As part of ongoing research into automated compliance testing against building regulations, the first set to have been fully implemented in ECOTECT is Part-L of the UK Building Regulations, which deals with the conservation of fuel and power. Now that most of the major issues have been overcome with this release, more regulations from different parts of the World should follow reasonably soon.


In terms of Part-L (Part-J in Scotland), ECOTECT is the only building modelling and analysis tool to directly address all aspects of compliance, including the Elemental Method. Obviously the Whole Building Methods for Schools and Hospitals are dictated by Education and NHS guidelines, however the Carbon Performance Rating (CPR) for office buildings is supported. As ECOTECT uses the CIBSE Admittance method for its thermal analysis, you can also use these to demonstrate solar control even if you do not comply the prescriptive provisions and for the Carbon Emissions Method. As ECOTECT can export to many other thermal analysis and simulation tools, it is significantly easier to apply the Carbon Emissions Method as this is by far the most flexible option.


The new Part-L Wizard guides you through the process of compliance usng either the Elemental Method or by automatically generating a notional building for the Carbon Emissions Calculation Method.

You can choose to test compliance with L1, L2 or both.

Many of the basic settings in the method are built-in, however you can also choose to visit the SEDBUK database.

ECOTECT can also automatically generate a notional building based on your existing model for use as a comparison in the Carbon Emissions Calculation Method. This include full calculation of maximum window sizes based on the 25 W/m2 solar gains in the 6m zone rule.
This all means that you can continually check your model against Part-L right the way through its development, knowing as soon as you make a particular design decision what ramifications it is likely to have. For more extensive and detailed information on the application of the regulations, see the SUSTAINABILITY > UK Part-L in the main menu.


After setting options in the Part-L Analysis dialog box, ECOTECT generates a HTML report which summarises the aspects of your building model that are relevant to the many provisions within the regulations. The information presented relates directly to Tables 1-3 of Approved Documents L1 and Tables 1-4 of L2. You can either use just L1 or L2 depeneding on you building type, or you can individually show/hide each table in the final output. To see what the results look like, you can click on any of the table headers shown below in order to see where each is located within an Example Output page.

This table is not required as part of the compliance analysis, however it shows the number of heated and unheated thermal zones in the model as well as their floor areas and volumes. Part-L is concerned primarily with building heating loads. Thus, if you have not specified a heating or air-conditioning system for any zones, you obviously use no heating energy (see the Zone Management dialog box for setting HVAC systems). Simply check this table to make sure the right number of zones are listed in each section.

This table relates to Paragraph 1.8 in Approved Document L1. This states that the requirements would be met if the average U-value of windows, doors and rooflights matches the relevant figure in ADL1 Table 1 and the area of the windows, doors and rooflights together does not exceed 25% of the total floor area. Thus the table lists total floor area and the total area of windows, doors and rooflights. For a domestic building, this requirement must be met in order to use the Elemental Method – otherwise the Target U-value or a SAP rating must be used.

This table lists the area-weighted average U-values and surface areas of all the elements listed in Table 1 of both Approved Documents. If the resulting U-value of any element is above the allowable value, it is highlighted in red and your model will fail this method. The table also lists the total heal loss rate and U-value of the building for direct comparison with the Target U-value and Notional Building tests described below if your design fails this method.

The Target U-value only applies to domestic buildings and is slightly more involved than the Elemental Method. It takes into account the overall insulation level of the building fabric, the relative efficiency of the installed heating system and the potential for direct solar gains. It can be used for any type of heating system and, even where extensions are being assessed, must only be applied to the whole building.

The methodology simply generates a target U-value based on the overall exposed form factor of the dwelling, and then modifies this value based on the efficiency of the boiler and the relative area of exposed south-facing glazing. To comply, the overall U-value of all elements of the building must be no greater than the calculated target value. If your design fails this and the Elemental Method table, you must look at the Carbon Index Method using a SAP rating tool.

This table only applies to commercial buildings and relates to Paragraph 1.15 in Approved Document L2. This states that compliance would be achieved if the rate of heat loss from the proposed building does not exceed that from a notional building of the same size and shape that meets the criteria set out in Table 1 and Table 2; and the U-value of any part of an element is no worse than the values given in Table 3.

ECOTECT generates the notional building for you and displays a table in exactly the same format as the Elemental Method described above, using the maximum allowable U-values and apperture ratios for each element. As with the Elemental Method, a total building U-value and heat loss rate is derived. To pass, your model must have a lower total heat loss rate than the notional building.

If your design fails this and the Elemental Method table, you must use either the Whole Building Method or Carbon Emissions Method. The Whole Building Method pages contain a useful interactive calculator for the Carbon Performance Rating of office buildings.

This table is also applicable only to commercial buildings and relates to Table 2 and Paragraph 1.12 in Approved Document L2. It states that provision should be made to limit the rate of heat loss through glazed elements of the building. One way of complying would be to limit the total area of windows, doors and rooflights so that they do not exceed the values given in Table 2 – unless compensated for in some other way.

This table therefore lists the window-to-wall and rooflight-to-roof ratios. To comply with this option, both ratios must be less than those shown in ADL2 Table 2 for the specified building type. If your design fails this, each heated thermal zone must pass either of the two following tables.

This table is also applicable only to commercial buildings and relates to Table 4 and Paragraph 1.22 of Approved Document L2. It states that a way of achieving compliance for spaces with glazing facing only one orientation would be to limit the area of glazed opening as a percentage of the internal area of the element under consideration to the values given in Table 4. The internal area of the element in ECOTECT is taken to mean the internal surface area of the facade elements facing in the same direction as the window.

Thus ECOTECT lists all the heated thermal zones in the model with glazing only on one side, calculating the facade areas and apperture ratios. If any zones fail in this table, that zone must pass the following Solar Gains table or you will have to demonstrate compliance based on Paragraph 1.23 (b) of Approved Document L2 (described below).

This table is also applicable only to commercial buildings and relates to Paragraph 1.23 of Approved Document L2. Section (a) of the paragraph states that compliance can be achieved by showing that the solar heat load per unit floor area averaged between the hours of 07:30 and 17:30 would not be greater than 25W/m² if the building were to be subject to the solar irradiances for the particular location for the month of July that were not exceeded on more than 2.5% of occasions during the period 1976 – 1995.

Only multi-sided zones or single-sided ones that failed the Glazing Area by orienetation test in the table immediately above are included in this table. ECOTECT uses the procedure shown in Appendix H of ADL2 to calculate solar loads in perimeter and interior area of each zone based on UK average solar gains given in Table H1. The table lists each orientation for each zone with the relevant areas and gains. To comply the average solar gains in each area must be less than 25W/m².

Of interest, if you choose the Display Solar Zones option in the Part-L Analysis dialog, you can actually watch as ECOTECT calculates each zonal area in the 3D model, displaying coloured dots ofr each window and orientation as it goes.

If any zone fails this test, you will have to demonstrate compliance based on Paragraph 1.23 (b) of Approved Document L2. This states that a detailed calculation procedure such as that described in chapter 5 of CIBSE Guide A35 can be used to show that, in the absence of mechanical cooling or mechanical ventilation systems, the space will not overheat when subjected to an internal gain of 10 W/m². For this you can use ECOTECT’s thermal analysis functions or export to another thermal simulation package.

The final table is simply a full list of each material used in the model together with its surface area and U-value. Even though the area-weighted average U-values of each element may comply with the Elemental Method, there are still maximum U-value allowances for individual materials. If any of your assigned materials fail at this stage, either choose a different material or negotiate with your Building Control Officer to see if any compromises can be made elsewhere in the scheme.Building Regulations

Communities and Local Government is responsible for policy on the Building Regulations, which exist to ensure the health, safety, welfare and convenience of people in and around buildings, and the energy efficiency of buildings. The regulations apply to most new buildings and many alterations of existing buildings in England and Wales, whether domestic, commercial or industrial.

To help you understand the Building Regulations:

the Department published The Building Regulations Explanatory Booklet. It provides an introduction to the Building Regulations in England and Wales only, and can be found below in the Related Publications section
in the Legislation section you can find out more about The Building Regulations which are made under powers provided in the Building Act 1984, and apply in England and Wales, and in the supporting “Building Regulations 2000” (as amended) and “Building (Approved Inspectors) Regulations 2000” (as amended) regulations
guidance on how to meet the functional ‘requirements’ of the Building Regulations, are contained in the Building Regulations – “Approved Documents” (external link). Adobe PDF copies can now be downloaded from the Planning Portal website