When purchasing a building, it is crucial to determine the type of foundation walls and have them inspected by a structural engineer. We recommend that potential buyers carefully review the pre-purchase report and complete any inspections recommended by the inspector before making the purchase to avoid unforeseen issues regarding the condition of the foundation walls. We have handled numerous cases of latent defects where buyers failed to ascertain the type of foundation walls or their condition.
Firstly, foundation walls are the base of buildings, and the structure rests upon them. The role of these foundation walls is to transfer the loads applied to the building, including the weight of the building itself, to the ground.
Foundation walls must also be strong enough to contain the surrounding soil and withstand various forces , such as frost heave. These foundations typically include a waterproof membrane to prevent water from seeping into the basement.
In Quebec, with regard to houses and residential buildings, foundations can be categorized according to the materials used, namely three (3) different types: rubble foundations, poured concrete foundations and concrete block foundations.
Rubble foundations
In general, the foundation walls of buildings built before 1910 are made of stones (rubble stone) and the joints between the stones are filled with lime mortar.
These rubble foundation walls are thick. Sometimes one finds rubble footings below these walls. Occasionally, there are no footings and the wall rests directly on the ground.
The common problem with this type of foundation is that it is not watertight , as the mortar joints deteriorate over time and water seeps in through them. Rubble foundation walls are less stable than poured concrete foundation walls, and the stones can shift.
As for concrete block foundation walls, they are sensitive to lateral soil pressure because these foundations are composed of independent blocks connected with mortar.
Concrete block walls are very weak to lateral forces because the blocks can shift and move independently. Thus, the walls lose their structural integrity and become lead free.
Furthermore, concrete block walls are not watertight due to the mortar joints connecting the blocks. Water can penetrate the blocks and fill the drainage channels, then seep inwards. Water infiltration and high humidity within concrete block walls cause mold growth and structural rot (affecting or abutting the foundation walls).
Poured concrete foundations
There are three generations of poured concrete foundation walls:
- Poured concrete from the XNUMXs and earlier: this type of foundation was composed of coarse concrete, which was common in the 1930s and earlier. Very often the Concrete from this time is friable and in poor condition. In addition, it showed no mechanical resistance and crumbled easily. This concrete, executed in the 30s and earlier, was of poor quality. Concrete technology was not advanced and, for this reason, the concrete was poorly dosed and large stones were added to reduce the quantity of concrete.
- Poured concrete from the forties and fifties: this type of concrete is better than the concrete of the 30s. However, the concrete of that time was porous (not waterproof). Therefore, the walls are not waterproof and the foundations must be waterproofed from the outside to prevent water infiltration and humidity in the basement. Finally, it is necessary to ensure a good drainage around these foundations.
- Poured concrete after the 60s: in general, from the 60s, the concrete is of good quality and it is less porous than the old concrete. In addition, this type of concrete demonstrates good compressive strength.
It should be mentioned that all types of foundations can be affected by soil subsidence, lateral soil force, frost force, high loads, and others. Note that water infiltration can occur with all types of foundations depending on several factors, such as the quality of the materials used in the manufacture of the foundations, the drainage around the building, the presence of cracks, the absence of waterproofing. the exterior, etc.
© Lateral displacement of the concrete block foundation wall
© Collapse of a rubble foundation wall during underpinning work in the basement.
© Generally, the concrete in foundation walls from the 1930s is crumbly.
