Install a conservatory or bioclimatic pergola

Extending the house out into the garden without pushing the walls is exactly what a conservatory and a bioclimatic pergola offer. Two close cousins but profoundly different: one creates a genuine extra heated and enclosed room, the other a flexible covered terrace, open or shaded on demand thanks to its adjustable louvres. Choosing between the two depends on use (living in it all year round or only on fine days), on budget (one to four times more) and on the planning framework (Lawful Development Certificate or Planning Permission depending on the area, or in France: declaration prealable / permis de construire). This guide details the two solutions side by side: structure, planning, foundations, weatherproofing, motorisation and installation steps, to nail your outdoor extension as a self-builder without falling into the local urban planning code (PLU) trap or facing a leak three years later.

Conservatory or bioclimatic pergola: what you really want

Before comparing prices or profiles, you need to clarify the use. The two solutions answer completely different needs, and the choice takes 30 seconds once the question is asked correctly.

Simple rule: conservatory if you want an extra heated room, bioclimatic pergola if you want a flexible covered terrace. And if you hesitate, the pergola almost always wins on cost / enjoyment ratio.

The bioclimatic pergola: structure and operation

A bioclimatic pergola is an outdoor aluminium shelter whose roof is made of motorised adjustable louvres. In a few seconds, it switches from full shade (closed louvres) to maximum opening to the sky (louvres at 90 degrees), with all intermediate positions to regulate light, ventilation and heat. It is the modern evolution of the wooden pergola or gazebo, with the added bonus of weatherproofing when the louvres are closed.

Adjustable louvres: the heart of the system

The louvres are extruded aluminium profiles (12 to 18 cm wide, 200 to 600 cm long depending on span), connected to each other by a synchronised mechanism that orients them all together via a tubular motor housed in a crossbeam. Three main families coexist.

• Centre-pivot louvres: rotate around their centre. Good weatherproofing with EPDM side seals. Rotation generally 0 to 135 degrees.
• Off-centre pivot louvres: rotate towards one end. Optimised water drainage as the closed louvre overlaps the next with more pitch.
• Sliding-pivoting louvres (premium bioclimatic): can both pivot and slide on a rail, opening 100% of the roof like a classic pergola in addition to orientation.

Wall-mounted or freestanding

Two configurations dominate the market:

• Wall-mounted to the house: one side is fixed to the facade wall by a header beam anchored with chemical anchor plates. The most economical and stable solution.
• Freestanding (island): 4 independent posts, to be installed in the middle of the garden or by the pool. More expensive (more material plus extra foundations) but allows free positioning.

Wall-mounting brings two constraints: the orientation is dictated by the facade, and the rainwater drainage must be controlled to avoid flooding the wall (see below).

Common dimensions and span limits

Beyond 4 m of free span, the crossbeam becomes load-bearing and its inertia increases: 200 mm deep sections, sometimes profiled box beams. This is also the limit at which the storm warranty drops a class.

Options that change everything

• Vertical ZIP side blinds integrated: close the sides against wind, low-angle sun and insects. Best specified at order (provision built into the profile).
• LED lighting in the louvres: evening ambience, no extra installation cost.
• Rain / wind sensor: closes the louvres automatically at the first drop, opens them to 90 degrees as soon as wind exceeds 80 km/h to avoid acting as a sail.
• Suspended infrared heater: to wire on a dedicated circuit, extends use into the shoulder seasons.
• Home automation (Somfy IO, Bubendorff): smartphone control, automatic scenarios.

The conservatory: heated extension or amenity room

A conservatory is a genuine extension to the house: insulated floor, load-bearing structure, high-performance glazing, watertight roof, heating and electrical connections. It increases the habitable area (SHAB in France), hence the value of the house, but also the procedures and the cost.

Three families of structure

• Aluminium: the reference for new builds for 25 years. Slim profiles (50 to 80 mm), 50-year durability, no maintenance. Correct thermal performance with thermal break (RPT). Anthracite grey (RAL 7016) or white profiles.
• Timber (glulam): warm aesthetic, excellent native thermal insulation, but heavy maintenance (stain every 4-5 years, weatherproofing check every year). Best in zones protected by Bâtiments de France (ABF) heritage architects.
• Mixed alu/timber: aluminium on the exterior (zero maintenance), timber on the interior (visual warmth). Premium solution, high price.
• Steel or wrought iron: Victorian “winter garden” style. Bespoke build, very high price, rare expertise.

Roof: glazed, opaque or sandwich panel

The roof determines summer use of the conservatory:

Whatever the choice, plan for a minimum roof pitch of 7 to 15 degrees to drain water properly. Below 7 degrees, standing water degrades the seals within 5 years.

RE2020 and RT existant compliance

This is the trap that 80% of self-builders forget.

• Heated conservatory > 5 m² integrated into an existing building: subject to RT existant (decree of 22 March 2017). In practice, the glazing must be Uw <= 1.8 and the roof Up <= 2.0.
• New conservatory > 30 m² or thermally inseparable from the dwelling: subject to RE2020. Full thermal study, mandatory insulation level on the entire envelope.
• Unheated conservatory (buffer space, known as a “cold conservatory”): outside thermal scope but still subject to declaration or planning permission depending on the area.

For overall envelope compliance and RE2020 obligations, see our guide understanding RE2020 in self-build.

Regulations and planning

Both conservatories and bioclimatic pergolas are constructions within the meaning of the planning code. Neither is “free”: at minimum a declaration prealable (DP) must be filed.

Floor area and declaration

A wall-mounted bioclimatic pergola is almost always subject to DP minimum (roof created, hence ground footprint). A pergola on pads under 5 m² may slip through, but check the local regulation.

PLU, distance and height

The local PLU also sets:

• the minimum distance to boundary lines (often 3 m, sometimes 0 if construction at boundary is permitted)
• the maximum height (often 3.5 to 4 m to ridge for outbuildings)
• the permitted materials and colours (tiles, stone tone, RAL imposed in protected zones)
• the remaining ground footprint coefficient to respect

Before any application, request an operational planning certificate (CUb): it freezes the rules applicable to your plot for 18 months. See our guide understanding the PLU and how to consult it and planning permission vs declaration prealable.

Bâtiments de France heritage architect

In a safeguarded sector, near a historic monument, AVAP / SPR or classified site, the opinion of the Bâtiments de France (ABF) heritage architect is mandatory and processing time extends to 5 months. In these zones, plan for: profiles in imposed RAL (often dark grey or stone tone), restricted dimensions, sometimes a ban on adjustable louvres visible from the street.

Foundations: where the pergola beats the conservatory

This is the technical difference that explains the gap in cost and time.

Conservatory foundations

A conservatory is a heavy construction (300 to 800 kg / m² of roof + structure + glazing) with an insulated floor at the same level as the house. Three solutions:

1. Reinforced concrete perimeter ground beams on strip footings: the standard solution, HA10/12 reinforcement, 30 to 40 cm deep, descent to the frost line (80 cm in lowlands, 100 cm in mountain areas). See calculating and pouring foundations.
2. Floating concrete slab with perimeter beam: faster, compliant on stable soils.
3. Helical screw pile foundations: modern kit, descent in 2 hours, no concrete. Interesting solution for self-build, to be validated by a structural engineer.

In all cases: G2 soil study recommended on clay soils or sloped ground, and strict respect of the frost line depth (a frozen post lifts 1 cm each winter and cracks the conservatory in 3 years).

Bioclimatic pergola foundations

Much simpler because the structure is 3 to 5 times lighter:

• Individual concrete pads under each post: common dimensions 40 x 40 x 40 cm with anchored M16 threaded rod or base plate bolted flat onto slab. Concrete dosed at 350 kg/m³, light reinforcement (4 HA8 + HA6 stirrups).
• Base plates screwed onto existing concrete slab: if the terrace is already poured and at least 12 cm thick correctly reinforced, use chemical anchor M12 or M16 without redoing a pad.
• Screw piles: clean and reversible option if you want to avoid damaging a finished surface.

Pad depth: 60 to 80 cm below natural ground level to reach the frost line. The wall-mounted header beam is anchored with M12 chemical anchors into the facade wall (never anchor into a single block, always into a ringbeam or slab edge).

Installing a wall-mounted bioclimatic pergola: step by step

Allow 2 days with 2 people for a 4 x 4 m wall-mounted pergola. Operation order:

1. Set out and prepare

• Mark the post positions on the ground (usually 2 or 4 depending on the module): perfect squareness using the 3-4-5 method
• Mark the header beam position on the facade with a laser, perfectly level, at the defined height (often 2.40 to 2.60 m finished under closed louvre to allow head clearance with arms raised)
• Check the height under existing eaves: the pergola stops 5 cm below the gutter to avoid breaking it

2. Pour the concrete pads

• Dig down to frost line depth (60-80 cm)
• Form a 40 x 40 cm pad with light reinforcement
• Pour the concrete and embed the M16 threaded rod or anchor cage in the centre, perfectly vertical
• Allow 7 full days to cure before erecting the structure

3. Fix the header beam to the facade

• Mark with a laser, drill the masonry with an SDS hammer drill
• Chemical anchor (two-component epoxy resin) with M12 stainless rod every 50 to 70 cm
• Check that the fixing bears on a structural element (top ringbeam, edge slab) and not on a single block or cladding facing
• Compressible EPDM tape between header beam and facade for air and driving rain seal
• Bolt the header beam, check level, torque-tighten

4. Erect the posts and bottom crossbeams

• Position the posts on their base plates, fix with flanged nuts (manufacturers usually supply adjustable base plates with 20 mm of adjustment to make up the level)
• Check plumb with laser or plumb bob on 2 axes
• Screw the bottom crossbeam opposite the facade (garden side) between the two posts
• Check diagonal squareness (same measurements on both diagonals to within 5 mm)

5. Install the louvres

• Position each louvre in its housings at both ends
• Engage the synchronisation mechanism (linkage rods or rack depending on manufacturer)
• Check that all the louvres move together when you actuate one louvre manually
• Insert the tubular motor in the header beam, connect to the mechanism

6. Rainwater drainage

This is the most critical point. Closed louvres turn the pergola into a watertight roof: 800 to 1,500 L of water can run off in 10 minutes during heavy storms.

• The crossbeams are themselves integrated gutters (gutters profiled into the aluminium)
• Water descends through the hollow posts which act as downpipes
• Outlet at the post foot: mandatory connection to the stormwater network by PVC pipe O50 or O63
• Without connection: plan a soakaway chamber or infiltration into a drainage trench (but never run-off onto the house slab)

7. Electrical connection and finishes

• Run a dedicated 230 V circuit from the consumer unit (3G1.5 or 3G2.5 depending on length, protected by 10 A MCB + 30 mA RCD)
• Connect motor, sensors and LED lighting in the integrated junction box
• Programme the remote or home automation hub
• Test all louvre positions, the rain sensor, the wind safety stop

8. ZIP side blinds (option)

• Screw the cassettes onto the posts and the header beam
• Insert the fabrics into the ZIP rails, unroll manually the first time
• Connect the motors to the same bus as the pergola

Installing a conservatory: overview

Self-build conservatory installation takes 5 to 15 days depending on dimensions and structure, and demands broader skills than a pergola: masonry, aluminium joinery, electrics, possibly plumbing. Overview:

1. Permission obtained (and clear of third-party appeal, i.e. 2 months after posting)
2. Earthworks and foundations: excavation, perimeter reinforced concrete ground beams (frost line depth), services routed under slab (supply, drainage, earth)
3. Insulated slab: polythene, 80 mm XPS insulation, mesh, 12 cm reinforced concrete slab. See pouring a concrete slab
4. Plinth wall (sometimes 20 cm block over 50-80 cm height) or direct start of the aluminium frame
5. Aluminium structure assembly by modules: posts, crossbeams, trusses, rafters
6. Glazing installation (laminated glass for vertical modules, laminated roof glazing + safety against ice fall)
7. Perimeter weatherproofing (compriband, EPDM, SP1 sealant) at the facade junction
8. Roof covering (roof panels or roof glazing) with perimeter gutter connected to stormwater
9. Electrics (sockets, lighting), heating (electric radiator, underfloor heating or connection to existing circuit)
10. Interior finishes (floor, skirting, paint)

The facade junction weatherproofing is the most-failed item: plan for an aluminium or EPDM flashing under cladding or render, with drip edge projecting 4 cm and compriband under the header beam.

2026 costs: pergola vs conservatory

Installed bioclimatic pergola

Self-build saving: 30 to 45% of contractor-installed price, i.e. EUR 2,000 to 8,000 depending on dimensions.

Installed conservatory

Conservatory self-build saving: 25 to 35% of contractor-installed price, but with a real insurance risk. The manufacturer’s ten-year warranty only covers manufacturing defects, never the installation if done by the self-builder.

Common mistakes to avoid

Decision tree: conservatory or bioclimatic pergola?

Standards and resources

• DTU 39: glazing, mirror work (conservatory glazing)
• DTU 36.5: installation of external windows and doors (conservatory junction)
• Eurocode 1 (NF EN 1991): actions on structures (climatic loads on pergola)
• NF EN 13561: performance of external blinds (ZIP fabric)
• Decree of 22 March 2017: RT existant for extensions and storey additions
• Planning code articles R421-9 and R421-14: DP / PC thresholds
• Service Public: declaration prealable de travaux
• AnIL: planning and works information
• Géoportail de l’urbanisme to consult the PLU
• Biossun: bioclimatic pergolas (leading French manufacturer)
• Renson: Camargue / Algarve pergolas
• Akena Vérandas (conservatory kit)
• Vie & Véranda

Checklist: before ordering

Further reading

• Before planning permission, validate your file with understanding the PLU and planning and planning permission vs declaration prealable
• For foundations: pouring foundations yourself and pouring a concrete slab
• For connection to the house: installing a sliding patio door (conservatory / lounge opening) and fitting a front door
• For overall performance: understanding RE2020 in self-build and choosing your glazing single, double, triple or low-E
• For summer thermal comfort: installing electric roller shutters