Improving the performance of windows and doors in a period commercial building is rarely a choice between leaving everything untouched and replacing everything with modern units. The best solution usually begins with understanding what is significant, what is causing the problem and which intervention will achieve the required improvement with the least effect on the building’s character.

Written by: Stuart Conroy, Managing Director, H&C Joinery
Published: [Insert publication date]
Relevant experience: Stuart leads H&C Joinery’s bespoke heritage window, door and secondary-glazing projects, including profile matching, draught reduction and conservation-sensitive commercial work.
Estimated reading time: 8 minutes

Key takeaways

Repair, draught-proofing and secondary glazing should be considered before complete window replacement.
The performance brief must be coordinated with historic profiles, sightlines, glazing and opening methods.
Early input from a specialist joinery manufacturer can help turn conservation objectives into a practical, buildable specification.

Architects can improve period windows and doors without compromising historic character by choosing the least intrusive measure that meets the project brief. Depending on the building, this may involve repair, draught-proofing, secondary glazing, carefully integrated heritage glazing, accurate like-for-like replacement, or Period window and door upgrades. The decision should be based on significance, condition, required performance, consent and the practical limitations of the existing fabric.

Five steps to choosing the right intervention

Identify what is significant

Record the original materials, profiles, mouldings, glazing bars, glass, ironmongery and opening methods that contribute to the building’s character.

Diagnose the actual problem

Separate general dissatisfaction from measurable issues. Is the concern draughts, heat loss, external noise, water ingress, security, difficult operation or deterioration?

Start with the least intrusive option

Consider maintenance, repair, adjustment and draught-proofing before moving to secondary glazing or replacement.

Test the proposed improvement against the building

Check how glass thickness, seals, hardware, ventilation and frame alterations would affect the original proportions and appearance.

Agree the approval and evidence route

Confirm whether drawings, sections, samples, test information or listed-building consent may be required before the specification is fixed.

Why is this such a difficult balance in period commercial buildings?

Traditional windows and doors are often central to the significance of a historic building. Their value may lie in more than their age.

Important characteristics can include:

The width and depth of the timber sections.
The proportions of the opening.
The arrangement of panes.
Fine glazing bars and meeting rails.
Historic glass and its visual variation.
Moulded profiles.
Traditional joints and construction.
Original shutters, architraves and linings.
Surviving handles, catches and hinges.

A replacement unit may fit the opening and still be visually wrong. Slightly heavier glazing bars, wider meeting rails or different glass reflections can alter the appearance of an entire elevation.

Historic England recommends approaching changes to windows and doors as part of a whole-building assessment. The appropriate measure will vary according to the building, its condition, its significance and the proposed use.

Commercial projects add another layer of complexity. The architect may also need to consider:

Occupant comfort.
Energy use.
External noise.
Security and access control.
Safety glazing.
Ease of operation.
Maintenance.
Ventilation.
Business continuity during the work.

The challenge is therefore not to make a period window behave exactly like an unrelated modern product. It is to achieve a proportionate improvement without removing the details that make the building special.

Should existing period windows be repaired or replaced?

Repair should normally be investigated before complete replacement, particularly where historic material and detailing survive.

Traditional timber windows were generally constructed from separate, repairable components. Localised deterioration does not necessarily mean the entire window has failed.

A condition survey may find that the main problems relate to:

Failed paint coatings.
Loose joints.
Deteriorated lower rails or sills.
Broken sash cords.
Worn pulleys.
Poorly adjusted casements.
Missing putty.
Open perimeter gaps.
Inappropriate previous repairs.
Layers of paint restricting movement.
Failed or poorly fitted ironmongery.

Targeted repairs can retain more original material while restoring proper operation. Repair can also avoid the visual compromises that arise when a replacement system requires heavier sections.

Historic England’s traditional-window guidance emphasises the contribution that original design, materials and workmanship make to the significance of historic buildings. It covers repair and upgrading as well as replacement considerations.

Replacement becomes more likely where:

The existing unit is structurally beyond viable repair.
Extensive original fabric has already been lost.
A previous replacement is inappropriate for the building.
The required opening arrangement cannot be achieved safely through repair.
The condition and project brief justify a carefully detailed new unit.
The relevant authorities and project team accept replacement as the appropriate intervention.

Where replacement is proposed, the specification should define what “like for like” means. It should not be left as a vague visual instruction.

Can draught-proofing make a meaningful difference?

Draught-proofing is often one of the least disruptive ways to improve comfort around traditional windows and doors.

Air leakage can occur around:

Sliding sash meeting rails.
Staff and parting beads.
Casement rebates.
Door perimeters.
Thresholds.
Letter plates.
Poor junctions between frames and surrounding construction.

The right approach depends on how the window or door moves. A seal that works on a hinged casement may not be appropriate for a sliding sash.

For traditional sash windows, discreet brush seals can often be integrated into replacement beads or carefully formed channels. Hinged windows and doors may use compression seals where the sections allow them to be introduced without damaging important details.

Historic England describes draught-proofing as a comparatively low-impact method of improving comfort and reducing unnecessary air leakage, with little or no visible change when it is designed properly.

However, the specification must still consider ventilation. Eliminating uncontrolled draughts is not the same as removing the building’s need for managed ventilation.

When is secondary glazing the right specification?

Secondary glazing is often suitable where the original external windows should remain unchanged but better thermal comfort, acoustic control or draught reduction is required.

A separate glazed system is fitted internally behind the primary window. This creates an additional barrier while retaining the original window on the external elevation.

It can be particularly useful for:

Listed buildings.
Conservation-area properties.
Traditional sash windows.
Historic offices.
Hotels and hospitality buildings.
Schools and institutional properties.
Buildings affected by traffic or urban noise.
Occupied properties where wholesale replacement would be highly disruptive.

Available configurations can include:

Vertical sliding units.
Horizontal sliding units.
Hinged casements.
Lift-out panels.
Fixed units for openings that do not need regular access.

The best configuration should follow the primary window. A vertical slider behind a sash window, for example, can allow the secondary sightlines to align more closely with the original meeting rails.

Secondary glazing is not automatically invisible. Poorly positioned frames, heavy sections or mismatched sightlines can still affect the interior. The design should therefore consider:

Frame colour.
Frame depth.
Position within the reveal.
Alignment with existing glazing bars.
Access for cleaning.
Operation of shutters.
Handles and ironmongery.
Curtains and blinds.
Opening requirements.
Ventilation and condensation risk.

Historic England’s guidance discusses secondary glazing as a way to improve window performance while retaining existing fabric, provided that the design responds properly to the historic window and surrounding construction.

H&C Joinery supplies made-to-measure secondary-glazing systems for period and commercial properties, including sliding and lift-out arrangements designed around the existing opening.

Can slimline or vacuum glazing be used in heritage windows?

Slimline and vacuum glazing can provide options where improved glass performance is required but standard double-glazed units would demand sections that are too heavy for the historic design.

Their suitability is project-specific.

The architect and joinery manufacturer need to assess:

Overall unit thickness.
Edge-seal visibility.
Required glazing rebate.
Glass weight.
Glazing-bar dimensions.
Pane size.
Safety-glazing requirements.
Expected appearance and reflections.
Compatibility with the frame.
Manufacturer requirements.
Consent and conservation considerations.

A thin glazed unit does not automatically make a proposal acceptable. The complete window must still preserve suitable proportions, detailing and sightlines.

H&C can manufacture traditional box sash, casement and specialist windows that replicate original profiles, with concealed draught-proofing and slimline or vacuum glazing considered where the project and relevant approvals permit.

The glazing decision should be made while the timber sections are being developed, not added after the joinery drawings have been approved.

When is accurate replica replacement appropriate?

Replica replacement may be appropriate where existing windows or doors are beyond viable repair, where unsuitable modern replacements are being corrected or where an approved scheme requires new joinery.

A convincing replica should be based on evidence from the building.

Useful evidence may include:

Surviving original windows elsewhere on the property.
Adjacent buildings of the same period.
Historic photographs.
Existing paint lines.
Original pockets, pulleys or shutters.
Removed timber samples.
Archive drawings.
Repeated mouldings elsewhere in the building.

The manufacturer may then record:

Overall frame dimensions.
Sash or casement proportions.
Rail and stile sizes.
Glazing-bar profiles.
Mouldings.
Sill details.
Horns and sash features.
Panel arrangements.
Ironmongery positions.
Junctions with the surrounding fabric.

Samples and first-off sections are particularly useful where a complete elevation or repeated window type is involved. A small adjustment made before the production run is far easier than correcting dozens of completed units.

How should modern security and hardware be integrated?

Security should be considered as part of the complete door or window design.

Adding locks after the timber sections have been agreed can create problems. Lock cases, keeps, access-control cabling, door closers and hinges may require more timber, different reinforcement or changes to the frame.

For period doors, the architect may need to balance:

Original panel proportions.
Existing or reclaimed ironmongery.
Modern locking requirements.
Access control.
Door-closing requirements.
Threshold details.
Weather seals.
Glazing and safety requirements.
Everyday commercial use.

The goal is to integrate modern components discreetly rather than allowing them to dominate the joinery.

Hardware schedules should be reviewed alongside the joinery drawings. This helps identify conflicts before manufacture and allows preparation to take place accurately in the workshop.

Which improvement route is most appropriate?

Existing condition and objective	Route to investigate first	Main watch-out
Sound original window with localised deterioration	Repair and overhaul	Confirm the cause of decay rather than covering it
Window operates poorly and feels draughty	Adjustment and draught-proofing	Maintain appropriate ventilation
Original external appearance must remain unchanged	Secondary glazing	Coordinate internal sightlines and access
Existing frame can accept a specialist glazed unit	Slimline or vacuum glazing assessment	Check rebates, weight, edge details and consent
Existing unit is beyond viable repair	Accurate replica replacement	Define profiles and materials precisely
Previous replacement is visually inappropriate	Evidence-led reinstatement	Base the design on the building, not a generic “heritage” style
Noise is a major concern	Secondary glazing with a carefully designed air gap	Review the whole opening and surrounding construction
Modern security is required	Integrated hardware and locking design	Coordinate components before finalising timber sections

This table is a starting point, not a substitute for a project-specific survey and specification.

What information should architects provide to the joinery manufacturer?

The most useful early package includes:

Existing and proposed elevations.
Window and door schedules.
Photographs of each type.
Measured survey information.
Available historic drawings or images.
Heritage statements and consent conditions.
Required opening methods.
The thermal, acoustic, safety and security brief.
Proposed glass types.
Ironmongery information.
Finish requirements.
Access and phasing constraints.
Details of retained shutters, linings and architraves.
Responsibilities for installation and making good.

Where information is incomplete, the gaps should be identified explicitly. It is better to mark an opening as requiring confirmation than to manufacture from an assumed dimension.

Common mistakes when upgrading period windows and doors

Mistake 1: starting with the product rather than the problem

The consequence: The project jumps straight to replacement glazing without establishing whether draughts, poor adjustment or failed perimeter details are the real cause.

The fix: Diagnose the condition and required outcome before selecting the intervention.

Mistake 2: treating all windows on an elevation as identical

The consequence: Variations are discovered during manufacture or installation.

The fix: Survey representative openings carefully and identify where individual measurement is required.

Mistake 3: specifying a glass unit before checking the joinery

The consequence: The required rebate or weight changes the original frame proportions.

The fix: Develop the glass and timber sections together.

Mistake 4: using “match existing” as the complete specification

The consequence: The tender relies on interpretation and different suppliers price different solutions.

The fix: Include measured profiles, sections, samples and clearly identified reference windows.

Mistake 5: overlooking the internal appearance of secondary glazing

The consequence: New frames conflict with shutters, linings, glazing bars or interior finishes.

The fix: Draw the internal elevation and key reveal sections before approval.

Mistake 6: assuming listed-building approval

The consequence: Joinery is ordered before the relevant proposal has been accepted.

The fix: Confirm the consent route and provide the required drawings and samples before manufacture.

What should architects ask before approving the proposal?

What original fabric will be retained?
Which defects can be repaired?
What evidence supports complete replacement?
How have the existing profiles been recorded?
Will the proposed glass alter the frame dimensions?
How will new sightlines compare with the original?
Can modern seals and hardware be concealed?
How will the secondary glazing align with the primary window?
Can shutters, blinds and curtains continue to operate?
What samples will be provided?
Which details require conservation approval?
Who is responsible for final site dimensions?
How will individual units be identified?
What maintenance information will be supplied?

Quick specification checklist

Before approving a period window or door package, confirm:

The building’s significant window and door details are understood.
A condition survey has been completed.
Repair has been considered before replacement.
The required improvement is clearly defined.
The least intrusive suitable route has been assessed.
Existing profiles and sightlines are recorded.
The proposed glass suits the joinery sections.
Draught seals are appropriate to the opening method.
Ventilation has been considered.
Ironmongery is coordinated.
Secondary glazing does not obstruct shutters or access.
Samples or first-off units are included where needed.
Consent requirements are understood.
Final site dimensions have an agreed sign-off point.
Installation and making-good responsibilities are clear.
Maintenance and handover information are specified.

Project example: heritage commercial joinery in Gateshead

For a Gateshead Council regeneration scheme, H&C Joinery manufactured and installed three traditional timber shopfronts while working for main contractor Wentworth Construction.

The wider joinery package included 25 traditional sliding sash windows and hardwood doors. H&C worked with the architect and conservation specialists to translate the intended historic appearance into a coordinated manufacturing and installation package.

The project shows why heritage commercial joinery needs to be considered across the complete elevation. Shopfronts, windows and doors must share appropriate proportions, profiles, finishes and visual relationships rather than being specified as unrelated products.

Frequently asked questions

Must original windows always be retained?

Not in every circumstance, but their condition and significance should be properly assessed before replacement is proposed. Localised deterioration can often be repaired. Complete replacement may be justified where the unit is beyond viable repair or an inappropriate previous replacement is being corrected.

Is secondary glazing suitable for listed commercial buildings?

It can be, particularly because it allows the external primary window to remain in place. However, the design, fixing method and effect on the interior still require project-specific assessment and may require approval.

Can traditional sash windows be draught-proofed?

Yes, concealed or discreet seals can often be incorporated while retaining the sliding operation and traditional appearance. The exact method depends on the construction and condition of the window.

Is slimline double glazing always acceptable in a listed building?

No. Acceptability depends on the significance of the window, the proposed alterations, the appearance of the glass and the position of the relevant planning authority. Approval should not be assumed.

Can new heritage windows include modern locking?

Modern locking and security hardware can often be integrated, but the hardware must be coordinated with the timber sections, frame and ironmongery schedule before manufacture.

When should H&C Joinery become involved?

Ideally, H&C should be consulted while the joinery detail can still be developed. Early involvement allows profiles, glass, hardware, samples, surveys and installation constraints to be reviewed before the package is fixed.

Repair, draught-proofing and secondary glazing should be considered before complete window replacement.
The performance brief must be coordinated with historic profiles, sightlines, glazing and opening methods.
Early input from a specialist joinery manufacturer can help turn conservation objectives into a practical, buildable specification.

Answer-first summary

Architects can improve period windows and doors without compromising historic character by choosing the least intrusive measure that meets the project brief. Depending on the building, this may involve repair, draught-proofing, secondary glazing, carefully integrated heritage glazing or accurate like-for-like replacement. The decision should be based on significance, condition, required performance, consent and the practical limitations of the existing fabric.

Quick Decision Framework: five steps to choosing the right intervention

Identify what is significant

Record the original materials, profiles, mouldings, glazing bars, glass, ironmongery and opening methods that contribute to the building’s character.

Diagnose the actual problem

Separate general dissatisfaction from measurable issues. Is the concern draughts, heat loss, external noise, water ingress, security, difficult operation or deterioration?

Start with the least intrusive option

Consider maintenance, repair, adjustment and draught-proofing before moving to secondary glazing or replacement.

Test the proposed improvement against the building

Check how glass thickness, seals, hardware, ventilation and frame alterations would affect the original proportions and appearance.

Agree the approval and evidence route

Confirm whether drawings, sections, samples, test information or listed-building consent may be required before the specification is fixed.

Why is this such a difficult balance in period commercial buildings?

Traditional windows and doors are often central to the significance of a historic building. Their value may lie in more than their age.

Important characteristics can include:

The width and depth of the timber sections.
The proportions of the opening.
The arrangement of panes.
Fine glazing bars and meeting rails.
Historic glass and its visual variation.
Moulded profiles.
Traditional joints and construction.
Original shutters, architraves and linings.
Surviving handles, catches and hinges.

A replacement unit may fit the opening and still be visually wrong. Slightly heavier glazing bars, wider meeting rails or different glass reflections can alter the appearance of an entire elevation.

Historic England recommends approaching changes to windows and doors as part of a whole-building assessment. The appropriate measure will vary according to the building, its condition, its significance and the proposed use.

Commercial projects add another layer of complexity. The architect may also need to consider:

Occupant comfort.
Energy use.
External noise.
Security and access control.
Safety glazing.
Ease of operation.
Maintenance.
Ventilation.
Business continuity during the work.

Should existing period windows be repaired or replaced?

Repair should normally be investigated before complete replacement, particularly where historic material and detailing survive.

Traditional timber windows were generally constructed from separate, repairable components. Localised deterioration does not necessarily mean the entire window has failed.

A condition survey may find that the main problems relate to:

Failed paint coatings.
Loose joints.
Deteriorated lower rails or sills.
Broken sash cords.
Worn pulleys.
Poorly adjusted casements.
Missing putty.
Open perimeter gaps.
Inappropriate previous repairs.
Layers of paint restricting movement.
Failed or poorly fitted ironmongery.

Targeted repairs can retain more original material while restoring proper operation. Repair can also avoid the visual compromises that arise when a replacement system requires heavier sections.

Historic England’s traditional-window guidance emphasises the contribution that original design, materials and workmanship make to the significance of historic buildings. It covers repair and upgrading as well as replacement considerations.

Replacement becomes more likely where:

The existing unit is structurally beyond viable repair.
Extensive original fabric has already been lost.
A previous replacement is inappropriate for the building.
The required opening arrangement cannot be achieved safely through repair.
The condition and project brief justify a carefully detailed new unit.
The relevant authorities and project team accept replacement as the appropriate intervention.

Where replacement is proposed, the specification should define what “like for like” means. It should not be left as a vague visual instruction.

Can draught-proofing make a meaningful difference?

Draught-proofing is often one of the least disruptive ways to improve comfort around traditional windows and doors.

Air leakage can occur around:

Sliding sash meeting rails.
Staff and parting beads.
Casement rebates.
Door perimeters.
Thresholds.
Letter plates.
Poor junctions between frames and surrounding construction.

The right approach depends on how the window or door moves. A seal that works on a hinged casement may not be appropriate for a sliding sash.

Historic England describes draught-proofing as a comparatively low-impact method of improving comfort and reducing unnecessary air leakage, with little or no visible change when it is designed properly.

However, the specification must still consider ventilation. Eliminating uncontrolled draughts is not the same as removing the building’s need for managed ventilation.

When is secondary glazing the right specification?

Secondary glazing is often suitable where the original external windows should remain unchanged but better thermal comfort, acoustic control or draught reduction is required.

A separate glazed system is fitted internally behind the primary window. This creates an additional barrier while retaining the original window on the external elevation.

It can be particularly useful for:

Listed buildings.
Conservation-area properties.
Traditional sash windows.
Historic offices.
Hotels and hospitality buildings.
Schools and institutional properties.
Buildings affected by traffic or urban noise.
Occupied properties where wholesale replacement would be highly disruptive.

Available configurations can include:

Vertical sliding units.
Horizontal sliding units.
Hinged casements.
Lift-out panels.
Fixed units for openings that do not need regular access.

The best configuration should follow the primary window. A vertical slider behind a sash window, for example, can allow the secondary sightlines to align more closely with the original meeting rails.

Secondary glazing is not automatically invisible. Poorly positioned frames, heavy sections or mismatched sightlines can still affect the interior. The design should therefore consider:

Frame colour.
Frame depth.
Position within the reveal.
Alignment with existing glazing bars.
Access for cleaning.
Operation of shutters.
Handles and ironmongery.
Curtains and blinds.
Opening requirements.
Ventilation and condensation risk.

H&C Joinery supplies made-to-measure secondary-glazing systems for period and commercial properties, including sliding and lift-out arrangements designed around the existing opening.

Can slimline or vacuum glazing be used in heritage windows?

Slimline and vacuum glazing can provide options where improved glass performance is required but standard double-glazed units would demand sections that are too heavy for the historic design.

Their suitability is project-specific.

The architect and joinery manufacturer need to assess:

Overall unit thickness.
Edge-seal visibility.
Required glazing rebate.
Glass weight.
Glazing-bar dimensions.
Pane size.
Safety-glazing requirements.
Expected appearance and reflections.
Compatibility with the frame.
Manufacturer requirements.
Consent and conservation considerations.

A thin glazed unit does not automatically make a proposal acceptable. The complete window must still preserve suitable proportions, detailing and sightlines.

The glazing decision should be made while the timber sections are being developed, not added after the joinery drawings have been approved.

When is accurate replica replacement appropriate?

A convincing replica should be based on evidence from the building.

Useful evidence may include:

Surviving original windows elsewhere on the property.
Adjacent buildings of the same period.
Historic photographs.
Existing paint lines.
Original pockets, pulleys or shutters.
Removed timber samples.
Archive drawings.
Repeated mouldings elsewhere in the building.

The manufacturer may then record:

Overall frame dimensions.
Sash or casement proportions.
Rail and stile sizes.
Glazing-bar profiles.
Mouldings.
Sill details.
Horns and sash features.
Panel arrangements.
Ironmongery positions.
Junctions with the surrounding fabric.

How should modern security and hardware be integrated?

Security should be considered as part of the complete door or window design.

For period doors, the architect may need to balance:

Original panel proportions.
Existing or reclaimed ironmongery.
Modern locking requirements.
Access control.
Door-closing requirements.
Threshold details.
Weather seals.
Glazing and safety requirements.
Everyday commercial use.

The goal is to integrate modern components discreetly rather than allowing them to dominate the joinery.

Hardware schedules should be reviewed alongside the joinery drawings. This helps identify conflicts before manufacture and allows preparation to take place accurately in the workshop.

Which improvement route is most appropriate?

Existing condition and objective	Route to investigate first	Main watch-out
Sound original window with localised deterioration	Repair and overhaul	Confirm the cause of decay rather than covering it
Window operates poorly and feels draughty	Adjustment and draught-proofing	Maintain appropriate ventilation
Original external appearance must remain unchanged	Secondary glazing	Coordinate internal sightlines and access
Existing frame can accept a specialist glazed unit	Slimline or vacuum glazing assessment	Check rebates, weight, edge details and consent
Existing unit is beyond viable repair	Accurate replica replacement	Define profiles and materials precisely
Previous replacement is visually inappropriate	Evidence-led reinstatement	Base the design on the building, not a generic “heritage” style
Noise is a major concern	Secondary glazing with a carefully designed air gap	Review the whole opening and surrounding construction
Modern security is required	Integrated hardware and locking design	Coordinate components before finalising timber sections

This table is a starting point, not a substitute for a project-specific survey and specification.

What information should architects provide to the joinery manufacturer?

The most useful early package includes:

Existing and proposed elevations.
Window and door schedules.
Photographs of each type.
Measured survey information.
Available historic drawings or images.
Heritage statements and consent conditions.
Required opening methods.
The thermal, acoustic, safety and security brief.
Proposed glass types.
Ironmongery information.
Finish requirements.
Access and phasing constraints.
Details of retained shutters, linings and architraves.
Responsibilities for installation and making good.

Where information is incomplete, the gaps should be identified explicitly. It is better to mark an opening as requiring confirmation than to manufacture from an assumed dimension.

Common mistakes when upgrading period windows and doors

Mistake 1: starting with the product rather than the problem

The consequence: The project jumps straight to replacement glazing without establishing whether draughts, poor adjustment or failed perimeter details are the real cause.

The fix: Diagnose the condition and required outcome before selecting the intervention.

Mistake 2: treating all windows on an elevation as identical

The consequence: Variations are discovered during manufacture or installation.

The fix: Survey representative openings carefully and identify where individual measurement is required.

Mistake 3: specifying a glass unit before checking the joinery

The consequence: The required rebate or weight changes the original frame proportions.

The fix: Develop the glass and timber sections together.

Mistake 4: using “match existing” as the complete specification

The consequence: The tender relies on interpretation and different suppliers price different solutions.

The fix: Include measured profiles, sections, samples and clearly identified reference windows.

Mistake 5: overlooking the internal appearance of secondary glazing

The consequence: New frames conflict with shutters, linings, glazing bars or interior finishes.

The fix: Draw the internal elevation and key reveal sections before approval.

Mistake 6: assuming listed-building approval

The consequence: Joinery is ordered before the relevant proposal has been accepted.

The fix: Confirm the consent route and provide the required drawings and samples before manufacture.

What should architects ask before approving the proposal?

What original fabric will be retained?
Which defects can be repaired?
What evidence supports complete replacement?
How have the existing profiles been recorded?
Will the proposed glass alter the frame dimensions?
How will new sightlines compare with the original?
Can modern seals and hardware be concealed?
How will the secondary glazing align with the primary window?
Can shutters, blinds and curtains continue to operate?
What samples will be provided?
Which details require conservation approval?
Who is responsible for final site dimensions?
How will individual units be identified?
What maintenance information will be supplied?

Quick specification checklist

Before approving a period window or door package, confirm:

The building’s significant window and door details are understood.
A condition survey has been completed.
Repair has been considered before replacement.
The required improvement is clearly defined.
The least intrusive suitable route has been assessed.
Existing profiles and sightlines are recorded.
The proposed glass suits the joinery sections.
Draught seals are appropriate to the opening method.
Ventilation has been considered.
Ironmongery is coordinated.
Secondary glazing does not obstruct shutters or access.
Samples or first-off units are included where needed.
Consent requirements are understood.
Final site dimensions have an agreed sign-off point.
Installation and making-good responsibilities are clear.
Maintenance and handover information are specified.

Project example: heritage commercial joinery in Gateshead