Foundations

All diy outbuilding projects require a foundation as do structures attached to a dwelling on a property.

Outbuildings include: sheds, garages, barns, stables, coops, greenhouses, playhouses, storage units, gazebos, pool houses, outhouses, workshops, carports, patio covers, sunrooms, garden sheds, chicken coops, tool sheds, and even tree houses; essentially Any freestanding structure separate from the main dwelling or attached to an existing structure on a property.

Do you need Need a Foundation?

The answer is yes. An outbuilding / add-on structure needs a foundation. An outbuilding / add-on structure foundation provides a stable base, preventing it from shifting or tipping over during strong winds or heavy rain. Without a solid foundation, the outbuilding / add-on structure can shift, tilt, or even collapse over time. A foundation also helps to keep the outbuilding / add-on structure level, preventing water from pooling inside the structure and causing damage.

Load bearing weight

One of the biggest factors you must consider is how much does your outbuilding / add-on structure weigh and how must weight will you be putting inside the structure. For instance a hot tub enclosure will require additional foundation support as a hot tub can weigh 3000 to 8000 lbs or more. That is a lot of extra weight.

A second consideration is snow load. The weight of snow depends on its moisture content and density. Snow can weigh between 1 and 21 pounds per cubic foot. Contact your municipality or local county to obtain your local snow load.

What is the best foundation option for a an outbuilding / add on structure ?

The best foundation for an outbuilding / add on structure depends on several factors, including the size of the outbuilding / add-on structure , the type of ground it will be located on, and your budget. A concrete pad is a good option if you have a large outbuilding / add-on structure or the ground is soft or marshy. A gravel pad or super spikes may be a better choice if you are looking for a more budget-friendly option. We will review the most common outbuilding / add-on structure foundations ideas so you know what works best for you.

Concrete Slab Foundation

A concrete slab foundation is the most common type of an outbuilding / add on structure foundation option. It is a flat surface of concrete that provides a solid and stable base for the outbuilding / add-on structure . It is ideal for areas with heavy foot traffic or where the ground freezes in the winter. It is easy to get installed and requires minimal maintenance, making them a popular option for homeowners.

Pros and Cons of Concrete Slab Foundation

Pros:

Durability: It is known for its longevity and can last for decades with proper maintenance.
Cost-Effective: Compared to other foundation types, concrete slab foundation is relatively affordable and requires fewer materials and labor cost.
Energy Efficient: Concrete is a good insulator, which can help regulate the temperature inside a building and reduce energy consumption.
Low Maintenance: It requires minimal maintenance, making it a hassle-free option for property owners.

Cons:

Limited Versatility: Once concrete slab foundation is poured, it is difficult to make changes to the layout or add plumbing or electrical lines.
Susceptible to Cracking: It is prone to cracking over time, especially in areas with frequent temperature fluctuations.
Poor drainage: Without proper drainage systems in place, water can collect underneath the foundation, leading to potential, moisture issues and structural damage.

Poured Concrete Foundation

A poured concrete foundation is similar to a concrete slab foundation, but it is made by pouring concrete into forms that have been set in place. Just like a concrete slab, it also requires minimal maintenance.

Pros and Cons of Poured Concrete Foundation are the same as Concrete Slab Foundation.

Wooden Deck Foundation

Another outbuilding / add-on structure foundation idea is the wooden deck foundation. A wooden deck foundation involves building a wooden deck and placing the outbuilding / add-on structure on top of it. This type of foundation is ideal for smaller outbuilding / add-on structures and provides a stable base for the structure. However, a wooden deck foundation requires more maintenance than a concrete foundation.

Pros and Cons of Wooden Deck Foundation

Pros:

Cost-Effective: It is generally less expensive than other types of foundations, such as concrete.
Easy to Work With: Wood is a relatively easy material to work with, which means that building a wooden deck foundation can be a relatively simple project for a skilled DIYer or a professional contractor.
Aesthetically Pleasing: Wood is a natural material that can add warmth and character to your deck.

Cons:

Vulnerable to moisture: Wood is a porous material that is susceptible to moisture damage, particularly in areas with high level of humidity or frequent rainfall.
Limited Lifespan: Even with proper maintenance, a wooden deck foundation will typically have a shorter lifespan than other types of foundations.
Highly Maintenance: Wood requires regular maintenance to keep it in good condition. This may include cleaning, sealing, and staining.

Pier/Sonotubes Foundations

A pier foundation involves using concrete piers to support the outbuilding / add-on structure . This type of foundation is ideal for an outbuilding / add-on structure on sloping or uneven ground, as it provides a stable base for the structure.

Pros and Cons of Wooden Deck Foundation

Pros:

Easy to install: They can be set up quickly and require little preparation work.
High Load Capacity: They have a high load capacity, which means they can support heavy structures such as buildings and bridges.
Environmentally Friendly: They are made from recycled materials, making them an eco-friendly choice for construction projects.

Cons:

Cost: They can be more expensive than other type of foundations, such as poured concrete.
Limited Size: They are typically limited in size, which means that they may not be suitable for larger structures.
Vulnerable to Frost Heave: In colder climates, they can be susceptible to frost heave, which can cause them to shift and crack over time.

Patio Stones

Patio Stones are placed on a level surface and leveled to provide a stable base for a outbuilding / add-on structure . The outbuilding / add-on structure is then anchored to the stones to prevent it from shifting and tipping over. When using patio stones as a foundation for a outbuilding / add-on structure , it is important to select large and heavy stones to provide stability. It is also important to place a barrier between the stones and the ground to prevent weeds and grass from growing up through the stones and affecting the stability of the foundation.

Pros and Cons of Patio Stones

Pros:

Aesthetically Pleasing: They are available in a wide variety of colors, shapes, and textures, making it easy to create a custom look that complements your home’s architecture and your personal taste.
Durable: They are made from a variety of materials, including concrete, natural stone, and brick, and designed to withstand heavy foot traffic, and weather.
Easy to repair: If one or more patio stones become damaged or cracked, they can be easily replaced without having to replace the entire patio.

Cons:

Cost: They can be more expensive than other types of outdoor flooring, such as concrete or wood decking.
Slippery: Some types of patio stones can be slippery when wet, which can be a safety hazard for homeowners and their guests.
Uneven Surface: Depending on the type of patio stone you choose and how it is installed, the surface may be uneven, making it difficult to move furniture or walk on.

Cinder Blocks

This type of outbuilding / add-on structure foundation is easy to install and is a cost-effective option compared to other types of foundations, such as concrete or pier foundations. The cinder blocks are placed on a level surface and leveled to provide a stable base for the outbuilding / add-on structure . Cinder blocks are also a durable option for a outbuilding / add-on structure foundation, as they can withstand harsh weather conditions. They are also moisture-resistant, making them a good choice for outbuildings / add-on structures in areas with heavy rainfall or high humidity.

Pros and Cons of Cinder Blocks

Pros:

Affordable: They are a cost-effective building material, making them a popular choice for projects with limited budgets.
Fire-Resistant: They are highly fire-resistant, making them a safe choice for building in areas prone to wildfires or other fire hazards.
Easy to Work with: Cinder blocks are easy to work with and can be cut and shaped to fit specific design needs.

Cons:

Limited Design Options: They have a very distinct look, which may not be suitable for all design aesthetics.
Heavy: They are heavy and can be difficult to transport and handle, requiring heavy machinery or multiple people to move.
Prone to Moisture: They can absorb moisture, which can lead to mold and mildew growth, as well as other moisture-related damages.

Gravel Pad

This type of foundation is ideal for areas with soft or marshy soils or where the ground freezes in the winter. It is also inexpensive to install, making it a popular choice for many homeowners. Additionally, a gravel pad allows for better drainage and ventilation, helping to keep the outbuilding / add-on structure dry and well-ventilated.

Pros and Cons of Gravel Pad

Pros:

Affordable: They are affordable materials, making it a cost-effective choice for creating a foundation.
Easy to Install: A gravel pad is relatively easy to install and requires only basic tools and equipment.
Good Drainage: Gravel allows for good drainage, which can help prevent water damage to your structure.

Cons:

Uneven Surface: They may not provide a completely level surface, which can make it difficult to install and use your structure.
Can Shift Over Time: They can shift over time, which can cause your structure to become unstable or uneven.
Limited Durability: They are not as durable as other building materials and may need to be replaced or topped up over time.

Super Spikes or Helical Screw Piles

Super spikes are metal spikes used to secure a outbuilding / add-on structures to the ground. They are designed to be driven deep into the soil to ensure that the structure remains level and stable where the ground is soft and uneven. They are relatively easy to install and can be used with other types of outbuilding / add-on structure foundations, such as concrete or gravel pads, for added stability. Super spike foundation provides a low-maintenance and durable solution for securing a outbuilding / add-on structure .

Pros and Cons of Super Spikes

or Helical Screw Piles

Pros:

Easy to Install: They are relatively easy to install and require only basic tools and equipment.
Good Load-Bearing Capacity: They have a good load-bearing capacity and can support heavier structures.
Minimal Site Preparation: They require minimal site preparation and can be installed on a variety of soil types.

Cons:

Limited to Specific Soil Types: They are not suitable for all soil types and may not work on particularly rocky or unstable ground.
Limited Stability: They may not provide the same level of stability as other foundation options and can be prone to shifting or sinking over time.
Limited Durability: They may not be as durable as other foundation options and may need to be replaced or repaired over time.

How Deep Should Footing Be for a outbuilding / add-on structure ?

The depth of the footing for a outbuilding / add-on structure depends on several factors, including the climate, soil type, and the outbuilding / add-on structure size. In this case, it is always best to consult with a professional to determine the appropriate depth for the footing for your outbuilding / add-on structure

Your local municipality or local county office should be able to to provide the frost line for your area. .

The bottom line, a proper outbuilding / add-on structure foundation is essential for a safe and stable structure. Consider your budget, the size of the outbuilding / add-on structure , the type of soil in the area, and your personal preferences when choosing the best foundation for your outbuilding / add-on structure .