Property

My neighbours are building an extension. What height is allowed without approval?

Property clinic: Legislation allows for 12sq m at first floor level without approval

There are a range of issues to be considered when a neighbour is building an extension. Photograph: iStock

Wed Nov 3 2021 - 06:00

Q. We live in a semi-detached house. Our neighbours are in the process of building an extension, but they do not have planning permission. I can see that they are building within the 40sq m allowed but what bothers me is the height of this extension. It reaches up to the first-floor window. Is this allowed?

A. A single-storey extension is permitted to the rear of a dwelling once it is less than 40sq m of which up to 12sq m can be at first-floor level where the house is terraced or semi-detached. This is provided for in the Planning and Development Regulations 2001 – Schedule 2 Part 1 Class 1. If you check this you will see all the limitations. It is important to count any existing extensions or garage conversions that were made after October 1st, 1964, including those that have previously been granted planning permission, as it is the cumulative floor area that must be under 40sq m.

I assume when you say it reaches up to first-floor level you mean that a mono-pitched roof reaches up to window sill level of a first-floor window. If this is the case, your neighbours also need to consider Part B of the building regulations, which deals with fire escape. They will need to ensure the extension’s roof will be of sufficient strength to facilitate escape and rescue from a rear first-floor window in the event of a fire; in other words, it can’t have a glass or perspex roof.

There are some other issues you, as a neighbour, may have, namely:

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– Encroachment over the boundary with you

– Knitting into your own extension roof, should you have one. Any flashing details should be agreed with you

– Impeding a chimney stack draw

– Restricting a wall vent or boiler flue

– Building over a mains drainage line. If this is the case, adequate tolerance must be left and an engineer should be involved in the design

Wall construction

Another matter to consider is the form of wall construction proposed. Your neighbour’s choice may limit or restrict your own ability to extend to the rear of your house in the future. Pay attention to the location of the proposed side wall. Where it is in line with the party wall the foundations may encroach on your side – a more expensive boot-type foundation may be required if building close to the party wall. Where the wall is built with hollow block it will not be suitable as a shared party wall in the future. Finally, a parapet wall detail is recommended at roof level on the party line to accommodate the roof on any future extension to your side. These are all questions to be agreed with the neighbour or his or her professional adviser.

If it is found that the extension is not exempt from planning permission, you can notify the local authority planning enforcement section of the breach of planning laws and an enforcement notice may be issued.

If your neighbours are not breaching any planning regulations or any building regulations, then you have nothing to worry about except whether or not you’ll be invited to the house-warming party.

Pat McGovern is a chartered building surveyor and a member of the Society of Chartered Surveyors Ireland, scsi.ie

Society Of Chartered Surveyors Ireland