exists then I would object to its removal/demolition.

The proposed glazing will be 12mm double glazed units fitted into 22mm glazing bars a decision based on improving thermal efficiency. I questions whether the inclusion of double glazed units will meet the 'comfortable family dwelling' aspiration. I would recommend a whole building approach to improving energy use and heat loss. Draught proofing it can reduce air infiltration by over 80% and closing curtains, blinds and shutters can produce the same heat savings as double glazing without harmful intervention into historic fabric. As a rule secondary glazing will generally be more thermally efficient than replacing the existing glass with double glazing due to thermal bridging through the frame and glazing bars. Therefore if the sole purpose of the work is to improve thermal efficiency then there would be less harmful ways to improve the level of thermal comfort.

The works to carefully remove and re-use the existing hung slates is acceptable with the introduction of reclaimed Delabole slate to match the existing. If recycled delabole cannot be sourced then we would need to be notified, and any replacement agreed prior to installation. The render repairs are also acceptable, however we would like confirmation that the render will be lime render to allow breathability.

Before the proposal can be considered acceptable, we would require the submission of detailed information on the condition of each window including dimensions and existing glazing. Without this information the impact and harm of the propsed alterations cannot be accurately determined. If it can be shown that the windows cannot be repaired the proposal to include more thermally efficient glazing into new Accoya sash windows would likely be considered compliant with the Barbican Conservation Area appraisal and Management Plan, DEV21 of The Plymouth and South West Devon Joint Local Plan, NPPF guidance (July 2021) and Section 72 of the Planning (Listed Buildings and Conservation Areas) Act 1990.