Flues, chimneys and soil vent pipes under Class G

A flue for a wood burning stove on an ordinary house is permitted development under Class G of Part 1 of Schedule 2 to the General Permitted Development Order 2015, provided it does not exceed the highest part of the roof by one metre or more. That is the rule that decides most installations, and it is the one installers most often measure after the scaffold is up.

Class G covers the installation, alteration or replacement of a chimney, a flue, or a soil and vent pipe on a dwellinghouse. Three different jobs, one set of limits.

The one metre height limit

The measurement is from the highest part of the roof of the house to the top of the flue, and the terminal counts. A twin wall system that clears the ridge by 800 millimetres is within the limit. One that clears it by 1,100 millimetres is not, and needs planning permission.

Two situations catch people out.

A flue rising through a rear single storey extension is measured against the highest part of the roof of the house, which is usually the main ridge, so there is normally generous headroom. The flue can be tall in absolute terms and still comfortably within Class G.

A flue on the ridge itself has almost no headroom. Where the appliance sits in a room directly under the ridge and the flue exits at the top, the one metre allowance is consumed quickly once the required terminal height above the roof surface is added.

Building regulations pull in the opposite direction, which is the tension at the heart of these jobs. Part J sets minimum terminal heights above the roof surface and minimum distances from openings, ridges and adjacent structures, all of which push the flue up. Class G pushes it down. On a steep roof with the appliance set back from the ridge, the two requirements can conflict, and that is when a planning application becomes necessary rather than optional.

Protected land and the elevation rule

On what the order calls article 2(3) land, which covers conservation areas, National Landscapes, National Parks, the Broads and World Heritage Sites, a second limit applies. The chimney, flue or soil pipe must not be installed on a wall or roof slope which fronts a highway and forms either the principal elevation or a side elevation of the house.

Read that as three conditions that all have to be met before the restriction bites. The wall or roof slope has to front a highway. It has to be the principal or a side elevation. And the property has to be on protected land.

A rear elevation is not caught, whatever it faces. A side elevation facing a private drive rather than a highway is not caught. A front elevation in a conservation area facing the street is caught, which is why flues in conservation areas so often emerge at the back and run internally to get there.

Corner plots deserve care. Where two elevations front highways, both can be restricted, leaving only the rear.

There is a design consequence worth thinking through before the stove is bought. Running a flue internally from a front room to a rear roof slope means boxing it through the first floor, losing cupboard space, and accepting bends that reduce the draw. Installers will tell you the system tolerates two 45 degree offsets more happily than one 90 degree turn. Work that out with the installer before the appliance position is fixed, because the alternative is a planning application for a flue on a front elevation in a conservation area, which is a difficult case to win.

What Class G does not do

It does not apply to flats or maisonettes. Part 1 of Schedule 2 covers dwellinghouses, and a building containing flats is outside it entirely, so an external flue on a converted house in multiple ownership needs planning permission.

It does not override an article 4 direction. Councils in conservation areas remove householder rights routinely, and the direction may name Class G specifically.

It does not override a condition on the original permission. New build estates frequently have permitted development rights removed by condition.

And it does not touch listed building control. Listed building consent is a separate consent under different legislation, required for works affecting the character of a listed building, and an external flue on a listed cottage will need it. Where the building is listed and the works are more extensive, a heritage statement explaining the significance of the building and the effect of the flue is what the conservation officer will expect to see.

The other regimes that apply anyway

Building regulations approval is required for a new appliance and flue under Part J, covering the flue route, terminal position, clearances to combustible materials, the hearth, ventilation and a carbon monoxide alarm. This is independent of planning and is not optional. Installation by a registered competent person under a scheme such as HETAS, or a building notice to the council, are the two usual routes.

Smoke control areas are the third regime. Councils declare them under the Clean Air Act 1993, and within one only an exempt appliance or an authorised fuel may be used. Large parts of urban England are covered. Check with the council before buying a stove, because the appliance choice is narrower inside a smoke control area and the rules are enforced.

Chimney and flue works can also engage the Party Wall etc. Act 1996 where a flue is cut into or supported by a party wall. That is a civil matter between neighbours rather than a planning one, and it still stops a job.

Confirming the position

The only formal confirmation that a flue is lawful without planning permission is a certificate of lawfulness for proposed use or development under section 192 of the Town and Country Planning Act 1990. It carries a fee and takes around eight weeks, and it produces a document that answers the question at sale.

For most straightforward installations on unprotected land, owners take the view and proceed. On protected land, on a corner plot, or where the flue is near the ridge, the certificate is worth having.

1. Measure the highest part of the roof and the proposed flue terminal, and confirm the difference is under one metre.
2. Establish whether the property sits on article 2(3) land using the council's constraints map.
3. Identify the principal elevation and any side elevation fronting a highway.
4. Check for an article 4 direction and for conditions on the original permission.
5. Confirm the building regulations route and whether a smoke control area applies.

Illustrative example: a Victorian terrace in a conservation area, with a stove proposed in the front room. The flue cannot go on the front roof slope, which fronts the street and forms the principal elevation. It is instead run internally to the rear slope, where it terminates 600 millimetres below the main ridge. Class G is satisfied, Part J clearances are met with a taller terminal at the rear, and no planning application is needed. This example is illustrative.

Where a flue does need permission, the application is small and the supporting material is short. PlanScope drafts a planning statement structured to UK planning policy, with site facts flagged where they need confirming. Enter your postcode on the PlanScope home page to see what a householder application on your property is likely to need.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.