01
Existing and new
Mark the house as existing and the extension as new. Drawings dimension the new part and show the house for context.
House extension
Design your house extension to match
Rear, side-return or wrap-around: draw the existing house, add the new part and produce drawings where the extension is clearly shown.
Design my extension
02
Matching heights
Storey heights, floors and roof follow the existing house so floors and eaves line up.
03
Permitted development or planning
Many single-storey rear extensions fall under permitted development; larger ones need planning permission.
04
Drawings for the council
With Project Pass you get block plan, floor plan, elevations and a section through the extension on A3.
THE RULES AT A GLANCE
Permitted development or planning permission?
Depth, height and distance to the boundary decide which route your extension takes. Check the current guidance for your house type.
Single-storey rear extension
Under permitted development, often up to 3 m deep on a semi or terrace and 4 m on a detached house, with larger depths possible via prior approval.
Height limits
Usually no higher than 4 m, and lower eaves within 2 m of the boundary. Flats, maisonettes and listed buildings have no permitted development rights.
Materials that match
Permitted development expects materials similar in appearance to the existing house. Conservation areas add restrictions.
Building Regulations apply
Even without planning permission, structure, fire safety, insulation and drainage need Building Regulations approval and Party Wall notices may be needed.
THREE COMMON EXTENSIONS
More space where you need it
Examples to start from. Draw them in centimetres and see how they meet the existing house.
Side return
Fill the narrow side passage to widen the kitchen, with roof glazing to keep the back of the house bright.
Kitchen-diner at the back
An open kitchen and dining area with wide glazing to the garden.
Garden room or office
A bright room with its own garden door, without moving load-bearing walls.
FROM SKETCH TO APPROVAL
How it works
- 1
Draw the existing house
Enter its measurements and heights and mark it as existing. A photo gives matching colours and roof.
- 2
Add the new part
Sketch the extension, choose a roof and see distances to the boundary instantly.
- 3
Produce drawings
Choose Extension in the drawings dialog – the new part is dimensioned, the house shown for context.
- 4
Council and Building Control
Apply or seek a Lawful Development Certificate, then get Building Regulations approval.
THE DRAWING SET
What councils usually ask for
Drawings showing what is new and how it joins the house – with the same measurements everywhere.
Block plan
The extension shown against the house with distances to the boundaries.
Floor plan
The new rooms, openings and connection to existing rooms.
Elevations
Every side with ground line and declared materials.
Section
Through the extension with floor levels, ceiling height and roof pitch.
Rules differ in England, Scotland, Wales and Northern Ireland, and in conservation areas. Always check with your council. Structure must be verified by an engineer.