Permitted development: the rules that apply across Hampshire
Under Class B permitted development, a loft conversion on a house (not a flat or maisonette) can usually go ahead without a planning application if:
- The extra roof volume is no more than 40m³ on a terraced or end-terrace house, or 50m³ on a semi-detached or detached house — including any earlier roof extensions.
- Nothing extends beyond the plane of a front roof slope that faces a highway.
- No part is higher than the highest part of the existing roof.
- Dormers are set back, so far as practicable, at least 20cm from the original eaves (this does not apply to hip-to-gable conversions).
- Side-facing windows are obscure-glazed and fixed shut or opening only above 1.7m from the floor.
- Materials are similar in appearance to the existing house, and there are no balconies, verandas or raised platforms.
Class B does not apply in conservation areas, National Parks or National Landscapes (AONBs). Rooflight-only conversions are often still possible there, but dormers and hip-to-gable conversions need planning permission. Even when a scheme is permitted development, we recommend a Lawful Development Certificate — it gives you written proof for when you sell.
Not sure whether your loft works at all? Read Is my loft suitable for a conversion? and Dormer vs hip-to-gable.
Winchester (Winchester City Council)
Covers Winchester, Alresford, Bishop's Waltham, Wickham, Denmead and the surrounding villages. Winchester has a large number of conservation areas, and parts of the district fall within the South Downs National Park, where the South Downs National Park Authority is the planning authority. In those areas, rear dormers and hip-to-gable conversions need a householder planning application, and design quality — proportions, materials, dormer size — carries real weight. Outside them, many Winchester semis and detached homes convert under permitted development. See also our Winchester extension cost guide.
Eastleigh (Eastleigh Borough Council)
Covers Eastleigh, Chandler's Ford, Hedge End, Fair Oak, Bishopstoke and Botley. Much of the borough is suburban housing where full-width rear dormers and hip-to-gable conversions often fall within permitted development. Check your title deeds and any planning conditions on newer estates, as some removed permitted development rights when they were built.
Test Valley: Romsey and Andover (Test Valley Borough Council)
Covers Romsey, Andover, Stockbridge and the Test Valley villages. Romsey town centre and many of the villages include conservation areas, so roof extensions there need planning. Andover's larger estates often suit permitted development dormers and hip-to-gable conversions.
New Forest (New Forest District Council and New Forest National Park Authority)
This is where it matters most which authority you are under. Homes inside the National Park — including Lyndhurst and Brockenhurst — fall under the New Forest National Park Authority, and Class B permitted development does not apply. Dormer and hip-to-gable conversions need a planning application, and the Park places a strong emphasis on keeping homes in scale with their setting. Towns outside the Park boundary, such as Lymington, New Milton, Ringwood and Totton, are under New Forest District Council, where the standard permitted development rules apply.
Southampton (Southampton City Council)
Southampton's terraced streets and inter-war semis are well suited to rear dormers and hip-to-gable conversions. Remember the lower 40m³ limit on terraced and end-terrace houses, and check for conservation areas in older parts of the city. Our Southampton house extensions guide covers the city in more detail.
Basingstoke, Fareham, Havant, Hart, Rushmoor and East Hampshire
The same national rules apply in every Hampshire council. Petersfield and much of East Hampshire sit inside the South Downs National Park, so planning permission is needed for dormers there. For Basingstoke, see our new Basingstoke house extensions guide.
Building Regulations: needed everywhere
Whether or not you need planning, every habitable loft conversion needs Building Regulations approval. The key areas are:
- Fire safety — a protected escape route and mains-wired, interlinked smoke alarms.
- Stairs — compliant headroom (loft conversions can use a reduced headroom of 1.9m at the centre of the stair and 1.8m at the side).
- Structure — new floor joists, steels and any alterations to the roof, designed by an independent qualified structural engineer.
- Insulation and sound — current energy-efficiency standards and sound insulation in the new floor.
Our Future Homes Standard guide explains what is changing, and our loft conversion cost guide helps you budget.
How Hampshire Build designs your loft conversion
We design loft conversions across every Hampshire council on a fixed fee. A standalone loft conversion is our package fee from £1,950 + VAT. If you are planning an extension at the same time, the loft can be added for £950 + VAT when both are designed and engineered together. Your measured survey is booked within 10 working days of your deposit, and your first drawings follow within 15 working days of the survey. With 20+ years in residential design and a 95% planning approval rate, we choose the right route for your council — permitted development, Lawful Development Certificate or full householder application.
Frequently asked questions
Often not. Many loft conversions fall within permitted development. You will need planning in a conservation area or National Park, for front dormers facing a road, or if you exceed the 40m³ / 50m³ volume limits.
Inside the New Forest National Park, dormers and hip-to-gable conversions need planning permission from the New Forest National Park Authority. Outside the Park boundary, normal permitted development rules usually apply.
Usually, on houses outside conservation areas and National Parks, as long as the total added volume stays within 40m³ (terraced) or 50m³ (semi-detached and detached) and the other conditions are met.
Both towns are in Test Valley, so Test Valley Borough Council is the planning authority.
Yes. Any loft converted into a habitable room needs Building Regulations approval, covering fire safety, stairs, structure, insulation and sound.