10 step guide to planning an extension

1. Check whether you need planning permission

You don’t necessarily have to get planning permission to extend your home but you need to tick all the boxes to qualify. There are restrictions on floor area (in ROI less than 40sqm), eaves height (in NI no more than 3m high), etc. If you have any doubt, ask for a Section 5 Declaration from your local authority (ROI) or a Certificate of Lawful Development (NI) to make sure your plans don’t require planning permission. After that, make sure you abide by all relevant building regulations.

2. Check the purse

Embarking on an extension project is all about keeping an eye on the budget; check finances are in place and assess how much you will realistically need with design and planning fees, insurance and warranties as well as build costs.

3. Think design

It’s not because it’s small that you shouldn’t give the design the due diligence that it deserves – for example if you’re adding a kitchen would you like it to be exposed to the morning sun? Then it needs to face the eastern elevation. And don’t forget to take into account the context of the site and connection to existing house. To help you design the extension and put it to paper, you’ll need an architectural designer, but consider too that you may need a structural engineer for things like specifying steel or a building energy assessor if you’re looking at an energy upgrade. Check references and insurance.

4. Check the regs

The building regulations apply to renovations; check the technical guidance documents and technical booklets, and consult with your building professional for advice.

5. Choose as many of the finishes you can in advance

To save on costs have a look at which windows, doors, kitchen, tiles or other relevant products you will need to source yourself. It takes a long time to find what you want and at the right price – knowing this in advance will help the design process immensely, and will assist in the costings. By getting detailed construction drawings done you’ll be able to accurately price your project – you need a detailed specification otherwise costs are likely to creep up.

6. Comply with Building Control requirements

If you secured planning permission you will need to go through the building control process by filing a commencement notice (ROI) on the Building Control Management System as you would for a new build. In NI even if the work is exempt from planning permission you still need to advise Building Control, e.g. in the case of a roof space conversion or to install a wc under the stairs. All structural work must be filed with Building Control, also insulation work. Exemptions include porches of 5sqm or less at ground level that protect an external access (but the glazing must comply with Part V of the Regulations), conservatories 30 sqm or less that have at least 75 per cent of the roof and 50 per cent of the external wall made of translucent material, and detached garages that are 30sqm or less and are either built substantially of non-combustible material or are not less than one metre from a dwelling or boundary of the site or a road.

7. Comply with health and safety requirements

If the project lasts more than 30 days or poses a significant risk, you must advise the health and safety authority (HSA in ROI and HSENI in NI) and appoint health and safety supervisors for both the design and construction stages. This work involves keeping a health and safety ledger on site.

8. Check the insurance

Check whether your house insurance is still valid during construction and whether it can be extended to site insurance during the works. With a contractor taking on the project management, check that their insurance covers all the necessary for your site, most importantly public liability but also employer’s liability.

9. Get the neighbours involved before work begins

You may or may not need to get planning permission but in all cases, let your neighbours know what you’re up to as early as you can – ideally at the dreaming stage. It’s common courtesy and they may have information about your house or site that could be interesting to know!