A practical decision guide to soil, loads, climate, and foundation cost estimation.
The four qualities that determine the right basis on which to build are Soil bearing capacity, building load, local climate and site conditions, and cost. Test the soil first, do your calculations second, narrow your options to foundation types third, and compare cost estimates last.
Key Takeaways
• In the beginning, test soil conditions to determine which foundations can be considered before designing.
• Lighter buildings on firm soil are well suited to shallow foundations such as strip, pad and raft.
• Deep foundations (piles, piers, caissons) are appropriate for weak soils or heavy structures.
• It is not the cheapest foundation that is the best. The correct foundation size is.
• The estimation of the cost of foundations prior to construction helps to avoid overbudgeting.
What is a building foundation?
The base of a building that bears the weight of a building is called the building's foundation. It stabilizes the structure, prevents settlement, and guards against moisture, soil movement, and environmental forces.
It is difficult to detect and costly to correct foundation errors since it is concealed after construction has completed.
The first step is to begin with the soil.
A foundation's ability to support soil determines what it can. The ability of a foundation to support soil determines what a foundation can. A geotechnical (soil) investigation tests the bearing capacity, water table depth, and settlement risk.
Common soil behavior:
• Rock and dense gravel: firm and sturdy, easy to build simple and shallow foundations.
• Sandy: well draining soil that can shift under heavy loads.
• Clay: swells under moist conditions and shrinks under drought conditions and may fracture badly designed foundations.
• Silt and loose fill: poor, needs deep or reinforced foundations
So, if there's one thing you can take away from this article, it is this: Do not design a foundation without knowing soil.
If calculating the building load, proceed with Step 2 below.
There are three types of loads that must be carried by foundations:
• Dead load: weight of walls, floor, and roof—permanent.
• Dead load: people, furniture, and equipment.
• Environmental load: wind, snow, rain, seismic forces
The foundations of heavy structures like a 10-story building are deeper and wider than those of a single-story house.
Choose a foundation that suits you. Step 3: Foundation Awareness
There are two types of foundations.
Shallow foundations are placed close to the surface and do their job when the top layers of soil are firm:
A continuous band of concrete under a set of walls that carry the load, which is usually found under load-bearing walls in homes.
• Pad (isolated) footing: footings for individual columns.
• Slab (mat) foundation: a single large foundation slab, effective in low demand soils.
Deep foundations are required to transmit loads to deeper, stronger soil or rock:
• Pile foundations: long columns driven or drilled into the ground.
• Pier foundations: supports that descend to a deeper, more stable layer of soil.
• Drilled Shaft (Caisson): large diameter concrete shafts for heavy commercial and industrial construction projects.
Shallow foundations are cheaper and are appropriate for light buildings on good soils, in general. Where the surface soils are not able to support the loading, deep foundations are required and are more expensive.
Step 4: Take into account the climate and site conditions.
• Flood risk or high water table: Drainage, waterproofing, or raised designs are necessary.
• In cold climates foundations should go below the frost line to prevent frost heave.
• Earthquake zones—designs need to withstand lateral forces and ground movement.
• Sloped sites: may require stepped footings or retaining walls
It is important to verify the local building codes, as they may differ depending on the area.
Step 5: Compare Costs Before You Commit
One of the most significant early costs in construction is foundation work and mistakes in quantity and cost estimates just keep growing in the course of the project. A good estimate includes:
The amount of earth being moved. The quantity of earth to be removed.
• Concrete quantities
• Reinforcement steel
• Formwork
• Labor and equipment
• Waterproofing and drainage
Accurate numbers can be used to make comparisons like raft foundations versus pile foundations based on actual numbers and not assumptions. Building estimation software solutions such as quantity takeoff and cost estimation services from design estimation assist contractors, builders, and owners in acquiring extremely thorough quantity takeoff pricing estimates before the work is carried out, and the foundation choice is based on facts.
A Simple Decision Process
• Have a soil test done.
• Determine the size, height and use of the building.
• Check the local codes and climatic conditions.
• Collaborate with a structural engineer to narrow down your choice of foundation to 2 or 3 options.
• Obtain in-depth quotes for every option.
• Check out the prices, durability, and building time and pick the one that's best.
• Common Foundation Mistakes
• It is important to avoid this as it is a costly error.
• Replicating a neighbour's foundation without taking soil tests;
• The purchase is a first based on the lowest price alone
• Failure to consider drainage and waterproofing.
• Beginning construction without a detailed cost estimate.
Frequently Asked Questions
What type of foundation is the most suitable for building a house?
A strip footing or a slab-on-grade foundation is typically used and is an affordable option for most houses built on stable soil. The last decision is made according to the soil report and local building code.
What is the difference between shallow and deep foundations?
Shallow foundations are shallow and distribute loads over rigid topsoil. Deep foundations are used where the surface soil is weak or loads are heavy, and they extend deep into stronger layers of soil.
When is it necessary to get a deep foundation?
A geotechnical report will indicate if surface soil is capable of supporting the surface load of your building. Deep foundations are generally indicated by weak soils, high water tables, or a heavy structure.
What is the price of a foundation?
The cost of a foundation depends on the type of foundation, the condition of the soil, building size, materials, and local labor rates. The best way to obtain a number for your project is with a detailed quantity takeoff and estimate.
Is it possible to get an estimate for the cost of the foundation before the final design is completed?
Yes. Preliminary estimates provide an idea of your options early and can be adjusted as your design progresses.
Does it always make sense to dig deeper?
No, in good soil, a deep foundation is a waste of money. The objective is to create a foundation that is just the correct size for your site.
Final Thoughts
The key factors to consider when selecting a foundation are soil, load, climate and budget. Test the soil, and know loads, match the foundation to the site, and check cost before building.
For an exact cost of your foundation and construction, check out our estimating services at Design Estimation to see if you need further information to help you decide.
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