27 September 2026Alterations
Replacement Windows and Planning Permission in Jersey
When replacement windows need permission in Jersey, across standard, conservation-area and listed properties — and how to get them approved.
Replacement windows are one of the most common jobs we handle, and one of the most commonly got wrong. The rule that matters is simpler than most people expect: whether you need planning permission depends on where the house is, not on what the windows are made of.
Where you stand, by property type
| Your property | Replacement windows, any material |
|---|---|
| Unlisted, outside a conservation area | No planning permission needed |
| In a conservation area, not visible from a road or the foreshore | No planning permission needed |
| In a conservation area, visible from a road or the foreshore | Planning permission needed, assessed on character |
| Listed | Permission needed, and a material change is unlikely to be approved |
That comes from Class F of the General Development Order, which allows replacement windows and doors without an application. It sets no rule about matching the old material. It does not apply to listed buildings or shop fronts, and it is lost if a condition on an earlier permission removed your permitted development rights.
Check your own position with the States’ replacement windows and doors tool.
Where you do need permission: what gets approved
On a listed building, or a conservation-area window you can see from the road, like-for-like is what the planners measure you against. It is a genuinely tight test. It means matching:
- Material — timber replaced with timber
- Opening style — a sash replaced with a sash, not a casement
- Glazing pattern — the same number and arrangement of panes
- Sightlines — the visible width of frame and glazing bars
- Reveal depth — how far the window sits back within the opening
Replacing timber sliding sashes with uPVC casements fails on every one of those. It is not a repair, it is an alteration to the external appearance — and in a conservation area or on a listed building it is the alteration most likely to be refused.
Why the planners care so much about windows
It can feel disproportionate. It is not arbitrary.
Windows are the single largest visual element in most elevations, and their proportions, depth and glazing pattern are what make a Jersey granite cottage look like a Jersey granite cottage. Replace the windows across a terrace and the terrace stops reading as historic, even though nothing else has changed. That is precisely what conservation area designation exists to prevent.
The reveal depth matters more than people expect. A traditional window sits well back in a thick wall, creating a shadow line. A modern replacement set flush at the face of the wall loses that shadow, and the building looks flat even if the window pattern is correct.
How to get modern performance and still get approval
The good news is that the choice is no longer between historic appearance and a cold house.
- Slim-profile double glazing in timber frames now achieves sightlines close to traditional single glazing.
- Accurate timber sash replacements can be made to match existing profiles precisely, with modern draught sealing.
- Secondary glazing is often the right answer on listed buildings — it leaves the historic window intact and reversible, which is exactly what a conservation officer wants to see, and it performs well.
- Repair rather than replace. Historic timber windows are frequently repairable at lower cost than replacement, and repair rarely needs consent.
Two of our team are accredited Domestic Energy Assessors, and one holds the NOCN Level 3 in Energy Efficiency for Older and Traditional Buildings. Improving a traditional building’s performance without causing condensation problems is a design question, not a product question.
The bye-law side
Replacement windows also engage the building bye-laws, separately from planning. You need bye-law permission to replace windows in a house unless the installer is an approved competent person who notifies the department within 30 days of finishing — so ask your installer before you sign. Relevant requirements include thermal performance of the new units, escape windows in habitable rooms where required, ventilation provision, and safety glazing in critical locations.
On a straightforward replacement this is manageable. Where windows are being enlarged, or openings formed, there is a structural element too — new or altered lintels. See new or larger openings.
Specify it properly on paper
Window applications are won or lost on drawn detail. An application that shows horizontal and vertical sections through the frame, sightline dimensions, reveal depth and a materials schedule gets determined. One that says “new double glazed windows to match” invites a request for more information, and weeks of delay.
Related pages
- Replacement windows in Jersey
- Replacement windows in a conservation area
- Heritage windows
- Building in a conservation area
Before you order
Get the planning position confirmed before you place an order with a window supplier. Windows ordered to the wrong specification are not returnable, and installing them without permission on a listed building, or on a conservation-area elevation the public can see, invites enforcement.