House extension drawings in Hillingdon

Two-storey and side extensions in the borough

Going up is judged by daylight and outlook. A two-storey extension must stay clear of a line of 45 degrees; 21 metres, taken from the nearest neighbouring window. We plot that test on the plan and section so it can be checked at a glance.

Side extensions follow a different test: half width; 1 m set-in; 1 m set-back. In practice the upper floor of a side extension is narrower than the ground floor, and the front wall steps back so that a semi-detached pair still reads as a pair.

If you are weighing a ground-floor addition against a two-storey one, our double-storey extension drawings in Hillingdon set out that route in more detail.

Green Belt, trees and listed buildings on Hillingdon plots

In Hillingdon about 42 per cent of it is covered by Green Belt. An extension to a house inside the Green Belt is judged on proportionality, so the size of the original house matters as well as the neighbour's window.

The council also publishes 33 conservation areas, 731 tree preservation orders and 436 listed building entries. A protected tree in a rear garden can limit where an extension may go, because its roots have to be protected.

We check every address against those layers in the free constraints check, before any design work starts.

Article 4 directions and the permitted development route

The council has published 150 Article 4 directions. Where one covers your street, rights that other houses enjoy may be removed, and an extension that would otherwise be permitted development needs an application.

Where the house is free of those controls, a single-storey rear extension may be built under the national rule: 3 m (attached) / 4 m (detached) beyond the original rear wall, single storey. A Lawful Development Certificate in Hillingdon confirms that in writing. Deeper extensions can go through prior approval, where the council has 42 days to respond before work may begin.

Hillingdon's own record shows how that route is used: in its latest published year it granted 29 larger home extension prior approvals and refused 13. Those counts say nothing about one house, but they show that the neighbour consultation is a real test.

How Hillingdon decides householder applications

In its latest published year the council decided 1,147 householder applications, granted 90.2 per cent of them and decided 94.3 per cent within eight weeks or an agreed extension. A householder application carries a council fee of £548, paid to the council and separate from ours.

Statistics like these cover every type of householder project. We use them to set expectations on timing, not to predict an outcome.

What the drawings include and what they cost

A Hillingdon householder set shows existing and proposed floor plans, elevations and sections, the location plan and the block plan, all from one Revit model so the sheets agree. Extension drawings start at £695 with VAT included, and a second MCIAT chartered technologist checks every sheet before it is submitted.

If the council asks for changes we redraw at no charge until approval. For a single room at the back, see rear extension drawings in Hillingdon; for everything we draw in the borough, start at architectural drawings in Hillingdon. Owners next door in Hounslow work to a different set of limits.