New foundations and slab-on-grade
The first step to Green home design and construction is deciding what sort of base you will rest it on. The Guide pages below help choose between slab-on-grade construction, traditional strip foundations with crawlspace and basement foundations - then show step by step how to build them better.
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New foundations and slab-on-grade
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While home construction in North America has traditionally started with a crawlspace or a full concrete basement foundation, modern building science presents other options that can be more durable, affordable, and better for your home's air quality and energy efficiency. These alternative approaches, particularly slab-on-grade designs, are especially important for achieving the high-performance targets required by standards like LEED (Leadership in Energy and Environmental Design), Passive House, and Zero Net Energy (ZNE) homes. Making the right choice from the outset is a critical step in building a resilient and sustainable home.
Comparing Foundation Types: Basements, Crawlspaces, and Slabs
The first factors to consider when designing the foundation of a new home are your lot size, soil conditions, local climate, and budget. When space is limited by a small property footprint or by municipal height restrictions, a basement foundation may be the best option to maximize living area. However, basements require extensive excavation and meticulous waterproofing to prevent moisture issues that can compromise structural integrity and indoor air quality. Crawlspaces offer easier access to services but can also be prone to dampness and energy loss if not properly sealed and insulated. Where lot size allows, there is a strong case for avoiding below-grade spaces altogether in favor of a well-designed slab-on-grade foundation.
The Advantages of Modern Slab-on-Grade Foundations
A slab-on-grade foundation, which is a structural concrete slab poured directly on the ground, eliminates the potential for common basement and crawlspace problems like flooding and musty air. Modern monolithic or frost-protected shallow foundations (FPSF) offer significant benefits in terms of performance and construction efficiency. By resting on a robust base of compacted fill and a thick, continuous layer of sub-slab insulation, these foundations are thermally broken from the cold ground, leading to warmer floors and substantially lower heating costs. This design is less complex to air seal, which is a critical component for achieving the airtightness levels required by high-performance building standards like Passive House, helping to create a more comfortable and healthier indoor environment.
Key Considerations for High-Performance Foundation Construction
Achieving a high-performance foundation requires careful attention to detail in three critical areas: insulation, water management, and air sealing. For a slab-on-grade, continuous sub-slab insulation (typically rigid foam) is essential to minimize thermal bridging, and robust insulation must also be applied to the slab's edges. A durable vapor barrier placed directly beneath the concrete is crucial for preventing ground moisture from wicking up through the slab, protecting interior finishes and air quality. Effective perimeter drainage and proper site grading are also necessary to direct water away from the foundation. These integrated strategies ensure the foundation is not only strong and stable but also a key component of the home's overall energy efficiency and resilience. We also have Canada's and the USA's most comprehensive high performance and sustainable prefabricated and modular homes directory available here, searchable by Province or State, as well as the largest online directory of green construction contractors here on EcoHome.