Structural Waterproofing

If adding a room for residential purposes, then the building regulations will become applicable. Exceptions may apply depending on the use of the building for example plant rooms not visited by people. If unsure you should always consult a building control body who will provide advice when the regulations apply.

Responsibility for ensuring that the work complies with all applicable requirements of the building regulations falls to those that carry out the building work, this includes the designers, installers and the building owners.

Was last revised in 2019 and covers precautionary measures necessary to provide safety from fires for building occupants, persons in the vicinity of buildings, and firefighters and.
The effect that this document will have on basement conversions will be dependent on the intended use. Basements being designed to habitable grade should have one of the following.

• a. An emergency escape window or external door providing escape from the basement” to ground floor level ensuring any such opening well may need to be guarded to stop people falling into the well.
• b. “A protected stairway leading from the basement to a final exit.”

In addition, Approved Document B may influence the choice of internal linings to prevent internal fire spread. Particularly the ceiling areas within the basement may need to be upgraded to be fire resistant.

In some circumstances a basement should be separated from the rest of the house using an FD20 fire door. Mains operated and interlinked smoke detectors may be required to the ground floor hallway and first floor landing. If the basement becomes a kitchen a heat detector should be provided to the kitchen.

This document will be applicable in relation to any drainage of Type C Systems but also any land drains that maybe used within the waterproofing system.

This document sets out the requirements of the building fabric to prevent heat loss and may influence the requirements of insulation to the ceiling, walls and floors within the basement conversion. In addition, for grade three environments where appropriate ventilation, de-humidification or air conditioning are required, this document sets out the requirements to prevent energy loss. Most insulation manufacturers provide U-value calculations to show compliance with current Building Regulations / Standards and best practice. These can be supported with a detailed report.

For the purposes of any structural waterproofing projects below ground below (such as basements), these areas should be fitted with lighting that is energy efficient lighting.

Basement, cellars and below ground spaces by their very nature will have reduced rates of air exchange and in basements (that are habitable), greater emphasis is placed on the need for the provision of adequate ventilation. For basements with a large permanent opening, ventilation should be classed as part of the whole dwelling. However, properties with an isolated basement may require special consideration and might need to be considered a separate entity to the remainder of the property.

Further guidance on distinguishing between atmospheric moisture and ground water issues in basements can be found in the: PCA Code of Practice for Waterproofing of Existing Underground Structures and the discussion paper Considering Ventilation and Air Management in Basements as part of an Overall Waterproofing Strategy.

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Walls between domestic dwellings are required to have a certain resistance to the passage of sound. This Approved Document sets out the acceptable limits and may also be applicable for deciding the make up between floors of the same building.

This Document will be applicable for connecting pumping systems and any subsequent electrical wiring. These works should always be undertaken by suitably qualified persons.

Note: Power points, cables, light switches, pipes and any other services must be remounted in front of the membrane in type C systems.

A design team includes an experienced waterproofing specialist, who should be engaged at the earliest possible stage.

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It Is important that the geology and hydrogeology, as well as the external drainage options and groundwater conditions of a site, are carefully considered. The type of soil and the water table also need to be evaluated, as well as any ground gas concerns.

There are four grades to consider, 1a, 1b, 2 and 3. Examples of a grade 1 structures include a car park and plant room without electrical equipment, where it’s considered tolerable to have some seepage and damp areas. No water penetration is acceptable for grade 2 structures, and for damp areas that are tolerable, ventilation might be required. No water penetration is acceptable again for grade 3, and this performance level also specifies ventilation, dehumidification or air conditioning as necessary appropriate to the intended use. If you are looking to use the new basement room as habitable space then you will need to achieve grade 3.

There are three waterproofing systems, Type A, B and C. However in reality for most basement conversions you will be limited to certain type A and type C systems.

Type A, usually referred to as ‘tanked protection,’ is a structure with no integral protection against water penetration. It relies totally on a waterproofing membrane to keep water out. Type A forms of waterproofing may be applied internally or to the outside of the structure or, in some cases, sandwiched between two skins of masonry or concrete.

Type B are structures built with a water-resistant shell, usually constructed out of reinforced concrete to an appropriate design code, which gives guidance in the grade of concrete to be used and spacing of the reinforcing steel. Special additives may also be used.

Type C or ‘drained cavity’ systems rely on a drained cavity within the basement structure. There is a permanent reliance on the cavity to collect groundwater that enters through the fabric of the structure. The drainage system directs the water to a drain or sump, where it can be removed from the building by gravity or pumping.

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First and foremost, the construction teams applying, installing and building the underground space must be fully aware of the critical nature of what they are doing, the importance of accuracy and the implications of any defects and errors.

Contingency planning for any localised defects should also be included as part of the overall water-resisting design for the structure. If feasible repair is not possible, then it may be required to look at what can be done in respect of the risk posed by groundwater.

In most cases, planning permission is unlikely to be needed when converting an existing basement or cellar. However Before progressing with a basement conversion, you should check with your local authority whether planning permission is required.