Plenty of conservatories in the Five Valleys went up with a roof of twin-wall polycarbonate: light, quick to fit and cheap to carry. When that roof clouds over or starts to leak, the natural thought is to swap it for something that keeps the house warmer and quieter. Solid roofs do that, but they weigh far more than the sheets they replace. Homebuilding & Renovating makes the same point from the other side: frames that once held up light sheeting are being given a heavier job.
This guide is about that single question: the structure. It covers what the load path looks like, what we inspect from the footings up to the wall plate, how a frame is strengthened when it falls short, and where the paperwork sits. For the roof itself, the layers and finishes, read our guide to solid and tiled conservatory roofs. The wider picture is on the conservatory roof replacement page.
How a light roof turns into a heavy one
A conservatory frame is a kit. It was designed around a particular roof, and the sections, the glazing bars and the fixings were chosen for the weight of that roof and no more. Polycarbonate is about as light as a roof covering gets, so a frame made for it has little spare capacity. Glass is heavier, and a solid roof, with its timber rafters, insulation, battens, tiles or slates and a plastered ceiling beneath, is heavier again.
The load does not sit still. Every part of the roof passes its weight to the next part down: the covering to the rafters, the rafters to the ridge and the eaves beam, the eaves beam to the posts, the posts to the base. Wind and snow add loads that push and lift as well as press down. A heavier roof raises the force at every step, and the weakest link sets the limit. That link is rarely the part you can see. It may be a slim eaves beam, a post that was never meant to carry more, or a dwarf wall resting on shallow footings.
What the rules say about extra weight
Approved Document A treats added roof weight above 15% as a significant change, and the Planning Portal gives 15 per cent or more as the point where Building Regulations approval is needed. If the structure underneath cannot sustain the extra load, the document expects strengthening to be done. Swapping polycarbonate for a solid roof clears that threshold by a wide margin, so the structural question is always live. Solid conservatory roofs need a Building Regulations application in any case, which means the frame check is part of the approval, not an optional extra.
Starting at the ground: footings and dwarf walls
We begin with the base because a frame can only be as sound as what it stands on. Most conservatories sit on a low brick wall, called a dwarf wall, which in turn rests on a concrete footing. Neither is visible in full without some digging, so the survey works from what can be seen and measured.
Signs of movement
Cracks running up through the brickwork, mortar joints that have opened in a wedge shape, doors and windows that have started to bind, and a gap opening where the conservatory meets the house are all clues. A hairline crack may be old and settled. A crack you can slide a coin into, or one that has grown since last winter, needs a closer look before you add any weight. On the sloping plots common around Stroud, we also look at whether the ground falls away at the downhill corner, because that is where a shallow footing is most likely to have shifted.
What the wall itself tells us
We check the dwarf wall for bulging or leaning, sound mortar, and a sound damp-proof course. We note how the cill, the board that the frame sits on, is bedded and whether the frame is plumb and level. A frame that is already out of square will not suddenly behave better under a bigger roof.
If anything points to a weak base, a structural engineer is the right person to say what happens next. For a covering that is markedly heavier than the old one, the Planning Portal says to take advice from a qualified engineer or surveyor ahead of any work. We would rather raise it at the survey than find out halfway through a job.
Reading the frame: posts, transoms and the eaves beam
With the base looked at, we turn to the frame. Conservatory frames come in uPVC, aluminium and timber, and the material changes what we are looking for. Many uPVC frames have steel reinforcement inside the plastic sections; some of the lighter ones have little or none. We often cannot tell without opening a section or finding the manufacturer's details, so a frame with no paperwork is one more reason to bring in an engineer.
The parts that carry the load
The posts, or mullions, are the vertical members at the corners and between panes. The transom is the horizontal member across the top of the glazing. Above the transom, many frames have an eaves beam that supports the foot of the rafters. These are the parts that have to take a heavier roof, and we measure them: section sizes, spans between posts, and any place where a long run has no support. A long, slim eaves beam with a wide span is the classic weak point.
Deflection and movement
We sight along the eaves beam and the ridge for sag. A beam that already bows under the weight of a light roof will bow further under a heavy one, and the glazing units below it can crack or leak as the frame moves. Looseness in the corner joints, gaps at the mitres, and fixings that have pulled out of the frame all suggest the frame is working harder than it should.
If the frame passes visually, that is still not a structural opinion. Sizing the members for a new load is a calculation, and it belongs to an engineer or the designer of the roof system, who can state in writing what the frame can carry.
The wall side: wall plate, abutment and the house itself
One side of the roof rests on the house. The rafters in a lean-to or Edwardian style conservatory are normally fixed to a wall plate, a timber member bolted along the house wall, and a flashing seals the joint. Both matter when the roof gets heavier.
Is the house wall up to it?
The bolts or screws holding the wall plate must bite into sound masonry. In older stone houses, which are common here, the wall may be rubble-filled with a soft lime mortar, and a fixing that grips well in brick can pull out of loose rubble. We tap and probe the wall around the plate, check how it was fixed originally, and look for any damp or cracking that suggests the wall has been losing material. Where the house is listed, or lies within a conservation area, put the question to Stroud District Council's planning team before anything heavier is fixed to its wall.
Flashing and movement
Where the two buildings touch, they rarely move together. The frame settles a little; the house stays put; the flashing absorbs the gap. If the abutment is already open or lifting, we note it, because a heavier roof can widen that gap. Leaks along this line are covered in our guide to conservatory roof leaks.
Before any roof is ordered, we photograph the wall plate, the eaves beam and the frame joints and give you the pictures, so the survey record shows what was there on the day.
When a frame needs strengthening
A frame that falls short is not a dead end. There are well-worn ways to bring it up to the job, and which one fits depends on what the engineer's calculation shows.
Common measures
Steel can be fitted into or alongside the weak members: a steel beam in place of a slim eaves member, a steel post or flitch plate where a mullion is overstressed, or a steel section tying the corners together. Where the dwarf wall carries a heavier load than its footing was designed for, the footing can be underpinned or widened. In some cases the better answer is to choose a lighter solid system, so the frame needs little or no change. That is the subject of our solid roofs guide and, for tile and slate systems built to save weight, of our guide to lightweight tiled roof systems.
What it costs
MyBuilder's 2026 conservatory roof replacement guide gives structural reinforcement a typical range of £500 to £2,000, as part of an overall conservatory roof range of £2,000 to £10,000 or more. It lists solid roofs at £5,000 to £10,000, glass at £3,000 to £8,000 and polycarbonate at £2,000 to £5,000. Treat those as national guide figures from a third party, never as our price. A frame needing several steel members, or a base needing underpinning, can sit above that range, so we wait for the engineer's findings before putting a number on the roof.
The quote that follows the survey covers any reinforcement as well as the roof.
Paperwork, sequence and what you will receive
Because a solid conservatory roof counts as a material alteration, a Building Regulations application is needed. A registered building control approver or the council's building control service then inspects the work. For a house in Stroud District, that is the Gloucestershire Building Control Partnership, which it shares with Gloucester City. Whichever route applies, we walk you through the consent steps and send the notification ourselves when the job calls for one.
The Planning Portal sets three tests for a new conservatory roof: safe structure, energy performance and ventilation. It adds that planning permission may follow where the roof's appearance changes a great deal. Our guide to insulating a conservatory roof covers the energy side of that test.
The order of work
The sequence runs: survey and photographs, structural advice if the frame or base is in doubt, strengthening where needed, then the roof itself. Strengthening comes first because it is far cheaper to do before the new roof is on than after. Once the roof is built, the work is carried by our 10-year workmanship guarantee, in writing.
What to have ready
Photographs of the outside corners and the eaves help most, along with any paperwork from the build and the frame maker's name if you know it. A manufacturer's stamp inside a window opening often settles the question of what the frame is. You can reach us on 01453 933613, over WhatsApp, or through the form on this page.