Conservatories can often be built without the need for a full planning application under the Permitted Development Rules (PDRs), subject to meeting a number of conditions (which also
apply to extensions). The maximum depth to the rear of the house allowed under these rules is six metres (or eight metres for detached houses), with a height limit of four metres and no wider than the existing rear elevation – which in most cases should provide ample space. But before proceeding, in some cases you will first
need to write to your Local Planning Authority with a description of the proposal. They will then notify adjoining neighbours who will have 21 days to make an objection. For full details go to There are some important exceptions to these rules, so always check with your local Planning Authority at the design stage.

Building regulations

Conservatories are also exempt from the building regulations provided they meet certain criteria:

  • The internal floor area has a size limit of no more than 30m2.
  • Not less than 75% of the roof and 50% of the walls should comprise a translucent material – either glass or polycarbonate sheeting. All critical and low-level glazing should be toughened or laminated safety glazing and window sill heights should be a minimum 800mm above floor level.
  • Conservatories must be thermally separated from the main house with exterior quality doors (including patio or French doors).
  • No fixed heating system should be installed – i.e. not linked to your existing central heating system. Portable heaters are acceptable.

But even with all the above boxes ticked, there are some other areas where the building regulations could potentially still apply:

  • If the structure is built over a shared drain run (check before excavating!). N.B. you are not allowed to build over a Public Sewer – to find out if there are any Public Sewers on your property check with your local Water Authority.
  • Any new electrical circuits must comply with Part P of the building regulations, so an application will need to be made unless the work is carried out by a ‘competent person’.
  • Any structural alterations, such as a new opening from the house to the conservatory will require building regulations approval, even if the conservatory itself is an exempt building.

Conservatory design

When it comes to designing your conservatory, there are some general points to bear in mind:

  • Better quality designs have base walls of cavity masonry construction laid to normal foundation depths, upon which the superstructure is fixed – as opposed to simply being erected upon a thin concrete slab (which can lead to problems with structural movement).
  • Flues serving wall-mounted boilers are often located so they clash with the proposed conservatory. This normally means having to relocate the boiler so the flue is well clear of the building.
  • Ventilated roof ridges should be incorporated to relieve air pressure and prevent ‘wind uplift’ that can push out lightweight roof panels.
  • Try to avoid building the conservatory where it could hamper rescue by ladder in the event of fire to windows serving upper floors.

Replacement of conservatory roofs

Many conservatories are now reaching the end of their natural life or are starting to cost substantially more to heat. Homeowners are now looking for cost effective ways of
retaining their existing floor space whilst improving the energy efficiency of the conservatory. To this end they are giving consideration to replacing their existing
obsolete translucent roofs with solid ones.

Conservatories have been exempt from compliance with building regulations for many years – as long as it is a lightweight structure comprising of predominantly
glazed walls/roof and that the conservatory is thermally separated from the main dwelling.

When building work is carried out to significantly reduce the proportion of glazing or level of translucence to the roof – the conservatory can no longer be classed
as exempt from building regulations compliance.

So, if you intend to replace your existing conservatory roof with either a

  • Traditional timber roof construction with tile/slate covering immediately on top of the existing glazed conservatory frame

or a

  • Lightweight composite roof immediately on top of the existing glazed conservatory frame - a Building Regulation application must be submitted.

The main issues of awareness in your conservatory construction are:

Foundations – trial holes will need to be excavated in order to assess the existing conservatory foundations. This will be required to ensure that the foundation is
suitable to support the new roof loading.

Roof construction – structural assessment of the existing conservatory framework will need to be carried out to ensure that it is suitable to support the new roof loading –
It will be necessary to verify the type and extent of reinforcement within the existing vertical frames.

If there is no suitable reinforcement in the existing frames to support the new roof loading – then it may be necessary to install new window frames or additional
reinforcement installed abutting the existing frames.

Energy efficiency – the new roof construction should be provided with satisfactory thickness of insulation so as to comply with current building regulations.
The separating wall/doors between the conservatory and the main dwelling must always remain in position.

Please contact your Building Control team to discuss the upgrading of your conservatory roof prior to commencing building work.

You will be advised regarding the following:

  • How to submit your Building Notice application – and appropriate fee.
  • Arranging an initial site inspection from Building Control in order to discuss the project with you and your contractor.
  • Providing trial holes so that your Building Control Surveyor can assess the suitability of your existing foundations
  • Discussing and agreeing support to your proposed roof construction with your Building Control Surveyor.

Garden rooms

Where your conservatory doesn’t meet the necessary building regulations criteria, it will be classed as a home extension which will need to fully comply. This is covered in the booklet ‘Extending Your Home’, but the following points are worth noting:

  • Adding a conservatory to create a large open plan kitchen/diner can create a pleasant, bright feel. But without any dividing doors to separate it from the main house, much of your room heat will be channelled straight out to the conservatory, sending energy bills rocketing. Simple polycarbonate roofs can allow more than 15 times the amount of heat to escape than conventional tiled roofs. In summer the opposite problem can occur, as the sun heats the enclosed space to unbearable temperatures. So where there is no thermal separation from the house, new rooms must be designed so they don’t leak heat, and the design will need to meet demanding thermal efficiency requirements (Part L).
  • There are limits on the extent of glazed areas (normally equivalent to no more than 25% of the extension’s floor area + an additional area to compensate for any existing doors or windows which are covered up due to the works).
  • Some kind of heating system will be required, such as an extra radiator or new underfloor heating. It should be capable of being controlled separately from the rest of the house so it can be set to a lower temperature