When building a house, one of the important components of a competent organization of the whole process is the correct calculation of the amount of materials used. Of course, all stages of construction are important, but one of the first will have to calculate the foundation, namely the number of materials that need to be spent when pouring it. At the same time, if exact calculations are obtained in specialized programs or manually, approximate figures will be issued online by the strip foundation of the house - if its geometry is not too complicated, then this data will be quite enough.
You have to understand , that any automatic calculation of the foundation online calculator can produce with a certain error. Its value depends at least on whether a simple formula is used to calculate the volume, or it additionally takes into account the correction factors derived to calculate the amount of concrete. Additionally, the difference in the geometry of a standard rectangular foundation or calculated for additional bearing walls inside the perimeter should be taken into account.
As a result, on the websites they lay out either a free calculator of the cost of the foundation as a whole, or programs that calculate its individual parameters - the amount of concrete, the number of reinforcement, and the boards that are needed to create the formwork. Together with the boards, one must not forget to count the bars for the spacers and the nails with which all this will be fastened.
One must also remember that online calculations will never give a 100% guarantee of the correctness of the result, because the required data should be entered on the website and the program will simply issue the final result of the calculations without any explanation. So that you do not have to take them all on faith, you need to understand by what formulas and data you can double-check the result of online calculations.
Example of using an online calculator on a video:
When using online calculators It is assumed that all loads have already been calculated for the foundation. This means that it is calculated how many bricks will go on the walls and how much weight will put pressure on the foundation. It is also necessary to take into account the impact of wind loads and the weight of snow that will lie on the roof in winter. Simply put, all the calculations have already been made, the user has decided on the linear dimensions and now you just need to calculate the amount of concrete that will be poured.
Here it is necessary to take into account a number of nuances, ignoring which will lead to the order of insufficient or excessive amount of concrete:
At first glance, the calculation of the strip foundation is simple - length is taken , width and depth, everything is multiplied and the volume is obtained. The nuance here is that this method works ideally for a straight line, but since the foundation is at least rectangular, serious errors creep into the calculations.
For example, the simplest case is a 6x8 foundation with a perimeter (6x8) * 2 = 28 m, without internal load-bearing walls, 0.4 m wide and 1.7 m high - if you simply multiply all these values, then get 19.04 m³. With such calculations, if the formwork is done correctly, concrete will remain in the machine after casting. This will happen, because when calculating the concrete on the foundation, the calculator did not take into account the difference between the external and internal perimeters of the foundation.
If you calculate each wall separately and mark for yourself already “counted” places, the picture will be as follows:
The larger walls of the foundation are calculated separately. Length 8 is multiplied by the width 0.4 and height 1.7 - it turns out 5.44. Since there are two walls, the result is doubled: 5.44 * 2 = 10.88 m³.
Now turn the smaller walls. If you mark already calculated large walls on the plan, it becomes clear that not all 6 meters of length must be taken into account, because 40 cm on each side are already “occupied”. With correct calculations, 6-0.4-0.4 = 5.2 m is taken. This value is multiplied by the width and height and it is 5.2 * 0.4 * 1.7 = 3.536 m³. For two walls it will be 3,536 * 2 = 7.072.
As a result, instead of the originally calculated 19.04, 17.95 m³ will go to all the walls of the foundation, and an extra cube of concrete is a few thousand rubles because of the seemingly childish, and lying on the surface mistakes.
Clearly the reasons for the wrong calculation on the video:
Of course, with complex forms, a standard concrete calculator for a foundation to calculate all the nuances is unlikely. This means that it will be necessary to calculate everything manually for each element separately, noting for myself how much has already been taken into account, and what has not yet been taken into account. In addition, experts take into account the space that will not be occupied by concrete - it is fittings and ventilation holes, which in total also occupy a significant amount.
Is it worth it to count with a stock and how much concrete to foresee for it depends entirely on the professionalism of those who will assemble the formwork. If an error is made even in 1 cm across the basement width, this will seriously affect the volume. For example, with the same values, but the width of the foundation 1 cm larger is (8 + 8 + 5.2 + 5.2) * 1.7 * 0.41 = 18.4 m³ - an extra half a cube of concrete.
As a result, everything depends on the correct fixing of the formwork, the strength of the bars holding it and the integrity of the builders, but in any case it is advisable to order concrete 5–10% more and provide a place for it if it does. where it can be used.
When Professional calculation of reinforcement for the foundation must take into account a large number of factors affecting the choice of cross-section of rods and their number. It takes into account the type of soil, depth, the presence or absence of additional soles. The number of nuances is quite large, so it is clear that the calculator can only calculate the reinforcement for the strip footing approximately. Approximately the following algorithm is used:
Four supporting rods are most often laid in the base frame for low-rise construction - they are located at the corners of the ribbon at the corners. Accordingly, in order to obtain their total length, the length of all the walls of the foundation (perimeter, and if so, internal) must be multiplied by four. In our example, the perimeter is (6 + 8) * 2 = 28, multiplying it by 4 - it turns out 112 meters of the total length of the rods. The quantity must be taken with a margin, since the rods are likely to overlap (overlap length 50 cm). The number of overlaps must be calculated based on the length of the bars of the reinforcement to be purchased. If it is 12 meters, then 28: 12 = 2.3 - this means that there will be 3 overlaps on each rod. If 6 meters, then 28: 6 = 4.66 - there will be overlaps of 5.
It should also be borne in mind that the number of tapes and rods in each of them will be different, depending on the type of foundation, the soil on which it fits, etc. No online foundation calculator will be able to predict their exact number, since here too many variables must be taken into account.
If you look at the foundation tape in cross section, the lintels are located 5 centimeters from the edge of the concrete fill. With a tape width of 40 cm and a height of 170, respectively, lintels 30 and 160 cm long will be needed.
The lintels are 0.5 meters apart. With a perimeter of 28 meters, their number will be 28 * 0.5 = 56. In each jumper there are two pairs of bars, one 30 cm long, and the second one 160 each. That is, only one bridge will cost (30 * 2) + (160 * 2) = 3.8 meters of reinforcement and this length is necessary multiply by the number of jumpers. As a result, the jumpers will need 3.8 * 56 = 212.8 meters of reinforcement. Based on the length of the rebar purchased, the rebar calculator online will help to calculate the number of scraps, and accordingly how many rods need to be purchased, but again with a certain error.
Experts do not recommend welding the pieces of reinforcement between themselves, as this violates the molecular structure of the metal - it becomes brittle and poorly resists deformation. The best option, which should take into account the calculation of the cost of the foundation, is twisting the rods together at the points of contact with the annealed metal wire. The usual is also better not to use - it has low tensile strength.
In our example, there are only 56 jumpers, each with 4 touch points. Total need to make twist on 56 * 4 = 224 connections. Depending on the thickness of the reinforcement, 0.3-0.5 m of wire is required for each twist, and this is a bay of 67.2-112 meters in length.
Here you just need to calculate the area of all the walls of the foundation. From the first example it is clear that using only the outer perimeter is a partially wrong decision. So it is necessary to make a calculation for two perimeters - external and internal. In the first case it is (6 + 8) * 2 = 28, and in the second all walls will be 80 cm shorter - it means that we get (5.2 + 7.2) * 2 = 24.8. The total perimeter of the foundation walls will be 28 + 24.8 = 52.8 meters. To get the area we multiply this number by the height of the walls, we get 52.8 * 1.7 = 89.76 m².
To find out the required number of boards, let's calculate the area of one of them. For example, boards with a length of 6 meters, a width of 20 cm and a thickness of 2.5 cm are purchased. The area of each of them will then be 6 * 0.2 = 1.2 m², and the volume 1.2 * 0.025 = 0.03 m³ .
Accordingly, the number of boards to be acquired will be 89.76: 1 , 2 = 74.8 (rounded to 75), and if the order is placed in cubic meters, then 75 * 0.03≈2.25 m³.
Of course, it is better to purchase with a margin, because any calculations should take into account the error - in this case it will be trimming, the number of which depends on the length of the boards and the perimeter of the walls of the foundation.
With proper installation of the formwork, after its disassembly the boards are quite suitable for further use. Of course, in finishing they are unlikely to be applied, but for the subfloor or scaffolding they will be very useful - this point should not be disregarded during the initial calculations, especially if there is an implicit desire to save on the formwork.
Usually, such functionality is not added to the online calculators of the foundation, since there are enough materials on the construction site. But you should not forget about them if the construction will be carried out in a new place, where tools and consumables have not yet been delivered. If you want to save on props, you can evaluate the possibility of using different versions of the stops - install independent, on each wall separately, or use a circular pattern.
On our website you can see the list companies providing services for the construction of the foundation of country houses , and houses presented at the exhibition Low-rise Country.
From the above examples, it can be seen that calculating the amount of material that will be required for the foundation is a fairly simple task. If its form is simple, then the calculation of cement will be performed by the foundation calculator without any specific inaccuracies and, in addition, it will issue recommendations on the amount of other materials to be purchased - fixtures and boards.
Another question is if the foundation is of a complex shape or will be installed on specific soils. In this case, it is better to trust the specialists who will perform calculations in accordance with all standards and requirements, and use online readers only for an approximate calculation of the amount of materials.