Glass sides turn a louvred pergola from a shaded structure into a room you can use in poor weather. In England a glazed pergola is usually exempt from the Building Regulations — under Class 6 if it is detached and under 30m², or Class 7 if it adjoins the house — but the exemption is conditional, and heating it is what breaks it.
An open louvred pergola already does more than most people expect. Close the louvres and it sheds rain; open them and it vents heat. What it does not do is stop wind, and wind is what actually ends an English evening outdoors in April or October.
Closing the sides is what converts it. It is also the point at which a garden structure starts to meet the building control system, and the rules are more specific — and more forgiving — than most of the advice online suggests.
What does “a pergola with glass sides” actually mean?
Three different infills get called glass sides: sliding glass panels that stack away, fixed glazed screens, and zip screen blinds. They differ in whether the side can be opened, how much weather they stop, and whether they count as a wall for building control purposes.
On our aluminium louvred pergolas each side is specified separately and made to measure, so a single structure can be glazed on the windward side, screened on another and left open to the garden.
| Infill | What it stops | Opens? | Best used |
|---|---|---|---|
| Sliding glass panels | Wind and driving rain | Yes — panels stack to one side | The main outlook and the prevailing-wind side |
| Fixed glazed screen | Wind and driving rain | No | A boundary side, or where a run of glass needs no access |
| Zip screen blind | Wind, low sun, insects; sheds light rain | Yes — retracts into the beam | Shading, privacy, and sides you want to disappear |
| Louvred side panel | Low sun and overlooking | Adjustable blades | Privacy without losing airflow |
The sliding option is the one that makes the room. Our pergola takes up to five tracks and ten panels on a single side, in a choice of glass specifications, so a long elevation can be opened almost completely in summer and closed in minutes when the weather turns.
Do you need planning permission for a pergola with glass sides?
Usually no. A pergola is normally treated as an outbuilding under permitted development, which allows a maximum overall height of four metres with a dual-pitched roof, three metres for any other roof, and a maximum eaves height of 2.5 metres. Within two metres of a boundary the limit drops to 2.5 metres overall.
That last figure is the one that catches people, and it catches our own standard product. The standard pergola height is 2.7 metres. Site it within two metres of a boundary at that height and it is no longer permitted development, because the Planning Portal’s limit there is “a maximum height of 2.5 metres in the case of a building, enclosure or container”. Either pull it off the boundary, or specify it lower.
The other conditions that matter on a real garden:
- Outbuildings must not cover more than half the area of land around the original house.
- Nothing may go on land forward of a wall forming the principal elevation.
- No verandas, balconies or raised platforms — and a platform must not exceed 0.3 metres in height. A pergola over a raised deck is the common trap here.
- In a conservation area, national park, AONB, World Heritage Site or the Broads, a structure to the side of the house needs permission.
- Within the curtilage of a listed building, all outbuildings need planning permission.
Permitted development rights apply to houses, not to flats or maisonettes, and can be removed by an Article 4 Direction or a planning condition. Check before you design, not after.
When does a glazed pergola become a building under the Building Regulations?
It becomes a building the moment you enclose it, but two exemptions in Schedule 2 of the Building Regulations 2010 usually cover it. Class 6 covers detached structures up to 30m²; Class 7 covers ground-level conservatories and covered ways up to 30m² attached to the house.
If it stands alone in the garden, Class 6 exempts “a detached single storey building, having a floor area which does not exceed 30m², which contains no sleeping accommodation” and which is either no less than one metre from the boundary of its curtilage, or “constructed substantially of non-combustible material”.
That second limb is worth reading twice. An aluminium frame with glass infills is substantially non-combustible, so a glazed aluminium pergola can sit closer than a metre to the boundary and stay exempt — where a timber garden room in the same position would not. It is a genuine, and largely unremarked, advantage of the material.
If it adjoins the house, Class 7 exempts the addition at ground level of “a conservatory, porch, covered yard or covered way” where the floor area does not exceed 30m², provided the glazing satisfies the impact-safety requirements of Part K. A wall-mounted pergola with glass sides is, in building control terms, a covered yard that has become a conservatory.
What happens if you heat it?
Heating it can cost you the exemption. Approved Document L exempts a conservatory from the energy efficiency requirements only if it is at ground level, under 30m², the glazing complies with Part K, the separating wall, door or window is retained or replaced, and the dwelling’s heating system is not extended into it.
Approved Document L is explicit about the consequence: “A conservatory or porch must have thermal separation from the existing dwelling. If the thermal separation is removed or the dwelling’s heating system is extended into the conservatory or porch, the conservatory or porch should be treated as an extension.” At that point the full energy efficiency standards apply to the glazing you have just installed.
The practical reading is simple. A plug-in electric heater under the beam is a heater. Running a radiator off the house system, or taking out the back doors to open the room up, is an extension — and an uninsulated louvred roof will not pass the standards an extension has to meet. If you want the pergola to become part of the house, that is a different project, and it should be designed as one from the start.
What glass do the rules require in the sides?
Almost all of it will be impact-safe glass. Approved Document K treats glazing in doors and door side panels below 1500mm, and glazing in walls below 800mm, as critical locations. In a pergola the panels run to the ground and sit next to an opening, so in practice every pane is critical.
Requirement K4 says glazing people are likely to come into contact with must, if broken on impact, “break in a way which is unlikely to cause injury”, or resist impact without breaking, or be shielded from impact. In a critical location that is met by glass that breaks safely, glass that is robust, glazing in small panes, or permanent screen protection.
For the specification itself, Approved Document K accepts glazing that satisfies Class 3 of BS EN 12600 or Class C of BS 6206. Where a pane in a door or door side panel is wider than 900mm — which almost every sliding pergola panel is — Class 2 of BS EN 12600 or Class B of BS 6206 is accepted. Toughened glass throughout is the straightforward answer, and it is what we specify.
One thing the regulations do not require at home: manifestation. Requirement K5.2, which makes large areas of transparent glazing apparent with markings at two levels, “does not apply to dwellings”.
Will it actually be warm in January?
It will be dry, still and several degrees warmer than the garden, but it is not a heated room. A louvred roof is a single-skin aluminium deck with no insulation, so an enclosed pergola behaves like a sheltered porch: excellent in the shoulder seasons, usable in winter with local heating.
The mechanism is worth stating plainly rather than dressed up with a percentage. Enclosing the sides removes wind chill and stops driving rain, which is most of what makes an outdoor space unusable. It does not add meaningful thermal resistance overhead, and because the roof is a cold surface, warm moist air from people, food and heaters will condense on it on a cold night. Ventilation — which a louvred roof has by design — is what manages that.
So the honest positioning is this. A pergola with glass sides gives you March to November instead of June to September, plus dry winter use for an hour at a time with a heater running. If you want a room that holds a steady indoor temperature on a January morning, you want a glazed extension with slim-framed sliding doors and an insulated roof, and you should budget and design for one. Buying the wrong one of those two is the regret worth avoiding.
What to specify on day one if you want to add glass later
Glass can be retrofitted to a louvred pergola, but only if the structure, the levels and the drainage were set up for it. The decisions that are difficult to reverse are post positions, the finished floor level, water management at the perimeter and power routing.
- Post positions. Sliding panels need a clear structural opening. Our pergola spans a single bay up to 6m × 4m with no mid-post, which is what lets a whole elevation glaze cleanly; a mid-post lands in the middle of your view and your track.
- Levels and threshold. Decide early where water goes at the base of the glass. Retrofitting a threshold detail into finished paving is the expensive version of this job.
- Drainage. Enclosing the sides means the roof’s integrated gutter and in-post drainage must discharge somewhere deliberate, not onto the paving you are about to stand furniture on.
- Power. Run more than you need. A heater, lighting, a ceiling fan and a rain sensor are all far easier to cable before the sides go on.
- Access for delivery. This one is routinely forgotten. The structure arrives in plywood crates of three metres or more at over 400kg each, on an artic, kerbside, needing a forklift to unload. If your property is down a lane or behind a gate, that is a design constraint, not a delivery detail.
Where we install the glass
Across 197 orders carrying our sliding, folding or structural glazing systems, 182 had a full delivery postcode, spread across 140 distinct outward codes and placed between October 2022 and September 2026. The pergola range is new; the glass that encloses it is not.
We manufacture and install throughout the UK from the factory in Slough. These are the areas where that glazing work is densest.
Esher, Cobham, Walton and Weybridge (KT10–KT13)
Nine of our 24 orders in these four districts carry sliding or folding glass. The work here is largely for developers and architects rather than retrofit homeowners, because the private estates — St George’s Hill, Burwood Park, Oatlands, the Fairmile — run a continuous rebuild cycle on large plots. We are used to estate hours-of-restriction, gate protocols and vehicle access rules, which matters more than any specification when a 40-tonne delivery is involved.
Wimbledon (SW19)
Five of 15 orders here are glazing systems. The stock is Victorian and Edwardian villas under Merton’s conservation control, and the dominant project shape is the side-return or rear extension — exactly where slim-framed sliding glass goes, and exactly the garden geometry a wall-mounted pergola suits.
East Finchley, Finchley and Whetstone (N2, N3, N20)
Five of 31 orders across the Barnet belt carry glazing systems. The inter-war and Edwardian family houses here have the deep rear gardens that make a detached garden structure worth doing. One local point that is easy to miss: in N2, Hampstead Garden Suburb Trust consent is statutory and separate from council planning, so a garden building there needs both.
Hove (BN3)
Three of ten orders. Regency and Victorian seafront stock, with the Brunswick Town conservation area on the front and the Tongdean avenues inland. Exposure is the design driver on the coast — this is where the glazed windward side earns its keep.
Windsor and Maidenhead (SL4, SL6)
Forty orders across these two districts, two of them glazing systems. The factory is ten minutes away, which shortens survey-to-fit and makes a site visit trivial. Worth knowing locally: RBWM applies unusual heritage rigour near the Castle, so planning specificity is repaid here.
Sources
- The Building Regulations 2010, Schedule 2 — Exempt Buildings and Work (Classes 6 and 7)
- Approved Document K, 2013 edition — Section 5 and Diagram 5.1, critical glazing locations
- Approved Document L, Volume 1: Dwellings (2021 edition incorporating 2023 amendments) — paragraphs 0.14 and 10.12
- Planning Portal — Outbuildings
Related reading: slimline bi-folding doors for elevations where the whole opening needs to disappear, and our louvred aluminium pergola range for the structure itself.
Planning a pergola you can actually use in April
Send us your drawings or a photograph of the garden and we will tell you which exemption route your structure falls under, what the sides need to be, and what to run before the paving goes down. We manufacture in Slough and install nationwide.
