Section 6 ‘Energy’

Non-domestic Handbook (Scotland)

This section covers all types of non-domestic building. It includes standards for both new-build as well as work to existing buildings, including extensions and conversions. The only way of showing compliance for new buildings is to use an approved calculation tool such as the Simplified Building Energy Model (SBEM). This calculation method adopts a whole building approach to energy performance.

For extensions, conversions and renovation work to existing buildings, there are basically two levels of improvement, as explained on the opposite page. There is also guidance on work to historic buildings.

The SBEM

The SBEM is a computer programme that provides an analysis of a building's energy consumption. It is based on a set of CEN standards. It has been developed in order to comply with the EPBD. The first approved version of SBEM was issued in December 2005. The latest version can be downloaded free from www.ncm.bre.co.uk/index.jsp.

The SBEM calculates monthly energy use and carbon dioxide emissions for a building and takes into account the building geometry, construction, use, HVAC and lighting equipment.

How to comply – new buildings

The criteria set out below describe the process the designer and builder must go through to show compliance. The SBEM or other approved simulation software calculates the building’s energy performance in terms of CO₂ emissions per m2 per year for heating, cooling, hot water, ventilation systems and lighting. The SBEM allows the designer a high degree of flexibility in deciding how to achieve the required energy target. However, the Technical Handbook does set certain ‘backstop’ limits (see table from clause 6.2.1).

1. Calculate the CO₂ emissions for the notional building

Input the size and shape data of the proposed building into the SBEM calculation tool, together with the Scottish standard package of construction and building services performance measures.

Approved software, such as the SBEM, will automatically generate the CO2 emission rate for a notional building of the same size and shape as the proposed building.

2. Calculate the Target CO₂ Emission Rate (TER)

This is arrived at by applying an improvement factor and a LZC (Low or Zero Carbon energy source) Benchmark factor (see table right) to the CO2 emission rate for the nominal building.

The SBEM or other approved software will automatically generate the Target Emission Rate using the improvement factor and LZC benchmark in the table, right.

3. Calculating the BER

Once all the data for the proposed building is input, the building carbon emission rate is generated (known as the BER). If the BER is equal to or less than the TER, compliance with this section is achieved.

4. Design ‘backstops’

Standards 6.2 to 6.6 in the Technical Handbook mainly recommend ‘backstop’ levels of performance, which in most cases will need to be exceeded in order to meet the level of energy efficiency required in Standard 6.1 of the Handbook. The maximum U-values are shown in Table 22.

Other backstops include:

levels of air permeability
heating and hot water systems and controls
insulation of pipes, ducts and vessels
artificial lighting
mechanical ventilation and air conditioning

**Table 22: Improvement in whole building carbon dioxide emissions**
Building services strategy	Improvement factor	LZC benchmark factor	Overall improvement
Heated and naturally ventilated	0.15	0.10	0.235
Heated and mechanically ventilated	0.25	0.10	0.280
Air conditioned	0.20	0.10	0.280

5. Air tightness testing

There are three alternative approaches as far as the air-tightness of the building is concerned:

Adopt Accredited Construction Details (Scotland) and assume air leakage of 10m3/m2/hr at 50 Pa in the design
Where Accredited Construction Details are not used and no testing is planned, then the design must assume an air leakage rate of 15m3/m2/hr at 50 Pa
Air-tightness testing should be used where an air leakage rate of less than 10m3/m2/hr at 50 Pa is proposed in the design. Note that air leakage testing can also be used to justify a design input of between 10 and 15m3/m2/hr at 50 Pa where Accredited Construction Details are not used

6. Other requirements

As well as ensuring the CO₂ emission rate for the building is within target, the Technical Handbook lists four additional criteria that must be met to achieve compliance.

Commissioning of building services – services should be commissioned to achieve optimum energy efficiency, ductwork should be leakage tested and facilities should be provided for testing
Written information – covers requirements for user and maintenance instructions and the need for a logbook
Energy Performance Certificate – this must be displayed in a prominent place
Metering – as well as meters supplied by the utilities, sub meters are required for each activity area

**Table 23: New buildings – maximum U-values for building elements of the insulation envelope**
Type of element	(a) Area weighted average value for all elements of the same type (W/m²K)	(b) For shell of buildings to be fitted out later (W/m²K)	(c) Individual elements (W/m²K)
Wall	0.30*	0.25	0.70
Floor	0.25	0.22	0.70
Roof	0.25	0.16	0.35
Windows, doors and rooflights	2.20	1.80	3.30
Vehicle doors	1.50	-	-
* 0.35 for modular and portable buildings. This table combines the tables from clauses 6.1 and 6.3

How to comply – existing buildings

The level of improvement to the building fabric of an existing building depends on the type of work involved and whether the area to be converted was previously heated or not. There are also special considerations for historic buildings.

As far as maximum U-values are concerned, there are basically two standards for work to existing buildings. The first and most onerous covers new extensions, conversions of previously unheated buildings and reconstruction work (see column 1 in Table 24).

For work to an existing heated building, if the U-values are better than the maximum in column 2, then no upgrading work is necessary. However, if the U-values are worse than in column 2 and alterations are being made to the building fabric, then the element should be improved to at least the standard in column 2 in the case of walls, floors and roofs. Replacement windows, doors and rooflights should achieve the standard in column 1.

Building services

All new heating appliances, pipework, ducts and vessels should conform to the standard for new buildings. New artificial lighting and any mechanical ventilation or air-conditioning should also meet the standard for new buildings.

Conversions must also comply with the requirements for commissioning of building services, providing written user and maintenance instructions and for sub-metering. However, there is no requirement for an Energy Performance Certificate.

**Table 24: New buildings – maximum U-values for building elements of the insulation envelope**
Type of element	(a) Area weighted average value for all elements of the same type (W/m²K)		(b) Individual element (W/m²K)
	For extensions and reconstruction work	For conversion of heated buildings
Wall	0.27	0.70	0.70
Floor	0.22	0.70	0.70
Pitched roof insulation between ceiling ties or collars	0.16	0.35	0.35
Flat or pitched roof insulation between rafters or roof with integral insulation	0.20	0.35	0.35
Windows, doors, roof windows and rooflights	1.80	-	3.30