Timber windows for conservation areas: the specification that gets approved

This page is a specification guide, not a guide to whether you need permission. Take that question first: for a house in England, replacing windows is often permitted development and conservation area designation does not by itself remove that right — start with the complete guide to conservation area windows and then planning permission for windows in a conservation area. Everything below assumes you have found that an application is required, or that the building is listed and needs listed building consent regardless.

Most of the published detail below comes from English local planning authorities and the Planning Inspectorate, and is flagged as such; Scotland works differently in a way that matters here and has its own section, plus a fuller treatment in Scotland, Wales and Northern Ireland. The counterpart to this page is uPVC windows in a conservation area, where the material argument runs the other way.

Why the argument is about millimetres

Read enough decision letters and a pattern emerges: refusals cite dimensions and detailing, not species. At 27 Cobham Street, Gravesend, the inspector’s reasoning was that “The UPVC frames are markedly thicker which contrasts negatively with the properties which have retained the traditional timber framed sliding sash windows. Also, the windows have a lack of architectural detailing compared to the original windows typical to the area.”

Appeal APP/K2230/W/25/3366705, dismissed 13 October 2025

Timber is the answer to a question about thickness, not a virtue in itself: it is the material that allows slender sections, so a timber window drawn with fat sections wastes its own advantage. Torbay Council puts the point institutionally, requiring drawings to specified scales “so that the planning officer can ascertain the width of visible framework”, and giving as an example of an unacceptable drawing one where “a frame cannot be presented as a single line”.

Torbay Council, Details for windows in Conservation Areas or Listed Buildings, January 2015 — torbay.gov.uk (PDF)

The one published set of numbers, and what it shows

There is an exception to that, and it is the most useful drawing in the whole subject. Historic England’s windows guidance carries a sightline comparison — Figure 118 — showing a typical eighteenth to mid-nineteenth-century sash profile alongside what the same sash needs to become to accommodate three different insulating units. The dimensions in red are captioned as “the minimum rebate and glazing bar dimensions recommended by the IGU manufacturer”.

Manufacturers’ own published requirements are consistent with that, and in one case worse. One heritage-unit supplier states its minimum rebate in trade terms as a “12mm Upstand – 26mm Platform” — the upstand being the timber covering the glass edge, the platform the flat base the unit sits on — which by the same arithmetic gives a 28 mm glazing bar. Histoglass publishes a constant 10 mm upstand across its five slim build-ups. LandVac’s data tables give an 8 mm sightline on the edge seal with 12 mm edge deletion, rising to 16 mm on shaped items.

Westcountry Heritage, Recommendations for Glazing and Materials (2019); Histoglass, thin double glazing options; LandVac Data Tables v3.1.2 (17 October 2025)

Two consequences for a drawing. First, if you are trying to keep a 12 mm Georgian bar, no insulating unit we found published rebate figures for will do it, and the honest options are repair plus draughtproofing, or secondary glazing. Second, on a one-over-one Victorian sash with no glazing bars at all, the constraint largely disappears — which is why Historic England’s own detailed guidance names a late Victorian or Edwardian one-over-one sash, or a simple casement, as its example of the kind of window where inserting a sealed unit could be considered at all.

In Scotland the point is put as policy rather than geometry. Historic Environment Scotland requires that “true, or through, astragals should be provided”, warns that “astragals sandwiched between panes alone, will be very unlikely to be acceptable”, and states the consequence directly: “the thicker astragals required by standard units … mean they often cannot successfully replicate historic multi-pane patterns”.

Historic Environment Scotland, Managing Change in the Historic Environment: Windows, §5, updated 3 February 2020

The details officers and inspectors actually assess

Glazing pattern and the date of the building

A six-over-six is not interchangeable with a one-over-one; the two belong to different periods. Where the conservation area appraisal describes the characteristic fenestration, expect that description quoted back at you.

The corollary is that if the existing windows are already the wrong pattern, that helps you. Historic England’s fourth principle is that where historic windows have been replaced with ones whose design does not follow historic patterns, replacing them with new windows of a sympathetic historic pattern “may cause no additional harm” and “provides an opportunity to enhance the significance of the building”. That is the express basis on which the Thornhill House appeal was allowed.

Historic England, Modifying Historic Windows as Part of Retrofitting Energy Saving Measures, principle 4, updated 23 July 2024; applied in appeal APP/A4710/Y/23/3316687 at DL11

Horns: a date test and a style test, and they do not agree

Two authorities publish different tests for the same detail. Warwick uses a date: “most sash windows before 1870 did not have horns and these should not be included in replacement windows where to they did not previously exist.” Gravesham uses style: horns “would not have been used on a Georgian house with multi-pane windows but are a common feature on Victorian and later properties.” Blackpool adds a construction requirement: horns “should ideally have run-through sash horns (as opposed to ‘planted on’).”

An inspector took a third view at Thornhill House, accepting horns as “a traditional detail used in the Georgian era to strengthen window joints” without evidence that they had been present there. Treat horns as a detail to justify on the evidence of your own building, not as a default.

The meeting rail, and the only number anyone publishes

Gravesham’s is, so far as we found, the only numeric meeting-rail dimension in any published local authority window guidance: “Particular attention must be paid to the meeting rail, where the upper and lower sashes overlap; this should not exceed 34mm when closed or where an original window survives it should match that window.”

Gravesham BC, Conservation Areas: Maintenance/Replacement Windows and Doors Guidance SPD, adopted 29 June 2020, §8.7

It is worth knowing because it is one of the details that most readily betrays a modern window at street level, and because 34mm is tight for a unit-glazed sash. If the meeting rail on your drawing is 50mm or 60mm, that is the number an officer will pick out.

Glazing bars: integral, and never applied

This is the most consistent point in the entire published record, and the one where the industry and the decision-makers are furthest apart.

• Historic England, AN18 paragraph 82: “Stuck-on or applied glazing bars rarely replicate the character of historic windows and are unlikely to be acceptable.” HEAG039 §4.3 adds that with a single unit and applied bars, “It is highly unlikely that this arrangement will be acceptable for listed buildings”, and captions one such job — good workmanship, wrong result — as “rather flat and lifeless”.
• Gravesham §7.18: “Windows must use solid (through) glazing bars to replicate any original windows … Glazing bars applied to the surface of a sealed glazing unit will not be acceptable.” §8.5: “Machine routing after assembly is not appropriate to the character of traditional glazing bars.”
• Bath and North East Somerset: “Applied (i.e. false) glazing bars or applied lead cames will not be considered appropriate.”
• RBKC’s 2023 listed building consent order, condition (iii): “Glazing bars are to be integral to the window construction, and not applied.” Note the Order’s scope: it grants consent only for windows installed after the building was listed and with the benefit of consent, so original windows still need a full listed building consent application. The conditions are still a useful published statement of what that borough considers acceptable detailing.
• Warwick: artificial glazing bars, sandwiched or stuck on, are unlikely to be supported in listed buildings.

The High Court point is the one usually mis-reported. In Guinness, the 2014 challenge often described as the double-glazing “test case”, the inspector had found that “Superficially applied glazing bars, as proposed in this case, lack authenticity and the spacers and beads would add to the bulky appearance and suburban character of the window.” The court held the weight given to that was “a matter for the inspector and was not irrational or perverse”, and dismissed the claim. The case decided nothing about double glazing in principle; it was lost on detailed design and evidence.

Guinness v SSCLG [2014] EWHC 4114 (Admin) at §§17 and 46 — National Archives Find Case Law. The same judgment records that the claimants “chose to present photomontages, and not scaled drawings” (§34)

How the glass is held, and how deep the rebate has to be

The external line where glass meets timber reads from the pavement. Islington requires that glass “should always be putty mounted in integral glazing bars and the spacer bar inside the double glazed unit should match the colour of the window frame”. Gravesham describes the target result: the unit “can be puttied into conventional size timber sashes/casements and glazing bars, leaving no signs of double glazing”. BANES adds the precondition: “If the rebate is sufficiently deep, the panels can be putty fixed to match the original glass.”

That precondition is a joinery fact rather than a policy one, and it is where schemes come apart. Historic Environment Scotland records that narrow-profile units are “thicker and heavier than a normal pane and will need the checks of the existing sash or rebates in the astragal which hold the glass to be made deeper to fit the new unit (approx. 6mm)”, with the new panes “commonly 12mm thick”. Historic England’s still-published detailed windows guidance is blunter: “Experience has shown that where slim-profile IGUs are inserted, window sashes often have to be replaced.” Note too that standard linseed oil putty can damage the edge seals of sealed units — a caution given independently by Historic England, HES and Northern Ireland’s Historic Environment Division.

HES, Guide to Energy Retrofit of Traditional Buildings, updated 17 November 2023; Historic England HEAG039, Traditional Windows, February 2017, currently flagged as under review

For how the thin-unit options compare on thickness, see slim-profile double glazing and vacuum insulated glazing; for the permission question, double glazing in a conservation area.

Reveal depth, set-back, cill and finish

Gravesham gives the historical reason officers care where the frame sits: “By 1709 The London Building Act required the sash box to be set back four inches with the sash box still fully exposed. The 1774 Act required the sash box to be hidden behind the reveal for fire protection.” Set-back is therefore a period marker, and a window brought forward flush with the brickwork reads as wrong even when every other dimension is right. Camden lists “the depth at which the window is located in the reveal” among the features that must match. Cills and surrounds are protected as a category: RBKC’s order conditions require “no alteration or removal of existing features surrounding the windows including cills, sub cills, jambs, aprons, casings, shutters or shutter boxes”, and Warwick’s placement rule is that “Hardwood for replacement should generally be reserved for the cill.”

On finish, colour is well documented and locally variable. Warwick: “Sash windows are normally painted white unless a historical precedent exists for other colours. Stained timber windows are not appropriate.” Blackpool, describing its own Victorian stock, says the popular colours “would probably have been white, dark green and dark brown”. Both are right for their own areas, which is the lesson: paint colour is a local evidence question. RBKC requires a “hand-painted finish to match the consented colour of the existing windows”. We found no authority specifying a sheen level — no eggshell-rather-than-gloss requirement, no gloss percentage. If sheen matters on your building it is a conversation, not a published rule.

The drawing standard: there is no national one

This is the most practically useful thing on this page, and it is a genuine mess.

Three points follow. First, the drawings are what gets validated. Torbay: “If the frame width is not shown or if the plan is not drawn to an identified scale then we cannot validate your application”, and an application without all the listed details “cannot be validated and it may be closed”. Second, photographs are often accepted in place of existing elevations, but on conditions: Lewisham requires that “each window to be replaced must be individually identified by a number or letter on the photograph” and that “photographs where elevations are obscured e.g. by trees will not be acceptable”. Third, the person who should be producing all this is your joiner — Lewisham says it in terms: “The contractor who is making your windows should be able to supply these drawings.” A supplier who cannot produce a dimensioned section of what they intend to make is telling you something.

Detail can also be secured after the event: West Suffolk’s draft list notes that “It may be possible to agree these details by condition in some instances”. The fuller treatment of forms, fees and validation is in applying for windows: drawings, fees and what officers look at.

New sashes in the original box frame is a different proposal

If the box frame is sound, the strongest proposal is usually not a new window at all. New sashes in a retained original box keeps the reveal depth, the set-back, the linings, the cill, the staff and parting beads and any shutter boxes exactly as they are — removing several of the details in the table above from the argument entirely, and reducing the loss of historic fabric to the sashes themselves.

Historic England’s AN18 paragraph 82 states that original windows contributing to special interest “should not be replaced (although their panes could be replaced with slim-profile or vacuum double-glazing within the existing frames)”; paragraph 81 adds that “Original glazing bars should be retained, and windows should be refurbished and draught proofed at the same time to fully benefit from double-glazing”. HEAG039 records that this is what happens in practice: “In double-hung sash windows without glazing bars, the sashes are often replaced but the sash boxes are retained and heavier weights added.” Historic Environment Scotland treats the scope as a choice — “This can involve replacing just the individual sashes or the sash case as well” — and where a new case is unavoidable it “should be set wholly within the wall’s rebate, with no, or minimal, protrusion of the case’s facing plate”, with “Internal shutters and joinery … always … retained.”

Historic England HEAG039 §4.3; HES, Managing Change in the Historic Environment: Windows, §5, updated 3 February 2020

There is a building regulations consequence in England too. Approved Document L Volume 1 paragraph 10.6 states that a controlled fitting is “the entire unit of a window … including the frame”, and that “Replacing glazing, or a window or door in its existing frame is not providing a controlled fitting. Such work does not need to meet the energy efficiency requirements.” How much of the original frame survives therefore affects which tests apply, and where a sash-only replacement falls is for the building control body, not the conservation officer. For the standards themselves, see building regulations for replacement windows.

Repair first, and the condition survey that carries it

“The frames are rotten” is, on its own, one of the weakest arguments available. Almost every authority we read puts the burden of proof on the applicant, and the appeal record shows what happens when it is not discharged.

The starting position is minimum intervention, and Historic England states it as a rule: “Careful repair is always preferable to new work and should be the minimum required to rectify the defect.” Also: “Most traditional windows can be repaired. Even those in very poor condition can be returned to good working order.” City of York: “Often windows look in worse condition than they actually are. Repairs should seek minimal intervention.” Northern Ireland’s Historic Environment Division is the most direct: “Common reasons given for replacing windows are that they are draughty or rotten or that they stick or cannot be opened. All of these problems can be rectified by an experienced joiner.”

The techniques are established, and HEAG039 specifies them tightly enough to put on a drawing:

• Spliced or scarfed repairs — inserts “shaped to obtain the maximum strength and to match the existing profiles”, worked “to the line of the existing” and following “any existing deformations”, with the joint designed so water “cannot lie on or enter the repair joint”. “Excessive trimming of the existing timber should be avoided.”
• Resin consolidation — the worst decay is cut away “but not back to sound wood” and the weakened timber consolidated: “a very effective way of maximising the amount of original fabric retained”. Paint it promptly, because “resin degrades in ultra-violet light”.
• Cill repair rather than cill replacement — the detail that saves most windows: “To avoid removing the whole window, the outside half of the cill alone can be replaced; the butt joint between new and old work should be covered by the bottom rail of the sash when it is shut.”
• Open joints — “re-secured by cramping, glueing, re-wedging and pinning” rather than renewed.
• Record before you touch it — photographs and measurements, parts labelled “to ensure that they go back in the correct positions”, and “Any historic glass and its characteristics should also be recorded.”

For listed buildings in England, Historic England confirms the consent position: “Careful repairs by piecing in members of timber windows, such as rotten cills and sections of the window which match in dimensions and species of timber … would not therefore need listed building consent; nor would renewal of broken sash cords.”

Historic England HEAG039 §§3 and 4, February 2017 revision; Modifying Historic Windows as Part of Retrofitting Energy Saving Measures, updated 23 July 2024

The survey must be per window, not per building — Gravesham asks for reports “describing the extent of decay to each window that it is to be replaced and discussing the options for repair or why such repairs cannot be carried out” — and must come from “an architect, surveyor or specialist timber joinery workshop”. It must address repair options and say why they were rejected, not merely record decay. And it must not rely on the wrong defects: Islington notes that “Defects to glass, putty, paintwork and hardware/opening mechanisms can be addressed with routine repairs and renewal and do not necessitate replacement.” Blackpool publishes the only quantified threshold we found, windows “more than 3/5 rotten”, and it is one authority’s benchmark, not a national test.

Timber species and quality

Two separate conversations are usually muddled here. Species and quality are between you and your joiner. Appearance is the planning question. No local planning authority document we read specified a named species — treat “the council requires Accoya” as a claim to check against that council’s own guidance. Historic England, however, is specific, and it is worth quoting because it settles most arguments.

What to specify. HEAG039: sashes were usually “slow-grown deal (pine)”, most of them “heartwood of imported Scots pine (Pinus sylvestris) grown slowly in natural forests”; and now, “Repairs and replacements should be of the same type of timber as the existing, although a hardwood is acceptable for the cill”. Where new timber is needed, “heartwood of one of the more durable softwood species, such as Scots pine/ European redwood (Pinus sylvestris) or imported Douglas fir (Pseudotsuga menziesi), should be used”, and new cills should be “durable hardwood, such as English oak, thoroughly primed and painted and where appropriate incorporating a drip”. Warwick’s version of the same rule is that hardwood “should generally be reserved for the cill”.

Modified timber is expressly contemplated. HEAG039: “As it is very difficult to ensure that timber is entirely free of sapwood, pre-treatment with preservative is generally recommended. An alternative would be to use chemically modified (‘acetylated’) softwood which is exceptionally durable, and dimensionally stable.” That is Historic England opening the door to Accoya-type timber without naming the brand. It also warns that untreated “Modern softwood has poor resistance to decay and should be double-vacuum impregnated with preservative by the supplier.” The mechanism it gives for that is sapwood: plantation timber “contain[s] a larger proportion of sapwood”, which “is more permeable than heartwood and contains sugars and starches that provide an excellent food source for fungi”.

Historic England HEAG039, Traditional Windows: their care, repair and upgrading, §4, February 2017 revision. We could not verify any primary source for a numeric slow-grown specification such as growth rings per 25 mm; it is widely repeated in trade material and we do not publish it.

Moisture content, jointing and coatings. HEAG039 requires inserts “similar in species and moisture content to the parent timber”, with “the grain orientated to match the existing” — but gives no percentage, and we could not verify the commonly quoted 12 to 16 per cent against BS EN 942:2007 or BS 644:2012, both paywalled, so no figure appears here. On paint it records that “Good results on timber windows have been obtained with linseed oil paints and 100% acrylic resin paints”, on a five to eight year redecoration cycle.

The industry specification is more prescriptive and pulls the other way on one point. The Wood Window Alliance and British Woodworking Federation Specifier’s Guide to Timber Windows (2016) requires visible surfaces to class J2 of BS EN 942:2007, coatings to BS EN 927-1 and BS 644:2012 at “a minimum of 120mu on exposed or semi-exposed surfaces and 60mu on concealed surfaces”, and engineered stock — sashes “manufactured from clear, finger-jointed or laminated timber” so as “to remove knots and defects and increase stability”. Conservation guidance starts from the opposite premise: match the parent timber, and avoid “shakes, resin pockets, knots or sapwood”. Both can be right, because finger-jointed stock is standard for new factory-made windows and invisible under paint, while a spliced repair to eighteenth-century joinery is a different operation. We found no statement from Historic England, HES, Cadw or the Historic Environment Division expressly permitting or prohibiting finger-jointed timber in listed building work.

Service life. The same industry guide, from a service life planning study to ISO 15686-8, gives 56 to 65 years for timber windows built to its specification, 68 to 80 for modified timber and 25 to 35 for PVC-U. Historic England’s independent comparison: “The service life of PVCu windows is relatively short (less than 25 years) compared to well-maintained traditional windows (many of which survive for over 100 years).”

WWA/BWF, The Specifier’s Guide to Timber Windows, §§1, 7 and 10 (2016) — an industry document, not a statutory adviser’s. Note that its citation of BS EN 350-2:1994 is out of date; that standard has been superseded by BS EN 350:2016. Historic England, Modifying Historic Windows…, updated 23 July 2024

A window beautifully specified in durability terms and drawn with a 55mm meeting rail will still be refused.

Trickle vents and agreeing ventilation early

Two things are conflated whenever an installer says “regulations force us to fit trickle vents”.

The regulation. In England, regulation 4(4) and 4(5) of the Building Regulations 2010, inserted with effect from 15 June 2022, provide that where Part L imposes a requirement on the work, the building must on completion comply with Part F or be “no more unsatisfactory” in relation to that requirement than before the work was carried out. Blackpool states the practical test that follows: “Building Regulations only require a trickle vent in a new replacement window if there was trickle ventilation within the window being replaced.”

Building Regulations 2010, reg.4(3)–(5), reg.4(4)–(5) inserted by S.I. 2021/1391 reg.4 in force 15 June 2022; Blackpool Council conservation area window design guidance

Note also that, in England, regulation 21(3)(a) disapplies the energy efficiency requirements — Part L and the associated regulations — for listed buildings and buildings in conservation areas “where compliance with the energy efficiency requirements would unacceptably alter their character or appearance”. That is conditional, not a status-based exemption, and it does not disapply Part F, Part K safety glazing or Part B escape.

The conservation position. Gravesham: “Visible trickle vents are not acceptable on un-listed historic buildings. Trickle vents are not acceptable on listed buildings”, adding that often “ventilation can be achieved by a ventilation latch on the window itself”. Islington: “Visible trickle vents and rubber seals should be avoided.” Brighton and Hove: “Where trickle vents are required these must be concealed.”

Because those positions pull against each other, settle ventilation before the joinery is drawn, not after the units are ordered. If you are also fitting secondary glazing, note that heritage guidance wants the primary window left un-draughtproofed so the cavity can breathe — RBKC’s order prohibits adding draught-proofing to the primary window by condition.

Weights, cords and balance

A sealed unit is heavier than the single glass it replaces, and a sash that is not re-balanced will not stay where you put it. Historic England’s AN18 paragraph 81: “Sash windows may need heavier weights to balance the increased weight of the glass.” Gravesham §7.19 and Islington say the same. Any reglazing quote for a box sash that does not mention re-cording and re-weighting is incomplete.

Mechanism matters as well as weight. Gravesham: “Spring balances are sometimes used on modern sashes, these are not acceptable in listed buildings but will be considered appropriate on non-listed buildings.” Warwick goes further: “The introduction of any form of spring balance mechanism isn’t appropriate in an original sash window.” See sash windows in a conservation area.

Costs

Prices are on their own page, because they need their own health warnings and their own sources: what it costs. In outline, consumer price guides put a timber sash replacement at roughly £1,000–£3,000 per window and a full refurbishment at £620–£920, with draughtproofing at £248–£388 — but those are whole-market averages, not conservation-grade tender prices, and heritage joinery routinely sits above the top of them. Note also that the same publisher’s two guides disagree about restoration, giving £620–£920 in one and £80–£488 in the other a month apart. We found no published UK price per square metre for vacuum glazing from any manufacturer, trade body or independent source; AGC says in writing that “It is therefore difficult to provide an average cost per square meter.”

Checkatrade cost guides, tables self-dated Sash window refurbishment cost July 2026 and Cost to replace sash windows June 2026; AGC FINEO FAQ, live July 2026. Consumer price-guide averages, not quotations.

Of the authorities we read, only Lewisham publishes application fees — £548 for a flat or an Article 4 house and £1,083 for more than one dwelling as at the date of that page, and fees change. On sequencing, the statutory advisers agree: Historic England says “Repair, draught-proofing or secondary glazing is likely to be more cost-effective than replacement with double glazing”, and Historic Environment Scotland that “Replacing traditional sash and case windows with double glazed units is very costly. The other energy efficiency measures listed here are far more cost-effective.”

If your building is in Scotland, Wales or Northern Ireland

Scotland. Since 24 May 2024, altering or replacing an existing window has its own permitted development class — Class 7A of the 1992 Scottish Order, inserted by SSI 2024/102. On a front or road-facing elevation in a conservation area, prior notification is avoided only if the replacement is the same or substantially the same as the existing on the opening mechanism, the number, orientation and colour of the panes, and “the dimensions and colour of the frame of the window or any astragal bars”. Material is expressly excluded. Class 7A does not apply at all inside a World Heritage Site, which takes in central Edinburgh and New Lanark. The specification consequence is sharp: thicker astragals to accommodate a fatter unit are precisely what trips the third test, so in Scotland the millimetres are not merely a merits question, they are the statutory trigger.

Scottish Government Planning Circular 1/2024, ch.7, §§7.10–7.11 — gov.scot; Class 7A(2) on World Heritage Sites and Class 7A(3)(b)(iii) on frame and astragal dimensions

Northern Ireland publishes the clearest numeric threshold anywhere in the UK: the Historic Environment Division “will generally consider acceptable slim profile units with an overall thickness of less than 10mm”, while noting that listed building consent is required for all forms of replacement double glazing and that the threshold does not apply to windows retaining historic glass.

Wales. Cadw’s position on material is firm — “UPVC windows, for example, will not normally be acceptable” — but its listed buildings guidance says nothing about double, slim-profile, vacuum or secondary glazing, and we verified no Welsh local authority window guidance document with drawing requirements. Ask your authority for its validation list rather than assuming the English standard applies.

What to put on the drawing

1. A measured section of the existing window, taken on site, at the scale your authority requires — 1:1 Torbay, 1:2 West Suffolk, 1:5 Lewisham and Islington — with part of the surrounding wall where that is asked for.
2. An elevation of each window, existing and proposed, individually numbered, showing the glazing and opening pattern.
3. Dimensioned face widths for frame, mullions, transoms, glazing bars and meeting rail. Not single lines.
4. The glazing bar in section, showing bars integral and how the glass is bedded — putty line or bead — with the spacer bar position and colour.
5. The rebate, showing whether the unit fits the existing check or the joinery is being deepened, and by how much.
6. The reveal, showing set-back from the face of the wall, plus cill and sub-cill.
7. Horns: present or absent, with your reason, run-through rather than planted on.
8. The finish: colour, hand-painted, matched to precedent on the building rather than a catalogue.
9. Numbered photographs of every elevation, unobscured, each window lettered and annotated as included or excluded.
10. A per-window condition survey by a joiner or surveyor, addressing repair options and why they were rejected, wherever original joinery is being lost.
11. A ventilation note agreed with both the conservation officer and building control.
12. A weight and balance note: re-corded, re-weighted, no spring balances in original boxes.

Terms of art are defined in the glossary, and every document cited here is listed with its date on the sources page. If an Article 4 direction is what put you into the application process, read Article 4 directions and your windows — the wording of the direction determines which elevations are caught, and that changes what you need to draw.