Chimney removal, flues and roof alterations

Chimneys and flues are not covered by the roof alterations right. Class C of Part 1 of the Town and Country Planning (General Permitted Development) (England) Order 2015 permits other alterations to the roof of a house, but it expressly excludes the installation, alteration or replacement of a chimney, flue or soil and vent pipe. Those works have their own class, Class G, with its own height limit and its own restriction on designated land. Removal of a stack is a third question again, because it is neither an installation nor an alteration of a chimney in the sense Class G uses, and councils read it differently.

If you want a short answer: a new flue is usually permitted development subject to a one metre height rule, a rooflight is usually permitted under Class C, and taking a stack down is the one worth a phone call before the scaffold arrives.

Alterations that fall within Class C

Class C is the catch-all for roof work that is not an enlargement. Rooflights, replacement coverings, re-tiling in a different material and repairs that change appearance all sit here, subject to three limits:

• the alteration must not protrude more than 0.15 metres beyond the plane of the original roof slope, measured perpendicular to that slope
• the highest part of the alteration must not be higher than the highest part of the original roof
• the class does not extend to chimneys, flues, soil and vent pipes, or to solar equipment, which have their own classes

The 0.15 metre limit is what governs rooflights. A conservation-style rooflight set into the plane of the slope passes comfortably. A proprietary unit on an upstand often does not, and the measurement is from the plane of the original roof rather than from the current covering, which matters on a roof that has been overlaid.

There is also a condition on windows. Any window inserted in a roof slope forming a side elevation must be obscure-glazed and non-opening unless the opening part is more than 1.7 metres above the floor of the room, which is the same requirement that drives obscure glazing conditions on side-facing windows elsewhere in Part 1.

Flues and their height limits

Class G deals with the installation, alteration or replacement of a chimney, flue or soil and vent pipe on a house. The governing limit is height: the flue must not exceed the highest part of the roof by more than one metre.

On designated land, which means a conservation area, a National Park, a National Landscape or a World Heritage Site, the right is narrowed. A flue cannot be installed on a wall or roof slope that fronts a highway where that elevation is the principal elevation or a side elevation of the house. The practical effect is that the flue has to go on the rear, and on a corner plot with two highway frontages the remaining options shrink quickly.

Two things sit outside planning and often decide the design anyway. Approved Document J of the Building Regulations governs where a flue may terminate relative to openings, roof planes and boundaries, and it frequently pushes the terminal higher than the planning limit allows, at which point permission is needed. And in a smoke control area declared under the Clean Air Act 1993, only an exempt appliance burning an authorised fuel may be used, which rules out a lot of wood-burning stoves regardless of where the flue goes.

A flue in the wrong position on a terraced roofscape also reads badly from the street, so pick the slope with the officer in mind even where no permission is needed.

Chimney removal and structural effects

Removing a stack changes the external appearance of the building, so it is development rather than exempt maintenance under section 55 of the Town and Country Planning Act 1990. Whether it is permitted development is less settled. It is an alteration to the roof for the purposes of Class C on one reading, and the exclusion in Class C is framed around installing, altering or replacing a chimney rather than removing one.

In practice many authorities treat removal of a stack on an unlisted house outside a conservation area as permitted development, and many publish guidance saying so. Some do not. Because there is no fee for asking, the sensible sequence is to put the question to the duty planner in writing and keep the answer, or apply for a lawful development certificate if certainty matters for a sale.

The structural and construction consequences are more certain:

1. The stack is usually carrying load, or at minimum restraining the roof structure at the ridge, so the roof needs propping and the opening framing designing.
2. Where the stack sits on a party wall, cutting into it engages the Party Wall etc. Act 1996 and requires notice to the adjoining owner.
3. Flues serving other dwellings in a terrace may pass through the stack, so nothing comes down before the flues are traced.
4. The hearth, breast and flue above and below need removing or making good consistently, which is where costs run over.
5. The roof covering and any lead work around the stack has to be made good to match.

Conservation area and listed positions

On a listed building, removing a stack is almost always a work affecting its character as a building of special interest, so listed building consent is required under the Planning (Listed Buildings and Conservation Areas) Act 1990 and carrying it out without consent is a criminal offence. Replacement flues on a listed building need consent too, including the internal route.

In a conservation area the position depends on whether the authority has made an Article 4 direction. Many have, specifically to control chimney removal, window replacement and roof alterations on terraces where the rhythm of stacks is part of the character. Where a direction applies, planning permission is needed and the application will be judged against the section 72 duty to pay special attention to preserving or enhancing the character and appearance of the area. That is the same test discussed in removing a chimney stack in a conservation area.

Check the authority's Article 4 register before assuming. A direction can cover a handful of streets rather than the whole area.

Street character and replacement details

Where stacks survive along a terrace, the regular interval of brick masses against the sky is doing visible work. Take one out and the gap reads from a hundred metres away. Officers assess the loss against the group rather than the single house, which is why a stack on a rear slope is treated more leniently than one on a front roof plane.

If the stack has to go for structural reasons, the alternatives worth proposing are retaining the stack above roof level as a capped feature with the internal breast removed, rebuilding the stack in salvaged brick to the original profile and height, or reducing rather than removing it. For a replacement, match brick type, bond, mortar colour and the detail of the oversailing courses and pot, and specify them on the drawing rather than leaving them to the contractor.

The same reasoning applies to other visible roof changes, including rear dormers on a semi-detached house, where the design is judged against the pair and the terrace rather than the single roof.

Building regulation implications

Planning and Building Regulations are separate consents and both may apply. Removing a stack is notifiable structural work under Approved Document A. A new or relined flue and any combustion appliance fall under Approved Document J, with a commissioning and notice plate requirement. Blocking up a fireplace affects ventilation under Approved Document F, and a vent is normally needed to keep the flue dry where the stack is retained. Replacing more than a set proportion of a roof covering triggers the thermal upgrade provisions in Approved Document L.

None of this is optional, and none of it is dealt with by planning permission.

Evidence for a small application

Where permission or listed building consent is needed, keep the submission tight and visual:

• existing and proposed elevations and roof plans at a measurable scale
• photographs of the stack, the roof plane and the wider street or terrace group
• a brick and mortar specification with the bond and oversailing detail for any rebuild
• a structural note explaining why removal or reduction is proposed
• for a listed building or conservation area, a short Heritage Statement identifying the significance of the stack and the group, the harm proposed and the justification

PlanScope drafts that heritage statement and the other supporting documents from your answers about the property, flagging the facts it does not have, and you can enter your postcode on the home page to see which reports a small application is likely to need. Reports should be reviewed before submission and PlanScope does not guarantee planning approval.

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