A long time ago, a wise carpenter once said, “The foolish man builds his house on the sand.” I recall the words through a silly song sung when I was but a child:
“Don’t build your house on the sandy land; don’t build it too near the shore;
“Well it might look kind of nice, but you’ll have to build it twice;
“Oh you’ll have to build your house once more.
“You better build your house upon a rock; Make a good foundation on a solid spot;
“Oh the storms may come and go, but the peace of God you will know.”
Though the song was just a children’s jingle that I thoroughly enjoyed singing when I was young, it was memorable enough for me to recall it decades later. And though the words were silly to me at the time, they held wisdom I can appreciate now. For though the master carpenter used the image as an illustration for deeper meaning, there is truth in the base elements of the allegory. That ancient wisdom is still practiced in today’s homebuilding techniques.
For the last several weeks we have been talking about how cracks develop in the basement foundation walls. Before we launch into a discussion of the more serious structural problems that can occur, we will explore the reasons why foundations are built the way they are.
There are basically three types of foundations for homes: 1) slab on grade; 2) crawlspaces; and 3) basements. Several factors determine which foundation a house may have, including cost, the frost line of the ground, moisture, and security of the ground at different depths.
First, the slab on grade is usually the most cost effective method of building house foundations. As it sounds, the slab on grade is concrete which is poured at ground level. This method is usually only available for locations with warmer climates, as the ground must not freeze regularly. Freezing causes the water in the ground to expand, which in turn causes the ground soil to shift. This can damage the foundation over time, which may lead to stress cracks in the home as well. Also, the surface soil must be compact enough that it will not shift over time under the full weight of the house and its expected occupants. Otherwise, again, the foundation will shift with detrimental consequences. As long as an engineer determines that the ground and temperature meets these standards, slab on grade may be the most money-saving method for home builders.
This style of foundation would obviously exclude the types of problems we have been discussing and will go into further later. However, it is not without some serious drawbacks. For one, all of the house piping and oftentimes the wiring as well must be laid down before the concrete is poured. Therefore, they are otherwise inaccessible after the house has been built. This is fine if they never wear down. However, if a pipe bursts for some reason, the homeowner may go many months without even realizing it, losing money needlessly as water is leaked out. Even after the problem has been discovered, the homeowner must then break into the concrete to repair the broken pipes. This means any flooring in the area must be removed and the home may be uninhabitable during the repair process. So while in the short run, slab on grade foundations may be cheaper to build, in the long haul they may be more expensive to maintain.
Second, if the engineer determines that the soil within a few feet of the surface is sufficiently load-bearing to handle the weight of the house, the house may be built on a crawlspace foundation. One could think of the crawlspace foundation as a compromise between the cost effectiveness of the slab on grade and the easy maintenance of the full basement. Again, the frost line must be considered. It must be sufficiently close enough to the surface that the builders could place the footers of the foundation below the frost line, to ensure the foundation does not shift during freezing climates. The foundation walls are built a couple feet above the grade, upon which the sill plate and floor joists are laid to build the actual house. An entryway into the resulting space is made just big enough for a person to crawl into, thus the name, “crawlspace.”
The crawlspace can have the advantage of allowing the house builders to lay the pipes and wires underneath the first floor easily accessible by going into the crawlspace. This means that if any problems occur in the future with the wiring or piping, they can much more easily be remedied than if the house was built on a slab foundation. Additional piping or wiring can also be easily added, which would not be possible with a slab foundation.
The crawlspace foundation, however, has many drawbacks as well. Oftentimes, the crawlspace is left open, which could lead to moisture and pest problems, which may invade the house from underneath. The crawlspace can be sealed and climate controlled. Though this adds additional costs, it may be preferable in the long run as it will reduce moisture, pest, and temperature infiltration from below.
Third, as in most locations in the Northeastern seaboard of the United States, the frost line may be deep enough and the surface soil too loose for the house to be built with a shallow foundation. This leads to the building of a basement foundation. While the crawlspace may be 4 feet or less in height, the basement is usually a full 7 to 8 feet, with the final few feet extending above the grade. After the footers are placed below the frost line, the foundation walls built up (usually cinder block or poured concrete for more modern houses) and a concrete slab is poured on the floor of the basement. The house may then be built upon the joists which are laid on top of the foundation walls.
One of the biggest advantages to the basement is the additional storage or living space (if the homeowners decide to finish the basement at a later time) which extends the entire area of the house. Also, all of the house’s utilities may be put in the basement, including the heater, HVAC, water heater/conditioner, and laundry appliances, which frees up additional space in the house.
Besides being the most expensive of the three types of foundations, the basement may also face problems with moisture. The water level of the surrounding ground may be high enough that the basement is under constant water pressure. A water management and pressure relief system can remedy this problem, though it does incur additional costs. The basement can be more easily flooded when it does not have a water management system under heavy weather conditions. Finally, when these problems are not addressed soon enough, the foundation walls may deteriorate and cause serious damage to the house above (which we will look at in the following weeks).
These three are the basic types of house foundations. This blog deals primarily with the basement and secondarily with the crawlspace foundation types. Very rarely do we address the slab on grade foundation. Whatever your house’s foundation may be, I hope it will remain secure and solid throughout its occupancy! As always, keep your basement dry and enjoyable.