Solar Panels and a New Roof

You do not need a new roof to fit solar panels, and no UK standard says you do. What MCS requires is narrower and more useful than that: a competent person has to check that your roof structure can carry the array, and the installation must not damage the weather tightness or structural integrity of the building for the life of the system. Whether that check sends you to a roofer first comes down to two numbers your quote will not show you. One is what your existing roof covering weighs. The other is how many years that covering has left against the 25 years or more the panels have.

This page works through both, using the primary sources rather than the trade folklore. Everything below was verified on 21 August 2026 against both current versions of MCS standard MIS 3002, Approved Document A and Approved Document L for England, HMRC VAT Notice 708/6, the Energy Saving Trust, and published technical data from a roof tile manufacturer.

Does MCS require a new roof before solar panels?

No. MIS 3002, the MCS standard every certified solar installer works to, contains no requirement about the age or condition of a roof covering. What it requires is a structural check and a promise about weather tightness.

MCS currently publishes MIS 3002 as two parallel documents, both dated 18 March 2026 and both mandatory from 18 June 2026: version 6.0 for the current installer scheme, and MIS 3002:2025 version 2.0 for the redeveloped scheme. The clause text is the same. The numbering is not, so both numbers are given below.

• Clause 5.9.1, or 3.9.1: "PV systems should not adversely affect the weather tightness or structural integrity of the building to which they are fitted. The system should be designed and installed to ensure this is maintained for the life of the system."
• Clause 5.9.4, or 3.9.3: "The MCS Contractor shall ensure that the roof structure is checked by a suitably competent person to ensure it can withstand the loads imposed by the solar PV system."
• Clause 5.9.6, or 3.9.5: "Where the roof structure is in any way unusual, or there is any doubt whatsoever, a qualified structural engineer shall be consulted."

Note the difference in force. The weather tightness clause is a "should". The structural check is a "shall", which in MCS language means mandatory. So an installer who quotes without anyone looking at your roof structure is skipping a requirement, not a nicety.

The standard then lists what counts as an unusual roof, and one entry on that list is the reason this page exists. A roof is unusual, and needs a structural engineer, if it "shows signs of post construction modification (e.g. removal of timbers, notching, change of roof covering to a heavier material)". The others are a roof shape not shown in the standard's own table, signs of structural distress, a pitch below 30 degrees to the horizontal, and a design prone to snow build-up such as dormers, valleys or parapets.

The arithmetic your installer is doing, and why the covering decides it

MIS 3002 sets out the calculation in one line, and the roof covering is the term that dominates it. For a roof built from timber trussed rafters, which covers most UK houses built since the 1960s, Table 1 of the standard gives Method 1 verbatim:

"Assuming a typical design dead load of 0.785kN/m2, deduct the load of the existing roof covering to give the maximum allowable residual load available for the solar array."

That is the whole game. You start with a fixed budget of about 0.785 kilonewtons per square metre, you subtract what your roof covering weighs, and whatever is left is what the solar array is allowed to weigh.

So what does an array weigh? Take a current 630 watt module. AIKO's own datasheet for the A630-MAH72Mw, version 4.1 of October 2025, gives a weight of 27kg and a size of 2278 by 1134 by 30mm. That is 2.58 square metres of panel, which works out at 10.5kg per square metre, or about 0.10 kN/m2 for the modules alone. Rails, brackets and clamps add more on top.

And what does a covering weigh? Marley publishes the figures for its own tiles, in the same units the standard uses. Set the two side by side and the picture is stark.

On the two interlocking coverings there is comfortable room. On plain concrete tiles, Method 1's simple arithmetic leaves 0.065 kN/m2, which is less than the modules alone need before you add a single rail.

Read that carefully, because it does not mean a plain-tiled roof cannot take solar. Method 1 is a generic starting assumption about a typical trussed rafter roof, and a roof actually built to carry plain tiles was designed for that load. What the sum shows is why plain-tiled and heavy-covering roofs are the ones that get sent for a real structural calculation instead of a rule of thumb, and it is exactly the situation clause 5.9.6, or 3.9.5, was written for. It also shows why the covering, not the panel, is the variable that moves the answer. A module weighs about a tenth of a kilonewton per square metre. Choosing between a plain tile and an interlocking slate moves nearly three times that.

If you are re-roofing anyway, this is the moment to ask the roofer what the replacement covering weighs, and to give that figure to the solar installer before either job is priced.

The counter-intuitive part: a lighter roof can make the paperwork harder

Approved Document A, the building regulation covering structure in England, does not care what your roof weighs in absolute terms. It cares how much the work changes it, and the trigger is a percentage.

Section 4 of Approved Document A, "Re-covering of roofs", exists precisely because roofs get re-covered late in a building's life and the new covering rarely weighs the same as the old one. Paragraph 4.4 sets the threshold in one sentence: "A significant change in roof loading is when the loading upon the roof is increased by more than 15%." Where that happens, paragraph 4.3 requires the roof structure and the supporting structure to be checked so that the finished building "is not less compliant with Requirement A1 than the original building", and paragraph 4.5 classifies any resulting strengthening work as a material alteration, which brings building control into it.

Now put the solar array back into that sum. The same module load of roughly 0.10 kN/m2 is about 14% of a plain concrete tile covering, but about 24% of an interlocking slate-profile covering. The lighter the roof you are adding panels to, the larger the same array looms as a percentage.

Two honest caveats. The regulation measures the increase against the loading on the roof, not against the covering alone, and the covering is only part of that loading once battens, membrane and structure are counted, so real percentages come out lower than the ones above. And the array covers part of the roof, not all of it. The direction of travel is the point: strip heavy tiles, fit a light covering, then add solar, and you are closer to Approved Document A's trigger than you were before, not further from it.

There is a mirror-image rule for going the other way. Paragraph 4.7 reads: "Where work will significantly decrease the roof dead loading, the roof structure and its anchorage to the supporting structure should be checked to ensure that an adequate factor of safety is maintained against uplift of the roof under imposed wind loading." Swapping heavy concrete tiles for lightweight slate does not only free up capacity. It removes ballast, and the roof then has less weight holding it down in a gale. Anyone proposing a lighter covering to make room for panels needs to have thought about that before the tiles come off.

Approved Document A applies in England. Scotland, Wales and Northern Ireland each run their own building standards system, so ask your builder which document governs the work where you live.

Doing both jobs at once: the savings the Energy Saving Trust actually names

The single biggest argument for combining a re-roof with a solar install is that you only pay for the access once. The Energy Saving Trust, whose guidance was last updated on 13 August 2026, puts it plainly: "You can lower the cost of installation costs if you already have scaffolding up for roof repairs or if you're building a new house."

The Trust also lists what moves the price of a solar system, and two of the five entries are about the roof itself: "whether you integrate the panels into the building" and "whether you need to renew the roof covering". Its benchmark is a 4.5kWp system at around £7,600, covering 20 to 30 square metres of roof with about 12 panels. Our guide to what solar panels cost in the UK breaks that figure down, and cost by system size shows how it scales.

On flat roofs the Trust goes further and recommends the combined job outright: "Sometimes it might be recommended to renew the roof covering so that your roof remains in good condition while the solar panels are attached to it. Even though it may add to the cost, the overall solution will be cheaper in the long run." Our page on solar panels on a flat roof covers the mounting rules that follow from that.

The other thing a re-roof unlocks is the choice of mounting method. Two routes to a flush finish are hard to justify on a sound roof and easy to justify on one that is coming off anyway:

• In-roof solar panels replace part of the covering with a flashing tray, so the strip-out you are paying the roofer for is work the solar installer would otherwise duplicate.
• Solar roof tiles lay like a covering in their own right, which only makes economic sense when a covering is being bought regardless.

Timing matters more than most people expect. Panels should last 25 years or more, and the Energy Saving Trust says the inverter usually needs replacing after about 12. Our page on how long solar panels last goes through those numbers. If your covering has fewer years left than the panels do, you are choosing between doing the roof now while the scaffolding is already booked, or paying to take an array off and put it back later.

The building regulations bill nobody puts on the quote

Strip more than half your roof back to the rafters in England and you are legally obliged to insulate the whole of it to a modern standard, whether or not that was your plan.

This is the part of a combined roof and solar job that catches people out, and it comes from Approved Document L Volume 1, the 2021 edition incorporating 2023 amendments, which has been in force in England since 15 June 2022. Paragraph 11.2 defines renovation of a thermal element, and item (c) is a re-roof described in construction terms: "Replacing an existing layer through stripping down the element to expose basic structural components (e.g. bricks, blocks, rafters, joists, frame) and then rebuilding."

Paragraph 11.3 then sets the trigger. If a thermal element is renovated and either "more than 50% of the surface of the individual thermal element is renovated", or the job is a major renovation meaning "more than 25% of the surface area of the external building envelope is renovated", then "the whole of the thermal element should be improved to achieve at least the U-value given in Table 4.3, column (b)".

For a roof, Table 4.3 gives a threshold value of 0.35 and an improved value of 0.16 W/(m2K). In plain terms: re-cover more than half the roof and the whole roof has to reach 0.16, not just the half you touched.

Worth knowing before you assume the worst: paragraph 4.13 provides an escape. If reaching 0.16 "is not technically or functionally feasible" or "would not achieve a simple payback of 15 years or less", the element only has to be upgraded to the lowest U-value that is feasible and pays back inside 15 years, though generally it should not end up worse than 0.7. A note to Table 4.3 adds that where the standard would limit head room, a lesser standard may be appropriate provided the insulation depth is at least the depth of the rafters.

The widely repeated builder's rule that "25% of the roof" triggers an insulation upgrade is not what the current document says. In Approved Document L the 25% figure applies to the whole external building envelope, and the roof-specific figure is 50% of that element. Approved Document L Volume 1 applies in England only.

VAT: the panels are zero-rated, the roof almost certainly is not

Zero-rate VAT covers the solar installation. It does not cover a new roof, and bundling both into one price can put the whole invoice at risk rather than saving you tax.

HMRC's VAT Notice 708/6 sets the window: this relief "covers supplies of installations of energy-saving materials made between 1 May 2023 and 31 March 2027. From 1 April 2027 onwards, supplies of installations of energy-saving materials will revert to the reduced rate of VAT of 5%." Photovoltaic panels "with cabling, control panel and AC/DC inverter" are named in the list of qualifying materials. Our page on VAT on solar panels covers the relief in full.

Where a re-roof runs alongside the install, section 2.5 of the notice applies the single supply test: "A single supply is where one element of the supply is the principal element to which all other elements are ancillary. An ancillary element does not constitute, for the customer, an aim in itself, but is a better means of enjoying the principal supply." Its indicators of a single supply are a single price, the work advertised as a package, components not available separately, and everything installed at the same time.

That test cuts both ways, and Example 4 in the notice shows the losing side of it: "If you constructed an extension to a house and the walls and roof space were insulated as part of the construction, this would be one single standard-rated supply. This is because the construction of the extension is the principal element of the supply, which is standard-rated." A new roof is emphatically an aim in itself for the customer, not a better means of enjoying the panels, so it is hard to argue it is ancillary to them. Get the roofing element and the solar element itemised separately on the paperwork, and ask each contractor to state in writing which VAT rate they are applying and why. The notice gives no roof-specific example, so this is a question for your installer and their accountant rather than something a comparison site can settle for you.

The 2027 timing trap, and it is not just the VAT

Two separate deadlines land within nine days of each other in spring 2027, and both make a combined roof and solar job more expensive after they pass.

• 24 March 2027: the 2026 edition of Approved Document L takes effect in England "for building work that is not in connection with higher-risk building work", with the higher-risk version following on 24 September 2027. Transitional arrangements are set out in Circular Letter 01/2026 on gov.uk.
• 1 April 2027: the zero rate on installing energy-saving materials reverts to the reduced rate of 5%.

On a £7,600 system, moving from 0% to 5% is £380 of VAT that did not exist before. That is not a reason to rush a decision you are not ready to make, and neither date is a cliff edge for work already under way. It is a reason to know where you stand if a roof and a solar install are both on your list for the next 18 months.

If the roof fails later: taking the panels off and putting them back

No UK body publishes a cost for removing and refitting a solar array, so treat any figure you are quoted as a price rather than a benchmark. What you can do is get the terms nailed down before you sign, and MCS gives you two specific hooks.

The first is your roof warranty. Clause 5.9.2, or 3.9.2, says: "Where the existing roof covering is under warranty, then the roof warranty provider should be consulted to establish if warranties will be invalidated by the installation." If your roof was re-covered recently and came with a guarantee, fixing brackets through it is exactly the sort of thing that guarantee may exclude.

The second hook is stronger, and it depends on which MCS scheme your installer sits under. Version 6.0 of MIS 3002, for the current installer scheme, adds clause 5.9.3: "Where any existing warranty may be invalidated by the proposed installation, the MCS Contractor shall notify the customer in writing and obtain explicit written agreement from the customer if the installation is to proceed." A note underneath closes the obvious loophole: "a clause in the MCS Contractor's standard terms & conditions would not satisfy this requirement."

MIS 3002:2025 version 2.0, the redeveloped-scheme document, has no equivalent clause. It stops at the "consult the warranty provider" line and moves straight on to pitched roofs. Both documents are current, both are mandatory from 18 June 2026, and the written-consent protection appears in only one of them. If your roof covering is under warranty, ask your installer for that written notice by name rather than assuming it arrives automatically.

What to ask before you sign anything

1. "Who is the competent person checking my roof structure, and what did they conclude?" Clause 5.9.4, or 3.9.3, makes the check mandatory. Ask for it in writing rather than as a verbal reassurance on the doorstep.
2. "What is my roof covering, and what does it weigh per square metre?" That number is the one being subtracted in the Table 1 calculation. If nobody on the job can tell you, nobody has done the sum.
3. "Does my roof fall into any of the unusual categories?" Pitch under 30 degrees, dormers, valleys, parapets, signs of distress, or evidence that timbers have been cut or the covering changed. Any of those and clause 5.9.6, or 3.9.5, requires a structural engineer.
4. "If the covering is being replaced, is more than half the roof coming off?" If so, price the Approved Document L insulation upgrade into the roofing quote, not as a surprise later.
5. "How is VAT split between the roofing work and the solar work?" Ask for it itemised, in writing, before you accept.
6. "Is my roof covering under warranty, and will you notify me in writing if the install affects it?" The answer tells you which MIS 3002 document your installer works to.

Get three quotes and compare the answers to those six questions, not just the totals. Our guide to choosing a solar panel installer in the UK covers how to check MCS certification and consumer-code membership, the installation process sets out what happens on the day, and you can request quotes through RenewQuote to start comparing.

Frequently asked questions