Double-Storey & Multi-Storey Extensions

Planning a double-storey or multi-storey extension? EvoHome Improvements is an independent consultancy. We help you settle the brief, understand planning, structural and party wall considerations, and coordinate comparable written quotations from vetted independent building contractors who carry out the physical work. We support homeowners across Hampshire and the wider South of England.

A double-storey extension usually delivers the lowest cost per square metre of any extension type, because one set of foundations and one roof serve two floors. It is also the extension type most likely to need full planning permission, most likely to affect neighbours, and least forgiving of a weak specification. ## Planning permission and permitted development Some two-storey rear extensions fall within permitted development, but the conditions are far tighter than for single-storey work: depth limits, distance to the rear boundary, eaves and ridge heights, matching materials, and obscure glazing to side-facing upper windows.

Rights are commonly removed in conservation areas, on listed buildings, on new estates by planning condition, and where an Article 4 direction applies. Flats and maisonettes have no permitted development rights. Whether your project qualifies is site-specific: confirm it with your local planning authority or through a lawful development certificate rather than relying on a contractor opinion or what a neighbour built.

## Structure, foundations and the existing house A second storey imposes loads that a single-storey design never has to carry. Expect a structural engineer to specify foundation depth and width, padstones and beams over new openings, floor construction, lateral restraint straps and the connection detail into the existing wall.

Where the ground is clay or there are trees nearby, foundation depth is a major cost variable and should never be left as a vague provisional sum. ## Party wall matters Building up to or astride a boundary, cutting into a party wall for beams or joists, or excavating close to a neighbour's foundations all bring the Party Wall etc.

Act 1996 into play. Notices must be served in good time, typically one or two months ahead depending on the notice type, and a surveyor is often appointed. This is a scheduling issue as much as a legal one: late notices delay a start on site. ## Roof, upper floor and how the house works afterwards The design decisions that homeowners most often regret are on the first floor: where the landing runs, whether an existing bedroom loses its window, how the new roof meets the old one, and whether the bathroom drainage can realistically be reached.

Heating capacity also needs checking, because adding two floors of space frequently exceeds what the existing boiler and radiator sizing were designed for. ## Disruption and programme A double-storey extension typically runs longer than a single-storey project and involves a period where the existing house is opened up.

Scaffolding,…