A lean-to conservatory is a single-storey glazed room with one roof slope that runs down from your house wall to a lower front frame. It is the simplest conservatory shape, usually the least expensive, and often the only one that fits under bungalow eaves, below a first-floor window or into a narrow garden. This guide goes into the detail that decides whether a lean-to will work for you: how much wall height you need, how shallow the roof can go, which sizes make sense and what pushes the price up or down. For a quick comparison of every style, start with our main conservatories page.
How a lean-to is put together
A lean-to has no ridge and no hips. Its rafters are fixed to a wall plate on the house at the top and sit on a beam along the front frames at the bottom, with a gutter running the length of the front edge. All the rainwater runs one way, so the gutter and downpipe end up on the garden side, which matters if your nearest drain is at the opposite end of the wall. The two side walls finish in a sloping top, either fully glazed or built in brick. That plain geometry is why a lean-to is quick to build and easy to furnish: you get a clean rectangle of floor with three straight walls.
Height is the measurement that decides everything
The first figure we take on a lean-to survey is the clear height on the house wall. The top of the roof has to tuck in below whatever is already there, such as bungalow gutters, a bedroom window sill, soffits or a soil pipe, and still leave room for flashing to seal the joint with the brickwork. From there the roof falls towards the garden, and the front frames still need enough height for a door you can walk through without ducking.
The calculation works backwards from those two fixed points. The further the room projects from the house, the more height the roof loses over that distance at any given angle. On a bungalow with low eaves, a deep lean-to can leave the front frames too low, so we often suggest a shallower, wider room instead of a deep, narrow one.
How low can the roof pitch go?
Roof pitch is the angle of the slope, and low-pitch lean-to systems exist for exactly this problem. One widely used roof is BBA accredited down to 2.5 degrees with polycarbonate or sealed glass units (Ultraframe), and an NBS-listed PVC-U lean-to quotes pitches from 2.5 up to 45 degrees (NBS Source). The safe minimum for your room depends on the roof system, the glazing and the rafter length, so ask us and we’ll confirm for your sizes. Bear in mind that a very shallow glass roof sheds leaves and grime more slowly, which makes self-cleaning glass worth considering.
Upstairs windows
On a two-storey house, a lean-to often sits right under a bedroom. The Planning Portal advises against building where a conservatory would get in the way of ladder access to windows serving rooms in the roof or loft, especially escape windows (Planning Portal). We check this at survey before drawing anything.
Who a lean-to suits best
- Bungalow owners, because the low eaves rarely leave room for a ridged Victorian or Edwardian roof.
- Terraced and semi-detached houses with narrow gardens, where a room that runs along the back wall keeps the lawn usable.
- Owners of modern homes who want a minimal look. In slim aluminium with sliding doors, a lean-to reads as a simple glass box rather than a traditional conservatory.
- Anyone working to a tighter budget, as the roof is the simplest to make and fit.
It is less suited to a house with a very short ground-floor wall, or to anyone who wants a tall, airy room. In that case an Edwardian conservatory gives more headroom, and an orangery gives a more solid, extension-like feel.
Planning a lean-to in a narrow garden
On a terrace or semi, the side walls often land close to, or on, the boundary. A few rules come into play here:
- Permitted development: a single-storey rear conservatory can normally project up to 3 metres on a semi or terrace and 4 metres on a detached house, with a maximum height of 4 metres, and eaves no higher than 3 metres if it is within 2 metres of a boundary (Planning Portal). The eaves also cannot be higher than the eaves of the house (government technical guidance).
- Party walls: if you build on or at the boundary, or dig near and below the level of your neighbour’s foundations, you must tell them under the Party Wall etc. Act 1996 (gov.uk).
- Drains: terraces often have a shared sewer running behind the houses. Thames Water requires a build over agreement for building work within 3 metres of a public sewer (Thames Water).
A practical tip for tight plots: build the side wall that faces your neighbour in brick. It gives you privacy, stops the room overlooking next door and gives you a solid wall for a sofa or shelving, while the garden side stays fully glazed.
Doors, frames and roof options
In a shallow room, a hinged door swinging inwards eats floor space. Sliding doors such as Reynaers ConceptPatio 130 keep the floor clear, while Smart Visofold or Cortizo bifolds open a whole side to the garden. French doors that open outwards are a good middle ground. Frames can be UPVC on our Selecta Advance 70 system, including woodgrain-finish foils if you like a timber look, or powder-coated aluminium from Cortizo and Alunet. For the roof you can choose glass, a solid tiled lean-to or a mix of both; a solid roof is heavier and usually means Building Regulations approval, which we cover at survey.
What a lean-to costs, and why
As a market guide only, not our prices, Checkatrade’s conservatory cost guide (price table last updated June 2026) gives £9,000 to £11,500 for a 3.5 m by 3.5 m uPVC lean-to, with an average of about £10,250 (Checkatrade). Your own figure depends on factors that are particular to lean-tos:
- the length of wall and the condition of the brickwork where the roof meets the house;
- dwarf walls in brick or full-height glazing;
- whether gutters, downpipes or a drain need moving;
- groundwork on a sloping garden, which can mean a stepped base;
- roof type, from polycarbonate to glass to solid;
- UPVC or aluminium, and the doors you choose.
Lean-to mistakes we help people avoid
- Projecting too far for the available height, which leaves the front frames uncomfortably low.
- Putting clear glass on a south-facing roof with no vents, then finding the room unusable in July.
- Forgetting which way the gutter drains until the downpipe lands on the patio.
- Blocking an upstairs window that someone may need to reach from outside.
- Choosing an inward-opening door in a room that is only a couple of metres deep.
Arrange a free lean-to survey
We will measure your wall height, check the eaves, drains and boundaries, and show you what depth and pitch will really work before you commit. We cover Windsor, Maidenhead, Berkshire, Buckinghamshire, Surrey, west Kent and north West Sussex from our workshop at Fifield. Call 01753 965 005 or request your free quote online.
Frequently asked questions
What is the minimum roof pitch for a lean-to conservatory?
It depends on the roof system and glazing. Some lean-to roofs are accredited down to 2.5 degrees with polycarbonate or sealed glass units, which helps on bungalows with low eaves. A very shallow roof sheds dirt more slowly, so self-cleaning glass is worth considering. We confirm the minimum pitch for your exact room size at survey.
Can I put a lean-to conservatory on a bungalow?
Usually, yes. A lean-to is often the best choice for a bungalow because its single slope can sit below low eaves where a ridged roof would not fit. The key is balancing depth against height, so the front frames are still tall enough for a comfortable door. We measure this carefully before suggesting a size.
How deep can a lean-to conservatory be without planning permission?
Under permitted development, a single-storey rear conservatory can normally extend 3 metres on a semi-detached or terraced house and 4 metres on a detached house, up to 4 metres high. Eaves within 2 metres of a boundary cannot exceed 3 metres. Conservation areas and homes without permitted development rights differ, so check with your council.
Do I need my neighbour's agreement to build a lean-to on the boundary?
If you build on or at the boundary, or dig near and below your neighbour's foundation level, the Party Wall etc. Act 1996 requires you to notify them. That is a formal notice rather than planning permission. A brick side wall facing next door also gives you privacy and stops the room overlooking their garden.
Is a lean-to the cheapest type of conservatory?
It is normally the least expensive shape, because the roof is simple and there are fewer corners. As a market guide, Checkatrade lists around £9,000 to £11,500 for a 3.5 m square uPVC lean-to. Groundwork, roof type, frame material and doors all change the price, so we quote individually after a survey.