Two Storey Extension Guide

Some councils use a 45-degree line or other local daylight/outlook guidance as an initial design test. The relevant window, the point from which the line is drawn and whether the test is in plan or elevation depend on that authority's adopted guidance.

It is not a universal national rule and passing it does not guarantee permission. A proposal may still affect sunlight, privacy or outlook; failing a screening diagram may require more detailed assessment rather than automatically ending the project. Identify the actual local policy before designing to a line.

Certain two-storey rear extensions to eligible houses may have permitted development rights, but the conditions are restrictive, including rear depth and distance from the rear boundary. Designated-land restrictions and matching roof-pitch requirements also matter. Do not transfer the larger single-storey prior approval depths to a two-storey scheme.

For full planning, read the council's residential design guidance and relevant nearby decisions. Consider whether the roof should be subordinate and how the extension affects the rhythm of the street or a group of houses.

Record neighbouring habitable-room windows, ground levels, gardens and existing boundary features. Show meaningful plans, sections and elevations, including the relationship to the neighbours, rather than drawings clipped at the site boundary.

Where the scale or orientation warrants it, obtain a proportionate daylight/sunlight assessment from a competent specialist. Reduce excessive projection, reposition upper windows and use roof form to address the actual harm instead of relying on a generic statement that neighbours will not object.

Stack rooms and drainage sensibly. New upper-floor loads can require different foundations, walls or frames from a single-storey scheme, and the existing building may need investigation. Check roof drainage, maintenance access, fire protection and escape before agreeing room sizes.

Discuss the concept with neighbours where appropriate, but do not treat their support as a replacement for policy compliance, planning permission or statutory party wall procedures.

Submit a consistent survey, existing and proposed drawings, clear material information and the local validation documents. A short design explanation should identify constraints and explain the specific changes made to reduce impact.

If officers identify a difficulty, respond with a revised design and evidence. Keep enough time in the programme to resolve amendments rather than assuming an eight-week target is a guaranteed decision date.