In most cases, when it comes to foundations, we mean a strip type.
It is the most common and has an optimal combination of performance qualities and cost-effectiveness of construction.
In addition, strip bases have a lot of design options, which expands their capabilities and allows you to choose the most successful option.
Such qualities have made the tape a recognized leader among all alternative options.
Despite some negative aspects, this type of foundation is the most preferable for the construction of buildings for various purposes, especially for private houses.
Types of strip foundations for a timber house
A characteristic feature of wooden houses is their low weight. The material has excellent heat-saving properties, so creating thick walls is impractical.
In addition, the specific gravity of wood is significantly less than that of brick, concrete or other dense material.
Therefore, the load on the foundation is significantly reduced, which makes it possible to use a lightweight version of the foundation.
Suitable for a house made of timber:
- Shallow strip foundation.
- Recessed strip foundation.
The first option allows you to get a fairly reliable foundation, making do with less excavation and construction work. At the same time, there are some limitations associated with hydrogeological conditions, complex soil composition, the presence and depth of groundwater.
The second option requires a lot of labor and money, so for log houses it is considered irrational and is used only in difficult conditions.
IMPORTANT!
It is impossible to unambiguously determine the most successful type of foundation based on the material of the walls. It is necessary to consider the specific conditions and factors influencing the choice of tape type.
To help the tape builder
Anyone can build a strip foundation for a house, provided all calculations are completed and all work is carried out responsibly. Our users, without much construction experience, made their monolithic strip foundations and structures from FBS, literally following the technology and strictly observing SNiPs. The materials on our portal will help you achieve a successful result.
On FORUMHOUSE you can get all the necessary theory, documents, constructs, reports, find step-by-step instructions for making a strip foundation with your own hands, study the strip design algorithm, read articles with arguments against carrying out geotechnical surveys and finally decide for yourself the main question: is it true? you need a sand cushion under the tape.
Our video talks about how to independently build a reliable foundation on problematic soils.
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Shallow strip foundation
A shallow strip foundation differs from the classic version in its shallow depth of immersion into the ground. The traditional type requires immersion to a level below the freezing point. This requires creating a trench 2 m or more deep.
Increases the size of the tape, automatically increasing the consumption of building materials and money. Shallow foundations are immersed to a relatively shallow depth, not exceeding the freezing level of the soil.
The option is attractive, but it can create problems with frost heaving, so it is necessary to first study the hydrogeological situation on the site, find out the depth of groundwater, explore the composition of the soil and other data.
However, for light buildings, the use of a shallow strip foundation is considered the most rational solution.
Preparatory work
Before calculating the foundation for a house, the designer needs to find out the geological data of the site. For large buildings, special geological surveys are carried out. In private construction, it is permissible to conduct research yourself. In this case, all characteristics are assigned based on visual inspection.
To correctly calculate the foundation, the soil is examined in two ways:
- excerpts of pits, which are deep holes with plan dimensions of 1x2 m (on average);
- drilling wells with a hand drill.
In the first case, the type of soil is looked at by the walls of the pit. In the second, they check the soil on the drill blades.
To study the soil, the walls of the pit are inspected
Research is carried out to a depth that is 50 cm greater than the intended laying of the tape (which was determined only by the freezing mark). When carrying out work, you need to find out the following characteristics:
- soil type at the base level;
- location of the groundwater level (GWL);
- the presence of weak soil in the lens area.
To accurately understand the GWL, it will be necessary to conduct research at several locations. At least one of these points must be located at the bottom of the site. Working in a drought does not give an accurate result, since moisture can go deep into the ground.
It is best to find out the ground level in the spring. In this case, the strip foundation will not be afraid even of floods.
Soft ground lenses can be difficult to find. To do this, you need to make pits or wells very often. In most situations this is not necessary. If such a nuisance is discovered during construction, it is covered with crushed stone, gravel or a sand-gravel mixture.
If the groundwater level on the site is deep, then you can use a deep tape (more than 1.5 m). In this case, the water should be located 50 cm below the base of the building. When the groundwater level is located at a distance of less than 1.5 m from the surface, it is reasonable to choose a shallow structure. But this type has limitations. If the moisture is higher, it is worth considering another foundation option: slab or piles.
The choice of foundation depth depends on the groundwater level
To calculate the foundation base, you will need to know the strength of the soil. The characteristic features of each type of soil can be found in GOST 25100-2011 . Particular attention should be paid to the appendices to this document. The load-bearing capacity of each type is taken from the table below.
| Base type | Maximum load-bearing capacity in kg/cm2 |
| Pebbles mixed with clay | 4,50 |
| Gravel | 4,00 |
| Coarse sand | 6,00 |
| Medium sand | 5,00 |
| Fine sand | 4,00 |
| Sand of silt fraction | 2,00 |
| Loam or sandy loam | 3,50 |
| Clayey | 6,00 |
| subsidence | 1,50 |
| Bulk with compaction | 1,50 |
| Bulk without compaction | 1,50 |
Types that have a strength of 2 or less kg/cm2 are not recommended for use as a base. Before construction, you will need to replace them with medium or coarse sand.
How to choose concrete
The optimal choice of material is M300 concrete. Heavier grades are used for multi-storey residential or industrial buildings. The use of less dense and durable grades is impractical, since practically no savings or advantages are achieved, but the margin of safety of the base disappears.
Therefore, in practice, no one thinks about the choice, using a proven and reliable option.
Which is better
The optimal choice of foundation for low-rise construction consists of a detailed analysis of many indicators of the object, as well as the features of the area where the house will be installed.
Pile and column structures are used for construction, but have not proven themselves sufficiently in terms of practicality and durability. A monolithic slab is relevant for the construction of both one-story and two-story houses, which are built on landslide soils or in zones of movement of the earth’s crust.
In areas with stable seismic activity, a monoplate is a very expensive method. Practice shows that for a two-story brick house, the best choice is tape technology. And the installation of foam block houses on a strip foundation is also gaining great popularity, since it has a number of advantages:
- resistance to various deformations (cracks, tears, shedding);
- ease of installation and ease of maintenance;
- high load-bearing capacity and operation;
- variety of layouts.
The listed advantages are possible only if the installation technology is followed.
Laying depth
Shallow foundations are usually immersed to a depth of 40-70 cm. This is an average value, but in practice it is necessary to consider the composition of the soil, heaving loads and other criteria. The more negative factors, the deeper the tape should be immersed.
At the same time, it is necessary to take into account the magnitude of frost heaving, which creates high loads on the side surface of the tape and forces the foundation to be strengthened. Sometimes the solution to the problem is to reduce the depth of the foundation, reducing the loads and balancing them along the entire length of the belt.
It is also necessary to take into account the size of the base, which is recommended to be at least 30-40 cm.
Marking
Marking is carried out by marking on the ground both the external and internal boundaries of the future foundation. To do this, it is best to use pegs or reinforcement rods and ropes. But it will be more effective to use special devices, such as laser levels. Remember that large errors in markings will noticeably affect the appearance of the finished building.
To achieve ideal results you need:
- determine the axis of the structure being built
- use a plumb line to mark an angle, and from it, at an angle of 90 degrees, pull a rope to two more corners of the structure
- use a square to determine another angle
- check the angles, focusing on the diagonals. If the test gives positive results, pull a rope between them
- take on the internal markings, retreating from the external markings to the distance of the thickness of the future foundation
When you are finished with the markings, study the differences in the surface at the construction site and select the lowest point to measure the depth of the trench and eliminate the difference in the height of the foundation. If the building is planned to be small, then the depth of the pit can be 40 cm.
General installation diagram
Work progress in order:
- Preparing the site, removing topsoil and leveling the surface.
- Marking the trench.
- Digging a trench to a specified depth.
- Backfilling the sand cushion.
- Installation of formwork.
- Creation of an armored belt.
- Concrete pouring, curing.
- Completion of work.
The procedure for creating a strip base almost never changes, which makes it more understandable and increases the reliability of the result.
Width of strip foundation for timber
The width of the tape is a value that requires calculation. The methodology and specifics of this event do not allow obtaining correct results without experience and preparation. Contacting specialists is the best option to resolve the issue, but this will require a certain fee and will take an unknown amount of time.
Usually the issue is resolved by using online calculators, obtaining quite high-quality calculations, or they act “like everyone else,” taking the width of the tape at least 10 cm larger than the thickness of the walls. In any case, it is not recommended to make a tape narrower than 30 cm, since additional loads may appear during operation.
It is also possible to change hydrogeological conditions, which requires a certain margin of safety and stability.
Calculation of the sole based on load-bearing capacity
The strip foundation, the calculation of which must be performed, requires the use of only one formula. To select the dimensions of the strip foundation, consider this:
B = P/(L*R),
Here the letter B means the width of the foundations that needs to be found. P is the mass of the entire building, taking into account the underground part, which can be found by calculating the collection of loads. R is the strength of the foundation from the first table of the article. L is the total perimeter of the strip structure. To correctly calculate the foundation, you need to include both the external and internal walls of the basement in the perimeter.
Foundation dimensions
Waterproofing
Waterproofing is carried out in order to cut off moisture from the concrete strip. This will keep it in normal condition and prevent the material from being destroyed by frozen water in the winter. Waterproofing also helps improve the microclimate in the house and prevent walls from getting wet due to capillary absorption.
For a house made of timber, this is very important, since the wood is prone to rotting, which makes waterproofing treated with increased responsibility.
There are two types of waterproofing:
- Vertical. It is applied to the side surfaces of the tape, both outside and inside. Different materials are used - impregnations, coatings, rolls, etc.
- Horizontal. A lower waterproofing is used, separating the sand cushion from the tape, and an upper one, separating concrete and wood. Most often, in both cases a double layer of roofing material is used.
Choosing concrete and reinforcement
For a shallow strip foundation, you can use a lighter type of concrete - M200. At the same time, there will not be a significant difference in cost, and the strength of the tape will be lower than when using the optimal option - concrete grade M300. The foundation is a critical element of the building, which requires the use of the most reliable materials.
The choice of reinforcement is determined by the width of the tape. In practice, they usually proceed from the ratio of 30 cm width - 12 mm diameter of the rods. Accordingly, 40 - 14, 50 - 16, etc. Usually there are no problems, but for those who want to clarify their choice, there is a calculation option.
The cross-sectional area of the tape is calculated. The total cross-sectional area of the reinforcement is 0.1% of the ribbon cross-section. The resulting value is divided by 4 or 6 (the number of working rods in the arm belt). After this, the most suitable diameter of the rods is determined from the SNiP tables.
NOTE!
You can use thicker rods, but you should not choose thinner rods.
Calculation of loads
Before calculating the foundation for the house, you will need to calculate the load. It is more convenient to collect foundation loads in tabular form. All loads are divided into two types: permanent and temporary. The latter are temporary, conditionally, since they include furniture, equipment, etc. The permanent ones consist of the mass of the building structures.
The calculation of the load on the foundation can be done completely independently, taking into account the exact characteristics of the materials used. But it will be enough to use the table below. It shows average values, but the load on the foundation will change uncritically.
| Design | Load value, kg/m2 | Reliability factor |
| Brick wall 510 mm | 920 | 1,3 |
| Brick wall 640 mm | 1150 | |
| Timber wall 150 mm | 120 | 1,1 |
| Timber wall 200 mm | 160 | |
| Wall on a wooden frame with 150 mm insulation | 30-50 | |
| Partitions made of plasterboard 80 mm | 30 | |
| Flooring made of PC slabs with cement screed | 625 | 1,2 |
| Wooden ceiling with insulation | 150 | 1,1 |
| Reinforced concrete foundation in kg/m3 (!) | 2500 | 1.2 - for prefabricated 1.3 - for monolithic |
| Roof depending on the type of covering | ||
| Metal | 60 | 1,05 |
| Ceramics | 120 | 1,2 |
| Bituminous materials | 70 | 1,1 |
| Live loads | ||
| From people and furniture | 150 | 1,2 |
| Snow cover | According to SP “Loads and impacts” table. 10.1 taking into account the location of the construction site | 1,4 |
In order to correctly calculate the cross-section, the load on the foundation of each type is multiplied by the reliability coefficient.
Pillow under the foundation
Sand and gravel preparation performs drainage and leveling functions. The bottom of the trench does not have an ideal surface, so a layer of backfill allows you to obtain a horizontal and level supporting platform for pouring the tape.
Water entering the layer passes into the lower layers and is either absorbed into the soil or removed through the drainage system outside the trench.
The standard backfill option is sand preparation 10-15 cm thick, a layer of fine crushed stone 10-15 cm and a surface leveling layer of sand. Pure river sand that does not contain organic inclusions is used.
Each layer is carefully compacted to maximum density. The criterion for determining the quality of compaction is the absence of shoe marks when walking on the backfill.
Installation of formwork
Formwork is a form into which concrete is poured. It is assembled from edged boards 25-40 mm thick. The shields are made outside the trench, but in close proximity to it for ease of carrying and installation.
The assembled panels are lowered into the trench, aligned along the axes and secured with spacers. They determine the width of the tape. From the outside, the panels are fixed with vertical strips driven into the ground, and stops are also used to ensure the formwork remains stationary when pouring concrete.
Example: MZLF 11*14 m
When building a foundation, future homeowners use different materials and offer their own solutions. Let's look at a few examples of tapes made by members of our portal. The work of our user with the nickname Alexey_$ received good reviews.
Alexey_$ FORUMHOUSE user
The height was 90 cm, they were buried 60 cm, of which in the end there was 30 cm of sand cushion and 30 cm of tape underground. The width varies and is indicated in the foundation design.
The trench was dug with a tractor according to markings made with white spray paint directly on the grass. While digging, Alexey “shot the level so as not to over-dig or under-dig.”
Small errors were eliminated with a shovel. High-density waterproofing material was laid in the trench.
The foundation design provided for a 30 cm sand cushion; pouring and compaction with a vibrating plate was done every 10 cm.
Alexey_$FORUMHOUSE Member
After all the manipulations, the error in level was within a centimeter over the entire area.
Ruberoid was laid out on the pillow in two layers
and set up the formwork: longitudinal boards 150x40 mm, every 60 cm - 100*50 mm. The inside of the formwork was lined with polyethylene and reinforced with 8-diameter studs.
12 mm reinforcement was knitted in 2-4 rows depending on the thickness of the tape (400 - 650 mm). The protective layer on the bottom was 5 cm, on the other sides 3-4 cm. Every 40 cm there were vertical jumpers with 8 mm reinforcement.
Alexey_$FORUMHOUSE Member
Spliced at least 50 cm, mating, where necessary, was carried out in a run.
Pouring concrete:
The foundation was covered with polyethylene. A little more than a week passed, the inside of the formwork was dismantled and waterproofing was done.
Backfilling: 10 cm of sand along the tape, the rest is sulinka - 5 cm below the level of the upper edge of the tape.
To reduce heat loss into the ground, the voids were insulated with EPS. This is part of the complex insulation of the sub-foundation space: voids + tape outside + blind area.
Alexey_$FORUMHOUSE Member
The house will have to spend the winter without heating for a couple of years and the influence of frost heaving forces will be reduced.
Reinforcement
The specificity of concrete is its lack of resistance to axial tensile loads. The material is capable of withstanding enormous pressures, but when the load vector changes, it immediately breaks. To strengthen the tape, an armored belt assembled from metal ribbed rods is installed inside.
The frame consists of horizontal (working) and vertical (auxiliary) rods. The working rods perform the functions of an armored belt, ensuring the integrity of the belt and taking on all the loads.
Vertical reinforcement is needed only to support the working rods in the desired position until the concrete is poured, so its thickness is less. The use of smooth rods is allowed. To assemble the frame, a special soft wire is used, but welding is also allowed.
Fill
You can mix concrete for pouring yourself, but this is a very labor-intensive and time-consuming task. It is easier and more correct to purchase the required amount of ready-made concrete, which will be delivered directly to the site and poured from a mixer.
The quality of the material produced using industrial equipment will in any case be higher than that of home-made concrete. It is also more convenient to do the pouring from a mixer, as it is faster, which will result in uniform quality of the concrete strip in any area.
IMPORTANT!
You cannot pour concrete in one place, hoping that it will spill throughout the formwork. You need to approach it from different points and pour the material evenly. This will allow you to obtain a casting with the same properties.
After pouring, it is necessary to water the casting with water every 4 hours for 3 days, and then, for a week, three times a day. The formwork can be removed after 10 days, but final hardening will occur after 28 days.
