Options in the Selection of Materials for Basement Construction

Selection of proper materials is essential to the construction of basements that will provide liveable and comfortable indoor space. This Update discusses some of the key materials issues in basement construction and reviews the options regarding available materials and methods, including recent developments that enhance performance and efficiency.

A multi-year research project carried out at NRC-IRC with the support of many industry partners produced a comprehensive publication, Performance Guidelines for Basement Envelope Systems and Materials ¹

The publication provides an extensive review of basement issues and guidelines for design and construction based on categories of intended basement quality (see "Classification of basements by intended use," Table 1.2 of the Guidelines). It also presents the wide spectrum of options that builders are faced with. This Update, drawing on the key features of the basement performance guidelines, focuses on material and system selection issues involved in specifying the basement system. Update No. 69 addresses site grading and basement drainage issues.

Basements in houses serve as the foundation for the superstructure of the building, and provide usable living space. When properly constructed, basements resist the imposed loads from the surrounding ground, control moisture and temperature fluctuations, and help maintain suitable indoor air quality and comfortable conditions for occupants. By selecting the most appropriate materials for construction, designers and builders can avoid many of the problems typically associated with basements.

In order to select suitable materials, one must first determine the intended use and expected quality of the basement. Basements intended to be used as living spaces usually require different materials than those used only for mechanical equipment and storage. As it is often difficult and costly to apply materials such as drainage layers to the outside of a basement after a house is constructed, it is important to identify the desired level of performance before beginning construction.

Key Considerations

The selection of appropriate materials for the basement envelope system requires careful consideration at the design stage of the various roles to be played by the materials, not only with respect to their individual properties but also as part of an interactive system. Proper design demands a good understanding of technical issues and the conditions under which construction will be undertaken. While there are often a number of solutions for dealing with particular conditions and circumstances, some may be more appropriate than others in achieving the desired performance objectives and occupant expectations cost effectively.²

The major considerations are as follows:

Performance related: strength to withstand soil stresses (including hydrostatic pressure, which may or may not be a factor), and the ability to control heat and moisture flow, air leakage, soil gas infiltration, noise transmission, and to minimize fire hazards.

Construction related: availability and cost of materials and labour.

Different elements of basement envelope system: above-ground portion, below-ground portion, floor slab, joints and intersections.

Roles of different materials used in basement construction: structure, drainage, dampproofing (see sidebar), waterproofing, framing/furring, insulation, air/vapour barrier, soil gas barrier, exterior and interior finishing materials.

Waterproofing: Treatment of the surface or structure to prevent the passage of water through the basement envelope under hydrostatic pressures. Dampproofing: Treatment of a surface or installation of a technology to resist the passage of moisture caused by differences in moisture content, vapour pressure and temperature across basement envelope components. Note: Most new Canadian house foundations feature footing drainage systems with complementary dampproofing elements in the wall. This approach normally precludes the need for waterproofing. The basement systems discussed in this Update are based on drained approaches that do not involve waterproofing.

Additional considerations essential to the selection of basement materials and systems:

• Will the materials fulfill their intended role with respect to critical control functions?
• Are the materials compatible with one another?
• What materials and systems are required to provide environmental control corresponding to the classification of the basement being constructed?³
• Are the selected materials and equipment permitted by the regulatory authority having jurisdiction?

Structural Materials and Systems

Preferences in structural systems are often related to geographical location and based on local economics and availability of materials, builder preferences and experience. In urban areas, the availability, speed of placement and low cost of transportation favour cast-in-place construction in tract-built developments. In rural communities, the economics of carting ready-mix preparations over longer distances and for longer periods of time favour concrete block, which is more transportable and storable. Similarly, the economics of a lighter-weight system such as permanent wood foundations (PWFs) have been favoured in some Western provinces, where builders have gained considerable experience with them.

Manufactured systems such as precast concrete panels are beginning to emerge as innovative building materials. Potentially these can minimize on-site defects, thereby increasing the probability of meeting the basement's long-term functional requirements.

Each structural approach (see Figure 1), if properly designed, can be used to fulfill the various functions of the basement envelope, taking into account site conditions and intended use.

Source : http://irc.nrc-cnrc.gc.ca