Log cabin planning rules changed: the 45m² garden home exemption explained

Ireland's planning rules for garden buildings changed on 27 July 2026, and the shift is bigger than any adjustment to the exempted development regime in almost 25 years. For the first time, a habitable detached dwelling of up to 45 square metres can be built in a back garden without planning permission.

The change arrives through S.I. No. 340 of 2026, which inserts a new Class 3A into the Planning and Development Regulations 2001. A separate instrument, S.I. No. 338 of 2026, lifts the long-standing 25 square metre limit for non-habitable garden structures to 30 square metres. Both took effect the same day.

Minister of State John Cummins signed the regulations on 16 July. Minister for Housing James Browne framed them as a response to planning bottlenecks, saying he wanted to "free up our planning expertise for more complex priorities" rather than have planners assessing bike sheds and rooflights.

What Class 3A actually permits

Class 3A allows the construction of a detached house in the rear garden of a principal house, subject to twenty separate conditions. The dwelling must be at least 32 square metres. Combined with any existing Class 3 structures in the same rear garden, it cannot exceed 45 square metres.

This is a genuine habitable dwelling, not a garden room reclassified. It can contain a kitchen and bathroom, and it can be lived in year-round. That distinction is what separates the 2026 regime from everything that came before it, where a garden structure could not lawfully be used as living accommodation unless it was ancillary to the main house.

The condition most coverage has missed

Condition 7 sets a combined cap. The Class 3A dwelling and any structures previously built under Class 3 must together stay within 45 square metres. Because Class 3A also carries a 32 square metre minimum, the arithmetic is unforgiving: only 13 square metres of existing garden structure can remain before the exemption becomes mathematically impossible to use.

A 4 by 3 metre shed at 12 square metres leaves room for a 33 square metre cabin, which clears the minimum. A 16 square metre garden office does not. Neither does a garden room built to the old 25 square metre limit, nor one built to the new 30 square metre allowance. In each of those cases the homeowner is locked out of Class 3A entirely unless the existing structure is removed.

There is a real irony here for anyone who acted early. A homeowner who built a generous garden office under the previous rules, or who takes advantage of the newly increased 30 square metre Class 3 allowance, may find they have spent their entire garden allocation and cannot add an auxiliary dwelling at all.

The other nineteen conditions

The exemption is narrower than the headline figure suggests. The dwelling may only be occupied in conjunction with the main house and cannot be sold or subdivided separately from it. It cannot be used for short-term letting. The exemption applies only where the principal dwelling is the owner's sole or main residence when work begins.

Height is capped at 4 metres for a tiled or slated pitched roof and 3 metres otherwise. The structure must sit at least 0.6 metres from any wall or party boundary, and any windows must be at least 0.6 metres from the boundary they face. Private open space for the main house cannot fall below 25 square metres. No new vehicular or pedestrian access onto a road may be created, though independent pedestrian or wheelchair access to the dwelling must be provided within the existing curtilage.

Services must connect through the principal house. There can be no separate utility connections, including water and wastewater. Where a septic tank or other non-piped treatment is in use, the structure cannot encroach on an approved percolation area, the system must have capacity for the additional loading, it must comply with the EPA Code of Practice, and no additional treatment units may be installed.

Caravans and mobile homes are excluded: the construction must not be temporary in nature. The exemption also cannot be used where the principal house has already been subdivided under the separate new Class 1A subdivision exemption.

You must notify the council first

Class 3A is not a permission-free free-for-all. A notification must be submitted to the planning authority at least 14 days before works commence, stating the location, the Eircode, confirmation that the site meets the requirements, and the reason for using the exemption.

Planning authorities must keep a record of every notification and report annually to the Minister on the numbers received. That reporting requirement is how the Department intends to monitor uptake, and it means the measure is being actively watched rather than simply released.

It expires at the end of 2030

Both Class 3A and the new Class 1A subdivision exemption are time-bound. The relevant period runs from the signing of the regulations to 31 December 2030, and the exemption applies only to development that is both commenced and completed within that window.

Anyone treating this as a permanent change to Irish planning law is misreading it. A cabin started in 2030 but finished in 2031 falls outside the exemption as drafted.

Building Regulations still apply in full

The regulations are explicit that building control legislation continues to apply, including Building Regulations, fire safety requirements and Building Control Regulations. Removing the planning application does not remove the technical standards a habitable dwelling must meet.

This is the most common misunderstanding circulating since the announcement. Exemption from planning permission is not exemption from construction standards, and a 45 square metre habitable unit is subject to the same fire safety and building performance requirements as any other dwelling.

What else changed on the same day

The wider package increases the rear extension exemption for a principal dwelling from 40 to 45 square metres, and raises non-habitable garden structures from 25 to 30 square metres. New exemptions cover dormer roof boxes and rooflights, external wall insulation in line with SEAI grant provisions, and cycle or bin storage at the front as well as the rear of a property. The existing heat pump exemption is no longer restricted to the rear of a property.

A further new exemption, Class 1A, permits subdivision of a principal dwelling into one additional self-contained unit within the existing building envelope, subject to a 32 square metre minimum floor area for each resulting unit. Like Class 3A, it requires 14 days' notice to the planning authority and expires on 31 December 2030.

The tax position is unresolved

The Department has said the tax treatment of auxiliary dwellings, and how it interacts with Rent-a-Room relief, will be clarified through the Budget process with any necessary changes introduced in the Finance Bill. Until that happens, the income position for anyone letting an auxiliary unit to a family member or tenant is not settled.

Given that the dwelling cannot be sold separately, cannot be short-term let, and must be occupied in conjunction with the main house, the realistic uses are family accommodation or long-term letting. Both of those depend on tax treatment that has not yet been confirmed.

Practical position for homeowners

The 45 square metre figure is real, but it is a ceiling reachable only by a homeowner with an empty rear garden, a main residence they occupy, mains or adequately sized wastewater services, and the ability to complete construction before the end of 2030. Existing garden structures above 13 square metres remove the option entirely.

Anyone considering a cabin should measure existing garden buildings first, confirm the wastewater position where a septic tank is in use, and lodge the 14-day notification before ordering anything. Suppliers advertising the change as blanket permission for a 45 square metre garden home are describing the headline, not the twenty conditions underneath it.