Extensions

Size, height, how close the extension sits to a boundary, its position relative to the original house, and how much of the garden it covers all feed into whether an extension is likely to fall within permitted development. These limits are specific and numeric, they are reviewed periodically, and they must be checked against current Planning Portal and local authority guidance rather than assumed from memory or a neighbour's project.

'The original house' is a defined planning term meaning the dwelling as it stood on a fixed reference date (generally 1948, or as built if later), not the house as it stands today. If previous owners have already extended, that earlier work usually counts against any permitted development allowance for further extension — a common and expensive mistake to discover late.

Side and rear positioning, single storey versus two storey, and eaves and ridge height relative to the existing roofline are all treated differently under permitted development rules, and the interactions between them are not always intuitive.

Inside the Lake District National Park, the Yorkshire Dales National Park, or a Conservation Area, permitted development rights for extensions are generally more restricted than in an unconstrained location, and design, materials and scale are scrutinised more closely even where an application is required anyway. See the dedicated Lake District guidance for how that authority approaches extensions specifically.

If the property is listed, listed building consent is a separate legal requirement from planning permission and can apply to work that would otherwise be permitted development on an unlisted house — including some internal alterations, not just external appearance.

Work near or on a shared boundary, or that involves excavating near a neighbour's foundations, can trigger obligations under the Party Wall etc. Act 1996, separate from planning permission. Notice periods apply, and starting work without serving the correct notice can cause delays and disputes that are avoidable with early notice.

Even where notice is not legally required, telling neighbours before scaffolding, deliveries or excavation start is worth doing on its own merits, particularly on narrower Cumbrian plots and terraces.

Building Regulations cover how the extension is actually built — foundation design, structural adequacy, thermal insulation standards, drainage, ventilation, fire safety and means of escape, and (where relevant) accessibility. Building Regulations approval is required whether the extension needed planning permission or was permitted development, and the two processes run independently.

Approved Documents set out the technical guidance behind Building Regulations; Building Control (either the local authority or an approved inspector) checks the actual work against them at agreed stages.

Long before the walls go up, the ground element usually determines the budget, and it is the part most often underestimated at quotation stage.

A conventional single or two-storey extension broadly follows the same sequence regardless of size, though the detail varies with ground conditions and design.

The clearer the information at enquiry stage, the more accurate the quotation and programme.

Foundation design for an extension is driven by ground conditions found on site, not by the size of the extension alone, and it is one of the most common places a fixed price falls apart once trial holes are dug.

Two-storey and wrap-around extensions are assessed more cautiously than a single-storey rear addition, both under permitted development limits (where eaves and ridge height relative to the existing house, and proximity to boundaries, are treated more strictly) and under full planning permission, where the impact on neighbours' light and outlook carries more weight the taller the addition.

Structurally, a two-storey extension usually means new foundations tied properly into the existing house foundations, careful management of differential settlement between old and new work, and — where the ground floor of the extension removes or alters a load-bearing wall — a full structural design for beams and their bearing points, not just the new external walls.

Where an extension needs to visually read as part of the existing house, or where planning conditions require it, matching brick, stone or render colour is a genuine technical exercise, not a paint-chart decision. Reclaimed or specially sourced brick and stone can have long lead times, and render systems need specifying to match both colour and texture, particularly on visible elevations in Conservation Areas or the National Parks.

Where the design deliberately contrasts with the existing house — a common contemporary approach for rear extensions not visible from the street — materials still need confirming against any planning condition requiring a sample panel or approval before work starts on that elevation.

Trees close to an extension footprint affect both the planning assessment and the foundation design. A tree subject to a Tree Preservation Order, or within a Conservation Area, needs checking before any excavation, pruning or removal near its root protection area — work that damages a protected tree's roots without consent is an offence in its own right, separate from the extension's planning status.

Where an extension involves altering a roof, checking for bats or nesting birds before work starts is good practice on any older property, and can be a formal requirement in some circumstances.

SHS is the contractor, not the planning authority. What SHS can do is look at your extension from a build point of view — access, ground conditions, levels, drainage, foundations and buildability — and tell you plainly what the construction side is likely to involve.

If drawings already exist, send them. If they do not, a site visit and a conversation usually establishes what information you need to gather next and who you need it from.