In my experience, several cases of hidden defect have been discovered, by new owners, during the renovation of their basement or because of a water infiltration or the presence of carpenter ants. More particularly, a very common hidden defect is that which is connected to a concrete terrace resting on the building's foundation wall.
Very often, the owners discover that the wooden structure is completely rotten, at the top of the foundation wall, behind the concrete terrace. Thus, the wooden structure - resting on the foundation walls - which can be rotten is found to be the seat beam, the joist edge and the ends of the joists or the beams [which rest on the seat beam in this location].
Cause of rotting structure
The main cause of this problem of rotting of the structure, behind the slab of the concrete terrace, is as follows:
- At the base of the masonry facing, there are no weepers to evacuate the water that may be behind the masonry. Thus, the base of the facing is completely closed.
First, at the base of the exterior facing, at the junction between the concrete slab of the terrace [which rests on the foundation wall] and the brick wall, there must be a waterproofing system composed of a basic flashing, an air barrier membrane (or covering paper) and weep chanters. This system must be installed in such a way as to prevent water infiltration towards the interior of the building, and to evacuate through the weepers, towards the exterior of the wall, as water may be behind the brick wall.
You should know that the masonry facing is not completely rainproof. During heavy rain, there is an amount of water that can pass through, the masonry facing, through the mortar joints, cracks, and bricks. The water that infiltrates inside the masonry wall trickles down the wall, which requires a well-made sealing and evacuation system [at the base of the masonry wall, at the junction between this last (base) and the concrete terrace]. Thus, at the base of the wall, we must find the basic flashing and the weeping rails.
If there is a concrete terrace that rests on the foundation wall, there must also be a waterproofing system below the threshold of the patio door leading to this terrace. This sealing system is composed of a membrane and sealing joints and must be integrated - with the sealing system - at the base of the adjacent facing. This waterproofing system prevents water infiltration (under the patio door threshold) to the wooden structure located directly under the patio door and above the foundation wall [inside the basement]. This wooden structure normally consists of the seat rail and the joist as well as the ends of the joists or beams (which rest on the seat rail and which are fixed against the joist).