Backfilling stem wall foundation
Hello! I will be building my own home this year and am planning on building a stem wall foundation pinned to sloping bedrock. Im planning on filling the foundation with compacted fill then pouring a slab/or using a concrete-less slab. Regardless im curious if it’s ok/or how to use the proper method to compact the fill within the foundation without backfilling on the exterior or minimal fill on exterior (the downhill side would have about 5ft of exposed stem wall. Hoping someone has dealt with something along these lines. I’m also contemplating a sealed conditioned crawlspace for simplicity/cost sake but would rather not have to heat another 1000 sq ft of crawl.
Any input would be greatly appreciated.
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Building a home on sloping bedrock with a stem wall foundation presents unique challenges and opportunities for creating a solid, energy-efficient foundation. Here are key considerations and steps for ensuring a successful foundation setup, focusing on compacting fill within the foundation and deciding between a slab and a conditioned crawl space:
Compacting Fill Within the Foundation
Proper Fill Material: Use well-graded, compactable fill material such as gravel or crushed stone. These materials have excellent drainage properties and can be compacted effectively.
Layered Compaction: Compact the fill in layers, typically 6 to 12 inches thick. This ensures uniform compaction throughout the fill area. Use a mechanical plate compactor or a vibrating roller for this task.
Monitoring Compaction: Consider hiring a geotechnical engineer to monitor the compaction process. They can perform tests to ensure that the fill achieves the required density and stability, preventing future settlement.
Minimal Exterior Backfill: For areas with significant stem wall exposure, like your downhill side, ensure the fill is well compacted against the foundation. You may need to use temporary shoring or formwork to hold the fill in place during compaction if minimal exterior backfill is planned.
Foundation Options: Slab vs. Conditioned Crawlspace
Slab-on-Grade: Pouring a slab directly over compacted fill is a common method, especially on stable bedrock. If you're considering a "concrete-less" slab, research alternatives like structural wood panels or insulated panels designed for load-bearing applications. Ensure any method chosen provides adequate insulation, moisture protection, and structural support.
Conditioned Crawlspace: Opting for a sealed, conditioned crawlspace can simplify construction on sloped sites and offer access to utilities without heating the space directly. Insulate the walls of the crawlspace rather than the floor above to include it within the thermal envelope of the house without significant heating cost. Ensure proper moisture control with a vapor barrier on the ground and adequate ventilation or dehumidification.
Additional Considerations
Water Management: Given the sloping site and exposed stem wall, effective water management is crucial. Include proper drainage solutions such as French drains, gutters, and downspouts that direct water away from the foundation. Consider waterproofing the exterior of the stem wall, especially on the downhill side.
Insulation and Vapor Barriers: Whether you choose a slab or a conditioned crawlspace, use appropriate insulation and vapor barriers to minimize heat loss and prevent moisture intrusion. On sloped sites, thermal bridging and water infiltration are critical concerns.
Final Thoughts
Building on sloping bedrock requires careful planning and execution. Compacting fill within your foundation correctly will provide a stable base for your home. Choosing between a slab-on-grade and a conditioned crawlspace involves weighing the benefits of simplicity and cost against the need for utility access and the desire to minimize heating unused spaces. Consult with structural and geotechnical engineers to tailor these general strategies to your specific site conditions, ensuring your new home is stable, efficient, and comfortable.