Approved Document O England

There are two routes to demonstrate compliance with Requirement O1(1):

1. The Simplified Method: a prescriptive approach, which defines maximum glazed areas and minimum window open areas, which can only be used where apartment district heating systems are not distributed in the common areas and where the measures detailed in Requirement O1(2) are met; and

2. Dynamic Thermal Modelling: a computational method offering additional design flexibility over the Simplified Method, including:

• Residential buildings with very high levels of insulation and airtightness
• Residential buildings with specific site conditions
• Residential buildings that are highly shaded by neighbouring properties, structures or landscape

Whichever route is taken, the study should culminate in a usable Overheating Strategy.

In Section 3 Ensuring the overheating mitigation strategy is usable there are standards relating to noise at night, pollution, security, protection from falling and protection from entrapment.

For noise at night, paragraph 3.3 states:

3.3 Windows are likely to be closed during sleeping hours if noise within bedrooms exceeds the following limits:

a. 40dBL^Aeq,T‘ averaged over 8 hours (between 11pm and 7am).

b. 55dBL^Aeq,T‘ more than 10 times a night (between 11pm and 7am).

For pollution, paragraph 3.5 states:

3.5 Buildings located near to significant local pollution sources should be designed to minimise the intake of external air pollutants. Guidance is given in Section 2 of Approved Document F, Volume 1: Dwellings.

These two paragraphs place environmental constraints on the extent of the use of an open window or a natural ventilation opening within the overheating strategy.

To maintain sufficient security, only the proportion of openings that can be opened securely should be considered to provide useful ventilation.

There is also guidance for the prevention of the risk of falling through openings and entrapment within devices used to reduce solar gain and prevent falling.