Going off-grid

Ian Digby of Calor discusses looks at how alterations to standard housing designs resulting from fuel choice can be reduced for off-grid properties, and the part played by Part L1A of the Building regulations.

Complying with Part L1A of the Building Regulations (‘conservation of fuel and power in new dwellings’) is one of the more challenging aspects of modern housebuilding. Because of these challenges, developers have spent a large amount of time and effort in recent years perfecting their standard house type range to deliver compliance in the most cost-effective fashion.

It is estimated that five per cent of new dwellings built each year are unable to connect to the mains gas supply. There are a range of alternative fuel options available to housebuilders – including liquefied petroleum gas (LPG) and oil and air source heat pumps (ASHPs). However, the choice of fuel source can have a significant impact on house designs.

Opting for oil

Traditionally, rural housebuilders would have considered oil heating as the default option for developments beyond the mains gas grid. However, in recent years the number of modifications required to a property heated by oil for it to pass Part L1A have made this an expensive option.

Firstly, because of the high CO2 emissions of oil in comparison to mains gas, the required changes in the fabric of the building (to reduce the amount of fuel used) means it is very difficult to achieve compliance without installing a significant amount of solar PV panels. The available roof space on smaller properties is often an issue, and in addition, the need to make these roofs south-facing to generate the required amount of electricity makes matters more complex.

This, coupled with the higher price of the oil boiler itself and the need to modify standard internal layouts to accommodate the larger floor-mounted or external boiler, have led to the majority of housebuilders discounting oil as an option.

Hidden costs

In more recent years, rural housebuilders have moved to air source heat pumps (ASHPs) as an alternative. However, while there is usually no need to alter the base fabric specification of a property with an ASHP, there are a range of additional opera- tional costs to take into account.

To deliver the best efficiency levels, ASHPs work best at low temperatures, delivering hot water at 35 degrees. To compensate for these low flow tempera- tures, most installations will require underfloor heating or larger-than-standard radiators to heat the property, which again, is a major, costly deviation from the standard housing design layout.

An ASHP is unable to deliver instantaneous hot water in the same way that a gas combination boiler can for properties of up to four bedrooms, and as such, will always require a hot water cylinder to be installed into the property. This will likely impact on bedroom space, as an associated cylinder cupboard needs to be fitted.

An ASHP will also require a large exter- nal pump, in the style of an air conditioning unit, to be located near the home – almost always attached to the property in the rear garden, detracting from the overall site aesthetics.

It is important for developers to remem- ber that an ASHP uses technology that new home buyers may not be familiar with, and that there are significant operational differ- ences over a gas boiler. An ASHP is designed to maintain house temperature at a constant level, as opposed to a gas boiler, which will quickly bring a house up to temperature on request.

This means new occupiers may struggle to operate the heating system as efficiently as possible, leading to after-sales issues for housebuilders and buyer dissatisfaction.

In addition, due to the significant electricity requirements of a new estate built with ASHPs, it may be a requirement for the developer to cover the cost of upgrading the electric supply to the site, which could include the requirement for a new sub-station.

However, the major drawback to housebuilders of ASHPs is the equipment costs – with a heat pump costing around £3,500 – £4,000 per house. Coupled with the factors already discussed, this means house- builders could be looking at build cost increases of between £5,000 – £8,000 per property as opposed to mains gas.

Price is right with LPG

In comparison, LPG is the closest alterna- tive to mains gas, and offers the lowest CO2 emissions of any rural fossil fuel. Fewer modifications are required to pass Part L1A than oil or electric heating, and a developer can save significant build costs by taking a ‘fabric first’ approach and looking to reduce the CO2 emitted by the house.

Indeed, low cost energy saving ‘bolt ons’ such as waste water heat recovery or hi- therm lintels, which typically cost less than £500 per plot, are a far more cost-effective alternative to the costs of Solar PV, and produce the required uplift in SAP to meet Part L1A.

LPG boilers have the added benefit of being exactly the same size and flue clear- ance of standard mains gas boilers, and therefore, standard housing design layouts can be maintained, with the use of combi- nation boilers on smaller properties.

Major boiler manufacturers also produce LPG-compatible versions of their standard boilers, meaning a housing developer is able to utilise any existing group purchase deals which are available.

Typical installation costs on a 30-home development are £500 per plot, which covers the LPG tank, installation, connec- tions, pipework and meters all being fitted onsite. Housebuilders should also allow a budget figure of around £800-£1,000 per property for modification and connection costs when using LPG as opposed to mains gas, which is a greatly reduced figure in comparison to either oil heating orASHP.

As the closest alternative to mains gas, it is clear that LPG offers larger cost savings than other non-mains gas fuel options.

Ian Digby is specification manager at Calor