Raised Concrete Slab vs Slab on Grade

What is a raised concrete slab?

A raised concrete slab is a structural element lifted above the ground, supported by columns or piers. This design proves advantageous in flood-prone regions, elevating buildings to prevent water damage.

The space underneath the slab allows for improved ventilation, reducing humidity and minimizing mold growth risks. Raised slabs provide easy access for maintaining utilities like plumbing and electrical systems.

Aesthetically, raised slabs contribute to a modern, open look with ample natural light. Various types include post-tensioned slabs reinforced with steel tendons, precast slabs manufactured off-site, and in-situ slabs poured on location for custom solutions.

By elevating living spaces, raised concrete slabs offer flood protection, enhanced ventilation, maintenance accessibility, and visual appeal – a versatile construction method tailored to specific project needs.

How it is constructed?

Constructing a raised slab is like baking a layered cake. First, the subgrade is prepared, and a vapor barrier is laid down to prevent moisture issues. Then, the concrete is poured onto the subgrade, often with insulation sandwiched in between. Finally, the slab is finished to perfection.

Why to invest in raised concrete slabs?

1. By lifting the structure off the ground, raised slabs effectively shield buildings from rising water levels, safeguarding against flood-related destruction in vulnerable areas.
2. The crawl space underneath the elevated slab promotes optimal airflow, reducing humidity buildup and minimizing the risk of mold and mildew infestations.
3. The raised design offers unobstructed access to utilities like plumbing, electrical systems, and ductwork, streamlining inspection, repair, and upgrade processes.
4. Raised slabs lend themselves beautifully to modern, minimalist architectural styles, with ample opportunities for large windows and open, airy living spaces.
5. When engineered strategically, raised slabs demonstrate resilience against seismic forces, mitigating structural damage risks during earthquakes.
6. By elevating the structure, raised slabs create a barrier against common pests like termites and rodents, which typically target ground-level buildings.
7. Enhanced ventilation beneath the slab helps maintain healthier indoor air by preventing the buildup of pollutants, allergens, and stale air.
8. In cold climates, the crawl space can act as a thermal barrier, improving energy efficiency by insulating the living quarters from the ground.

Challenges

Of course, no foundation is perfect. Raised slabs can be more expensive due to the additional materials and labor required. The crawl space may also attract pests if not properly maintained. Proper drainage is important to prevent water from pooling below the slab.

What is a slab on grade?

A slab on grade is a type of foundation where concrete is poured directly onto the prepared ground surface, without a basement or crawl space beneath. This cost-effective solution is suitable for areas with stable soil conditions and moderate climates.

Key components include:

• The ground is carefully leveled, removing any debris or vegetation, and often topped with a layer of compacted gravel for drainage.
• A moisture-resistant membrane is laid over the prepared subgrade to prevent moisture infiltration from the soil.
• Steel reinforcing bars (rebar) are positioned within the slab area to enhance strength and durability.
• Once the subgrade, vapor barrier, and rebar are in place, concrete is poured and leveled directly onto the ground surface, forming the slab foundation.

With minimal excavation required and a straightforward construction process, slab on grade foundations offer an economical option while providing a stable base for residential and light commercial structures.

Construction of slab-on-grade

Building a slab-on-grade is a straightforward process. The subgrade is prepared, and a vapor barrier is installed to prevent moisture from seeping through. Then, reinforcing steel is laid out, and the concrete is poured directly onto the subgrade. The slab foundation is then finished to create a smooth, durable surface.

Benefits of slab-on-grade foundations

1. Lower construction costs due to reduced material requirements and simpler construction process.
2. Faster build times compared to other foundation types, thanks to the straightforward preparation and pouring process.
3. Improved energy efficiency achieved through the ability to insulate the slab, creating a thermal barrier.
4. Elimination of potential drafts and air infiltration, contributing to better temperature control and energy savings.
5. Renowned strength and durability of concrete slabs, providing a stable and long-lasting foundation.
6. Resistance to termite infestations and other pest-related issues due to the absence of wood components and open spaces.
7. Resilience against minor flooding events when combined with proper drainage systems.
8. Greater flexibility in floor plan designs, enabling open and spacious layouts without the constraints of load-bearing walls.
9. Compatibility with modern architectural styles, contributing to a sleek and contemporary aesthetic.
10. Reduced environmental impact during construction, thanks to minimal excavation requirements and fewer materials used.

Common issues

Slab-on-grade foundations are not without their challenges. They are more susceptible to moisture issues, especially in areas with high water tables or poor drainage. Accessing utilities can be difficult since they are embedded in the slab. Future remodeling or expansions may also be limited.

Slab on Grade vs Raised Slab

Cost

When it comes to cost, slab-on-grade foundations usually have the upper hand. They require less material and labor compared to raised slabs, which need additional footings, foundation walls, and piers.

Insulation

Raised slabs have an advantage when it comes to insulation. The crawl space allows for the installation of insulation materials, creating a thermal barrier between the ground and the living space. Slab-on-grade foundations can be insulated, but it requires specialised techniques.

Durability

Both raised slabs and slab-on-grade can be durable and long-lasting with proper construction and maintenance. However, raised slabs may have a slight edge due to better ventilation and easier access for repairs.

Soil type

Soil type plays a significant role in choosing between a raised slab and a slab-on-grade. Expansive soils, which expand and contract with moisture changes, may favor slab-on-grade to avoid structural issues. Well-drained, stable soils can support either option.

Suitability for flood-prone areas

If you are building in a flood-prone area, a raised slab is the way to go. The elevation of the slab above the ground helps protect the structure from rising water levels and minimizes the risk of flood damage.

Summary

In the battle between raised concrete slabs and slab-on-grade, there’s no one-size-fits-all winner. The choice depends on a variety of factors, including:

• Climate and environmental conditions
• Soil type and stability
• Budget and cost considerations
• Maintenance and accessibility requirements
• Future expansion or remodeling plans

By understanding the key differences between these two foundation types, you can make an informed decision that suits your specific needs and ensures the long-term stability and durability of your building.

Your Foundation Experts in Fredericton

Looking for reliable foundation solutions? Atlantic Brick and Stone brings over 15 years of specialized expertise to your doorstep. As Fredericton’s trusted foundation contractors, we deliver exceptional results for both repairs and new installations.

Why Choose Atlantic Brick and Stone?

• Deep expertise in foundation construction and repair
• Professional team with 15+ years of experience
• Comprehensive foundation solutions
• Local knowledge of Fredericton soil conditions
• Quality workmanship guaranteed
• Competitive pricing
• Free consultations

Whether you need foundation repairs or are planning a new construction project, our experienced team is ready to help. We understand that your home’s foundation is crucial for its structural integrity, and we take that responsibility seriously.

FAQs about raised concrete slabs and slab on grade foundation

Other name of slab on grade?

A slab on grade is also referred to as a monolithic slab, emphasizing its single, continuous pour of concrete, or in some contexts, as a floating slab, although the latter technically refers to a specific type of slab that floats on the ground without deep footings. However, in general usage, both terms can be associated with slab-on-grade foundations, but it’s essential to note the distinctions between them.

Can you help me decide between a foundation, slab on grade, and crawlspace?

Yes, we can guide you in choosing the best option based on your needs, site conditions, and budget.

How long do raised foundations last?

With proper construction, maintenance, and care, a raised foundation can last for many decades, often 70 years or more. Regular inspections and repairs can help extend the lifespan of your foundation and ensure the long-term stability of your building.

How long do slab on grade foundation last?

A well-constructed slab-on-grade foundation can last for several decades, often exceeding 50 years with proper maintenance. Regular care and attention to drainage and moisture can significantly enhance its longevity, making it a reliable choice for homeowners.