Do You Need Planning Permission for a Dormer in Ireland?
Since 27 July 2026, a dormer to the side or rear of an Irish house needs no planning permission if its internal volume, together with any other dormers, is no more than 30 cubic metres, it is no higher than the roof ridge, and it is set back at least 20cm from the eaves. A front dormer still needs planning permission, but up to two front roof lights (each max 100cm x 90cm) are exempt.
Rules have conditions, and the conditions are where projects fail. Answer a few questions about your exact situation and get a plain-English answer with the regulation cited.
Check your project freeThe rules for a dormer
- 1.Side or rear roof slope only. A dormer on the front roof needs planning permission.
- 2.The internal volume of the dormer, taken together with any other dormer roof extensions on the house, must not exceed 30 cubic metres.
- 3.The dormer must be no higher than the roof ridge.
- 4.It must be set back at least 20 centimetres from the eaves.
- 5.Up to two roof lights on the front roof plane are exempt too, each no more than 100cm long and 90cm wide (Class 1C).
- 6.Exemptions do not apply to protected structures, and an Architectural Conservation Area can restrict roof works.
- 7.Building Regulations apply in full: converting the attic to a bedroom triggers fire escape, stairs, structure and insulation requirements.
Reference: Classes 1B and 1C, Schedule 2, Part 1, Planning and Development Regulations 2001, inserted by S.I. 344 of 2026
Frequently asked questions
Do I need planning permission for a dormer in Ireland?
Not for a side or rear dormer since 27 July 2026, if all dormers on the house combined are no more than 30 cubic metres in internal volume, it is no higher than the ridge and it is set back at least 20cm from the eaves. Before that date every dormer needed permission, and a front dormer still does.
How do I measure 30 cubic metres for a dormer?
The limit is the internal volume of the dormer roof extension itself, not the whole attic: roughly its internal width x depth x height. Add the volume of any dormers you already have. A typical rear box dormer of 4m wide, 3m deep and 2.4m high is about 29 cubic metres, so larger designs can exceed the limit quickly; have your designer confirm the figure.
Can I put Velux windows on the front of my house?
Yes, up to two on the front roof plane since 27 July 2026, each no more than 100cm long and 90cm wide (Class 1C, S.I. 344 of 2026). Roof lights on protected structures or in conservation areas can still need permission.
Turns out you need permission?
Start with the pre-submission checklist, estimate costs with the fee calculator, and read the step-by-step application guide. For uncertain cases, a Section 5 Declaration from your council (~€80) gives a formal ruling either way.
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Related projects
This page is general guidance on the Planning and Development Regulations 2001 (as amended), not legal advice. Exemptions do not apply to protected structures or in Architectural Conservation Areas, and conditions apply in every case. Confirm with your local authority before starting work.
