A house extension has to work twice: it needs planning drawings that satisfy the council, and structural calculations that satisfy building control. Most delays come from those two not agreeing with each other. Xpanza’s house extension design service handles planning and structural as one job, producing house extension plans that are ready to price from and build from, from a single storey rear extension to a double storey side extension.
Every extension type changes the structure of the house in a different way. Here’s what we design most, and what each one involves.
The classic: extending out into the garden for a bigger kitchen, dining or living space. Single or double storey, with the new space opened up to the existing house through new openings that need steels sized properly.
Building out to the side, often over a garage or along a detached wall. A smart way to widen the ground floor without losing garden length, and a common route to a wider kitchen diner.
A rear extension and side extension joined into one L-shaped space. The biggest single storey option, and the one that most often needs careful structural design, with multiple steels and new foundations working together.
Doubling up: new rooms above as well as below. More space and more added value, with more for planning and structural to get right, which is exactly why both are handled together from the start.
From small property extensions to large double storey builds, from rear extensions to a front of house extension, every project gets the same coordinated treatment. Building extensions of every shape are designed and engineered as one job, not handed between separate suppliers.
You send the measurements and photos; we produce the full technical pack. That means architectural design, extension planning drawings, a householder planning application or permitted development confirmation, extension structural calculations for steels, wall removals and foundations, and construction-issue drawings ready for the build. One team, one fixed fee.
Existing and proposed plans, elevations and sections, developed from your measurements from concept through to construction issue.
Extension planning drawings drawn to validation standards, forms completed, fee calculated, submitted and tracked through to a decision.
Many extensions don’t need full permission. We confirm it first, with a lawful development certificate where you want it in writing.
Extension structural calculations for steels, knock-throughs, wall removals and foundations, coordinated with the architectural drawings so nothing contradicts.
The technical pack building control needs: construction detail, insulation, drainage and structural information, all in one coordinated set.
Every extension has to satisfy two different audiences. When the drawings and the calculations come from separate suppliers, that is where delays start.
Plans and elevations drawn to validation standards, so the council can approve the design, or confirm it falls under permitted development.
Steels, wall removals and foundations calculated and detailed, so building control can approve how the extension will actually stand up.
Both are produced together, so nothing contradicts. The result is a pack that is ready to price from and ready to build from.
Measurements, photos of the house and garden, and what you want from the space. We confirm whether it’s permitted development or needs full permission.
Extension shape agreed, layout drawn, the junction with the existing house worked out. You react and adjust until it works.
Planning drawings and application where needed; structural calculations for steels, wall removals and foundations, all coordinated with the design.
Construction-issue drawings ready for the build, and we answer site and building control queries on our work.
Straight answers to the questions we’re asked most about home extensions, from planning rules to knock-throughs. If yours isn’t answered here, call 07446 197853.
Many single storey rear extensions fall under permitted development, but size limits, height limits and location rules apply, and the rules differ between Wales and England. We check what applies to your property and confirm it, including a lawful development certificate where you want it in writing.
Use our cost calculator for an instant indicative estimate based on our published rate card. Select your extension type and whether you need drawings only or the full package through planning and structural, and you’ll see the fee and delivery timeline upfront. Your exact price is confirmed in writing after a free consultation.
New foundations under the new walls, steels where load-bearing walls come down or new openings are formed, and sometimes goalpost frames for wide openings. Our structural calculations cover all of it, coordinated with the architectural drawings.
It depends on the size of the extension and how quickly we receive your information and feedback. Tell us your deadline at the start and we’ll confirm honestly whether we can meet it. Indicative timelines are shown in our cost calculator when you build your estimate.
Yes. Double storey extensions need the same coordinated approach, with extra attention to overlooking and privacy for planning, and the additional loads for structural design. We handle both as one job.
Foundation design depends on the ground conditions, nearby trees and drains, and the loads from the new structure. Our engineers specify the foundation type and depth as part of the structural package, so there’s no guesswork on site.
Send us your measurements, a few photos of the house and what you want from the space. We’ll confirm the route, quote a fixed fee and get the design moving.