Basement car parks

Basement car parks provide a significant amount of ventilation and this also makes them very effective in protecting against ground gas (see Box 8.7). 

Car parks should be ventilated passively (or naturally) wherever possible (Institution of Structural Engineers, 2002). The Institution of Structural Engineers (2002) and the Building Regulations Part F require the following ventilation  

Provision of vents in the two opposing longer sides with a ventilation area equal to 2.5% of the parking area (on each side and at each level in the car park). 

Mechanical ventilation to dilute carbon monoxide concentrations to 50 ppm (usually by providing a minimum ventilation of 3-8 air changes per hour depending on usage patterns). 

Assume a basement car park that is 30 m x 20 m in plan and 2.5 m high is to be built on a site with a surface emission rate of methane of 0.0231/h/m  

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Many inban developments include basement car parks that are well venhlated to deal with exhaust gases from cars. They are often constructed with thick reinforced concrete retaining walls and cast in situ suspended floor slabs. The basement is in effect a very large and effective ventilated void that provides more than adequate protection against low levels of ground gas. Care should be taken, however, to ensure that features such as lift shafts or service risers which extend to the base of the car park are provided with adequate protection. 

However, care needs to be taken in detailing basement car parks as there may be places, such as bin stores or parts of the main building that are not over the car park, that may require some form of specific ground gas protection. 

Commercial buildings with basement car parks, provided with ventilation in accordance with the Building Regulations, may not require gas protection for characteristic situations 3 and 4. However, features such as stair wells, lift pits, bin stores, etc that are located at basement floor level will require separate consideration and may still require some form of protection. 

Ventilated car park (basement or undercroft) 4 / sumes car park is vented to deal with car exhaust fumes, designed to Building Regulations Document F and IStructE guidance. 

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