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CONSTRUCTION INNOVATION, Fall 1995
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The fact that excessive basement moisture and leakage are widespread problems led to the requirement in the 1993 Ontario Building Code for the provision of a drainage layer for the exterior of foundation walls. This layer can be in the form of mineral fibre insulation, free draining granular material, or a system which can be shown to provide equivalent performance to either of these two materials.
Since the introduction of the drainage layer requirement, a range of new technologies for the residential construction market has been developed. As these new products required equivalent performance criteria, IRC was asked to develop guidelines, under contract with the Canadian Home Builders Association, with funding support from several manufacturers and other sources.
IRC addresses the problem
"Ideally," says IRC evaluation officer Ron Waters, "well constructed foundation basement walls will not permit the transfer of soil moisture if they are well damp-proofed for lower water tables.
"Leaks occur through cracks that are the result of poor or inappropriate construction practices. The fact that foundation walls are typically constructed with concrete, and subjected to ground movement due to shrinkage, swelling and settlement of the surrounding soils, also contributes to cracking."
The technical guide developed by CCMC, in conjunction with building envelope experts at IRC, classifies drainage products into two broad categories: Class A products, which are designed to deliver transient water to the footing drain, and Class B products, which have a proven capillary breaking ability (with a limited drainage capacity) to prevent moisture from penetrating the foundation.
Test methods
"Standard test methods to determine the drainage capacity of both classes of products were not available," says Waters. "Nonetheless, the existing ASTM D 4716-87 test method applicable to geotextiles and related products was adapted to test Class A products."
A side-water inflow test was devised to test Class B drainage products, and both methodologies are described in the CCMC technical guide.
"There is no doubt that other issues related to Class A and B products such as tear strength, puncture strength, clogging and durability need to be considered when evaluating their performance," says Waters. "Many of the criteria and test methods currently available for geotextiles can be readily adapted to the design of drainage products, and this is the approach taken in the technical guide."
A few suggestions
Foundation drainage layers will not perform their intended function unless additional simple, effective and economical measures are taken. These measures, which constitute good engineering practice, are as follows:
- provide an impervious topping-off layer of clay-silt mixture on top of the backfill with a positive slope leading surface water away from the building
- create a well defined drainage path for the water to enter the footing drain
- provide a footing drain (weeping tile) adjacent to the footing at the base of the foundation to channel water to the storm sewer. This drain should be embedded in a 150-mm layer of gravel or crushed stone. After a period of time, the footing drain lowers the water table to a steady state hydraulic condition.
End results
Once the manufacturers of these products complete their testing and prove conformance to the CCMC technical guide, each product will be assigned an evaluation number and the CCMC evaluation reports will appear in the CCMC Registry of Product Evaluations.
For more information about this work contact Mr. Ron Waters, telephone (613)993-6602, fax (613)952-0268.
