Contributed by Ian Moores. 16/05/08

Contributed by Ian. 16/05/08

Introduced a year ago the Code for Sustainable Homes is fast becoming a landmark on the horizon for Private Developers and the central focus of those working in the Public sector.

For private speculative housing production there is still no mandatory compulsion to undertake a Code Assessment, although from April 2008 a rating is mandatory (even if an assessment has not been carried out). Currently all social housing projects funded by Housing Corporation grants need to achieve level 3 of the Code, this is part of a stepped approach to ratchet up the standard over the coming years.

OVERVIEW OF THE CODE

The assessment itself is very much based on the Breeam Ecohomes scheme, with a number of minor changes. The code breaks the environmental performance of the dwelling down into nine categories, with mandatory elements within certain categories.

There are 4 entry uncredited level standards which must be achieved, even for code level 1: • Environmental impacts of materials • Management of Surface Water Runoff from developments • Storage of non-recyclable waste and recyclable household waste • Construction site waste management. If the mandatory minimum performance standard is met for the four un-credited issues, three further mandatory issues need to be considered. Two of these are awarded for every level of achievement recognised within the Code, and minimum mandatory standards increase with increasing rating levels. The two issues with increasing mandatory minimum standards are: • Dwelling emission rate • Indoor water use. The final issue with a mandatory requirement for Level 6 is Lifetime Homes. Categories with no minimum requirement include:

• Pollution • Health and Wellbeing • Management • Ecology

Of course, it is only when actual physical proposals are measured against the performance standards in the Code that the implications and costs of achieving them are understood.

ACHIEVING CODE LEVEL 3 AND ABOVE

ARK has been helping developers produce designs and specifications to achieve code 3 and higher. We benchmark specifications against cost to arrive at solutions which will achieve the desired code level in the most economic way possible.

Currently, ARK is currently working with Persimmon Homes to achieve code level 3 with the added complication of 10% renewable energy on site. In this case full data is required to produce reports on the total energy used to show how the 10% renewable portion is made up.

For many people the range of options is bewildering. There are infinite combinations of construction elements which will achieve the same level of the Code in different ways. Assessment of numerous combinations to value engineer compliant solutions has become an essential process. This process needs also to reflect other benefits gained from alternative construction techniques which could reduce build times with resultant cost savings.

SAP & Reduced Dwelling Emission Rates (DER)

Early on, the focus will naturally be on achieving the lower SAP dwelling emission rates, because it is necessary to hit the target on this mandatory standard:

Code Level Reduction DER/TER

Level 1 10% Level 2 18% Level 3 25% Level 4 44% Level 5 100% Level 6 100% of all emissions (true zero carbon)

Code Level 3

As SAP assessors our data consistently shows that achieving Code Level 3 without the use of renewable sources is possible but requires a very high performance building fabric. Much higher than many in the industry had originally thought. Typically the specification for a terraced house would include very high levels of insulation to walls, floors, roof, windows and doors combined with a low air leakage through gaps in the construction (which would preclude load bearing masonry building techniques). By adding some renewable energy like solar thermal hot water or an air source heat pump the insulation levels could be relaxed considerably.

Code level 4

Achieving Code Level 4 is proving practically impossible without the addition of a small amount of renewable power. We have completed calculations which indicate that, by super insulating the fabric of the building and using an airtight form of construction (comparable with the German Passivhaus specification) using mechanical ventilation with heat recovery, 44% reduction in DER is achievable.

Most developers are finding the cost of achieving code 3 & 4 is substantially in excess of the figure given in the costing prepared by Cyril Sweett for Central Government.

As one seeks to passively reduce the energy used by the dwelling, factors like the orientation and air leakage become increasingly important. Ideally code levels 3 & 4 should focus on conserving energy before adding expensive renewables. If the developer has not explored fully the fundamentals of reducing energy usage, going to the higher level 5 & 6 would require completely unfeasible levels of renewable energy.

Code level 5

Code 5 can only be achieved using renewable energy sources because net energy use should be zero for hot water, space heating and lighting.

Code level 6

Finally, reaching code 6 means providing renewables, not only for the power needed for heating, lighting and hot water but also the occupants other power needs, including appliances and cooking. Early examples, like the Kingspan Lighthouse at the BRE in Watford, have reached code level 6 with total energy use at around 85 Kw/m² /yr including an occupancy element of around 20 Kw/m² /yr.

It is somewhat debatable as to whether these figures truly reflect the kind of realistic usage that the average UK household is likely to generate. In Europe the German Passivhaus standard, which specifies super insulated and airtight construction suggests a combined figure of 120 Kw/m² /yr is a typical. What is clear is that generating even 85 Kw/m² /yr within the curtilage of the individual house is a huge challenge and very expensive.

Micro generation renewable sources could include:

Ground source heat pumps Air source heat pumps Wind turbines Photovoltaic panels Solar thermal panels Biomass boilers Mini combined heat and power plants

The Future

Looking to the future there is a big question mark over achieving code 6 on every new dwelling. Micro generation renewables will clearly play a part. Ultimately though will they realistically need be supplemented by centrally generated renewables ?