Will Your Conservatory Frame Take a Solid Roof?

Usually yes, and nobody can tell you from a photograph. The load a solid roof adds is small and documented; what is not documented anywhere is whether your mullions contain steel. This page sets out the check, who does it, what it costs when the answer is no, and what to demand in writing. It is the page behind lightweight roof tiles for a conservatory.

Structural reinforcement, if the survey finds no steel · conditional, never a headline

£800 to £4,000 plus £300 to £500 for the report

Reasonably evidenced2 publishers, 3.75× apart on the floor · no typical, because the two ends describe different work · checked 20 August 2026

Will the frame take it, and who decides?

In most cases yes. A lightweight solid roof adds approximately 0.5 kN/m, which LABC describes as less than 10 per cent over a typical translucent roof. The deciding factor is not the load. It is whether your existing mullions contain steel reinforcement, and only pilot holes or a magnet test answer that.

Here is the honest state of the published record, and it is the reason this page exists. No manufacturer and no installer in this market publishes a load table for a conservatory frame. There is no chart anywhere that says a 70mm uPVC mullion at 2.4m unsupported will carry X kilograms per metre. We have looked, and we are not going to print an invented one, because a fabricated kilogram figure on a structural page is the most dangerous thing this site could publish.

What exists instead is a method. A competent surveyor establishes what the roof will weigh, checks the frames for reinforcement, checks the foundations if the load increase warrants it, and either signs it off or prices the fix. That method is below in full, so you can ask for each step by name. If you want the cost of the roof itself while you are here, see what a new roof would cost you.

What a solid roof weighs, and what it replaces

Two published weights exist in this market, both from one manufacturer, and they are the only hard numbers in the conversation.

Structural figure	Value	Source and evidence
Solid roof system weight, published	31 to 38 kg/m²	Ultraframe, the only maker publishing any. Reasonably evidenced
Load a lightweight solid roof adds	approx 0.5 kN/m	LABC addendum, May 2018. Verified
Increase over a typical translucent roof	under 10 per cent	LABC addendum, May 2018. Verified
Typical loading of the existing glazed roof	under 10 kN/m	LABC addendum, May 2018. Verified
Threshold below which trial holes may be waived	load increase under 15 per cent	LABC addendum, May 2018, subject to local conditions
Load capacity of your specific frame	not published by anyone	Gap

Weights from Ultraframe technical literature; four of the six systems most often described as lightweight publish no weight at all. Structural figures from the LABC addendum on solid roofs to conservatories, May 2018. Checked 20 August 2026. What would close the gap in the last row: a published load table per frame profile from any UK systems house. We have asked the question and we will publish the answer if one arrives.

So the arithmetic is reassuring and slightly beside the point. A tiled system at 38 kg/m² on a 16 m² roof is around 600 kg of roof spread across the eaves beam and the frames. That is the 0.5 kN/m LABC describes. The cost of the roof that produces it is at tiled conservatory roof replacement cost, and the wider opaque category at what a solid roof costs.

What LABC actually says, in its own words

The single most useful structural document in this category is a four-page addendum most homeowners never see, and most quotes never mention.

“In most cases a 150 mm thick concrete strip foundation or reinforced concrete slab which bears onto original ground will be adequate.”
On the frames: verify steel reinforcement in the mullions by drilling pilot holes or using a magnet test. “If there is no reinforcement new window frames may be needed to support the weight of the roof, or additional reinforcement installed abutting the existing frames.”
LABC, Solid roofs to conservatories addendum, May 2018. Retrieved and checked 20 August 2026.

Read that in order, because the order is the point. The foundations are usually fine. The roof is usually light enough. The risk sits in the vertical frames, and it is a binary the survey either finds or does not: is there steel inside the mullions or not? A conservatory built for polycarbonate may have been reinforced only for polycarbonate, and there is nothing on the outside of a uPVC frame that tells you which.

One more clause worth carrying into a conversation with an installer. Where the new roof abuts the house, cavity trays and external flashings are required, and building control cannot require a cavity tray to be added retrospectively to the existing structure. That is a real limit on what you can be asked to pay for.

Where the addendum stops applying

Its scope is structures under 30 m², at ground floor, thermally separated from the house with external-quality doors. A larger conservatory, a first-floor structure, or one already opened up to the house is outside it, and the reassuring figures above do not automatically transfer. If yours is outside that scope, the structural question is a proper engineering one rather than a checklist.

When the answer is no, and what it costs

Two published bands exist for the fix and they do not agree, which is more useful than it looks. One publisher (May 2026) puts frame reinforcement on older frames at £800 to £2,500. Another (2026) puts a structural upgrade where the frame cannot take a solid roof at £3,000 to £4,000. That is 3.75× apart on the floor, and we grade the combined £800 to £4,000 band Reasonably evidenced and conflicted. Checked 20 August 2026.

Our reading, and it is a reading rather than a fact: the lower band reads as adding reinforcement alongside the existing frames, and the upper band reads as replacing the frames. Both are real outcomes of the same survey, which is exactly why no midpoint is defensible and why we publish no typical. Nobody publishes how often each outcome occurs, so we attach no probability to either.

The other conditional line is the report itself. A structural engineer's report is quoted at £300 to £500, and this figure carries a caveat we will not bury: it comes from Google's own AI Overview synthesis rather than from a named publisher. Google does not attribute it and we could not trace it to a source, so it is capped at Thin evidence and labelled wherever it appears. It is worth knowing because it is the figure a homeowner arrives with, not because we can stand behind it. Checked 20 August 2026.

Neither line belongs in a headline roof price. If a quote folds reinforcement into the total before anyone has drilled a pilot hole, either the survey has already happened and should be in writing, or the number is padding. What the roof itself costs, itemised, is at replacing the conservatory roof entirely, and you can ask for a conservatory roof quote that separates the two.

What you must be given, and what to do if you are not

Read this out on the sales visit, not afterwards.

A written statement of whether the mullions were checked, how they were checked (pilot holes or magnet test) and what was found.
The finished weight per square metre of the exact system being quoted, from the manufacturer's technical manual.
Whether trial holes were excavated at the foundations, or the stated reason they were not needed.
Structural calculations, or a named engineer's report, submitted with the building control application rather than kept in the installer's file.
Reinforcement priced as a separate, conditional line, not absorbed into the roof price.
Confirmation of who is notifying the work, and a completion certificate at the end from that body.

If an installer will not put the mullion check in writing, that is the answer to the question you were asking. The survey costs them an hour. Skipping it moves the risk onto you, and it surfaces years later when a solicitor asks for a certificate that was never issued.

Who checks this

Not the installer's own trade body. A solid roof stops the structure being an exempt conservatory, which makes it a material alteration and notifiable work, pulling in Approved Document A for foundations and loading. It goes to Local Authority Building Control or a Registered Building Control Approver, and no competent person scheme covers it. The full position, including which schemes explicitly exclude conservatories, is at building control, not FENSA.

Mullion, eaves beam, box gutter

Three words do most of the work in this conversation. A mullion is the vertical frame member between two window panes, and it is the one that may or may not contain steel. The eaves beam is the horizontal member at the top of the frames that the roof sits on and that spreads its load. A box gutter is the gutter formed where the conservatory roof meets the house wall, and it is a common leak point after a roof change. These and the rest of the vocabulary an installer will use are defined in our conservatory glossary.

Ask each installer how they will check the mullions

Then get it priced. Six questions, roof condition first, phone number last.

What would yours cost?

Six questions, about sixty seconds.

You can also get quotes for your roof and use the mullion question as your first filter. Whole-project figures, from a new build to a roof swap, are at conservatory cost.

Check what your roof will cost

Questions people ask first

Can any conservatory take a solid roof?

Most can. LABC puts the added load at approximately 0.5 kN/m, under 10 per cent more than a typical translucent roof, and says the foundations are usually adequate. What decides it is whether the mullions contain steel reinforcement. Frames built for polycarbonate may have been reinforced only for that lighter load, and no publisher gives odds on how often that turns out to be the case.

How do you check if a conservatory frame is reinforced?

By drilling pilot holes into the mullions, or by running a magnet along them. Those are LABC's two named methods. Neither is expensive and neither can be done from a photograph or a phone call, which is why a quote given without a site visit cannot tell you what your roof will cost.

How much does mullion reinforcement cost?

£800 to £4,000, conditional on the survey, Reasonably evidenced and conflicted: two publishers sit 3.75 times apart on the floor because one prices reinforcing the existing frames and the other prices replacing them. We publish both ends and no midpoint. Checked 20 August 2026.

Do I need a structural engineer's report?

Building control will want structural justification for the loading, which usually means calculations from the system manufacturer or a report from an engineer. The £300 to £500 figure in circulation for that report comes from Google's AI Overview synthesis rather than a named publisher, so we grade it Thin and flag it rather than presenting it as sourced.

What is the load capacity of a uPVC conservatory frame?

Nobody publishes one. No manufacturer, systems house or installer we could find publishes a load table per frame profile, which is why this page describes a survey method rather than quoting kilograms. Any site giving you a per-frame figure should be asked which document it came from.

Will the foundations need underpinning?

Rarely. LABC says that in most cases a 150mm concrete strip foundation or a reinforced slab bearing onto original ground is adequate, and that trial holes may be waived where the load increase is typically under 15 per cent, depending on local conditions. Trial holes are the check; underpinning is the exception.

Sources for this page

All retrieved and checked 20 August 2026.

The full list, with what each source is trusted for, is on sources we use. Checked 20 August 2026, next check due 20 November 2026. Where a figure is missing from this page it is missing because nobody publishes it, and the row says so.

Find out what yours costs

Six questions, about sixty seconds, and an estimate built from published UK figures with every source shown. Then up to four local installers can quote you, if you want them to.

Answer the six questions

No obligation, no countdown timers, no pre-ticked boxes. The calculator asks for your phone number last, and never before you have seen your estimate.