Zero Carbon Homes for London

"Bojo vs Osbo" Rivalry Sets Scene for Solar Boom in Capital

I have written many times about this government's shameful record on driving higher energy efficiency standards in new buildings.  If you want a summary of the numerous ways they have watered down, delayed and undermined standards, take a look at this earlier blog.

The latest blow to the many people in the construction industry that had invested heavily in developing skills, technologies and products to deliver the government's long-held Zero Carbon Homes plan was the announcement in July 2015 that the allowable Solutions carbon offsetting scheme was scrapped, as were plans for on-site energy efficiency standards slated for 2016.  Instead a wooly commitment to 'keep standards under review' was made.

The fact that the announcement was made in a Treasury document "Fixing the Foundations" suggested that it was the Chancellor himself that had decided that Zero Carbon Homes needed to go.

Government appeared to have bought the line from house builders that if standards were raised, they wouldn't be able to "solve the nation's housing crisis for us".

In late 2015, Scotland pressed on and tightened building regulations in 2015 beyond those in the rest of the UK.  Guess what?

The sky hasn't fallen in.

Housebuilding is as strong as ever north of the border.

Now the London Assembly has announced that it is going further still.  Way, way further.  London will be implementing its own version of Zero Carbon Homes for major development applications received after 1 October 2016 (for residential developments this means those with more than 150 residential units) .

The policy requires that new homes achieve a carbon compliance standard on site that is 35% better than the 2013 building regulations.  This corresponds to a 54% reduction compared to the 2006 Building Regulations, and seems to be based on a simplification of the proposals from the Zero Carbon Hub.  Its recommendation was an onsite carbon compliance level corresponding to a reduction of 44% for flats, 56% for attached houses and 60% for detached houses.

I reckon that an 85m2 semi-detached house would need a solar system of 1.2kWp to bridge the gap from the backstop fabric (insulation)  requirements considered achievable by the Zero Carbon Hub to the onsite carbon emissions requirement in this policy.

The developer can choose to aim higher than the onsite requirement, but the remaining gap to achieving zero carbon must be provided off-site or through a cash in lieu contribution to the relevant borough.  This money received by the local borough is to be ring-fenced to secure delivery of carbon dioxide savings elsewhere.   There's no details on what constitutes an acceptable use of the money, for example whether it has to be in London, or the UK or anywhere in the world, or whether it has to be on buildings or can include paying South American farmers not to chop down trees.  Guidance will apparently follow.  The GLA suggests a value of £60 per tonne of CO2 emitted by the building in its first 30 years is an appropriate level for boroughs to set for the cash in lieu payment.

If solar saves 950kWh/kWp and the carbon intensity of electricity is 0.522kgCO2/kWh then it needs to cost £0.89/Wp to be more cost effective than paying the £60/tonne cash-in-lieu offset.  On larger buildings this kind of price for solar is coming into view.

However, even on smaller buildings like homes, if the developer has already committed to needing solar to meet the on-site compliance requirement, then the extra cost for increasing the size a system from e.g. 1kWp to 3kWp could well be low enough to beat paying the cash fee.

Whichever way it goes, this is excellent news for solar in the capital, and potentially beyond.  New homes in London represent about one sixth of all new homes in the UK.

The GLA has commissioned research that demonstrated that the prices commanded in the capital can easily support the extra costs of this policy.  London is surely not the only place with high house prices (pretty much the whole of the South East probably would find the same).  If the policy proves to be robust to legal challenges or central government interference, then other local authorities could follow suit.

The Conservatives have left a Zero Carbon Homes shaped policy gap in building standards.  Fortunately a long-distance urination competition between two leadership rivals means that the baton has been picked up by regional government, to the benefit of future home owners and those businesses that invested in the government's original intentions to deliver world-leading building regulations.

MCS012 Finally Comes into Force

Image: Viridian Solar Roof Integrated Clearline Fusion System

That the implementation of MCS012 has been a challenging process must be obvious to any outside observer.  The standard for assessing the performance of solar roof mounting kits for wind resistance, weather tightness and spread of flame performance was first published in 2012.   Indeed, it was written into the 2013 Guide to the Installation of PV Systems as a mandatory requirement, and 130 different certificates have now been issued to roof mounting kits and components.

However, a first delay was made necessary when so many manufacturers had left things until the last minute that a log-jam was created at the test laboratories.  MCS wrote out to installers to announce that the requirement would be suspended until further notice.

A subsequent hold up due to concerns raised about EU notification was followed by inconsistencies between certifying bodies in the treatment of ‘universal’ roof integration kits that needed to be ironed out.

After such a delay, it feels like old news that the use of mounting kits accredited to MCS012 will eventually become mandatory for MCS registered solar PV installations on pitched roofs from May 2nd 2016, but it brings some big changes for the industry.

Read more about what MCS012 means for installers here.

Above-Roof Systems

MCS012 mounting systems intended to mount the panels above a roof covering are tested only for wind resistance (where they can be shown not to affect the fire resistance and weather tightness of the roof covering beneath).

This test is important because the resistance of most roof hooks to pull-out forces is determined not by the strength of the roof hook itself, but by the strength of its fixing to the roof.  In sound timber, this strength is determined by a combination of the size and number of the wood screws and the gauge of the timber into which they have been screwed.

Because of this, resistance values from tests where the hook is fixed to larger timbers than those used in the UK cannot be used as they would over-state the strength.

Some manufacturers have not tested at all, but instead used EN1995-1-1 (or similar) to calculate a resistance force for their fixings.  Such calculated screw pull out forces only apply when the timber to which the screw is attached is wider than 12x the diameter of the screw.  Unfortunately with slender UK roof trusses, this is usually not the case, making calculated resistances invalid.

A roof hook tested to MCS012 will have a certified, tested resistance in kN to uplift forces, creating a level playing field.  Solar installers can use this resistance with confidence to calculate the number of  hooks required for their installation that would have a combined resistance higher than the design wind pressure multiplied by the installed panel area.

In-Roof Systems

Solar systems that replace the roof covering have more significant testing requirements under MCS012, including a deluge test for weather tightness, a pressure test for wind uplift resistance and a test of the spread of flame.

The spread of flame test is a requirement for all building materials used as a roof covering.  Building regulations, e.g. Approved Document B in England, impose  limitations (area and location limitations) on the use of materials that do not achieve a high enough performance rating.  To comply with building regulations without a fire rating is impossible (which raises questions about how some roof integration systems were compliant before MCS012 forced those manufacturers that had not already done so to perform these tests).

Read more about building regulations for fire and roof integrated solar here.

It was this test of the spread of flame that has caused the most recent delay to MCS012 coming into force.  The original version of the standard had not properly accounted for universal roof integrated mounting systems (those that can be used with pretty much any solar panel).

MCS012 was previously silent on how to interpret the fire performance test for universal roof integrated mounting systems when these relied on the presence of the solar panel to achieve the fire rating of the system as a whole.  As a consequence, certifying bodies (CBs) were left to develop their own interpretation, which they duly did, but inconsistently.  Some CBs issued an MCS012 certificate that limited the system to be used with only the module with which the system had been fire tested, others tested with only one panel but issued the MCS012 certificate to apply when the mounting kit was used with any module at all.

The first interpretation is incredibly limiting for systems that give the installer freedom to choose any solar panel, implying that manufacturers of such systems would need to repeat costly fire testing with every single type of panel that their customers might want to use.  In theory, the second interpretation is dangerous to public safety as it extends the tested fire performance to an installation using solar panels made from plastic, wood or, for that matter, chocolate.

Solar panels had rarely been fire tested before MCS012 made it mandatory.  Their design appears so undifferentiated that it seemed obvious that they would perform identically in such tests.  However as tests proceeded, reports emerged that outwardly identical-looking products were performing very differently in the fire test.

At the same time, regulators in the US had found a similar issue with fire rating of solar panels and published standards (UL 1703) categorising panels into 15 families that could be considered to have the same fire performance for the US fire tests. An international precedent exists.

The MCS012 working group decided that the responsible reaction to this new information was to choose the most restrictive (and therefore most safe) option - that a certificate can only be issued for the roof integration system with the panel(s) with which it has actually been tested.  This change was implemented in the latest version of the standard.

Roof integration systems that use a dedicated solar panel or solar tile are unaffected by this change, as they will have already been tested with the only panel type they use.

However, manufacturers of universal solar roof integration kits that work with many types of solar panels now have a number of options available to them for their products to remain in compliance with the requirements of the MCS scheme (and building regulations).  They can either:

(1) Re-test the system without the solar panel in place to achieve a certified fire rating that is independent of the fire performance of the panel;

(2) Re-test with a range of panels to achieve a certified fire rating.  Installers must then choose panels to pair with the mounting system from a more limited range; or

(3) Change installation instructions such that the system must be installed above a material that achieves an adequate fire rating in its own right (for example a fire board or fire-proof membrane).

Now this is sorted out, and the certification consistently applied, the standard has been made mandatory for PV installations.  Work to understand which features of a solar panel's design affects its fire performance is planned, with the goal of creating a similar set of product families to those in use in the US, but based on UK fire testing standards.  In future, this would allow a manufacturer of universal systems to be used with a much wider range of panels based on a much smaller number of tests.