I want to add a dormer attic to my home. What do I need to know?
I have a question on the Government’s new planning exemption regulations. I am interested in building a dormer attic. On review of the new legislation, it looks like I can build a gable-to-gable dormer attic once I have the 20cm eaves setback and the attic is less than 30 cubic metres. Am I correct in this? I ideally want to turn all of my attic into a dormer (gable-to-gable). This aspect of the legislation is becoming a very hot topic, and you have picked up on the main requirements. The new Class 1B exemption, introduced by statutory instrument (SI No 344 of 2026) and effective from July 27th, 2026, covers dormer roof extensions and dormer windows to the side or rear of a house. It sets out two conditions: the internal volume must not exceed 30 cubic metres, including other dormer roof extensions, and the dormer must be no higher than the existing roof ridge, with at least a 20cm eaves setback. However, it is important that your proposal is reviewed in the round. It would be advisable to carry out an examination of the proposed drawings and the property’s planning history before confirming that your particular design is exempt. A review of the drawings would help identify whether the roof has already been altered – whether the roof was raised or the pitch changed when first built, or subsequently, for instance. A planning search would discover whether the conditions of the grant of permission for the house specifically restricts additional windows or alterations to the roof. There is also the cumulative rule. The 30-cubic-metre allowance applies to the proposed dormer in combination with other dormer roof extensions. Previous permissions and drawings can help establish what already exists and how much of the allowance remains. One clarification is that the 30-cubic-metre limit relates to the dormer development, rather than the volume of your entire existing attic. If you encounter any of these planning or construction issues, or if you have any qualms at all before starting construction, the way forward is to engage with your local planning office by way of a Section 5 Declaration. This submission will allow the local authority to determine whether your planned development is exempt or otherwise. The application form may be downloaded from the local authority’s website. There is damp in our attic following an insulation upgrade. Am I right to be concerned? If you are converting your attic, it is always advisable to get an experienced, qualified, insured designer. A good set of drawings will clearly show the dormer’s width, depth, height, relationship to the ridge and eaves, an internal volume calculation, and location of the stairs. Most importantly, the designer will generate construction drawings that will inform the builder of all requirements in your case, but also allow all interested builders you may be talking to to price for the exact same thing. Bigger extensions, dormers, subdivided homes, bike sheds: What planning changes are coming? Finally, planning exemption does not remove the need to comply with building regulations. Your construction drawings should address structural support, fire safety and escape, stair access, insulation, and ventilation regulations, particularly if the attic will become a bedroom or another habitable room. It is also important to note that exemptions do not apply to protected structures. Brigid Browne is a chartered building surveyor and a member of the Society of Chartered Surveyors Ireland Do you have a query? Email propertyquestions@irishtimes.com This column is a readers’ service. The content of the Property Clinic is provided for general information only. It is not intended as advice on which readers should rely. Professional or specialist advice should be obtained before persons take or refrain from any action on the basis of the content. The Irish Times and its contributors will not be liable for any loss or damage arising from reliance on any content