Magnum Inspections Inc.

Serving South Florida Since 1994          Martin County: (772) 214-9929 Broward/Palm Beach Counties: (954) 340-6615     

Email me at: ev@magnuminspections.com

 

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Foundations

This page will deal with different types of foundations. The foundation is the part of the structure that contacts the earth. It must be capable of holding the structure, and prevent excessive settlement. The house structure is attached to the foundation. Foundations today are generally made of concrete, or CMU (cement masonry units or cement blocks). Almost all foundations are reinforced with steel bar called rebar.


In the past foundations were made of bricks, stone and wood. Recreational home built in the mountains or on the beach are often constructed on pier foundations. There are four popular types of foundations that are used: Basements, crawlspaces, Monolithic slab and stem wall slab.  Your choice of foundation will depend on climate, use, and budget and building traditions in your area.

 

Foundation Construction Types

 

Slab-on-grade:

Slab-on-grade foundations are a building engineering practice whereby the concrete slab that is to serve as the foundation for the structure is formed from a mold set into the ground. The concrete is then poured into the mold, leaving no space between the ground and the structure. This type of construction is most often seen in warmer climates, where ground freezing and thawing is less of a concern and where there is no need for heat ducting underneath the floor.

 

The advantages of the slab technique are that it is relatively cheap and sturdy, and is considered less vulnerable to termite infestation because there are no hollow spaces or wood channels leading from the ground to the structure (assuming wood siding, etc., is not carried all the way to the ground on the outer walls).

The disadvantages are the lack of access from below for utility lines, a tendency to transmit cold upward in areas where ground temperatures fall significantly, and a very low grade elevation that may expose the building to flood damage in even moderate rains. Remodeling or extending such a structure may also be more difficult.

 

Over the long term, ground settling (or subsidence) may be a problem, as a slab foundation cannot be readily jacked up to compensate; proper soil compaction prior to pour can minimize this. The slab can be decoupled from ground temperatures by insulation, with the concrete poured directly over insulation (for example, Styrofoam panels), or heating provisions (such as hydronic heating) can be built into the slab (an expensive installation, with associated running expenses).

 

Care must be taken with the provision of services through the slab. Copper piping, commonly used to carry natural gas and water, reacts with concrete over a long period, slowly degrading until the pipe fails. Copper pipes must be lagged, run through a conduit, or plumbed into the building above the slab. Electrical conduits through the slab need to be water-tight, as they extend below ground level and can potentially expose the wiring to groundwater.

 

Monolithic:

Slabs are most common in warmer areas such as Florida, Arizona, California and Texas. Since there is often a shallow frost line, or no frost line at all the footings and slab can be poured right on top of the ground. The footings and slab can often be poured at the same time. When the footings and slab are poured together it is called a monolithic slab.
Slabs are the quickest and cheapest foundation because they require less labor, skill and materials cost. The typical critical path schedule for monopours: monolithic pour, sub-rough plumbing and heating, backfill (or bagging in some areas) pour slab and framing. Form

 

Supported:

The supported slab is similar to a monolithic slab, with the exception that the slab it self is poured over two to three courses of concrete block which make up the footings. The block is laid first, then, the slab poured over the footings. This method was used in the sixties and seventies, but gave way to the easier and cheaper monolithic slabs.

 

Crawl spaces:

Crawlspace is more popular in moderate climates such as the Pacific Northwest, the mid-Atlantic coast. The footings are placed below the frost line, and a stem wall is placed on top of the footing. The sub-floor structure is placed on top of the foundation. The typical critical path schedule for crawlspaces is: Footings, foundation, plumbing, backfill, framing and HVAC (note: subfloor plumbing and HVAC can be done after floor framing if necessary.)
 

Basement:

Basements are most often built in cold weather climates such as the Northeast, Midwest and Rocky Mountains. The footings in these colder climates need to be below the frost line which is fairly deep in these areas. Basements provide the cheapest square footage in most instances.


The upfront cost of basements is high, but the cost of the square feet that is gained is comparatively inexpensive. Check your area for basements. If basements are popular in your area, not having one may make your home harder to sell. There are three types of basements standard, walkout and daylight. Standard basements are not accessible by the outside and don't have exposed basement walls. Daylight basements have one or more walls exposed, and are typically built on hillsides. Walkout basements have access via an exterior door and staircase to the outside.  The typical critical path schedule for basements is:
Footings, foundation, sub-rough plumbing and heating, backfill, basement slab, framing.

 

Martin County: (772) 214-9929 Broward/Palm Beach Counties: (954) 340-6615

Email me at: ev@magnuminspections.com

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