A stained glass or leaded window is usually the one window in a period house that nobody wants to lose and nobody wants to sit next to in January. The trade offers to fix that in ways that sound alike and are not: some keep your glass, some keep it at a cost to the glass, and some replace it with a good imitation. Almost every page ranking for the question is a studio or an installer selling one of them. This guide lays the three side by side, with what each does to the original panel, what the published prices are worth, and what Historic England, Approved Document K and FENSA actually say.
The three routes at a glance
| Route | What happens to your glass | Best suited to | Price evidence |
|---|---|---|---|
| Encapsulation | Removed, repaired, usually trimmed, sealed between two toughened panes | An original panel in a frame or door that can take a thicker, heavier unit | Single installers only |
| Leaded-effect unit (stick-on lead) | Replaced by new glass with lead strips and film | A window where the original is gone, damaged beyond repair or of no historic value | Quote on request; no dated per-unit price found |
| Secondary or protective glazing | Left in place, untouched | Significant or listed glass, and anyone who wants the option to change their mind | Checkatrade (July 2026) for secondary glazing |
Sources: studio and installer pages, Historic England, Historic Environment Scotland and Checkatrade. Research in lib/research/stained-glass-double-glazing-2026.md.
Encapsulation: how it works and what it costs the panel
Encapsulation seals your existing panel inside a new double glazed unit, which is why some studios call it triple glazing and others double glazing; they mean the same process. The panel comes out of the frame, which is boarded or temporarily glazed, and goes to a studio. There it is repaired, cleaned, given a new border lead, blown free of dust and sealed between two panes of clear toughened glass. The stained glass sits in the middle. Four independent sources agree it cannot be one of the panes, because a leaded panel is not airtight and condensation would form against it. One studio holds it with a Y-shaped lead round the edge, its flange gripped by the spacers.
The part the brochures skip is the edge. A sealed unit needs a spacer, sealant and desiccant round its border, and the panel has to be made smaller to leave room. An Aberdeenshire studio says the border is cut down by almost an inch in total, which can remove part of the design if there is no spare border; two studios that sell encapsulation confirm they trim or resize the panel. The same studio calls the process "effectively irreversible", and we found no source describing a panel recovered from a failed unit and encapsulated again.
One of the biggest arguments against encapsulation, from the point of view of conserving stained glass, is that is effectively an irreversible process.
Morning Glass Designs, Aberdeenshire stained glass studio (2012)
Then there is the mismatch in lifespans. The same studio noted in 2012 that most domestic stained glass in the UK is Victorian or Edwardian, then around 80 to 120 years old, while even a high quality sealed unit lasts about 15 to 20 years; Historic England gives slim-profile units around 25, and one installer quotes 15 to 25 for encapsulation. When the seal fails, the moisture that mists an ordinary unit is trapped against the lead and paint of your panel, which speeds corrosion, and the whole assembly has to be replaced, with the risk of damage that brings. Mounting the panel dry, without putty near the edge seal, reduces the risk; nothing removes it. Historic England warns that condensation on stained glass can cause "irreversible loss of paint". What a failing unit looks like is covered in our blown double glazing guide.
An encapsulated unit is thicker and heavier than the panel it replaces. Studios warn that some frames and doors cannot take it and need modifying or replacing, that hinges must cope with the weight, and that sash windows usually need heavier weights. One installer puts the units at 20 to 28 mm; that figure has no second source. The slim heritage units in our slimline double glazing guide are no help here: one studio notes they cannot take a stained panel at all. Encapsulation works best where the frame was built for a modern unit, such as a small panel set into a new front door.
On warmth, every figure is a seller's. One studio says its low-e, argon-filled units give a Window Energy Rating of A to C in a new frame; another installer claims 1.2 to 1.4 W/m²K with no test cited. We found no independent measurement of a unit with a leaded panel in its cavity. Note that band C would not meet the band B route for a new window (below), so the 1.4 W/m²K route would have to be shown instead.
Leaded-effect units: new glass with stick-on lead
Most "leaded" double glazing sold today is not leadwork at all. Self-adhesive lead strips are applied to the glass of a sealed unit, on one side or both for a more convincing finish, in diamonds, squares or a bespoke pattern, with coloured film under the strips for a stained effect. Checkatrade draws the line clearly: traditional lead came windows are "different from modern leaded-effect windows" where strips are applied to the surface of double glazed units. Traditional jigsaw-style stained glass, small pieces with gaps between them, cannot itself be made into a double glazed unit, which is why makers offering double glazed stained glass use the overlay method.
Quality varies. A Dorset specialist makes a conservation-grade version, stick-on lead on specially made glass with deliberate imperfections, the joints soldered and patinated, fitted into existing frames. At the other end, a Somerset studio calls stick-on lead and film "non-traditional mass production type methods" that lose much of the reflection and life of a real leaded panel. Two installers fit lead strips to thin vacuum glazingunits in existing timber casements. On a listed or conservation-area building, expect scepticism: Bath and North East Somerset Council's guidance says applied lead cames "will not be considered appropriate". We found no dated per-unit price for a leaded-effect unit; suppliers quote on request, and one notes that twice the colour and detail can easily be twice the price.
Keeping the panel: secondary and protective glazing
The route that leaves the glass untouched is a second layer of glazing. Historic England calls secondary glazing "a low-risk intervention", and Historic Environment Scotland says internal secondary glazing can cut heat loss by over 60% while leaving the original window untouched, which it calls welcome where the window retains historic glass. Fitted inside, it is priced like any other secondary glazing: £300 to £500 a window including labour on Checkatrade's July 2026 figures, with the detail on our secondary glazing costs page. A sheet of toughened or laminated glass fitted outside the panel is the other version. An Aberdeenshire studio calls it the simplest way to add insulation without condensation problems, and generally cheaper than encapsulation, but it hides the texture of the panel from the street in daylight, and the gap attracts spiders that cannot be reached without taking the sheet off.
There is a warning here too. Historic Scotland's 2007 note on domestic decorative glass called secondary glazing "not an ideal solution" for protecting it, because a sealed gap can become a microclimate that speeds decay. Historic England's later research on protective glazing for church windows found the answer is ventilation: vent the gap at the top and the bottom, keep it at least 40 mm deep where possible and never under 10 mm at a pinch point, make the vents at least a third of the gap's depth, and vent towards the room rather than outside, where rain gets in. That research is at church scale, and we found no domestic version, but the principle carries: an unvented sheet over a stained panel is a risk, not a protection.
Bevelled, etched and printed glass
Bevelled glass is now usually made by bonding bevelled pieces onto a single sheet of toughened glass, and can be supplied single or double glazed. Etched glass is sandblasted to obscure it; one maker warns that some firms offering etching apply a vinyl sticker instead, which yellows and shrinks within a few years. Colour can also be printed onto the panes of a sealed unit: one Bath studio prices printed double glazing at £800 to £2,500 "per metre" depending on colours and lamination, with a set-up charge on small jobs.
What it costs, and how little of it is independent
No aggregator publishes an encapsulation price. Every encapsulation figure below comes from a single installer, and they use different units, per panel, per square metre and per package, so they cannot be averaged or compared directly. The repair and secondary glazing figures are Checkatrade's. Do not use the site's £55 to £145 figure for a misted standard sealed unit here: an encapsulated or leaded unit is a different product.
| Job | Price | Source and caveat |
|---|---|---|
| Leaded window repair | £150 to £500 (average £325) | Checkatrade (July 2026). Often quoted per panel rather than per window. |
| Re-sealing a leaded window | £40 to £70 per window | Checkatrade (July 2026). |
| New or replacement leaded window | £45 to £500 (average £272.50) | Checkatrade (July 2026). Does not say whether lead came or leaded-effect. |
| Encapsulation, small panel (fanlight, sidelight) | £100 to £300 | Golden Ratio Sash Windows, London. One installer, undated. |
| Encapsulation, standard panel | £300 to £500, or £300 to £900 in the same page's FAQ | Same installer; the page contradicts itself. |
| Encapsulation, heritage work | £1,000 to £1,500 per m² | Scott James Windows (October 2025), which sells a rival product. Its attribution to the GGF could not be verified. |
| Secondary glazing, one window | £300 to £500 including labour | Checkatrade (July 2026). |
Sources as listed. One London installer's 2026 package of stained glass repair, encapsulation and new sashes came to about £6,000 plus VAT, window count not stated. Research in lib/research/stained-glass-double-glazing-2026.md.
Repair usually comes first. Checkatrade says replacement may be more cost-effective only once more than 30 to 40% of the glazing is damaged or the lead is heavily corroded throughout, and that custom leaded windows take four to six weeks to make. Its average new leaded window (£272.50) sits below its average repair (£325), and it notes itself that a repair can sometimes cost more than replacing a modern window. Where the frames themselves are the problem, the timber window calculator and uPVC window calculator price the new window; the stained panel is a separate quote.
Listed buildings and conservation areas
Historic England's window guidance (2023, updated 2024) is plain on three points. Historic windows that contribute to a listed building's significance "should be retained and repaired where possible", and early glass "should be retained if possible". Inserting double or triple glazing into historic windows "will usually require Listed Building Consent", and replacing a window always does. Installing secondary glazing "does not generally need listed building consent". Its Advice Note 18, revised in February 2026, lists windows with leaded lights among the exceptions where slim or vacuum double glazing in historic frames is unlikely to be acceptable. We found no Historic England statement on encapsulation itself: one seller says Historic England supports it, another that it discourages it, and neither is backed by Historic England's own pages. The cost side of consent is on our listed building costs page.
In Scotland, Historic Environment Scotland says retrofitting double glazing to a listed building "will be likely to require consent", that secondary glazing "may sometimes require consent" depending on its design, and that some double glazing may be acceptable "where no historic glass remains". A Glasgow installer's line that encapsulation alone needs no consent is not supported by either heritage body. In a conservation area, planning permission is a separate question that turns on whether an Article 4 direction applies; our guide to conservation area window rules covers it.
Building Regulations, FENSA and safety glass
In England, Approved Document K says that replacing a whole unit, frame and glazing, is building work, while "the replacement of glazing whilst retaining an existing frame (e.g. as a repair) is not building work". FENSA's compliance guide (v2023.07) agrees that sash or glass-only replacement falls outside its scheme. So an encapsulated or leaded unit swapped into your existing frame needs no FENSA certificate. A whole new window with a stained or leaded unit is building work, certified by a scheme such as FENSA or by building control, and must reach Window Energy Rating band B or a whole-window U-value of 1.4 W/m²K; FENSA allows a centre-pane 1.2 W/m²K only in exceptional cases where the character of a listed building or conservation area has to be kept. And FENSA does not cover listed buildings at all: that work goes to local authority building control. Our FENSA guide covers the scheme in full.
Doors are where safety glass bites. Under Approved Document K, glazing below 800 mm from the floor, and glazing within 300 mm of a door below 1,500 mm, is in a critical location and must break safely, resist impact, or be protected by a permanent screen. Traditional leaded lights have their own route: they count as small panes, and 4 mm glass may be used where fire resistance is not important, provided each pane is no more than 250 mm wide and 0.5 m² in area. We found no official ruling on how that applies to an original panel sealed between two new panes, and read literally, a leaded panel whose individual pieces exceed those limits would not qualify on that route. The studios that state it all use toughened glass for the outer panes, and FENSA requires the safety mark to stay visible and legible after fitting. FENSA registers a replacement door only if more than half of it is glazed, but every door must still comply.
| Job | Building work? | FENSA | Energy standard |
|---|---|---|---|
| Panel encapsulated and refitted in the existing frame | No (AD K para 0.2) | Outside scope | None |
| Leaded-effect unit fitted in the existing frame | No | Outside scope | None |
| Whole window replaced, with a stained or leaded unit | Yes | Certificate needed | WER band B or 1.4 W/m²K; centre-pane 1.2 in exceptional heritage cases |
| Any replacement on a listed building | Yes | Outside scope: local authority building control | As far as reasonably practicable (AD L para 0.8), plus listed building consent |
| Secondary glazing inside the window | Not a replacement | Outside scope | None |
Sources: Approved Document K (2013 edition) para 0.2; FENSA Guide to Compliance, abridged fourth edition (v2023.07). Scotland and Northern Ireland have their own systems.
Ask any studio quoting encapsulation how much of the border it will cut, and what happens to the panel when the unit fails in twenty years. If the answers are vague, secondary glazing on the room side costs less and keeps the only irreplaceable part of the window out of harm's way.
Double Glazing Cost Calculator Team
Getting it priced
With every encapsulation price coming from one firm, the only reliable figure is a written quote on your own panel. If you want encapsulation, leaded double glazing, secondary glazing or new windows priced, tell us what you have and Leads 2 Trade will arrange quotes from installers covering your postcode.
Frequently asked questions
Yes, three ways. Encapsulation seals the original panel between two new panes inside a sealed unit, so the window becomes in effect triple glazed. Leaded-effect units are new double glazed units with self-adhesive lead strips and coloured film on the glass. Or the original panel stays as it is and secondary or protective glazing goes behind or in front of it. The first changes the panel permanently, the second replaces it, and the third leaves it untouched.
The panel is taken out to a studio, repaired and cleaned, given a new border lead, and sealed between two panes of toughened glass to form one insulated unit. The stained glass sits in the middle, in the cavity, never as one of the panes, because a leaded panel is not airtight. Studios usually trim the panel's edge to make room for the spacer and sealant, which is why a stained glass maker calls it effectively irreversible.
Encapsulation prices come from single installers only. One London firm quotes £100 to £300 for a small panel and £300 to £500 for a standard one, and up to £900 elsewhere on the same page; another firm, which sells a rival product, quotes £1,000 to £1,500 per square metre. Checkatrade (July 2026) puts leaded window repair at £150 to £500 and secondary glazing at £300 to £500 a window including labour.
New ones can: leaded-effect double glazing uses lead strips stuck to one or both sides of a sealed unit, which is how uPVC leaded windows are made. Original leaded lights can be encapsulated in a sealed unit, or kept as they are with secondary glazing. Historic England lists windows with leaded lights among the exceptions where slim or vacuum double glazing in historic frames is unlikely to be acceptable.
On a listed building, usually. Historic England says inserting double or triple glazing into historic windows will usually require listed building consent, that replacing windows always does, and that early glass should be retained where possible. Secondary glazing does not generally need consent. Historic England has published no position on encapsulation itself that we could find, whatever sellers say.
Not if only the glass changes. Approved Document K says replacing glazing while keeping the frame is not building work, and FENSA's compliance guide puts glass-only repairs outside its scheme. A whole new window with a stained or leaded unit is building work, needs certifying, and must reach Window Energy Rating band B or 1.4 W/m²K, and on a listed building it goes to local authority building control, because FENSA does not cover listed buildings.
Glass in a door, within 300 mm of one below 1,500 mm, or below 800 mm from the floor is in a critical location under Approved Document K. Traditional leaded lights have their own small-pane route: 4 mm glass is allowed where fire resistance does not matter, provided each pane is no more than 250 mm wide and 0.5 m² in area. The studios that encapsulate panels use toughened glass for the two outer panes.
It can. The border is usually cut down to fit the unit, taking part of the design with it unless the panel has a spare border. The sealed unit will fail long before a panel that has typically lasted since Victorian or Edwardian times, and when its seal goes, moisture is trapped against the lead and paint. Replacing the failed unit risks damaging the panel, and we found no source describing a panel recovered and re-encapsulated.