Do I Need Planning Permission for a Bay Window in 2026?
In most cases, no — a bay window can be added or replaced under permitted development. The exceptions matter though. If the home is listed, in a conservation area, or the bay projects more than the permitted-development limits at the rear, you will need planning permission. This guide explains the 2026 UK rules and how to apply for a Lawful Development Certificate if you are unsure.
When permitted development applies
Replacing an existing bay window or fitting a new one to a non-listed, non-conservation-area home is usually permitted development. The window must be similar in appearance to the existing windows on the house and must not contain an opening on a side elevation above ground floor that overlooks a neighbour. Material upgrades (uPVC to timber-look composite, for example) are fine within these rules.
When planning permission is needed
You will need planning permission for a bay window if the property is listed (listed building consent), in a conservation area, AONB, World Heritage Site or National Park on a principal elevation, or if the bay is part of a rear extension projecting more than 3 metres from the original rear wall (4 metres for detached homes). Article 4 directions in some councils also remove permitted development rights from terraces and period streets — always check the local plan.
Listed buildings and conservation areas
For listed homes you must apply for listed building consent before changing any window, even a like-for-like replacement. In conservation areas you may keep permitted-development rights for the rear but lose them for the front; the council can also enforce timber or steel frames over uPVC.
How to check and apply
1. Check the listing and conservation status
Use Historic England for listing and the council planning portal for conservation areas.
2. Check Article 4 directions
Type the postcode into the council planning portal to see if Article 4 removes permitted-development rights.
3. Measure the projection
A ground-floor rear bay over 3 metres (4m detached) needs planning permission.
4. Apply for a Lawful Development Certificate
If unsure, pay around £120–£150 for a Lawful Development Certificate — it confirms permitted development in writing.
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