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Friday, July 29, 2011

BASIC STEPS OF BUILDING A FOUNDATION

Survey and Stake
Before any construction can begin, the home site is surveyed to establish the home's basic footprint and to ensure the home is set back the appropriate distances from the property lines. The corners of the home are marked by surveyor's stakes. Offset stakes, which are about two feet out from the surveyor's stakes, also are placed. The excavator will dig at the offset stakes, creating a slightly larger hole than the foundation actually will occupy. The extra room enables crews to work on the exterior of the foundation walls.
Excavation
The depth of the excavation is determined by a structural engineer who considers the soil, the frost line and the height of the water table (the depth in the soil at which you find water). Surface soil is removed to expose soil that is compacted enough to bear the load of the home. The excavation must be deep enough to place the top of the footing below the frost line. This prevents the concrete from cracking due to the freeze-thaw cycle of the surrounding soil. The excavation cannot be so deep that it's below the water table, however, because that can cause a chronically wet or flooded basement.
Footings
Footings are poured concrete pathways that help to spread the weight of the home from the foundation walls to the surrounding soil. Footings are wider than the foundation walls they support, and form the perimeter of the home. Sometimes, additional footings are added inside the perimeter to support load-bearing interior walls.
Sub-slab Systems 
Plumbing lines are run from the street to the home's basement, by going under or over the footing. In some regions, soil gas mitigation systems are added to collect the soil gases trapped under the slab and vent them to the outside. Eventually, these systems will be covered with the poured concrete slab that is the basement floor.
Foundation Drainage Tile System
This system collects subsurface water and moves it away from the foundation. Foundation drainage tile consists of a continuous run of perforated drainage pipes embedded in gravel along the outside perimeter of the footings.
Some building codes require drainage pipes along the inside perimeter of the footings as well.
Sump
In regions where the earth is flat or the soil tends to be wet, a sump may be added to help collect subsurface water. A sump pump moves the collected water away from the home.
Walls
Foundation walls are constructed by pouring concrete between sets of form work (the total system of support assemblies for freshly poured concrete, including mold, hardware and necessary bracing.) Once the concrete gains its full strength, the form work is removed. Foundation wall thickness is determined by a structural engineer who considers the height of the wall and the load it has to bear. (Structural load is the force or combination of forces of gravity, wind, and earth that acts upon the structural system of a home). Wall thickness varies from home to home, and even within a home.
Anchor Bolts
Anchor bolts are embedded at pre-determined points along the top of the foundation walls. They'll be used during framing to secure the framing to the foundation.
Beam Pockets
Beam pockets are cast in the top of the foundation walls to receive, support, and hold beams in place.
Dampproofing and Waterproofing
A dampproofing or waterproofing seal is applied to the exterior of the foundation walls that eventually will be below-ground. This slows or stops water from traveling through the walls and into the basement.
Slab
A 3-inch to 4-inch thick concrete slab is poured between the walls. The slab helps to stabilize the base of the foundation walls, and also forms the basement floor.
Backfill
Backfill is pushed into the trenches around the exterior of the foundation walls, burying a portion or all of the walls below the surface for added stability. Ideally, backfill is soil that drains easily.

"If you have built castles in the air, your work need not be lost; that is where they should be. Now put the foundations under them." - Henry David Thoreau An indispensably integral structure of any construction, the foundation, carries deep implications with respect to the overall structure of a building. A lot rests on how well it is built for it is the base that supports the weight of the entire house. Commonly made from concrete for homes, it is vital that the foundation work is done carefully. It is that structure of the house that transfers the weight of the building onto the earth below and provides support for the intense weight above. The depth of the foundation varies with the size of the building structure. Small and medium homes are built upon shallow foundations whereas large construction buildings necessitate a deep foundation. There are certain factors that construction engineers must consider while laying a home foundation. Undoubtedly, building the foundation of your house is one of the most important tasks to be undertaken when building a house. A foundation can enhance the beauty of any building but if laid incorrectly it can become unstable. Here are a few pointers that you must remember while laying a house foundation.

How To Build House Foundation

  • It is always better to hire an engineer to inspect and approve of the concrete foundation that has been laid. This may cost you a bit but safety is best not compromised with. You definitely need to consult an engineer if you plan to have a basement.
  • You can approach a surveyor who will inspect the plot before your start footing work. This will also help get the outline of your house marked.
  • Once the surveyor has marked the position of the house, you need to get the excavator to dig soil for laying the foundation. Do not forget to consult your electrician and plumber to get the required excavation for these connections done at the same time.
  • The electrician will lay pipes for electrical connections, cable and telephone. The wires will be connected to the various utilities as and when required. The plumber will look after the water connections and drainage. You must get all these connections inspected by the concerned regulatory authorities.
  • Depending on the quality of the soil excavated, you may need to procure the appropriate soil type like pit run or drain rock. You may also need extra soil if you have to increase the level of soil. Ensure that the soil is leveled with proper equipment before the foundation is laid.
  • Contact your electrician, plumber and heating company to ask them if they want anything installed in the foundation before the concrete is poured.
  • Ensure that the footings and the foundation are laid at the same time. This way the concrete can be poured simultaneously for both.
  • The foundation is usually stripped a day after the concrete is poured. Place the material that is stripped in such a way that it stays clean and does not obstruct ongoing construction work.
  • Waterproofing is necessary for those areas of the foundation that are below the ground level.
  • You need to place drain tiles along the edge of the house if there is a basement in the house. The top of the drain tile must be placed adjacent to the footing or foundation joint. If your municipality does not allow you to connect your pipe to the sewer then you will have to run the pipe to a gravel pit.
  • All the electrical and water connections that you fix must be inspected by the authorities. Once the drain tile is inspected, backfilling and grading can begin.
  • The concrete part of the structure must be done thoroughly. For this, you can hire a professional concrete finisher.
To prevent your house from sinking into the ground or getting blown away, a strong foundation is a must. Use quality materials for your foundation, garage, driveway and sidewalks. Make use of steel wherever needed for strengthening and holding things in place. A robust and well-laid foundation can be your best investment.



How to Build a Foundation from Start to Finish DIY Guide


Types of foundation and their uses

Foundation of building as the name implies is the starting of a building construction on site really. Types of building, nature of soil and environmental conditions are the major determinant of type of foundation you will use for your building.
1)Strip foundation-This is the most common type, it is mainly used where you have strong soil base and non-waterlogged areas. Most small buildings of just a floor are constructed with this type of foundation .
Depends on the structural engineers recommendation , the depth of your foundation could be from 600mm to 1200mm mostly for small scale buildings . When the soil is excavated, a level at which the concrete will settle evenly is established, then concrete is poured this may be from 150mm(6”) thick to 450mm(18”) thick depending also on building after that block is set round the trenches at the center of foundation ,the foundation usually follows the block lines. The blocks are then layed to d.p.c level before another concrete is poured on top, this is the german or oversite concrete. This type seems to be the cheapest.

2)Pad foundation-This is where isolated columns (pillars) are casted from the foundation to carry a slab at the top of the ground. This is mostly used when you want to make use of the under of building as parking space or when the other space is not conducive to have foundation. Imagine you are planning to build a house across a flowing stream and you want a situation where you can use your boat to pass under the building because the stream is under . Then you may not need to dig foundation that will cut across the river but just by applying columns (pillars) at the edge of the river like a bridge, this columns are thus isolated and there foundations are reffered to as pad.

3)Raft foundation-This is where you have concrete spread around your building from the base of foundation all through to the german floor/oversite concrete/ground floor slab. It is mainly used in areas where the soil are sandy and loose, you spend more on this than the other previous two most of the time. It is also recommended in waterlogged areas but with buildings of less storeys
It has a ground beam which shuts out from the foundation base and is also attached to the ground floor slab to form a network of concrete embedded round the building space. The ground beam are usually from 600mm to 1200mm for low buildings.
4)Pile foundation-The most expensive and the strongest type of foundation, this requires specialist engineering to do. The soil are bored deep down the earth and filled with concrete to be able to support loads of multistory building on top. Most skyscrapers are constructed with this foundation type, a waterlogged area of high building may also require this.
It is the costliest hence it is used for high rise building mostly.

Slab Foundation
Slab is a type of foundation consisting of a structural concrete slab poured directly on the grade. No accessible space exists in slab construction. Slab foundations are popular in areas (i.e. the Southern United States) where there is a relatively high water table. (Water table refers to the depth in the soil at which you find water).

Crawlspace Foundation

A crawlspace is an accessible space with limited headroom, typically between the soil and the bottom of the first floor of a home. Crawlspace construction is predominant in areas where there is heavy clay content in the soil.
Basement Foundation

A basement is an accessible space between the soil and the bottom of the first floor of a home. It usually has more headroom than a crawlspace. Basement foundation construction is predominant in cold climates where the foundation needs to be situated below the frost level.
All three foundation types are usually constructed out of concrete, but can also use concrete masonry units or insulated concrete forms.
Concrete Masonry Units (CMUs) are hollow, concrete blocks. To create the foundation wall, mortar is used between blocks to hold them together, forming the wall.
Insulated Concrete Forms (ICFs) are made of rigid foam insulation forms (a system of support assemblies, including mold, hardware, and necessary bracing to hold concrete) into which concrete is poured. Once the concrete has gained its full strength, the outside forms, the inside forms, or both are left in place to insulate the wall. ICFs are common in regions in which the local building code requires the foundation to be insulated. Another benefit is that the homeowner or builder is able to finish basement immediately, without adding studs.
Some building jurisdictions permit the use of preserved or "treated" wood products for below-grade building foundations. These materials offer advantages of construction speed and low cost. As in the installation ofConcrete Pre-cast Foundation walls, treated wood foundations may be installed on a gravel pad rather than requiring a solid masonry footing.

Inspecting a preserved wood foundation:

  • Check for evidence of foundation leakage at butt-joints where gaskets or sealant may have been omitted.
  • Check for evidence of buckling or other damage;
  • Outside check for the presence of a moisture barrier against the foundation exterior.

Our opinion is that "30-year guaranteed treated wood foundation products" used below grade mean that no permanent building foundation has been provided. This sketch of the components of a preserved wood foundation is courtesy of Carson Dunlop Associates.
Buildings using a wood foundation are in our OPINION a temporary structure. In areas of wet soils and insect damage risk damage may occur sooner than the warranty period.


Choosing the Type of Foundation:

Homeowners and builders make decisions about which type of foundation to use by gauging cost, needs/desires, and soil and weather conditions. If you have high water tables then it may not be possible to have a basement. If your land has shallow bedrock or boulders then it may be more costly to dig a basement. If you have a sloping lot it may be difficult to use a slab foundation. If you have a cold climate then you may need to dig down at least four or more feet to put the home's footings below frost level. If you have to go at least four feet deep then it may be worth spending some extra money to dig a few feet deeper and have a full basement. Also, it is easier to install and maintain mechanical systems in basements (compared to a crawlspace). Your builder can help you determine what type of foundation is best suited for your area.
The choice of foundation is also affected by personal preferences and costs. Basements can add thousands of dollars to the cost of a home compared to the cost of a crawlspace. However, when you consider the extra useable space created by a basement it is some of the cheapest square footage space of a home. If you are tight on funds and can't afford the basement then it may be a good idea to find a slightly smaller plan and use the savings to create a basement. You'll end up with a lot more storage space and potential living space by doing this.
Changing the Type of Foundation on your home:
Almost any house plan can have its foundation changed. It's common for people to design a different foundation if the available foundations do not suit their needs. If you are currently working with a builder you may want to ask them if they will take care of making the foundation changes for you. Sometimes with foundation design it may be helpful for somebody who is near you to do those changes because they will have more knowledge about your local soil conditions and the slope of your lot.
When changing foundation types, pay attention to where you will put the furnace, water heater, and stairs. If you need to add basement stairs, the basement stairs can usually be put under other stairways or you may be able to replace a closet or small room with basement stairs. Another common place to put basement stairs is to replace a mechanical room with stairs and move the mechanical items (such as the furnace and water heater) to the basement. Sometimes space near the laundry room, or space near the garage can be used for a basement stairs. Larger walk-in closets are sometimes reduced in size to allow space for basement stairs. You can often add a basement stairs to a plan without increasing the size of the plan. However, sometimes space may need to be added to a plan to provide room for a basement stairs.
It should be noted that it is the owner's full responsibility to check with his/her local and state building authorities, his/her builder, and the designer of the house plan to ensure that the home meets all applicable building codes and requirements.

STRENGTHENING THE FOUNDATION


foundation strengthened with rebar
Concrete beams, masonry columns, beam pockets and filling in cells of the foundation with concrete and rebar are the ways this foundation is strengthened. Building performance specialist Anthony Grisolia also explains when to backfill and the importance of wall strength and weight.
Prevention is the key to eliminating any problems when building a house, and this is why the builder takes extra steps to make sure the foundation has the strength it needs to support the home:
Instead of using wood headers above the windows in the basement, the builder (and homeowners) chose to go with concrete beams for added support.
The Obergs have an elevated garage floor, and another example of added support are masonry columns with steel rods that will help hold the load of the house, especially under the garage. The builder says you never want to set a beam on hollow blocks because it will eventually crush the block.
The property itself poses some interesting challenges as well. When the builder backfills — or pushes the dirt back around the house — there will be a great deal of weight against the foundation wall. Without extra support the wall could crack. To remedy this problem, the builder had the masons reinforce the wall by filling up the open cells of the foundation with concrete every few feet. Once the cells are filled a piece of reinforcement bar (known as "rebar") is dropped down inside the wet concrete. This combination of extra cement and rebar will give the wall the added support needed to withstand the pressure of the hill. This added weight gives the block wall structural strength.

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