Dormer without planning permission: the 2026 rules
A dormer roof extension with a dormer window at the side or rear of the house needs no planning permission if its inside volume, together with any other dormers, is no more than 30 m³ and the ridge and eaves conditions below are met. This is a new exemption, in force since 27 July 2026.
The conditions
The exemption is Class 1B, added to the Planning and Development Regulations 2001 by S.I. No. 344 of 2026. Its conditions are short:
- Volume. The internal volume of the dormer, alone or combined with other dormer roof extensions, cannot exceed 30 m³. An existing dormer uses up part of the allowance.
- Height. The dormer cannot be higher than the ridge of the roof.
- Eaves. It must be set back at least 20 cm from the eaves.
- Position. The class covers the side or rear of the house only. Citizens Information states that a dormer on the front of the house needs planning permission.
The limit is a volume, not a floor area: it is the space enclosed by the dormer, in cubic metres.
Roof lights on the front roof
The same S.I. adds Class 1C for roof lights set into the existing front roof plane:
| Condition | Limit |
|---|---|
| Number of roof lights on the front roof | 2 at most |
| Length of each roof light | 100 cm at most |
| Width of each roof light | 90 cm at most |
Before you build
An exemption does not apply in some cases, for example if the work would break a condition of an earlier planning permission or extend an unauthorised structure (article 9 of the Planning and Development Regulations 2001). Citizens Information adds that there are restrictions for protected structures and houses in an architectural conservation area.
If you are unsure, Citizens Information suggests asking your council before you start. For a formal answer, anyone can ask the council for a declaration under section 5 of the Planning and Development Act 2000 on whether the work is exempted development.
If the dormer is too big
A dormer over 30 m³, on the front roof, or above the ridge needs planning permission. See planning application fees and decision times by council. Applications can be made through the national online planning portal, planning.localgov.ie, or to your council directly.
Related rules: rear extensions and taking down a chimney. All the 2026 limits are on the drawing of the house.