Guest blog from Graham Suttill, Sustainable Buildings Assessor at Darren Evans Assessments:
Increasingly stringent efficiency requirements within Part L of the Building Regulations mean that many projects struggle to achieve compliance without bolting on renewable technologies. However, despite renewables being an easy option this is not always appropriate. In these instances, creative thinking can instead be used to enhance the building fabric and services in ways that are cost-effective, easy to implement, and above all, low energy.
With the 2013 Part L revision having had a chance to bed down, developers, architects and housebuilders now have a good understanding of what is needed to comply with the regulations. However, it would appear that the majority of initial SAP calculations do not meet the emissions or fabric energy targets with the specification provided. The simplest approach in this situation might be to just add on a few PV panels, but this is rarely the route to compliance many clients want to take due to the additional cost added to a project and the resulting change in its appearance.
So what can we do? The first step should be to look at the fabric of the building, which would either mean increasing the insulation thickness or specifying a higher performing insulation product which provides a better U-value with the same thickness. This might increase the capital cost but would balance against savings on additional systems such as heat recovery which might be required to enable a building to pass.
Within the latest SAP software the thermal bridging calculation (heat loss across junctions such as where the wall meets the floor, known as the Psi value) has a large impact on whether the dwelling will pass or fail, as improvements here will positively impact emissions and the fabric energy efficiency targets. As a starting point we will always use accredited construction details (ACDs) but ideally you need to be offering a further improvement.
The most widely used set of calculated values which offer improvements over the ACDs are the Aircrete Product Association (APA) details; these can be used when a lightweight block is specified as the inner leaf of the external wall. The junction which has the largest impact on the heat loss figure is the lintel, so using an independent or high performance lintel such as the IG Hi-Therm in conjunction with the APA detail will offer a significant improvement to your SAP calculation.
There are other straightforward design approaches that can be modelled to offer enhancements to an SAP score in addition to improvements to the building fabric. The two most commonly specified are flue gas heat recovery systems (FGHRS) and waste water heat recovery systems (WWHRS) which are both used with combi boilers, however, WWHRS can also be used with a hot water cylinder. A FGHRS works by taking the combustion heat from a boiler which would normally be lost through the flue and using it to preheat cold water entering the boiler; this lowers the amount of energy needed to heat the water to the required temperature. WWHRS works by recycling the heat from waste water from a bath or shower to preheat cold water via a heat exchanger before it enters the boiler.
Both of these systems can make significant improvements to your SAP calculation which can be the difference between a pass or fail. They are also much cheaper to install than solar PV or solar hot water systems making them a preferred route to compliance for clients in many cases.
So the lesson is that by thinking outside the box and exploring alternative ways of ensuring a building meets the tougher demands of Part L on CO2, it is possible to arrive at a simple and effective solution which avoids the need for bolt-on renewables.