Smart House Foundation: compare 3 common types

The foundation is the heart and soul of all buildings, be it your house, office, backyard shed, or cottage.

Why? Well, because the foundation offers support, stability, and strength to the structure, ensuring it stands the test of time, terrain, and environment.

What is a house foundation?

A house foundation is the lowest load-bearing portion of your building – the base of the house.

A good house foundation does the following:

1. Supports the structure over it and protects it against the damage that could be caused by earth movement (earthquake) or disasters such as hurricanes and floods.
2. Restricts the entry of groundwater into your space.
3. Offers insulation against cold.
4. Protects against contraction and expansion of the soil.

 

There are various house foundations types. The type is typically called out by a geotechnical engineer and is based on what is commonly called a soil’s report. The engineer determines soil conditions and adjusts for the local specifics (say, earthquake-prone areas or flood-prone areas).

Most common types of house foundations built in the last century were slab and crawl space foundation. Concrete was the most common option. Gravel or cinder blocks could and still can be used for accessory non-habitable structures, but not for a new home.

The following three are the most common types of foundation today:

Beam foundation

Imagine a building erected on small poles – that’s basically the beam foundation.

Several holes are bored into the ground 5-10 feet away from each other. The holes must hit the bedrock. Now concrete piers with rebar are inserted into these holes.

Above them, the perimeter beams are laid horizontally; they are connected from one pier to another, and these are the beams that take the load off the foundation slab (flooring) and transfer them to the piers.

Piers can be made of concrete, wood, or steel. The latter are called helical screw piles.

Following are the pros and cons of beam foundations:

Pros

Provide better resistance against floods since they are elevated.

Have ample space beneath them, which makes plumbing and installing electrical lines easy.

Cons

Prone to pests, vermin, and insects if made of wood.

 

Slab-on-grade foundation

Also known as the floating slab foundation, slab-on-grade foundations involve creating a whole concrete slab several inches thick into or over the ground.

The edges are thickened using rods, and there is a whole frame of rods in between the slab to counter cracking. Also, there will be no space between the foundation and the floor of the building.

Following are the pros and cons of concrete slab foundations:

Pros

More stable and sturdy than other types of foundations.

Less prone to pests and termites.

Economical to manufacture.

Cons

Do not offer access to the foundation from below for installing plumbing and utility lines.

More susceptible to cracks if the soil shifts.

Crawlspace foundation

Crawlspace foundation consists of short concrete walls that are stabilized on concrete footings.

It forms a space between the ground and the flooring through which you can literally crawl, hence the name – crawlspace foundations.

Following are the pros and cons of a crawlspace foundation:

Pros

Walls are protected from flooding since they are raised.

Allows easy access to plumbing and wiring.

Best for uneven soils.

Cons

Prone to mold and mildew if no rat slab has been added to protect from underground moisture.

The most expensive option is the full basement or daylight basement foundations. Before you decide on this type of foundation, consider carefully all the trade offs. Are you constrained by the size of your property or lot coverage numbers? Are you planning to use the space as storage area mainly? Often what happens, is that people overestimate their financial situation, and as a result live with unfinished basements long after they move into the new house.

These days we often see what we have started to call hybrid foundations: using steel piers for footings and concrete for the foundation wall.

Now that you know all about the the main foundation types, how can you decide which of those different types of house foundations you should opt for? Well, it depends on a wide range of factors, including:

 

Soil type

Does your area have loose soil, clay soil, or sandy soil?

The quality of the soil (in terms of moisture, compaction, density, seismic design factors, etc. ) can be determined through the Geotech soil report that will be used by the site engineer and contractor to decide which foundation is the most suitable.

Each type of soil has a different soil-bearing capacity i.e. the capacity of the soil to bear the pressure of the building on top of it (SBC).

If you have a lower SBC, you need a stronger foundation, and vice versa. If you have loose soil, you will need deep foundation.

Without the report, your foundation will be over-engineered and prone to risk.

Based on the report, the structural engineer might also suggest changes like installing wider footings, fixing the ground slope, etc. to make the site fit for the building.

The other consideration is bedrock. Piers are supposed to be firmly grounded in bedrock, so your engineer will most likely call for the depth and diameter of concrete pillars or helical screw piles.

 

Climate

Weather plays a big role in the selection of your foundation. Cold climates make bigger demands on foundation. First, it should be ready for ground freezes. Second, when the snow melts or big rain falls, one should be conscious of the possible flooding, to the point that a sump pump may be considered to prevent basements from water damage. In warmer climates, the snow is less of an issue, but often these are the places where the engineers need to account for earthquakes or hurricanes.

If you want to build a cottage near a flood-prone area, you can not be on ground level. You should either choose a raised foundation option – most often, beam or pile foundations. It is because both consist of platforms that raise the floor of your building from the ground.

Similarly, if you are planning to build in a cold place, you should look for options other than slab foundations. Slabs are prone to developing cracks in case of freezing and frequent thaws.

So, do take into account the climate and decide accordingly.

 

Slope of the ground

Check whether the ground where you are planning to build is level or sloped.

If you have a minimal slope, you can go with the crawlspace foundation by building stem walls of different sizes.

But if the slope is steeper, opt for a walkout basement. This will be a smart option because you will have to invest a lot of money if you choose to flatten the land. Hauling away dirt is often a surprizingly expensive item.

 

Pest problems

Pesky pests like termites, mildew, grasshoppers, and animals like rabbits and rats can damage your foundation.

So, if you are moving to a place that has a history of pests, you might want to keep away from wood foundations.

Even if you opt for a crawlspace foundation with wooden piers, ensure to seal them off with pest control measures.

 

Access

If you are building a new house on a completely vacant lot, this might not be an issue. These days, however, most construction happens in a more constrained environment – with the heritage trees to protect or in backyards.  Will the heavy equipment be able to enter your property? Or will the foundation need to be hand dug?  May be, a mini-excavator is an option. An experienced contractor will help guide you and help select the best option out of various house foundation types.

 

Water level

If the water table at your desired place is high, you just can’t build a basement – make peace with it. Go for a slightly elevated space.

Either opt for a well designed crawlspace or shaft concrete piers.

But in any case consider a vapor barrier – it required for new construction in any case. Even if you are remodeling an old house or converting a garage into living space, you may be asked to add a vapor barrier (commonly referred to as “red guard”) to your existing slab foundation.

 

There are other ways to keep the water away as well, such as landscaping.

Landscaping guides water to street gutters and swales. But how to do it?

1. Plant trees away from the foundation because their roots can damage the base of the foundation.
2. Plan for drainage pipes. Don’t cover drains with bushes or trees.
3. Make sure the flower beds slope away from your foundation.
4. Grow fire-resistant plants like boxwoods and hydrangeas so your house is protected in case of a wildfire.

Also, the fire department has set a safe range of 30 feet for you to grow trees around your house. Follow that. You can grow less dense greenery like shrubs near your house.

The right type of house foundation is essential to building a stable and strong house, cottage or backyard shed.  It is all about the structural integrity of the building for years to come.

Make an informed decision about different types of foundation and the type of house foundation you should opt for.

In case you have need any help or have any questions or concerns, feel free to get in touch with us.