Must-Have Plans for Your Home Extension Project

Special Considerations for a Single Storey Extension

Single storey extensions are one of the most common types of residential works. But they come with rules and nuances:

Permitted Development thresholds:
For a detached house, a rear extension can extend up to 4m under permitted development; for terraced or semi‑detached houses, the limit is 3m. If you require more length (e.g. 6m or 8m), you may apply under prior approval under the House Extension Scheme.

Height restrictions:
Single storey rear extensions must generally not exceed 4m in height. If the extension is within 2m of a boundary, the eaves height must be no more than 3m.

Roof types:
Options include flat roofs, mono-pitched, pitched with matching pitch, or rooflights / lanterns. The roof pitch should match or complement the existing house whenever possible under permitted development rules.

Integration with kitchens / open plan layouts:
Many single storey extensions are used to expand or reconfigure kitchen/diner spaces. Your drawings must coordinate plumbing, drainage and appliance layout. Also, consider structural consequences of large openings between old and new spaces.

Daylight & overshadowing:
Ensure windows are sensibly placed, acknowledge neighbour rights and minimise overshadowing of neighbouring properties.

When Permitted Development Applies (and When It Doesn’t)

What Is Permitted Development

Permitted development (PD) refers to certain works that a homeowner can carry out without needing full planning permission, subject to conditions.

However, even under PD, you’ll often need to submit scaled drawings (existing & proposed, site plan) and potentially a Lawful Development Certificate (LDC) or prior approval in some cases.

Differences in Drawings under PD vs Full Planning

• Under PD, documents are typically more constrained; you must show your extension abides by the PD limits (size, height, materials)
• For full planning, you may need more context: impact analysis (neighbour amenity, visual impact), design statements, heritage or conservation assessments
• If your project exceeds PD limits, you’ll need a full planning application — your drawings must then be more robust and anticipate planning scrutiny

Common Challenges & Rejections

• Failing to adhere strictly to PD limits (depth, height, distance from boundaries)
• Using materials that do not match or complement existing property
• Poor drawings that lack clarity on dimensions or context
• Drawing errors or missing structural or drainage details

Why Detail Matters: Common Pitfalls & Rejections

Even a seemingly small omission or ambiguity can jeopardise your planning or building control approval. Common pitfalls include:

• Missing or incorrect site boundary, neighbouring building outlines or context
• No structural input (beams, lintels, foundations) or missing engineer’s details
• Inaccurate levels, heights or ground contours
• Poor annotation, missing dimension labels or unclear notes
• Not addressing drainage or connection to existing plumbing/sewer
• Overlooking insulation, ventilation or fire safety compliance
• Lack of clarity on materials, finishes and external appearance

By contrast, well-drafted drawings minimise ambiguity, help the planners and building control teams understand your proposals faster, and reduce the need for revisions.

How Kitchen Layouts & Interior Flow Influence Your Drawings

The kitchen is often the heart of a home, and when your extension involves a kitchen upgrade, your drawings need to speak both technically and functionally.

Plumbing and drainage: Show the location of sinks, appliances, waste pipes and drainage runs tying into existing mains.

Ventilation / extractors: Indicate extractor fans, duct runs, air inlets, etc.

Large structural openings: If you want a wide opening to integrate old and new space (e.g. removing walls or adding large glazed doors), coordinate with structural drawings.

Flow & circulation: Show layouts of worktops, movement paths, furniture and links to adjoining rooms.

Lighting & natural light: Indicate window sizes, rooflights or glazing arrangements to ensure a bright, workable space.

Including a “furniture layout / kitchen plan overlay” on your proposed plan can give planners and building control a clearer sense of how the space will function.