Foundations Flashcards
What are the three primary types of residential foundations in Southern California?
- Slab-on-grade: A single concrete slab poured directly onto the ground common in areas with stable soil. 2. Crawl space: Elevates the structure slightly above ground allowing space for utilities and moisture control suitable for uneven terrain. 3. Basement: Below-ground-level structure that provides additional living or storage space, with foundation walls supporting the building and a concrete slab forming the basement floor.
What is a stem wall in foundation construction and where is it commonly used?
A stem wall is a short masonry or concrete wall that extends from the footing to support the structure above. It is commonly used in crawl space and basement foundations providing a sturdy base and additional height for uneven terrain.
What is the role of rebar in foundation systems and where is it commonly used?
Rebar or reinforcing steel enhances the tensile strength of concrete preventing cracks from spreading. It is essential in footings slabs and grade beams to ensure the foundation’s structural integrity.
What are piers in a foundation and how do they function?
Piers are vertical structural elements that transfer loads from the building to the ground or deeper soil layers. They are often used in crawl spaces or pier-and-beam foundations to elevate the structure and provide stability on uneven or expansive soils.
What is a grade beam and how does it interact with other foundation components?
A grade beam is a reinforced concrete beam placed at ground level that spans between footings or piers. It provides lateral support and helps distribute loads evenly across the foundation.
How do control joints in a slab-on-grade foundation help prevent damage?
Control joints are intentional shallow cuts in the concrete that allow for controlled cracking due to shrinkage or thermal expansion. They reduce the risk of random structural cracks.
What is expansive soil and why is it a concern for foundations?
Expansive soil is clay-rich soil that swells when wet and shrinks when dry. This movement can cause foundation cracks uneven settling and structural damage if not accounted for during construction.
What is a vapor barrier and why is it critical in foundation systems?
A vapor barrier is a layer of material often polyethylene placed beneath concrete slabs or crawl spaces to prevent ground moisture from seeping into the structure. It protects against mold mildew and wood rot.
What is hydrostatic pressure and how does it impact foundation systems?
Hydrostatic pressure is the force exerted by standing water against a structure. It can push water through cracks or porous materials in the foundation causing bowing cracks and water intrusion especially in poorly drained soils or during heavy rainfall.
What is a post-tensioned slab and what advantages does it offer?
A post-tensioned slab is reinforced with steel cables that are tensioned after the concrete is poured. It provides higher strength reduces cracking and is particularly useful in areas with expansive soils.
What are the key layers in a slab-on-grade foundation and how do monolithic slabs differ?
A typical slab-on-grade foundation includes: 1. Finished floor. 2. Concrete slab. 3. Vapor barrier. 4. Compacted gravel or sand. 5. Stabilized soil subgrade. Monolithic slabs differ by combining the slab and footing into one continuous pour simplifying construction and improving strength.
What are the key layers in a crawl space foundation system?
- Finished flooring above joists. 2. Floor joists: Provide structural support. 3. Subfloor sheathing. 4. Moisture barrier or vapor barrier over soil. 5. Crawl space ground with compacted soil or gravel.
What additional layer is required in basement foundations compared to slab-on-grade?
Basement foundations include: 1. Concrete slab for the floor. 2. Foundation walls to support the structure above. 3. Footings beneath the walls. 4. Drainage layer or perimeter drain to prevent water buildup. 5. Vapor barrier and compacted gravel base beneath the slab.
Why is the footing-to-foundation wall connection critical and how should it be integrated?
The footing-to-wall connection transfers structural loads to the ground. Proper integration requires: Rebar extending from the footing into the wall; A seamless concrete pour or keying for additional strength; Waterproofing to prevent water seepage at this joint.
What makes the slab-to-wall connection a potential weak point for water intrusion and how is it managed?
Water can seep into the joint where the slab meets the foundation wall. Management includes: Installing a water stop or keyway in the joint; Applying waterproofing sealant; Ensuring proper slope away from the foundation to reduce hydrostatic pressure.
How does the crawl space foundation integrate with exterior walls to prevent water intrusion?
Integration involves: A continuous moisture barrier extending from the crawl space ground to the exterior wall; Proper sealing of vents and openings; Flashing and waterproofing where the wall meets the foundation to direct water away from the structure.
What role does a French Drain / Sub Drain / Perimeter Drain play in foundation integration?
A perimeter drain collects and redirects water away from the foundation to prevent hydrostatic pressure and water intrusion. It integrates with: The base of the foundation wall; Gravel layers for proper drainage; A sump pump if natural drainage is insufficient.
How should a vapor barrier be integrated with a concrete slab to ensure full moisture protection?
The vapor barrier must: Extend fully beneath the slab with sealed seams; Wrap up the sides of the foundation walls; Overlap with any additional waterproofing materials at integration points to create a continuous moisture barrier.
