Future Homes Standard - Homes that Cannot Meet the 40% Solar Requirement

 

The Future Homes Standard (FHS) will make solar PV panels mandatory on all new homes from 2027, with the government announcing that panels will have an area of at least 40% of the ground floor area of the building.  

In this article I'll take a look at how the calculation works, what amount of solar it might result in and how exceptions are dealt with when roofs don't have enough room.  I'll also share an early estimate of how many houses might not be able to meet the requirement in full.

How Much Solar?

The actual requirement for the amount of solar is, quite rightly defined in terms of the total rated power, which means that if you use higher performance panels, you can reduce the area or conversely if the panels you use are of low power rating then a greater area must be installed.  

The actual target is to install solar PV that has the same annual output as a solar array with the following characteristics: an area of 40% of the ground floor area, a specific power of 0.22 kWp/m2, facing SE or SW at a pitch angle of 45 degrees and with little or no shading.

So for an 85 m2 semi detached home, arranged across two floors we might have 42.5m2 of ground floor area and a target solar installation of:

40% x 42.5 x 0.22 = 3.74kWp

This figure could be met for example with ten 405Wp solar panels, or nine 445Wp panels.  It's worth noting that the current average installation we see under Part L 2021 is between four and five panels per house, so the Future Homes Standard represents a rough doubling in the quantity required.

Any amount by which the solar provided exceeds the target counts towards achieving the overall energy targets for the building, so there are benefits to going higher if the roof can fit more.

What About Complex Roofs?

The regulations makes allowances for roofs that are an interesting shape or that have features that limit the amount of solar that is possible, and this is outlined in Appendix B9.  The developer must provide evidence to the building control body to show that it is not possible to install sufficient solar on the roof to meet the requirement.

Roof diagrams showing the roof with and without solar panels showing that the installation provides the maximum PV capacity and annual generation possible for the roof orientation and layout must be provided.

The diagram showing the maximum possible roof area for solar PV has to be made using specific guidance given on the minimum allowable offset distances from other roof features.

An example of a suitable diagram showing the maximum solar possible on a house is shown at the top of the page.

The target for solar PV then becomes a system that produces an amount of energy each year that matches that of a system with the area of solar in the drawing, a specific panel power of 0.22kWp/m2 and the orientation and angle of the actual roof pitches.  This figure is then also used in the Notional House specification so there is no penalty there for having to use a smaller solar system.

At present there are no restrictions on how close to roof edges a solar panel installation can be made (subject to having a sufficient wind resistance to install in an edge zone and a sufficient fire rating to install adjacent to a party wall).  Consequently it might be possible to provide a B9 drawing showing a maximum solar area, and install something different -  so long as it matches or exceeds the annual power generation 

For example this could be achieved by using higher efficiency panels than those in the standard, and covering more of the most advantageous roof pitch, while dropping solar off the less advantageous roof pitches, to meet or exceed the annual energy yield of the B9 drawing.

However, on the same day that the FHS was revealed, the Health and Safety Executive opened a consultation on Approved Document B - the building regulations for fire safety.  This includes what would become mandatory provisions for minimum offset distances for solar panels, so reducing the possibility to use tighter margins to outperform the regulated max-fit.

Something that has been missed in the guidance is to define what size of solar panel should be used in the assessment. This really needs to be clarified because otherwise people will get very different outcomes depending on what panel size is chosen. 

How different panel sizes give different maximum-fit outcomes

 I have discussed this point with colleagues at the Future Homes Hub and the plan is to develop an industry guide in conjunction with representatives from building control bodies to fill in some of the missing detail from Appendix B9.  This way we can hopefully have a consistent approach across industry.

What Proportion of Homes Will Fit 40%

As part of our work at Viridian Solar in support of our housebuilder partners, the design team has performed studies on sample developments to assess which house types can meet a 40% requirement and which cannot.

So far we have seen around 80% of houses on a typical site can fit the full requirement of solar panels on the best elevation.  Of the houses that could not fit the requirement, on average one half of the requirement could be fit on the best elevation, so around 20% of the ground floor area. 

Under the approach in Appendix B9, these homes would need to use all the possible other elevations as well as the best elevation to maximise the solar generation possible, including North facing elevations if necessary.  Depending on the size of the less advantageous roof pitches, this might result in a greater number of solar panels being used due to the penalty that comes as panel orientation moves further away from South facing.  

Of course, this analysis was done before the final regulations were published, and so was using our own manufacturers' guidelines on offset distances which are tighter than those in the FHS.  It is likely that a higher proportion of houses will struggle to meet the 40% target using the Appendix B9 guidance.  No doubt the design team will continue to be working with housebuilders re-evaluating their house types to the final version of the standard.  I will post an update when we have got more data from this work.

When will Homes be Built to the Future Homes Standard?

 

Accompanied by much excitement in the solar industry, the Future Homes Standard (FHS) consultation response was finally published on 24th March 2026, and little wonder because the new regulations make renewable electricity generation (solar PV) mandatory on nearly all new homes.  But how long will it take for the new regulations to feed through into bricks and mortar on the ground, and more importantly solar panels on the roof?

The transitional arrangements published alongside the new regulations give developers some breathing room to get themselves ready to deliver the new specification at scale.  The rules come into force in 12 months.  From March 24th 2027, any new development that applies to Building Control for approval will see all homes on that site built to the new regulations.

A second deadline follows in March 2028.  After this, all homes not yet "commenced" will need to be meet the FHS, irrespective of when the Building Control application was lodged.

The transitional arrangements are identical to those that applied to the last update to the building regulations for energy efficiency - Part L 2021.  So we can use the last building regulations transition as a model for the next. 

What Went Before - Part L 2021

Part L 2021 was announced in that year, with a start date of July 2022 for new sites and July 2023 for houses not yet commenced.  The graph at the top shows the number of housing starts in England (black line) and completions (blue line) from 2018 to 2025.

The solid orange line shows the number of housing completions that were built to Part L 2021.  This data is provided by the Future Homes Hub and inferred from the software version used to generate the Energy Performance Certificates for the homes.  The dotted orange line is shifted three months as an estimate for roofing works going on, and solar panels being installed.

In December 2025, only 60% of homes that completed in England were built to Part L 2021 - some three and a half years after the regulations came into force.  How is this possible?

The clue to the answer to this question is found by looking at the black line.  There was an unusual spike in housing starts in the run up to the June 2023 cut-over date.  Housebuilders commenced nearly 30,000 more houses than in a normal quarter.  Strip foundations were excavated and concrete poured to classify plots as commenced.  These foundations were then mothballed for many, many months before being built on later - and locking in the older, and lower cost regulations.

What This Means for the FHS

The FHS imposes higher costs on developers, around £5,000 per house according to the Government's own Impact Assessment, so the incentive to delay the change over will definitely be there, just as it was for Part L 2021.  

There are a couple of potentially important differences this time around which may influence how long the transition takes.  

Firstly, the 2023 rush to lay foundations and beat the deadline for commencement occurred as mortgage rate increases precipitated a house buyers' strike.  The foundations lasted longer than they would have if the housebuilders were working at their usual rates.

Secondly, what counts as a "commencement" changed in late 2023 and now requires the first floor structure to be complete.  So for a house with a concrete slab ground floor, to the cost of the foundation you can now add the cost of building the below ground walls, a base-layer of hardcore and blinding and then pouring a concrete slab, plus all the drainage and service ducts required.

Will this second change be enough to change the financial calculations of the housebuilders - it's too early to say, but given the size of the prize from the cost saving, it's hard to see why the housebuilders won't rinse and repeat what they did for the 2021 regulations.

A sober assessment of how quickly the FHS will feed though to demand for more solar PV puts the start of the ramp in June 2028 and runs through to the end of 2030.