A conservatory was designed around a light roof. Twin-wall polycarbonate or sealed glass units sit on thin glazing bars, and the whole structure was sized for that modest load. A solid roof, with rafters, insulation, battens, tiles and a plastered ceiling underneath, is a different thing altogether, and the frame and base beneath it may never have been asked to carry anything like it. Before anyone talks about tile colour, the first question is structural: can this particular conservatory take the extra weight? This page covers the parts that carry the load, the checks that building control makes, and the choices open to you when a conservatory turns out to be too slight. For the wider picture of replacing these roofs, start with our conservatory roof replacement in Basingstoke page.
Why a solid roof asks so much more of the structure
Every roof puts weight on the walls and frame below it, but the sum is very different for a light roof and a solid one. Glass and polycarbonate are thin sheets held in an aluminium or uPVC glazing bar. A solid roof is built up in layers: structural timbers or steel, insulation between and over them, a waterproof underlay, battens, the covering itself, and then plasterboard or a lining on the underside. Each layer is modest on its own. Together they add up to a dead load (the permanent weight of the roof) that is several times what the original roof imposed.
There is also the live load, meaning what the roof must resist from outside: wind pressing down or lifting, and snow in a hard winter. A heavier roof is more stable against uplift, which sounds like good news, but the same weight pushes down through every post, plate and footing it touches. If any link in that chain is marginal, the movement shows up later as cracked plaster, sticking doors, a bowed eaves beam or gaps opening at the house wall.
That is why the rule is built the way it is. In practice that means a solid roof goes through a Building Regulations application, so that an independent inspector confirms the structure copes with the added weight. The weight of the covering you pick matters a great deal, and our note on how much a tiled conservatory roof weighs sets out how the layers compare. Any re-roofing that adds 15% or more to the weight of what was there before also needs approval, with strengthening where the structure falls short.
The frame: what is holding the roof up
Most conservatories built in the last few decades have a uPVC frame, though aluminium and hardwood versions are common too. What looks like a solid white frame is usually a hollow plastic profile wrapped around a steel or aluminium core, and sometimes it has no core at all. The windows between the posts carry no roof load whatever. The weight travels down the posts, which are the thicker vertical members at the corners and at intervals along the walls, and through the eaves beam, the horizontal member running along the top of the glazing.
The eaves beam is often where a standard conservatory runs out of capacity. It was sized to span between posts under a light roof. Under a heavy one it can sag in the middle over time, and a sagging beam pushes down on the window units beneath until they bind or crack. On the survey we sight along the beam, check the spans, and look at the joints at each post for signs of movement, such as hairline gaps, stained mastic or windows that no longer close squarely.
Many solid-roof conversions get around a weak frame by adding a new structure on top of the old one. A new steel or timber ring beam sits over the existing frame and carries the new rafters, taking the weight down through discreet posts or through the corners, so the existing frame is relieved of the work. Sometimes the new roof is designed to rest wholly on the house wall at one side and on strengthened posts at the other. Which approach fits depends on the frame, and the engineer's calculation decides it. We do not guess at this and we do not work from a catalogue photo.
The base: dwarf walls and foundations
Under a conservatory frame there is usually a low brick wall, called a dwarf wall, sitting on a concrete footing in the ground. These were often built to a different standard from the house, since the conservatory was not expected to carry much. Depth, width and the quality of the concrete all vary, and on older builds the footing may be shallow.
The ground itself is part of the question. On clay soils, which shrink in dry summers and swell in wet winters, shallow footings move, especially near trees and large shrubs whose roots draw water out of the soil. A conservatory that has already moved a little under a light roof will move further under a heavy one. In other places the ground is firmer and the footings sit happily for years. Either way, a conservatory's base needs looking at, not assuming.
Building control will want to see evidence about the foundations, and the usual way to get it is a trial pit, a small hole dug beside the base to expose the footing so its depth and width can be measured and photographed. If the footing proves too shallow or too narrow, the fix is underpinning in short sections or new pad foundations under the posts, so the load goes down to ground that can take it. The results of that digging decide whether the project goes ahead as a roof swap or turns into something bigger.
The house wall and the junction
A lean-to or Victorian-style conservatory leans on the house along one side, and the junction with the wall deserves attention of its own. The new roof's rafters either rest on a timber wall plate fixed to the house wall or hang from it, so the house wall takes part of the weight. That is fine if the wall is sound masonry in good order. It is a problem if the wall above has been weakened by a large opening, if the brick is soft, or if the fixings would sit in a cavity that cannot hold them.
Alongside the fixings, there is the waterproofing. The roof must be sealed to the house wall with a flashing (a strip of lead or membrane lapped over the roof covering and tucked into a cut in the brickwork) so that rain cannot run behind it. We look for the original flashing and for a damp-proof course, the layer meant to stop moisture rising or tracking sideways. Any leaks at the wall are better spotted now than after the new roof is on. Our guide to leaking conservatory roofs shows what these junction faults look like.
Finally, check what is above the conservatory on the house side. An upstairs window sill or a first-floor bedroom wall can limit how high the new roof can rise, and that affects the pitch and the covering you can use. Some solid roofs have to be set at a low pitch to clear a window, which rules out some tiles.
What building control actually checks
A solid roof is notifiable work, so an application goes to a building control body. That is either your council's building control team or a private registered building control approver, the title private inspectors have held since April 2024. Which route you take is your choice, and we deal with the paperwork on our side where the work is notifiable.
What the inspector wants to see falls into a few areas:
| Area | What is examined | Evidence usually offered |
|---|---|---|
| Foundations | Depth, width and condition of the footing under each wall and post | Trial pit photographs and measurements |
| Frame | Posts, eaves beam and joints under the new, heavier load | Engineer's calculation or a system supplier's design |
| House wall | Fixing of the wall plate and sound masonry above the junction | Survey notes and the fixing detail |
| Insulation | Thermal performance of the new roof as part of the building | Roof build-up drawing and product data |
| Waterproofing | Flashings, ventilation and the roof's weathering detail | Drawn details and inspection on site |
Some solid conservatory roof systems carry a registered or assured status through the Local Authority Building Control (LABC) scheme. Having an LABC Registered or Assured system speeds the approval, since the design has already been checked, but it does not remove the need for the application. The inspector still has to be satisfied about your frame and your foundations, and those are particular to your house. Our guide to conservatory roofs and Building Regulations goes through the process step by step.
If your conservatory cannot take it
A frame or base that cannot carry a standard solid roof is not the end of the idea. There are four honest routes, and which one is right depends on the survey.
The first is a lightweight system. Several manufacturers make solid conservatory roofs built from lightweight panels with a tile-effect or slate-effect surface, designed to put far less load on an existing frame than a conventional cut-timber roof. They suit older and slighter conservatories. Our explainer on lightweight tiled roof systems describes how they are built and where they stop being appropriate.
The second is to strengthen first and roof second. Adding steelwork, new posts or new footings can make a doubtful conservatory suitable. That adds cost and complexity, so you have to weigh it against the value of what you are keeping.
The third is to improve the roof you have without making it solid. Higher-performance glass with a solar-control coating and good blinds can transform a conservatory's comfort with almost no structural change. If your complaint is overheating or noise rather than appearance, this may cost less and avoid the structural question entirely. Panels fitted into a polycarbonate roof are another route, though they bring condensation questions of their own.
The fourth, for a conservatory in poor condition, is to accept that the building has reached the end of its useful life and plan a proper extension with its own foundations and walls. That is a bigger job and a bigger budget, but it removes every compromise. We will tell you if a survey points that way, rather than let you spend on a roof the building cannot support.
What the survey involves and what it costs
Our free survey takes in the whole conservatory. We look at the frame, base, junctions, existing roof and the ground around it, and photograph what we find so you can see your own conservatory rather than a generic drawing. If the findings call for an engineer or a trial pit, we tell you before you commit.
As an orientation figure, solid tiled conservatory roofs typically cost between £6,100 and £15,000 across the UK, which works out at roughly £650 to £1,200 per m². That range comes from a national cost calculator, not from us, and it does not include remedial structural work, so your fixed quote follows the survey. The structural findings are one of the main reasons that two apparently similar conservatories can end up at opposite ends of that range. Our conservatory roof replacement cost guide covers the other price drivers.
Whatever the survey shows, you get a written report and a fixed written quote. If a repair or a lighter option does the job, we say so plainly. Once the new roof is on, the workmanship is guaranteed for ten years in a written document, and the garden is left tidy with every offcut gone. Our number is 01256 213956, and a WhatsApp message reaches us just as well.
