Writing Job Specification
Write an original, well-structured, thoroughly researched, long-form (approx. 2000 words) blog post on strip foundations, their advantages, disadvantages, design features, etc. Include the following main keywords: strip foundation, strip foundations.
- Number of words: 2064
- Uniqueness: 100% (Advego Plagiatus)
- Readability score (Flesch): 59
- Keyword density:
- strip foundation: 26 (1.89%)
- strip foundations: 24 (1.74%)
A properly designed and built foundation is key to the durable and safe operation of any building or structure. There are a number of types of foundations, but strip foundations are undoubtedly the most popular types in private home construction. A strip foundation is basically a continuous strip of reinforced concrete closed around the perimeter and laid under all the walls of the house to be built evenly distributing its weight. This structure provides resistance to the heaving forces of soil and minimizes the probability of the walls sinking or skewing. Thanks to the fact that there is no need to use heavy mechanical equipment to build a strip foundation, anyone can do it on their own without hiring expensive contractors.
The purpose of this type of foundation is based on the distribution of the load of the above-ground structures (walls). It is designed to create direct resistance to soil movements, i.e. to prevent the building from sinking into loose soils or moving along its axes in any direction when the soil deforms around or directly under the house. A strip foundation can withstand enormous loads. It means that it is possible to build both lightweight structures and heavy houses on it. This type of foundation is also much more cost-efficient and easier to install than other foundation types.
In what circumstances is it advisable to choose this foundation type? Choose a strip foundation if:
- the ground of your construction site is uneven and there is a possibility of high-amplitude settlement
- you intend to use heavy materials in the house or structure to be built such as concrete blocks, bricks (the walls have a density of 1000 kg/cu.m to 1300 kg/cu.m)
- you plan to have a basement in your house (the walls of the strip foundation will be the walls of the basement)
The life expectancy of a foundation depends on many factors:
- correct calculation of strength characteristics and choice of foundation type
- compliance with process requirements during its construction
- waterproofing of the foundation edges and underside
- type of foundation protection against aggressive environmental effects
- protection of the inner walls of the foundation with antiseptic and waterproofing compounds
- quality of materials used
Depending on the material used, the service life of strip foundations may be:
- up to 150 years for monolithic concrete strip foundations
- 30 to 50 years for brick strip foundations
- 50 to 70 years for prefabricated concrete strip foundations
NOTE: DPC — damp proof course; DPM — damp proof membrane; GL — ground level.
A strip foundation has a number of advantages that make it the most popular one among all other types of foundations:
- Its construction is technically simple, inexpensive, and normally does not require the use of heavy machinery.
- The walls of a strip foundation can simultaneously serve as walls of the basement of the house.
- It is suitable for the construction of both small private houses and large apartment buildings.
- It is possible to build a house on a slope.
- The construction can be carried out in any weather conditions.
- The settlement of the structure is minimal.
- It is reliable and durable.
- It can withstand great loads.
- With a strip foundation, it is possible to provide better heat insulation of the floors of the house.
Strip foundations have a number of disadvantages as well:
- Building a strip foundation requires the use of a lot of materials.
- Waterproofing is required.
- With a monolithic concrete foundation, the most reliable type, you have to fill all the lot in one go; and this is very hard work that requires many people and the use of machinery.
- If the above-ground structure to be built is massive or you intend to build a basement, it requires a much greater amount of earthworks.
- It is not recommended to use this type of foundation on horizontally unstable grounds and on heaving soils (clays). It is also absolutely impossible to use it on peats.
Based on the construction method, there are:
- monolithic strip foundations
- prefabricated (block, panel, panel-and-block) strip foundations
The design of a monolithic strip foundation involves making a reinforcing cage and binding it with concrete on site thereby achieving integrity of the foundation base.
A prefabricated strip foundation implies binding reinforced concrete blocks with one another. This is done using cement and reinforcement bars. As mentioned above, monolithic strip foundations have the longest service life and are the most reliable ones.
Based on the laying depth, there are:
- shallow foundations
- deep foundations
A shallow foundation is more popular. Its dominance is due to its sufficiently high load-bearing capacity and its affordable cost.
It is used on all types of soils except for collapsing/heaving soils and peatlands and is the best option for lightweight houses with a height of up to two floors. As a rule, a shallow foundation is used in wood and wood-frame house construction. The laying depth is usually no more than 60 cm, and its base is similar to a floating load-bearing structure capable of resisting the bursting effect of soil.
If you have a heaving soil or the house will be build of heavy materials such as cinder block, gas silicate, or brick, or you intend to build a basement, you need to use a deep strip foundation. The laying depth is calculated taking into account the level of soil freezing, especially in cold-climate areas, and the lowest point of the foundation should be at least 20 cm to 30 cm below this level. For example, the soil freezing level is about 1 m to 1.5 m deep in the central European part of Russia, up to 2 m in the north-west of Russia, and up to 3 m in West Siberia. The monolithic strip is recommended to be pre-reinforced in this case.
In order to avoid the effects of excessive weight of the above-ground structure on the foundation, the foundation walls should be wider than the walls of the house to be built. As a rule, for the sake of stability of the house, the width of the foundation walls should be at least 10 cm wider than the walls of the house. Also, to make the entire structure more stable, it is recommended to make a strip foundation expanding towards the base. That is, its cross-section looks like a trapeze widening towards the base. However, a strip foundation with a rectangular cross-section is also quite stable.
The choice of the minimum width of a shallow foundation is based on the following main principle: the unit load per unit area of the soil located under the concrete base should be less than its load-bearing capacity. Namely, this difference should be at least 30% in favor of the load-bearing capacity.
NOTE: * In all cases, if your construction site is in peatlands, you will have to use a different foundation type.
Before you start pouring the concrete solution in, you need to choose the most optimal concrete grade for your foundation. The concrete grade to be used depends on a number of factors:
- weight of the entire structure
- additional loads on the foundation
- type of reinforcement used
- soil type
- climatic conditions of the area
To make a concrete pad under the main foundation, grade M7.5 or M10 will be quite enough. For light structures (panelized houses, bath-houses, and sheds) grade M15 will be fine. The construction of a house of wood or light blocks requires the use of grade M20. For massive structures and buildings, you should prepare high-quality grade M25 to M30 concrete. Higher grades of concrete are used for the construction of geometrically complex structures and on construction sites in areas with a harsh climate. In cold climates, you should not forget about another important parameter of concrete, freeze-thaw resistance.
In addition to concrete, you will need:
- 20 mm thick planed board for the formwork
- 8 mm to 12 mm thick steel bars and wires for the reinforcement
- river sand for the sand pad
Special attention should be given to reinforcement bars. The whole structure of the strip foundation is mainly exposed to longitudinal loads. These are associated with the uneven load of the building on its foundation and with the soil heaving forces. Therefore, the longitudinal reinforcement of the foundation should be made of ribbed bars (with a variable cross-section) that provide better adhesion of steel to concrete and allow it to withstand greater loads. Corners are the weak points in the strip foundation. They are most susceptible to chipping, fracturing, and other kinds of deformation. That is why the reinforcement of foundation corners should be done with the utmost care.
The main problems in the construction of a strip foundation are:
- water saturation
Incorrectly calculating the load of the above-ground structure or the footprint of the foundation, not taking into account the presence of collapsing soils with a low load-bearing capacity under the foundation, or leaving the soil in an undeveloped, uncompressed form — all this will cause additional complications during construction.
Heaving is due to freezing of the foundation base. The soil under a shallow foundation (especially water-saturated) expands, lifts the foundation up, forms cracks in it and, as a result, the foundation deforms and then transmits the load to the walls of the house thus resulting in their cracking as well.
The freezing of a strip foundation also makes humid air produce condensation, which saturates the foundation with water. Therefore, you should keep your foundation from freezing through in winter time.
Water, as a negative factor for the strength of the foundation, has several sources. First of all, it is the amount of atmospheric precipitation in the region and the local groundwater level. Wet concrete is well-known to be easily destroyed at low temperatures when the water freezes.
Basement foundations are very popular and are beneficial for a number of reasons. These foundations are normally dug at a minimum depth of 2.5 meters into the soil. The walls of the strip foundation are the walls of the basement.
- The greatest advantage to a basement foundation is the additional square meters of space you get at a much lower cost than other parts of your house.
- For small-footprint homes, the addition of a finished basement creates energy-efficient living spaces that stay warm in winter and cool in summer.
- It is easier and less expensive for technicians to fix your home utilities standing up rather than crawling in a crawlspace or digging into a slab.
- Basements can be great shelters from storms and hurricanes while still providing a solid anchor for your above-ground house.
- A basement foundation is quite expensive — even more so if you plan to finish this space. But even then, this finished basement space is most likely to be the cheapest square meters of your entire home.
- Potential flooding. To prevent potential flooding, check the groundwater level in your area beforehand.
- Lack of natural light. If you plan to convert your basement into a living space, you might have to find creative ways of bringing some light in there.
With a strip foundation, you can build various structures, from small wooden sheds to multi-story monolithic houses. At the same time, you use much less building materials and carry out a smaller amount of earthworks compared with slab foundations (and ultimately pay much less money for the entire foundation), which makes strip foundations the most popular type for the construction of country houses.
Author: Aleksei Afonin