Do dormers always need planning permission?

No. Rear dormers within the volume allowance can be permitted development on many houses, but designations and property type change that. Confirm your position with the local planning authority or the Planning Portal.

Which dormer gives the most space?

A box dormer, by a clear margin, because it creates full head height across its width. It is also the type most likely to attract planning comment on a visible elevation.

What finish works best in Cornwall?

Slate hanging and well detailed timber both age well here. On exposed coastal roofs the flashings and fixings matter as much as the finish material.

Can a dormer be added to a trussed roof?

Yes, but the trusses have to be structurally replaced within the loft first, which is a larger job than working with a traditional cut roof.

Project type · Cornwall

Dormer loft conversions in Cornwall, choosing a dormer that suits the roof

A dormer is the difference between a loft you can stand up in and a loft you can only sit in, but the type of dormer changes how the house reads from the street and how likely the proposal is to be accepted. On Cornish roofs, where slate and simple forms dominate, proportion does most of the work.

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The three common types

Each buys a different amount of space and carries a different visual weight.

Box dormer: maximum usable floor area, flat roof, heaviest appearance, usually best kept to the rear
Pitched roof dormer: sits naturally on a traditional slate roof, less internal gain, far more sympathetic
Multiple small dormers: works well on a wide rear elevation and can echo neighbouring stock

Where a dormer can go

Rear dormers within the permitted development volume allowance are frequently acceptable, while a dormer on a principal elevation facing a highway generally is not permitted development. Conservation Areas, AONB settings, listed buildings and Article 4 directions all change the position, so check your specific address rather than a general rule.

Detailing for Cornish weather

Dormer cheeks, flashings and the junction with the main roof are where water gets in when the detail is improvised on the scaffold. On exposed elevations we draw those junctions at large scale and specify the weathering rather than leaving it to be worked out on site.

Structure underneath

A dormer sits on the loft floor structure, which is being upgraded anyway to carry habitable loads. Designing the two together, rather than the dormer as an afterthought, keeps the steelwork proportionate and the ceiling below intact.

Frequently asked

Straight answers.

Do dormers always need planning permission?: No. Rear dormers within the volume allowance can be permitted development on many houses, but designations and property type change that. Confirm your position with the local planning authority or the Planning Portal.
Which dormer gives the most space?: A box dormer, by a clear margin, because it creates full head height across its width. It is also the type most likely to attract planning comment on a visible elevation.
What finish works best in Cornwall?: Slate hanging and well detailed timber both age well here. On exposed coastal roofs the flashings and fixings matter as much as the finish material.
Can a dormer be added to a trussed roof?: Yes, but the trusses have to be structurally replaced within the loft first, which is a larger job than working with a traditional cut roof.

Want to know which dormer suits your roof?

Send us a photo of the rear elevation and we will tell you what is likely to work.

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