The short answer
Not as permitted development. The Quantock Hills and Blackdown Hills National Landscapes are areas of outstanding natural beauty in law, and the General Permitted Development Order treats them as article 2(3) land, where Class B does not allow dormers. A planning application is the way in for a dormer there. Roof windows that stay within the Class C limits are a different matter.
The name changed in 2023 but the planning rules did not. A dormer in either hill range needs permission, while some roof windows still do not.
National Landscape means AONB in law
In November 2023 every area of outstanding natural beauty in England, usually shortened to AONB, was rebranded as a National Landscape. The Quantock Hills were designated an AONB in 1956, and the Blackdown Hills AONB was renamed the Blackdown Hills National Landscape. The renaming, in the Government's own words, is not statutory. Legally, then, they are still AONBs.
Does the new name change the planning rules?
No. The General Permitted Development Order 2015 still uses the words area of outstanding natural beauty, and it counts such an area as article 2(3) land, alongside conservation areas and National Parks. Anything the Order restricts on article 2(3) land is restricted in a National Landscape, and the rename removed none of those limits and added none.
That is why a house in a village on the Quantock or Blackdown slopes is treated differently from the same house on an ordinary suburban street. The planning team for your address decides what a proposal needs, and for most Somerset addresses that is Somerset Council. Ask them before commissioning drawings, since the reply shapes everything after it, from the size of the box to the materials on its cheeks, which are the side walls of the dormer.
Why Class B stops at the boundary
A dormer is a vertical window set into a small pitched or flat-roofed box that projects from the slope. The permitted development rules for adding one sit in Class B of the Order. Class B says development is not permitted if the dwellinghouse is on article 2(3) land, and a house in a National Landscape is on exactly that. Inside a National Landscape, a new dormer therefore needs planning permission from the local planning authority.
Are there other Class B limits?
Yes, and they apply elsewhere too. Where Class B does apply, a terraced house gets 40 cubic metres and any other house 50, and a dormer may not stand forward of a principal-elevation slope that faces a highway. In a National Landscape those limits never come into play, because the exclusion applies first.
Conservation areas and Exmoor National Park are treated the same way, so a dormer on a Taunton conservation-area street, or on Exmoor, faces the same planning route. The dormer question is similar in a Park, and our answer on planning for roof work on Exmoor explains who decides there.
Roof windows under Class C
A roof window lies flush with the slope rather than projecting out from it. Class C is the catch-all for alterations to a dwellinghouse roof, and article 2(3) land is not carved out of it. That is why a roof window within the Class C limits needs no application in a National Landscape, as long as no Article 4 direction or condition has removed the right.
What are the Class C limits?
Nothing may stand out from the original slope by more than 0.15 metres, measured at right angles to it. For a window in a slope on the side of the house, two conditions apply: the glass is obscure, and the sash is fixed shut unless its opening part is over 1.7 metres above the floor inside. Obscure glazing is needed in every case. The 1.7 metre height relaxes only the rule on opening.
Check whether an Article 4 direction is listed for your village. Somerset Council lists them, and what each covers needs confirming with the planning team. Our page on roof windows and skylights covers fitting, and a loft conversion also brings Building Regulations into play, including the upgrade to a 0.16 U-value that Approved Document L sets for renovated roofs.
Planning route and next step
If you want a dormer in the Quantocks or Blackdowns, the route is a planning application, not a certificate of permitted development. Early talks with the planning team, often called pre-application advice, help you find out what the officers expect for materials, size and position on the roof. Treat the answer as guidance on your own plans and not as a guarantee of the result.
Do the Building Regulations still apply?
Yes, separately. A dormer changes the structure of the roof, so it needs a Building Regulations application whatever the planning outcome. Somerset Building Control handles those in Taunton's area, and our guide to building control for Taunton homes explains how to reach them.
Listed buildings are another case again. A listed house is not stripped of Class B and C rights, but work affecting its character brings listed building consent into the picture as well. For any of these, we begin by surveying the roof, with photos of the slope and the structure behind it. Send yours through our homepage and we will go through what the roof can take before you spend on drawings.
More on dormers and protected landscapes
Does a roof window count as a dormer for planning?
No. A dormer projects from the slope and falls under Class B, which is closed on article 2(3) land. Lying flat in the slope, a roof window comes under Class C instead, where the exclusion never appears. A rooflight that rises above the slope may protrude, so check the 0.15 metre limit.
Does the Mendip Hills National Landscape work the same way?
Yes. It was renamed on 22 November 2023 along with every other AONB in England and Wales, and the rename was not statutory. Class B is closed in the Mendip Hills National Landscape in the same way, so the route there is also a planning application.
The full picture: Roofers in Taunton ยท More short answers