The Microgeneration Installation Standard 3002 V6 is now in effect. Sahir Raihan, structural engineer and managing director of Solar Surveys, cautions that a misreading of some clauses – and confusion over what it does and does not cover – could be costing both installers and clients
MIS 3002 V6.0 became mandatory on 18 June for every MCS-certified solar PV installation up to 50 kWp DC. Most of the argument I have heard about it since has
been about the wrong clause.
The general assumption is that the standard now requires a structural engineer. It does not, in the ordinary case. What clause 5.9.4 requires on a pitched roof, meaning one
steeper than 10 degrees and shallower than 70, is that the MCS Contractor ensures the roof structure is checked by a suitably competent person to confirm it can withstand the
loads the system imposes. That person need not be an engineer.
That is deliberate drafting and reading it as a blanket engineer requirement is the most common error in circulation.
Where an engineer genuinely is required
There are named cases, and they matter far more than the general rule. Clause 5.9.6 requires a qualified structural engineer where the roof structure is in any way unusual. The accompanying note defines that broadly: any roof showing signs of post-construction modification, such as removal of timbers, notching or a change of covering to a heavier material; any roof of particularly shallow pitch, under 30 degrees; and any roof with increased potential for snow build-up, for example dormers, valleys and parapets. Against existing building stock that is not an edge case. It is a large minority of roofs.
Clause 5.9.13(h) is the one most often missed. On a ballasted system an engineer shall be consulted to confirm the roof can withstand the load from both the array and the proposed ballast. There is no size threshold attached to it. Flat roofs are precisely where ballast becomes the governing load and 5.9.13(h) admits no exception.
Table 1 adds a third route, sending traditional cut timber roofs with hips or valleys, and asymmetric duo-pitched roofs, to an engineer as well.
The clause that is misread in the other direction
Clause 5.5.5 covers mounting systems outside the scope of MCS 012, and it is the headline change in V6.0. The standard’s own amendment record gives the reason for the March issue as an extension to 5.5.5.
Item (b) requires evidence that a structural assessment and a wind loading calculation have been completed for the specific mounting system. It is frequently quoted as an engineer requirement. It is not. The note permits that evidence to come from the system manufacturer, from a third-party structural engineer or from an appropriate software platform. An engineer is one of three routes.
The standard does add that such calculations do not constitute compliance on their own and must be directly linked to the design and installation of the system. A generic manufacturer calculation, filed but never connected to the building it sits on, does not satisfy it.
Both misreadings cost money
Told the standard never requires an engineer, an installer walks into a ballasted flat roof job that always does and finds out at handover.
Told it always requires one, a client pays for engineering on a straightforward pitched roof where 5.9.4 would have been satisfied by a competent person at a fraction of the cost.
Two gaps worth knowing about
The first is scope. MIS 3002 governs installations within the Microgeneration Certification Scheme, and the scheme stops at 50 kWp DC. Work above that threshold is not covered by the standard at all. On larger commercial schemes, this is a routine source of confusion. People reach for MIS 3002 as though it applies, and when it does not, nothing steps in to replace it.
The second gap is the deliverable. The standard requires that a check happens. It does not specify what the check must contain. Two assessments can therefore both be
compliant and share almost nothing: one a walk-round and a completed form, the other a member-by-member verification with the governing element identified and its remaining margin stated.
Three questions that separate them
If you are commissioning or accepting one of these, three questions do most of the work.
Which clause is being relied on: 5.9.4, 5.9.6 or 5.9.13(h)? Which element governs, and by what margin? And what was not accessible, and has therefore been assumed? None of them costs anything to ask at instruction. All three are expensive to discover afterwards.
Solar Surveys publishes an open dataset of 575 commercial rooftops assessed for solar PV structural feasibility between 2024 and 2026, free and without registration, here.
