Section 1: Simplified method

1.1 This section details a simplified method for demonstrating compliance with requirement O1. It is suitable for any building within the scope of requirement O1.

NOTE: Appendix B of this approved document includes a compliance checklist. The designer may use this checklist to demonstrate compliance to building control bodies.

Categorising residential buildings (simplified method)

1.2 For the simplified method, the strategy to reduce overheating risk should be selected according to the location of the new residential building and whether it has cross-ventilation, following paragraphs 1.3 to 1.5.

1.3 For the purposes of following the simplified method, the building’s overheating risk category is determined by its location in one of the following areas.

a. ‘Moderate risk’ location – England, excluding high risk parts of London in (b).

b. ‘High risk’ location – urban and some suburban parts of London detailed in Appendix C.

NOTE: Appendix C also provides guidance for some parts of central Manchester.

1.4 For the purposes of following the simplified method, it should be identified whether the dwellinghouse or each residential unit, shared communal room and common space is able to have cross-ventilation, i.e. it has openings on opposite façades.

NOTE: Having openings on façades that are not opposite does not meet the approved document definition of cross-ventilation, e.g. in a corner flat.

NOTE: A multi-occupancy residential building should not be categorised as having or not having cross-ventilation. Each residential unit, shared communal room and common space should be categorised separately.

1.5 The building’s overheating risk category based on location and whether it is cross-ventilated should be used to select the relevant guidance for both of the following purposes.

a. To limit unwanted solar gains in summer – follow paragraphs 1.6 to 1.9.

b. To provide an appropriate means of removing excess heat from the indoor environment – follow paragraphs 1.10 to 1.13.

Limiting solar gains

1.6 To limit solar gains, all of the following standards should be followed.

a. The maximum glazing area of the building or part of the building given in Table 1.1 or Table 1.2. This should be determined using the orientation of the façade that has the largest area of glazing.

b. The maximum glazing area of the most glazed room given in Table 1.1 or Table 1.2. This should be determined using the orientation of the façade that has the largest area of glazing.

c. Shading for buildings in the high risk location, following paragraph 1.9.

1.7 Buildings or parts of buildings with cross-ventilation should not exceed the maximum glazing areas in Table 1.1.

1.8 Buildings or parts of buildings with no cross-ventilation should not exceed the maximum glazing areas in Table 1.2.

1.9 Residential buildings in the high risk location should, in addition to following the maximum glazing areas in Table 1.1 and Table 1.2, provide shading for glazed areas between compass points north-east and north-west via the south. Shading should be provided by one of the following means.

a. External shutters with means of ventilation.

b. Glazing with a maximum g-value of 0.4 and a minimum light transmittance of 0.7.

c. Overhangs with 50 degrees altitude cut-off on due south-facing façades only.

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Table 1.1 Limiting solar gains for buildings or parts of buildings with cross-ventilation

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Table 1.2 Limiting solar gains for buildings or parts of buildings without cross-ventilation

Removing excess heat

1.10 Buildings or parts of buildings with cross-ventilation should equal or exceed the minimum free areas in Table 1.3.

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Table 1.3 Minimum free areas for buildings or parts of buildings with cross-ventilation

1.11 Buildings or parts of buildings with no cross-ventilation should equal or exceed the minimum free areas in Table 1.4.

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Table 1.4 Minimum free areas for buildings or parts of buildings without cross-ventilation

1.12 Openings should be designed to achieve the free areas in paragraphs 1.10 and 1.11. The equivalent area of the opening should meet or exceed the free area of the opening. The equivalent area of the opening should be assessed by either of the following means.

a. Measurement of the product to BS EN 13141-1.

b. Calculation using Appendix D.

NOTE: A system for purge ventilation should be provided in each habitable room to demonstrate compliance with Part F of the Building Regulations. The guidance in Section 1 of Approved Document F, Volume 1: Dwellings gives minimum standards for purge ventilation. When following this simplified method, applying the guidance in paragraphs 1.10 to 1.12 will usually result in free areas that exceed the free areas in Approved Document F, Volume 1: Dwellings.

1.13 The simplified method is not suitable for buildings with more than one residential unit which use a communal heating or hot water system with significant amounts of horizontal heating or hot water distribution pipework. Main distribution routes should be through vertical risers to minimise heat gains into common spaces.