A conservatory was designed around the roof it had on the day it was built. If that roof was polycarbonate sheet, the frame, the low walls and the foundations were sized for a light covering and for little else. Swap it for a tiled or insulated solid roof and you ask every part below to carry more, so the sensible order is to check first and choose afterwards. This page sets out what is checked and why: the frame that holds the roof up, the walls it bears on, the foundations under them and the point where the conservatory meets the house. It also covers who signs the result off, and what the realistic options are if a part comes up short. We look at the room from the roof down, and we take pictures of what we find so you can see it for yourself. The pricing and the choice between roof types are covered on other pages. Here the question is narrower: will this structure take a heavier roof, and how do we know?
Why a heavier roof changes the question
The covering is the first number to look at. A polycarbonate roof is very light. A tiled conservatory roof, with rafters, insulation, plasterboard and tiles, is a different kind of structure altogether, and even the lighter solid systems add a good deal more than sheet plastic does. For a sense of scale, one reconstituted Cotswold-style stone slate from Bradstone is quoted at about 84 kg/m² once laid, and that is the covering alone, before the timber, insulation and ceiling beneath it.
The rules treat weight as a trigger. Per the Planning Portal, building control approval is required when the new covering is at least 15 per cent heavier than the old. Swapping light sheet for tiles can leave that threshold far behind, and Homebuilding & Renovating treats a solid replacement as material alteration work: you will have to submit a building control application. Approved Document A, the part of the Regulations that deals with structure, is what building control looks at when it assesses the load.
That is the paperwork. The physical reason is simpler. Load follows a path. It travels from the covering into the rafters, along to the ridge and the eaves, down through the frame or the walls, and into the ground. Every link in that chain has to take the extra weight, and the chain is only as strong as the weakest link. A new roof laid onto a frame that was never meant for it can bow the eaves, push the walls outward or settle the footings unevenly. The cracks show up months later, and the leaks that follow are blamed on the roof when the real cause lies lower down.
So we do not start from the roof you want. We start from what is there, and we ask how much more it can take. If you are still weighing up covering types, our guide to conservatory roof options sets them side by side, and this page is the check that sits behind whichever you choose.
The frame: what holds the roof up
Most conservatory frames are uPVC, aluminium or timber, and each has a different story. The frame carries the roof at its edges: the eaves beam along the front and sides, the glazing bars that run up to the ridge, and the corner posts and mullions that bring the load down. In many conservatories these members are slender, because they were only ever meant to carry sheet and glass.
What we look at
We start with the obvious. Are the corners square? Are the eaves level, or has the front dipped? Do the roof bars sit straight, or have they twisted? A frame that has already moved is showing you its limits before any extra weight goes on. We then check the joints and fixings, looking for gaps at the corners, split or stained sealant, and fixings that have loosened.
Timber frames are checked for rot and softening, especially at the base of posts, in the cill and under the glazing beads, where water sits. Aluminium is checked for corrosion at the joints. For uPVC frames the question is whether the frame has steel or aluminium reinforcement inside it. Plastic alone is not a structural material in the way that steel or sound timber is. The cavities in the frame are often hidden, so where we cannot tell, we record that and recommend opening a section or asking the manufacturer or an engineer.
Reinforcing the frame
If the frame is sound but light, there are ways to strengthen it. A steel or timber eaves beam, a new wall plate, or posts that pick up the load more directly can all be added. These are details for the written specification, and building control will expect to see them described. Where the existing frame is poor, the cleaner answer may be to replace it, because the cost of reinforcing a tired frame can approach the cost of a new one. We cover that decision in more depth on our page about modern glass roofs, which are lighter than a tiled roof and may suit a frame that cannot be upgraded.
The walls the roof bears on
Many conservatories sit on low walls, usually called dwarf walls, with the frame above them. These walls carry the frame and, through it, the roof. They are usually brick or block, sometimes faced in stone, and they were built to hold up a light frame. We check them for cracks, for bulges and for signs that the top of the wall has moved relative to the frame.
The wall plate is the next thing. This is the timber or steel that spreads the roof load along the top of a wall instead of dropping it in a few places. A heavy roof wants a continuous bearing, so we look at whether one exists, whether it is level and whether it is fixed down. Where it is missing, it can usually be added during the roof job, provided the wall under it is sound.
Cracks need reading rather than just spotting. A thin vertical crack at a corner may be old shrinkage that has stopped. A diagonal or stepped crack, wider at the top than the bottom, can point to movement in the ground. A horizontal crack along a mortar course suggests the wall is being pushed outward. The width matters less than whether it is changing, so we note where cracks are and ask how long they have been there. If they have been there a long time and look dormant, the wall may be fine. If they are new, the cause comes first and the roof second.
The join to the house
The conservatory roof meets the house wall at its high end, and that junction is both a structural point and a weather point. Rafters or roof bars either bear on the wall or are fixed to it. On top of that line sits the flashing, lead (or a similar metal) shaped over the joint to throw rain clear. In an older Bath house, the wall may be stone laid in lime mortar, and a fixing that cuts into it needs care. Where the new roof will be fixed, we inspect the stone and mortar, since a loose or crumbling joint is a poor place to hang a heavier roof. Our guide to a leaking conservatory roof explains why this junction is among the first places water gets in.
Foundations: the part you cannot see
Foundations are where a conservatory most often differs from a house. A house is built on footings dug to a depth chosen for the ground and designed for walls that are heavy from the start. A conservatory is sometimes built on shallower footings, because its walls and roof were light. Every case differs, and looking is the only reliable test.
We begin with the evidence above ground. Stepped cracks that start at the base of a wall, doors and windows that stick, a gap opening between the conservatory and the house, or a floor that has dropped away from the walls can all suggest movement. We then look at the surroundings. A large tree close by can draw moisture from clay soil and let it shrink, and drains running under the structure can leak and wash soil away. These are common causes of movement, though whether they apply to your plot is a matter for the survey, not a rule.
Where the signs are unclear, the next step is to expose the foundation. A small trial hole beside the base of a wall shows how deep the footing goes, what it is made of and what the soil is like beneath. This is a routine step, quick for a builder to dig and well worth doing before committing to a heavy roof. The result goes into the engineer's note if one is needed, and it is also useful to you as a record.
A foundation does not need to be perfect. What matters is that it is adequate for the load it will carry, and stable. A footing that has carried a conservatory without movement for many years, and shows no sign of distress, is a good sign. Even so, it was sized for the old roof. If the new one is heavier, the engineer may accept the existing footing, ask for a modest extension to it or advise that a lighter roof is the better fit. We would rather tell you that before the work than after it.
Who signs it off
Checking a structure is one thing and approving it is another. For a solid roof, the approval has two parts: the design, and the building control application that goes with it.
Where the frame, walls or footings are in doubt, we recommend a structural engineer. The engineer looks at the survey findings, works out the loads and produces a calculation and a sketch of any strengthening. That document is what building control will read. It also protects you, because it ties the roof to the structure beneath in writing.
The application itself goes to building control. In Bath that is B&NES Building Control, the council's own service, or, as the private alternative, a registered building control approver. Either route can approve the work. Which you choose is a practical question of fees and availability, and we are happy to explain how each works. If the job is notifiable, the Regulations paperwork is ours to handle, so you are not left guessing which forms apply. Planning is separate, and a listed or conservation setting adds its own consent, which our page on conservatories on listed and conservation homes covers.
Order matters. The survey comes first, then the engineer's note if one is needed, then the application, and only then the roof. Ordering materials before approval is the most common way to end up with a roof you cannot fit.
Approved Document A is the document building control uses, and it does not take a single fixed view of every conservatory. Each roof is judged on its own structure, which is why a general answer from a website, including this one, cannot replace the check on your own building.
If a check fails
A failed check is information, not a dead end. There are usually several ways forward, and they trade cost against appearance and against how much of the old structure you keep.
- Strengthen and proceed. Add a steel or timber beam, a wall plate or an extension to a footing, then fit the solid roof you wanted. This costs more up front and gives you the roof as planned.
- Choose a lighter covering. A lightweight solid system or a glass roof can sit within the capacity of a structure that cannot take tiles. You lose some of the character of a tiled roof, and keep the structure you have.
- Rebuild the weak part. If one wall or a section of frame is the problem, replacing that section may be better than reinforcing it.
- Repair now, decide later. If the roof is leaking and the structure needs more thought, we can make the room watertight while you decide.
Typical UK conservatory roof replacement prices are typically £2,000 to £10,000 or more, averaging about £4,500, according to MyBuilder's conservatory roof cost guide (2026). Frame and foundation upgrades are among the factors that move a figure within that range. After the visit, the fixed quote names any structural work as its own line, so no surprise appears later.
Whichever route you take, the structure is recorded in the quote and in the 10-year written workmanship guarantee that covers our work. If you want a feel for what a typical upgrade involves, our guide on conservatory roof replacement sets out the whole service, and the survey is where your own building's answer is written down.