Freeing up underground space – either through new build projects or refurbishment works – can transform homes, creating flexible living opportunities which make the most of the land available underfoot.
However, such works can be particularly sensitive to failures due to poor workmanship or the inappropriate use of materials or bad design.
According to national trade body the Property Care Association (PCA) it’s crucial to call in the experts to create dry, warm and habitable areas.
In this article Michael Earle, a trainer in structural waterproofing for the PCA, gives an overview of some of the main areas to consider to keep projects on the right track.
Understand Grades – There are 3 grades of basement environment, 1, 2 and 3. Examples of a grade 1 environment include a car park and plant room without electrical equipment, where it’s considered tolerable to have some seepage and damp areas appropriate to the intended use. No water penetration is acceptable for a grade 2 environment, however damp areas that are tolerable and 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.
Groundworks – Factors such as the type of soil and the water table are just some of the issues which need to be considered and the input of specialists at this early stage of the development is critical.
Think about ventilation – for now and the future. For example, if you are planning a garage, which might eventually become a bedroom, then think about its use specifically for the future.
Know the A, B and C – There are three forms of structural waterproofing, Type A, B and C. Type A is usually referred to as ‘tanked protection.’ These are structures that have no integral protection against water penetration and rely 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.
Structures built with a water resistant shell are referred to as Type B waterproofing systems. These will usually be 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.
Build in maintenance features – It’s important that consideration is given towards remedial works to enable a feasible repair to the underground waterproofing should it be required.
Keep a close eye on workmanship – The best materials in the world are only as good as the people that install them. 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. With this in mind, underground waterproofing projects should be undertaken by experts who understand the industry.
Bring in the experts – British Standard guidance now states that a specialist in waterproofing should be included in the design team of any structure where usable space is either partly or fully below ground. In response to this, the Property Care Association (PCA) has developed a register of Waterproofing Design Specialists.
This enables architects and other construction professionals to access a pool of vetted and approved experts with specialist knowledge and qualifications in structural waterproofing to assist in the design and planning of projects involving underground waterproofing.
Download your free guide from the PCA: “Basement Waterproofing in Existing Buildings”