Permitted Development Rights review - phase 3: consultation analysis

4. Thermal Efficiency: Domestic and Non-Domestic Buildings

4.1 Replacement Windows

With respect to domestic buildings, existing PDR allow for the alteration or improvement of dwellinghouses (class 2B) and buildings containing flats (class 4A), outwith conservation areas, as long as the works do not extend beyond the so-called ‘1 metre bubble’. These provisions cover the replacement of windows, with no constraints on the design of the new windows installed. Classes 2B and 4A do not apply in conservation areas or, class 4A within the curtilage of a listed building. Replacing the windows of domestic buildings which are located in a conservation area will generally require an application for planning permission – unless the replacements are exact replicas of what is being replaced and the external appearance of the building is not materially affected.

For non-domestic buildings, replacement windows are permitted by general PDR classes 9A, 9C and 9D which provide for the alteration of specified types of non-domestic building. Not all types of building are covered, and the PDR do not apply within sites of archaeological interest, National Scenic Areas, historic gardens or designed landscapes, historic battlefields, conservation areas, National Parks and World Heritage Sites.

For domestic properties (houses and flats), it is proposed that new PDR should cover replacement of windows of buildings within conservation areas – subject to conditions or limitations specifying that:

(i) The PDR does not apply in World Heritage Sites.

(ii) For windows situated on the front elevation of the building, or side elevation fronting a road, the PDR would only apply if the replacement window matches the existing window with respect to:

• Its opening mechanism.
• The dimensions and colour of its frame and astragals.
• The number, orientation and colour of panes.

For non-domestic properties, it is proposed that PDR relating to the replacement of windows should be aligned with domestic properties so it is possible to replace the windows of all non-domestic buildings without a planning application, unless the building is located within a conservation area. Should new PDR be taken forward for the replacement of windows in houses and flats within conservation areas, subject to conditions, a similar approach to non-domestic buildings in conservation areas is proposed.

Listed Building Consent would continue to be required to replace the windows of any listed building.

Question 17: Do you agree with the proposed PDR for replacement windows of domestic buildings located in conservation areas?

Responses to Question 17 by respondent type are set out in Table 15 below.

Percentages may not sum to 100% due to rounding

The largest proportion of respondents – 48% of those answering the question – agreed with the proposed PDR for replacement windows of domestic buildings located in conservation areas. Of the remaining respondents, 25% did not agree, and 27% did not know. Excluding those who answered “don’t know”, 66% agreed and 34% disagreed. A majority of Planning authority respondents disagreed.

Please add any comment in support of your answer

Around 65 respondents provided a comment at Question 17.

Reasons for supporting the proposed PDR

In addition to general comments of support, there was reference to the proposed PDR being a reasonable compromise and a proportionate adaptation to address future climate challenges. It was suggested that the planning system must be streamlined in order to facilitate greater uptake of energy efficiency measures across Scotland’s homes and buildings. Related comments included that:

• The former recommendation of keeping single glazing in windows did not help good insulation and efficient heating.
• Many pre-1919 buildings in conservation areas have major deficiencies in energy efficiency, and the reduction of heat loss through windows by use of double glazing at a more affordable price is an opportunity that cannot be missed.
• With clear and sensible guidelines and framework, the proposed PDR should not pose a concern to wider heritage protection frameworks and should help speed up the process of window works for homeowners considerably.

In terms of other possible positive impacts, there was reference to:

• Unauthorised windows that have been installed in the past potentially being upgraded to a new uPVC window with appropriate opening method and proportions.
• The changes could reduce the number of people exposed to internal noise levels above the threshold at which adverse impacts are observed.

However, although agreeing with the proposed PDR, there was also a view that the public should be encouraged to retain or reuse existing windows, or replace windows with the appropriate original materials, wherever possible.

A view was also expressed that additional PDR should apply but not for replacement windows that are visible from public realm.

Suggestions relating to the detail of the PDR itself included that:

• To exclude World Heritage Sites is overly restrictive and the same criteria should apply as in a conservation area.
• Conditions should include materials and type of glazing.
• The PDR should cover all elevations of buildings.
• Where the current window is an obviously inappropriate past replacement, any new replacement should not be permitted to copy the existing wrong opening method or proportions.

It was also suggested that rewording the condition relating to ‘the number, orientation and colour of panes’ to reference ‘pattern’, rather than ‘orientation’ may be simpler for customers to interpret.

A prior notification procedure for windows on listed buildings and in conservation areas was also proposed. It was suggested they could be accepted as PD if they match or are of similar character to the style of the original windows in the building.

Queries raised, or points of clarification sought included:

• Whether there would be a need to define colour of the frame?
• What is meant by the colour of the pane, as this would be glass?
• Whether it would be possible to add that installing timber windows would not need planning permission subject to other conditions, including opening mechanism and style of window.
• Whether any replacement windows would be subject to a Building Warrant and therefore required to adhere to the technical standards for safety and energy efficiency.

It was also suggested that the use of the word ‘original’ might be an issue, including where later additions provide an important historical context towards the history of the building. The associated proposal was that the focus should be on ensuring that glazing patterns and opening mechanisms are retained and returned where they contribute to the character of the building or area.

Reasons for opposing the proposed PDR

Those disagreeing with the proposed PDR tended to raise concerns, some of which were detailed, about the potential negative impact on the appearance and character of conservation areas. It was suggested that windows are defining elements in the majority of conservation areas; for example it was reported that windows make a substantial contribution to the character, authenticity and physical integrity of the City of Edinburgh’s historic buildings and to the special character and appearance of its 50 conservation areas. A view was also expressed that windows visible from public spaces should not be PDR.

Concerns included that the existing restrictions are frequently breached already, and that a nuanced approach will only worsen the situation further and have a negative impact. In terms of the proposed PDR, the concern was that it would be cumulative, potentially considerable, and could lead to significant, potentially irreversible harm. It was also suggested that any harmful impact would be on arguably the nation’s biggest asset – Scotland’s outstanding historic environment. It was considered that such proposals are against the values and principles governing conservation and enhancement of the historic environment, set out in NPF4.

Whilst it was noted that local authorities can introduce Article 4 Directions, it was argued that such action would unlikely be adopted due to significant resource challenges experienced by local authorities.

Materials and design

A number of the specific concerns about the proposed PDR related to the consultation paper’s suggestion that the installation of new materials could be ‘more sympathetic in design terms’. Points included that using traditional materials in historic buildings is a key fundamental to protecting their special character, and that allowing the use of modern materials, such as uPVC, would undermine decades of work to preserve and enhance these areas. An associated point was that the proposed PDR would also reduce opportunities for enhancement in terms of removing unsympathetic windows and re-instating windows of sympathetic design and materials.

Other design and material-related concerns included that:

• There is the risk that in accommodating a different material this change encourages much wider use of uPVC and also removes any impetus to seek to repair or upgrade existing long life traditional timber windows.
• Property owners will be led by advice from window manufacturers and suppliers that are motivated to sell their product rather than observe planning restrictions.
• Even if the opening mechanism, dimensions and colour of frames and astragals and the number, orientation and colour of panes are met, some modern materials are still clearly noticeable.
• It is questionable whether modern materials can replicate accurately the frame dimensions and astragal details of historic timber windows.
• Many people will not be aware of different types of glass (including historic glass) and the differences in their appearance, so consultation with the local authority conservation officer as part of a planning application would be required.

There were also references to advantages of the current approach, including that the current requirement to apply for planning permission means the planning authority is able to retain control over replacement windows and negotiate an appropriate replacement design on a case-by-case basis.

However, it was also suggested that there is a clear disconnect between planners and the public that has made it challenging to have meaningful discussions. Further comments included that excessive bureaucracy and lack of communication damages the public’s understanding and appreciation of their surroundings and, by extension, is harmful to the built environment.

Environmental considerations

Other comments addressed the thermal efficiency issue, and included that:

• The thermal performance of uPVC and new windows should not be assumed to be superior to that of well-maintained timber windows with secondary glazing.
• Wooden window frames, if correctly specified and maintained, can be both more thermally efficient and have a significantly longer lifespan than modern materials, such as uPVC. It was reported that historic (already 90 years+ old) timber windows will, with appropriate maintenance, still have a longer lifespan ahead of them than any proposed short-life replacement.
• Both thermal and noise reduction improvements can be made to windows in historic properties without replacing them. For example, historic sash and case windows can be repaired and secondary glazing installed without the need for planning consent and thermal efficiency can be further enhanced by the addition of draught strips, shutters, blinds and curtains.

It was noted that Historic Environment Scotland (HES) guidance, such as the Short Guide: Fabric Improvements for Energy Efficiency, sets out ways to improve thermal efficiency in historic buildings without the need to replace historic windows.

In relation to reuse rather than replacement, it was noted that NPF4 recognises ‘conserving and recycling assets’ as an overarching spatial principle, and it was suggested that the whole life cost of material such as uPVC needs to be taken into account before it is encouraged further. It was noted that the consultation paper does not mention the environmental costs associated with manufacturing and disposing of plastic windows. It was argued that refurbishing timber windows would reduce or remove the inbuilt energy and sustainability issues arising from the use of some modern materials, and 2013 research comparing life cycle assessment and whole life costs of timber and uPVC windows was reported to have found that there is inherently less embodied carbon contained within good timber sash and case windows due to their ability to be maintained and repaired^[5]. It was also reported that HES is presently undertaking a fresh research project to compare life cycle assessment and whole life cost of a traditional timber casement window and a modern replacement uPVC window.

Application and enforcement

Other points and concerns raised by those who did not agree with the proposed PDR addressed the practical application of the PDR and enforcement. They included that:

• Ambiguity in the conditions could easily be misinterpreted by those not engaged with the planning system, even if the property owners have the best intentions.
• The reliance on non-specific/detailed window criteria measurements could lead to an upsurge in enforcement enquiries and debate about the extent to which windows match or are similar. It would add additional burden from a planning enforcement perspective, for example, how would the planning service know what was installed previously once the windows have been replaced?

Question 18: Do you have any comments on the conditions that we propose the PDR for replacement windows would be subject to?

Please add any comment in support of your answer

Around 60 respondents provided a comment at Question 18, albeit a number referred back to their views at the previous question.

General comments on the proposed conditions overall

There were some general comments in support for the conditions proposed (primarily from respondents who had agreed with the proposed PDR at Question 17). Supporting comments included that the conditions proposed in the PDR for replacement windows are appropriate, as they strike the balance between maintaining character and improving thermal efficiency.

However, there were also concerns that the proposed conditions would be difficult for Planning authorities to enforce, leading to the prospect of abuse of the PDR. As at the previous question, the connection was sometimes made to the ‘existing window’ and unauthorised replacement windows that do not reflect the character of an historic property having been installed. The associated concern was that the proposed PDR would effectively regularise this situation, with suggestions that any relaxation could cover making such windows match the style of the original windows, or that the existing window should be lawful for PDR to apply.

The PDR does not apply in World Heritage Sites

Relatively few respondents commented on the proposed PDR not applying to World Heritage Sites. Those who did raise the issue held mixed views, including that it should apply to neither World Heritage Sites nor conservation areas, or that not applying the PDR to World Heritage Sites will effectively widen the protection gap between World Heritage Sites and the rest of Scotland’s conservation areas.

The complexity of the relationship between World Heritage Sites and properties in or neighbouring those sites was also noted. It was reported, for example, that the Frontiers of the Roman Empire World Heritage Site (Antonine Wall) runs through urban areas, many of which are also conservation areas. It was suggested that the proposed PDR would lead to properties within the World Heritage Site boundary requiring planning permission, despite the fact that there is no prospect of an impact on that World Heritage Site from window replacement.

For windows situated on the front elevation of the building, or side elevation fronting a road

Respondents also raised some concerns about which elevations should (or should not) be covered by any relaxation of restrictions, and there was a call for the wording to be amended to read ‘For windows situated on the principal elevation, or an elevation visible from the street or public place’. In addition to a general observation that the proposed restrictions do not go far enough in respect of rear or side elevations, suggestions included that the requirements (relating to opening mechanism, dimensions of the frame etc) should apply to:

• Every elevation of a domestic property.
• Any elevation or windows visible from the street or a public place in a conservation area.

There was also reference to historic centres having lanes and piers which differ from a suburban layout so the approach in relation to ‘front’ or ‘rear’ elevations do not apply, and a call clarification on the definition of a side ‘facing’ road, as ‘facing’ is not the same as ‘visible from’ a road.

It was also suggested that including flats in this PDR could lead to an inconsistency across elevations and cumulative impact upon the character and appearance of a conservation area.

Opening mechanism, dimensions and colour of its frame and astragals, number, orientation and colour of panes

There was a general query about what is meant by ‘matching’ existing windows and “like for like” replacements, and there was a call for this to be defined.

Comments on the opening mechanism included that the condition seems overly restrictive and unnecessary if there is no change to the external appearance of the window. However, there was also a view that sash and case windows that have a tilt function in addition to sliding alter the character and appearance of an area when open and should not be permitted under PDR.

Other concerns raised included that:

• Requiring a match in terms of frame dimensions could have pitfalls. For example, a modern uPVC window is very unlikely to be able to match a timber window in terms of width of frame and will inevitably be thicker.
• The use of ‘plant on’ or replica glazing bars can also diminish character, particularly where the building is viewed at close range.
• Colours can often be changed to the benefit of the character of many conservation areas and uniform colour need only be required when stated in the Character Appraisal of that conservation area.
• Dimensions of traditional windows and replacement new windows will rarely ‘match’ in all aspects and may be open to interpretation. For example, ‘dimension’ does not distinguish between ‘contemporary’ and ‘traditional’ frame profiles.

A Public body respondent suggested replacing the ‘matching’ requirements as drafted with: design (including number and orientation of panes); colour and finish; opening method; dimensions; sections of components; and the placing of the new unit within the wall.

Material

As at Question 17, the lack of reference to the material from which the replacement window is made was a concern for some, with further comments including that the appearance of the new windows will not preserve or enhance the conservation area if windows which were originally timber are not timber.

The associated suggestions included that the PDR should state that any replacement window should match the existing window with respect to material. Other suggestions included that:

• It would be better for the PDR to be changed to allow existing timber window frames to be retained and upgraded and converted to accept insulated glass and sealed units.
• PDR could allow previous replacement frames of a different material and/or opening method to be replaced with a reinstatement of the original specification of window frame but with double glazed units, with planning permission still required for all other changes to the frame material and non-original frame material reinstatements.
• Before permitting change of materials, there needs to be some form of assessment of the value of the existing windows.

However, an alternative perspective was that the proposed relaxation on the choice of materials is especially welcomed.

Additional conditions or suggested actions

Other comments or suggestions relating to the coverage of a window-related PDR included that it should:

• Be extended to Category C listed buildings. It was reported that a large number of Scotland’s listed buildings do not have original windows, and indeed in many cases, windows are one of the main causes of a lack of thermal efficiency.
• Include a requirement that replacement windows must be of a certain performance level.
• Recognise that certain new build properties might have a Planning condition requiring a certain acoustic performance standard for the window and associated room ventilation system in order to be effective against an existing external environmental noise source (such as road traffic noise). In such circumstances, any PDR for the replacement of such windows should also have a requirement for these to meet the equivalent acoustic performance as the windows they replace.

In terms of the operation of any PDR, there was support for a prior approval/prior notification process as a way of mitigating negative effects on the historic environment but acknowledging that this would likely reduce the potential positive effects of the proposals on planning service resource. There was also agreement that best practice guidance can contribute to the mitigation of effects, in conjunction with other measures.

Question 19: Do you agree with the proposal to align non-domestic buildings with domestic buildings, as regards PDR for replacement windows?

Are there any types of non-domestic building that should be excluded?

Responses to Question 19 by respondent type are set out in Table 16 below.

Percentages may not sum to 100% due to rounding.

The largest proportion of respondents – 40% of those answering the question – agreed with the proposal to align non-domestic buildings with domestic buildings, as regards PDR for replacement windows. However, 38% of those answering the question did not know, and 22% disagreed. Excluding those who answered “don’t know”, 65% agreed and 35% disagreed.

Please add any comment in support of your answer

Around 50 respondents provided a comment at Question 19.

Respondents who agreed with the proposal were most likely to comment that the approach to domestic and non-domestic properties should align, albeit they sometimes renewed calls for changes to the domestic PDR. There were also references to agreeing with the same PDR applying to both domestic and non-domestic properties, but not agreeing that it should apply to conservation areas.

A number of suggestions were made concerning the framing of the non-domestic PDR, including that if extended to conservation areas, it should be limited to buildings where the existing windows are traditional sash and case, or other traditional window types which contribute to the character of the building/area. The associated concern was that a number of difficulties could arise if it applies to modern, non-domestic buildings such as portal framed buildings. Other comments or suggestions included that:

• As with domestic properties, some non-domestic properties, such as hotels or hospitals, might have a Planning condition requiring a certain acoustic performance standard for the window to be effective against external noise, such as from road traffic. Conversely, some non-domestic properties may require windows to be effective in preventing noise escape from the building and adversely effecting neighbouring residential properties. Any PDR should have a requirement to meet the equivalent acoustic performances.
• The list of places where PDR is restricted should be extended to cover all buildings in Sites of Special Scientific Interest or Scheduled Monuments, the Inventory of Gardens and Designed landscapes, National Scenic Areas, National Parks, Battlefields, and National Nature Reserves.
• World Heritage Sites should also be excluded.

Those who said they did not agree sometimes noted that they did not support the proposed PDR for domestic buildings and therefore, by extension, did not support its extension to non-domestic buildings. Specific points made about non-domestic properties included that the proposals could lead to unsympathetic alterations to shopfronts and other commercial buildings, to the detriment of the character and appearance of conservation areas.

4.2 External cladding

The ‘1 metre bubble’ provisions for domestic alterations (classes 2B and 4A) would currently cover the installation of external cladding in many cases. These PDR do not apply in conservation areas but, in view of the potentially substantial impact that the installation of external cladding could have on a building’s visual appearance and the character of an area, it is considered that such works should continue to require a planning application if located within a conservation area.

Although the consultation paper did not ask a question with respect to cladding, one respondent suggested that it is not clear why external cladding should be treated differently to solar PV panels and heat pumps, and why cladding on side and rear elevations should not be permissible.