﻿Foundations are a critical part of a building’s structure. They serve numerous purposes. They
bear the load of the building, its inhabitants, contents, snow and rain. They distribute these
loads over a large area to prevent excessive settlement. They provide protection against
natural forces like earthquakes, tornadoes and floods. Because they are embedded into soil,
they provide lateral stability and prevent buildings from sliding away. They resist
decay from bugs and soil. They protect buildings from freeze thaw cycles and the expansion and
contraction of soil. They also provide a level surface to start constructing a building.
Two popular types of foundations are pier and beam and slab foundations.
In this video, we’re going to look at how they are made, their upfront costs,
long term costs, protection from the elements, where they should be used and whether one is
better than the other. Let’s start with pier and beam or post and beam foundations,
the older construction method that is found on homes built before 1960.
First, a series of holes are dug in the ground, 5 to 10 feet apart. These holes must hit bedrock,
which can be 4 feet below the surface or 50 feet. Large cardboard tubes are sunk into the soil.
Plastic bases can be added to the bottom to increase the size and carrying capacity of
the piers. This helps to ensure the piers won’t shift. Circular rebar cages are placed in the
middle of the voids. These tubes must be perfectly straight and level. Next, the voids are filled
with concrete and a base connection is embedded in the top of the pier. Beams are extended from
one pier to another. These will support the joists and flooring of the home. Usually the crawl space
underneath the beams is about 18 inches from the ground. This is where the home’s plumbing
and electrical components are located. There are several variations of pier and beam foundations.
The piers can be made of precast concrete, brick, stone or cedar wood which is resistant to rot and
decay. The crawl space or the area under the building can be vented or unvented.
Slab on grade or monolithic slab foundations are a newer construction method. The concrete slab sits
directly on the ground. First, the surface is leveled and a perimeter form is created for the
foundation. 4 to 6 inches of gravel is spread inside. A layer of plastic sheathing is laid
down to act as a moisture barrier. Engineered steel rebar reinforces the concrete foundation.
Concrete is poured over the gravel and plastic sheathing and allowed to cure.
A newer version of slab on grade foundation is a post tensioned slab. Steel cables are laid out
in a grid inside the formwork. After the slab has been cast, the cables are tightened which
gives the foundation tensile strength. A type of monolithic slab is a floating slab foundation.
In this method, the horizontal slab is not connected to the vertical foundation.
It simply sits on the ground and can move above the frost line as a monolithic unit.
It is used for garages, workshops, sheds and ADUs or additional dwelling units.
Pier and beam and slab on grade foundations are mainly found in the southern parts of the US.
Northern states have conditioned crawl spaces and foundations with basements.
The reason slab on grade foundations are so popular nowadays is because it is easier to
construct and it has a lower upfront cost compared to pier and beam foundations.
Soils in Texas can vary drastically. They can have a couple of inches of topsoil,
3 to 4 feet of clay before hitting rock, or they can have more than 50 feet of clay
before hitting rock. The cost of pier and beam foundations is unpredictable because
of the different depths of clay soil. The cost of slab on grade foundations is more predictable
because it doesn’t need to hit bedrock. But the lower upfront costs of slab foundations
means higher long term costs, like foundation repair. Pier and beam foundations have individual
piers and beam members, so it is easier to isolate foundation problems and it’s cheaper to repair.
Slab on grade foundations can shrink, crack and even sink. They are more difficult and expensive
to repair. We had to install 22 concrete piers to level the foundation of our previous home.
Fortunately, they only needed to be installed on the perimeter and not inside our home.
If soils swell, the foundation will be pushed upwards.
If the soil shrinks and separates from the foundation, it will be unsupported and will crack.
Foundation repair is a huge business here because every home has either had repairs or will need it
in the future. Homeowners are encouraged to water the soils around their foundation to balance the
moisture levels throughout the year. Repairing electrical and plumbing issues
is also easier and cheaper when you have a pier and beam foundations, thanks to the crawl space
underneath. With a slab foundation, repairing any electrical and plumbing issues is a messy,
destructive and expensive process. You have to jackhammer the slab and cut steel rebar to access
any pipes. The lifespan on the concrete slab is lowered to get to the utilities underneath.
We discussed this in my video on planned obsolescence. I’ll link it up here.
Also, any foundation work on post-tensioned slabs is very dangerous. People have been
dismembered and killed because they hit a cable which then burst through the concrete.
I’ve heard plumbers compare cutting through post tensioned slabs to diffusing a bomb.
Another feature to consider is the ability to add levels or stories to your homes.
You could technically add additional piers and beams to support another level. You could also
detach your pier and beam home from the foundation and move it to a completely different site.
Last year, a 140 year old historic Victorian house was moved on dollies through the streets
of San Francisco. Moving it just 6 blocks from Franklin Street to Fulton street
cost a whopping $400,000. This is possible with pier and beam foundations because they can be
detachable. Houses built on slab foundations are anchored down and cannot be moved.
Before we move on to other differences between pier and beam and slab on grade foundations,
I’d like to introduce the sponsor of this portion of the video, Skillshare. I stepped away from my
architecture and drafting job because I felt stifled. I wanted to learn something new every
day. Skillshare is an online learning community that helps me do just that. It has thousands
of inspiring classes for anyone who loves learning and wants to explore their creativity and learn
new skills. From photography and illustration, to woodworking, storytelling, and more, you can find
classes that will match your goals and interests. I recently took MKBHD’s class on YouTube success.
Even though the subject matter of his videos is different from mine, he had a lot of invaluable
lessons. If you’d like to check this out, the first 1,000 people to use the link the description
will get a 1 month free trial of Skillshare. Now let’s compare how pier and beam and slab
foundations protect us from the elements. Unvented pier and beam foundations can be
insulated with fiberglass or spray foam. This can help lower your energy bill
and make your home feel more comfortable.. Vented pier and beam foundations are a different issue.
The floors of such homes can be cold in the winter months because of the air exchange that occurs in
the crawlspace. These spaces can also become damp and even accumulate water during heavy rains.
Slab on grade foundations don’t have this problem. However, if you don’t
use a vapor barrier underneath, moisture from the ground can seep through the concrete.
Pests and rodents often seek shelter in crawl spaces and can build nests beneath
your home. They can cause damage to wiring and structural members.
Larger pests can be kept out of the crawlspace by placing lattice over the access. Slab on grade
foundations don’t have this issue, but termites can enter through any cracks or openings.
In terms of comfort, floors on pier and beam foundations sound hollow and squeaky. But, they
are easier on your feet because they can flex. Concrete slab foundations are solid and quiet,
but standing on them all day long can be tough on your feet.
Finally, where to use them. Pier and beam foundations are better in areas with substantial
soil expansion and contraction, like Texas. They are also ideal for homes built on uneven grade,
homes built into a hillside or for homes built off the ground due to potential flooding.
Slab foundations are ideal for level sites, in regions that get a lot of moisture and areas where
freezing weather is common in winter. Underground pipes are insulated by the foundation and earth
and are less likely to burst. Slabs are also easier to build and require less expertise.
Both pier and beam and slab on grade foundations have their advantages and disadvantages.
I wouldn’t make a blanket statement saying one is better than the other
because there are so many factors to consider: your site,
budget, soil conditions, weather, etc. We should probably use pier and beam foundations in Texas
but it can be too expensive in certain areas. Slab on grade foundations built on stable soil
could last decades without any issues. I’d like to end this video with a story that a foundation
repair guy told me last year. He said that with old slab foundations, if the end breaks off,
it can be picked up with concrete piers, like the work that was done on my previous home. However,
with new post-tensioned slabs, ends don’t break off, the whole slab and house tilts.
So, he said that when newer homes get foundation repairs in a decade or so, they will pay 4 times
more and will need invasive interior piers. That’s something to look forward to.
Hope I was able to simplify these topics. Let me know if I should make additional videos on
helical piers, friction piers for skyscrapers, and even basement foundations in northern regions.
I’ll link my Patreon page in the description. If you can support me, I’d really appreciate it.
A big thank you to everyone already supporting me. Don’t forget to hit that like button,
subscribe button and the notification bell too. Thanks for watching. See ya.