Designing a Passive House slab

Designing a Passive House slab for a two-story home measuring 9 meters by 12 meters (108 square meters) in Canada requires meticulous planning to meet energy efficiency goals and adhere to the National Building Code of Canada (NBC). This guide provides a comprehensive overview of the materials, quantities, and costs involved in constructing an insulated slab-on-grade foundation for 2024, including considerations for soil preparation, insulation, reinforcement, concrete, utilities, and radiant floor heating.

1. Soil preparation

Proper soil preparation ensures a stable foundation and prevents issues like settling or frost heave.

Excavation: Remove topsoil and organic materials to reach undisturbed soil.
Compaction: Compact the subgrade to achieve the required bearing capacity.
Gravel Base: Place a layer of crushed stone or gravel to facilitate drainage and provide a solid base.
- Quantity: A 150 mm (6-inch) gravel layer over 108 m² requires approximately 16.2 cubic meters of gravel.
- Cost: At an average of $50 per cubic meter, the gravel totals around $810.

2. Insulation

High-performance insulation is crucial for achieving Passive House standards.

Material: Expanded Polystyrene (EPS) rigid foam is commonly used due to its compressive strength and insulating properties.
Thickness: To achieve an R-value of 50, a total insulation thickness of approximately 250 mm (10 inches) is recommended.
- Quantity: 108 m² area with 250 mm thickness equates to 27 cubic meters of EPS.
- Cost: EPS costs about $150 per cubic meter, totaling approximately $4,050.

3. Reinforcement

Reinforcing the concrete slab enhances its structural integrity.

Rebar: Use 15M (15 mm diameter) rebar placed at 300 mm (12-inch) intervals.
- Quantity: Each direction requires 30 bars (9 m / 0.3 m), totaling 60 bars. Each bar should be 12 m long to cover the 9 m span with overlaps, resulting in 720 linear meters of rebar.
- Cost: At $2 per linear meter, rebar costs approximately $1,440.
Wire Mesh: An alternative or addition to rebar is steel wire mesh for crack control.
- Quantity: Standard sheets cover 2.4 m x 6 m; thus, 8 sheets are needed.
- Cost: Each sheet costs around $80, totaling $640.

4. Concrete

A durable concrete slab forms the foundation of the structure.

Thickness: A 100 mm (4-inch) slab is standard for residential applications.
- Quantity: 108 m² area with 100 mm thickness requires 10.8 cubic meters of concrete.
- Cost: Concrete is approximately $200 per cubic meter, totaling $2,160.

5. Utilities Installation

Proper planning for utilities ensures functionality and compliance with codes.

Plumbing and Electrical Conduits: Install sleeves and conduits before pouring the slab to accommodate water lines, drains, and electrical wiring.
- Cost: Materials and labor for utility rough-ins typically range from $1,000 to $2,000.

6. Radiant Floor Heating

Integrating a hydronic radiant floor heating system enhances energy efficiency and comfort.

Piping: Install PEX tubing in loops, spaced 150 mm (6 inches) apart.
- Quantity: Approximately 1 meter of tubing per square foot, totaling about 1,160 meters.
- Cost: PEX tubing costs around $0.50 per meter, totaling $580.
Manifold and Controls: Essential for regulating the heating system.
- Cost: Approximately $1,000.

7. Labor Costs

Labor expenses vary based on region and complexity.

Excavation and Site Preparation: Approximately $2,000.
Insulation Installation: Around $1,500.
Reinforcement Placement: Approximately $1,200.
Concrete Pouring and Finishing: Around $2,500.
Radiant Floor Installation: Approximately $2,000.

8. Compliance with the National Building Code of Canada

Ensure all construction practices adhere to the NBC, focusing on:

Thermal Performance: Achieving the required R-values for energy efficiency.
Structural Integrity: Proper reinforcement and material specifications.
Moisture Control: Implementing vapor barriers and proper drainage.

Total Estimated Costs for 2024

Materials: Approximately $10,680.
Labor: Around $9,200.
Total: Approximately $19,880.

Please note that these are estimated costs and can vary based on market conditions, location, and specific project requirements. Consulting with local professionals and suppliers will provide more accurate figures tailored to your project.