Two Storey Extensions: Permitted Development Rules

The permitted development rules for two storey rear extensions in England, including size limits, height restrictions and notification requirements.

Two storey extensions can add significant living space to your home - often a ground floor kitchen-diner with a bedroom or bathroom above. While many homeowners assume a two storey extension always requires planning permission, some two storey rear extensions can be built under permitted development rights, provided they meet strict conditions.

Can You Build a Two Storey Extension Under Permitted Development?

Yes - but only rear extensions. Two storey side extensions always require planning permission. The rules for two storey rear extensions under permitted development are more restrictive than those for single storey extensions, reflecting the greater visual and neighbourhood impact.

Size and Distance Limits

To qualify as permitted development, a two storey rear extension must meet all of the following conditions:

• Maximum depth: the extension must not extend more than 3 metres beyond the rear wall of the original house. This applies to all house types (detached, semi-detached, terraced)
• Maximum height: the ridge height of the extension must not exceed the ridge height of the existing house
• Eaves height: the eaves of the extension must not exceed the eaves of the existing house
• Distance from boundary: the extension must be at least 7 metres from the rear boundary of the property (measured from the rear wall of the extension to the opposite boundary)
• Roof pitch: the roof pitch of the extension must match the existing house as far as practicable

Materials

The external materials of the extension must be similar in appearance to the existing house. This means matching (or closely matching) the brick, render, roof tiles, and window frames. A planning officer or building inspector assessing the completed work will check this.

Windows and Privacy

Any upper floor window in a side elevation of a two storey extension must be:

• Obscure glazed - to at least obscurity level 3
• Non-opening - or opening only at a height of 1.7 metres or more above the internal floor level

This rule is designed to protect neighbours' privacy. It applies to side-facing windows only - rear-facing windows at upper floor level do not have this restriction under PD.

The 7-Metre Rule

The 7-metre boundary rule is the most common reason two storey extensions fail to qualify as permitted development. Many terraced and semi-detached houses have relatively short gardens, and once you measure 3 metres of extension depth from the original rear wall, there may not be 7 metres remaining between the extension and the boundary.

For example, if your garden is 12 metres deep, a 3-metre extension would leave 9 metres to the boundary - which is fine. But if your garden is only 8 metres deep, you would only have 5 metres remaining, which is below the 7-metre threshold.

This measurement is taken from the rear wall of the extension (not the original house) to the opposite rear boundary.

What About Side Extensions?

Two storey side extensions are not permitted development. They always require a planning application. This is because side extensions at two storey height have a greater impact on the streetscape and on neighbouring properties, particularly in terms of the "terracing effect" where semi-detached houses start to look like terraces.

If you are planning a two storey side extension, you will need to submit a householder planning application to your council.

Properties Where PD Does Not Apply

Permitted development rights for two storey extensions do not apply to:

• Flats and maisonettes - PD rights only apply to houses
• Listed buildings - you will need listed building consent
• Properties in conservation areas - two storey rear extensions are not PD in conservation areas; you will need planning permission
• Properties in National Parks, AONBs, or the Broads - additional restrictions apply
• Properties subject to an Article 4 Direction - the council may have removed PD rights

Prior Approval (Larger Home Extensions)

The "larger home extensions" prior approval scheme applies to single storey rear extensions only (up to 6m for semi-detached/terraced or 8m for detached). It does not apply to two storey extensions. A two storey extension that exceeds the standard PD limits requires a full householder planning application.

Cumulative Limits

Remember that permitted development limits are cumulative. If the original house has already been extended (either by a previous owner or by you), those extensions count against the PD allowance. The total area of all extensions and outbuildings must not exceed 50% of the curtilage (the total area of land around the original house, excluding the footprint of the original house itself).

Getting It Right

Before starting a two storey extension under permitted development:

1. Measure carefully - the 3-metre depth and 7-metre boundary distance are strict limits with no flexibility
2. Check your property type - ensure PD rights have not been removed
3. Apply for a Lawful Development Certificate - this provides legal proof that the work does not need planning permission and is invaluable when selling
4. Consult an architect - a professional can confirm the measurements and design a scheme that complies with all PD requirements. Find an architect near you
5. Remember building regulations - regardless of whether planning permission is needed, a two storey extension will always need building regulations approval

Costs

A two storey rear extension typically costs significantly more than a single storey, but you get double the floor space for only around 40-60% more money (because the foundations, ground floor structure, and professional fees are shared). Typical costs:

Costs are higher in London and the South East (add 15-25%). Major cost variables include structural steelwork, the extent of glazing, quality of kitchen and bathroom fittings, and whether you need to upgrade existing services (heating, electrics, drainage). For more detail, see our complete guide to house extension costs.

Design Tips for Two Storey Extensions

• Match the roof pitch - PD requires this, and planning officers expect it. A mismatched roof looks like an afterthought
• Set back slightly from the main wall - a small step-back (100-200mm) at the junction between existing and new helps the extension read as a sympathetic addition rather than an awkward bolt-on
• Consider window proportions - match the style, size and alignment of windows on the existing house for a cohesive appearance
• Think about internal layout - plan both floors together. The upper floor layout is constrained by the ground floor structure below, so design them as a pair
• Use an architect - a two storey extension is a significant investment. Professional design ensures you maximise space, comply with all regulations, and create something that enhances your home's value. Find an architect near you

If your two storey extension does not meet the PD criteria, do not be discouraged. A well-designed householder planning application has a high chance of approval - nationally, over 85% of householder applications are approved.