Replacing your conservatory with a real extension for year round living

You may have noticed it over the past few weeks: as the evenings turn cool, the conservatory empties out and the door to the living room stays shut. Many conservatories built in the 1980s and 90s have become wasted space. Autumn is a good time to think about replacing them with a real extension, with building work starting in spring.

Why so many conservatories have become uncomfortable

At the time, the conservatory was a quick and inexpensive way to gain extra space. Thirty or forty years on, its drawbacks are well known:

• aluminium frames without thermal break, single glazing or old double glazing;
• a polycarbonate or glass roof that lets heat escape in winter and lets it in during summer;
• a slab laid directly on the ground, without insulation, often cold and sometimes damp;
• condensation on the glazing, worn seals, small roof leaks;
• a poor connection to the house, with the old rear facade left in place, cutting the conservatory off from the living room.

The result is a pleasant room for a few weeks a year, in spring and early autumn. The rest of the time it serves as a storage room or drying space.

Conservatory or extension, the difference lies in the regulations

Replacing a conservatory with an extension is not simply a matter of using different materials. It means changing building category, and that has consequences.

In Wallonia, the CoDT (town planning code) provides for a planning permission exemption for conservatories, under precise conditions. The regional planning administration sets these out in its classification table for article R.IV.1-1: the structure must be at least 2.00 m from the boundary line, the maximum floor area is 40.00 m², and the volume must remain single storey, with a flat roof or a roof with one or more slopes.

An extension with solid walls, an insulated roof and proper heating is a different matter. As soon as you create a heated, habitable room connected to the house, planning permission and the involvement of an architect are in principle required. The exemptions only cover specific cases, such as conservatories or certain non habitable ancillary structures of up to 40 m².

On the energy side, there is one point to keep in mind. The SPW Énergie (Walloon energy authority) points this out in its EPB (PEB) FAQ: the EPB procedure only applies to works subject to planning permission. However, the EPB requirements apply to all works, even those not subject to permission. Depending on the scale of the project relative to the existing house, this is referred to as simple renovation or major renovation. The EPB decree of 28 November 2013 defines major renovation as works affecting a surface area greater than 25% of the existing building envelope. In that case, an EPB assessor becomes involved.

In Brussels, the framework is stricter. Homegrade cites extensions or conservatories among the examples of renovation works that require an architect. You also need to comply with the Regional Planning Regulations (RRU/GSV) and any municipal regulations.

In both regions, have your situation confirmed by your local planning department before starting work.

What the architect changes in the project

Replacing a conservatory with an extension is not simply a matter of putting up walls where there used to be glass. It means designing a room that keeps what you loved about the conservatory, the light and the connection to the garden, without its drawbacks.

• Light, in the right place. A large window facing the garden, a roof light above the table, a low window for a reading corner. The aim is quality of light rather than quantity of glazing.
• Solar protection built in from the design stage. A properly sized roof overhang on the south side or sun shading on the west side prevents the July heat, without air conditioning.
• The volume. A flat roof, possibly a green roof, or a pitched roof, with a generous ceiling height. Careful attention is also needed for the junction with the upstairs windows and the existing roof.
• The opening to the house. In most cases the old rear facade is opened up widely, so the extension truly becomes an extension of the living room or kitchen. This requires a structural stability calculation, carried out with engineering firm Optibim.
• The materials. A brick in a shade close to the existing facade, timber, a bluestone threshold: the extension should look as though it has always been there.
• Comfort. An insulated floor, heating connected to or extended from the existing system, suitable ventilation, and rainwater management for the new roof.

The typical process for a single storey extension at STARC

Here is how we generally run this type of project, from the first meeting to completion.

1. Visit and listening. We look at how you currently use the house: where you eat, where the children play, what is missing. The conservatory often reveals a broader need, such as a kitchen that is too small or a living room cut off from the garden.
2. Precise survey. A 3D scan survey (BimBot) provides the levels, wall thicknesses and window heights. This avoids unpleasant surprises at the junction.
3. Sketches and budget. We compare several options for layout and roof shape, with an initial estimate for each. This is the moment to decide between an extension on the conservatory footprint or a slightly larger volume.
4. Permission and EPB. We prepare the planning permission file, with the energy aspects coordinated with Optibim where needed.
5. Construction. Dismantling the conservatory, new foundations, shell and core, roof, joinery, then opening up the existing wall at the most suitable time to limit disruption inside the house.

Allow several months between the first meeting and the start of construction, mainly because of the permission process. Starting the design in autumn makes it possible to aim for building work in spring or early summer.

Pitfalls to avoid

• Keeping the old slab without checking it. It is usually neither insulated nor designed to support masonry walls.
• Underestimating the junction with the house. Floor levels, the height of upstairs windows and the waterproofing at the base of the existing wall all require careful attention.
• Using too much glass again. A south or west facing window wall without protection recreates the problems of the conservatory.
• Forgetting the neighbours. Distances to boundaries, party walls and the rules on sight lines under the Civil Code need to be checked from the sketch stage onwards.
• Building without checking the rules. A habitable extension built without planning permission can cause serious problems when selling the house later.

Let's talk about your conservatory

Is your conservatory only used for a few weeks a year, and would you like to know what it could become? The STARC team can visit your home, explain the steps required in your municipality and sketch out a first idea with you. Contact our Gembloux office to arrange a visit, ideally this autumn if you are aiming for building work in spring.