Building regulations are not the same as planning permission

This is the single most common mix-up in home renovation, so let's clear it up first. Planning permission is about whether you are allowed to make the change at all — whether the extension fits the street, whether the use of the building changes. Building regulations are about how the work is done: structure, fire safety, ventilation, drainage, energy efficiency and electrical safety.

You can need one without the other. A two-storey extension will usually need both. A loft conversion often falls under permitted development and needs no planning application at all, yet it always needs building regulations approval because you are altering structure, insulation and means of escape. Replacement windows can be permitted development but still need to comply with the regulations.

Building regulations apply in England, Wales and Northern Ireland; Scotland has its own Building Standards system. In all cases the principle is the same — the work must meet minimum standards, and someone must check it.

The work that almost always needs approval

If you are changing the fabric, structure or key services of the house, assume approval is required until your local authority building control team tells you otherwise. In practice, that covers:

• Extensions, conservatories over 30 square metres, and conversions of garages or lofts into habitable rooms
• Removing or altering load-bearing walls, chimney breasts and structural floor joists
• Underpinning, basement excavation and the addition of new foundations
• New or replacement windows, roof lights, external doors and glazed screens
• Replacement of a boiler, or installation of a new heating, hot water or ventilation system
• New circuits, a consumer unit replacement, and most electrical work in bathrooms, kitchens and outdoors
• Installation of new drainage, bathrooms moved to a different room, or work to a shared sewer
• Change of use, such as converting a house into flats or a loft into a separate dwelling

Listed buildings add a further layer: listed building consent is needed for most alterations, and certain regulations may be applied more flexibly to protect historic fabric. Always ask before touching a listed structure.

Extensions, lofts and structural alterations

This is where the consequences of skipping approval bite hardest. Your builder may be excellent, but building control want to see calculations from a structural engineer, appropriate steel sizes, fire-resisting floors and walls, protected escape routes, and adequate insulation to meet current energy standards.

For a loft conversion, that typically means a fixed staircase, fire doors to habitable rooms, mains-linked smoke and heat alarms, and floor joists strong enough for bedrooms and storage. For an extension, it means foundation depth, damp-proofing, drainage, roof structure and thermal performance of the new walls and glazing — all measured against the current approved documents, not the standards in force when the house was built.

You should also expect inspections at defined stages: foundations before concrete is poured, drainage before backfilling, and structural work before it is covered up. Booking these in advance saves a great deal of expense later.

Windows, doors, electrics and heating

Replacement windows and doors must meet thermal performance and safety glazing requirements, and the installation must be notified. Many installers belong to a government-approved competent person scheme, which means they self-certify the work and you receive a certificate without involving building control directly. If your installer is not registered, you must notify the local authority yourself.

Electrics follow a similar pattern. Registered electricians can self-certify most domestic work, but notifiable items — new circuits, consumer unit changes, and anything in a bathroom or outdoors — still generate a compliance certificate. Boiler and gas work is covered by Gas Safe registration, and solid fuel appliances by their own competent person schemes.

Whatever route you take, keep the certificates. They are the proof a future buyer's solicitor will ask for.

Where you can usually relax

Some minor work is exempt, but the exemptions are narrower than most people assume:

• Like-for-like repairs to a roof covering, replacing a few tiles or slates
• Internal redecoration, plastering, and replacing kitchen units or flooring in the same layout
• Fitting a new kitchen or bathroom where services stay in the same positions and no new circuit is added
• Non-structural partitions that are not load-bearing, subject to fire and escape considerations
• Garden decking under 30 centimetres high, and most fencing and sheds close to the house may be exempt from both planning and building control

Even here, "usually" is doing a lot of work. A partition can affect means of escape; a shed can become a habitable annexe. A quick phone call costs nothing.

How to check, and what happens if you skip it

Start with your local authority building control team, or an approved inspector if you prefer a private route. Describe the work plainly, ask whether it is notifiable, and ask about fees and the inspection schedule. Get the answer in writing if you can.

If you proceed without approval, the authority can require you to remove or alter the work, and enforcement action can follow for years. Selling becomes difficult: buyers' solicitors ask for a completion certificate, indemnity policies rarely cover the real risk, and some lenders will not release funds. If work has already been done without approval, you can apply for a regularisation certificate — it will involve opening up finished areas so an inspector can see the structure and services, but it is far better than leaving the problem to surface at the worst moment.

Approval is not red tape for its own sake. It is the reassurance that your extension will not sag, your loft stairs will be safe in a fire, and your electrics will not be the thing that fails. Confirm the requirements first, book your inspections early, and the rest of the project will run far more smoothly.