Before purchasing any building material, it is necessary to determine the right amount as accurately as possible, otherwise you can lose some amount due to the remaining surplus or the need for additional purchases, as well as the unaccounted for the possibility of fraud by unscrupulous sellers. Timber, logs, boards and similar wood products, as you know, are sold in cubic meters, which means that you need to know in all subtleties the calculations for determining the volume of these materials, as well as converting the required number of pieces into cubes and back. And in the case of purchasing timber for building a house, when calculating the required amount of this building material, it is also necessary to take into account the design and features of the future building.
Basic calculations - volume determination and conversion from pieces to cubes and vice versa
Calculating the cubic capacity of timber, boards and similar lumber is very simple. To do this, you need to know the thickness, width (height) and length of the product. And, as you know from a school textbook on geometry, you need to multiply these dimensions:
V = T ∙ H ∙ L, where
V is the volume of timber, m 3;
T is the thickness;
H - width;
L is the length.
Before calculating, dimensions should be given in one unit of measurement: mm, cm or m. It is better in meters, so that later you do not have to convert from mm 3 or cm 3 to m 3.
Beam size table
For example, let's calculate the cubic capacity of a bar 150x200. These dimensions, as you know, are indicated in mm. That is, the thickness of the product is 0.15 m, and the width is 0.2 m. The standard length of timber and boards is 6 m (sometimes also indicated in mm - 6000). Or maybe another. But for example, let's take exactly 6 m. Then the volume of this lumber:
0.15 ∙ 0.2 ∙ 6 \u003d 0.18 m 3.
Now you can convert the required amount (in pieces) of this product into cubes. Let's say you need 49 pieces:
0.18 ∙ 49 \u003d 8.82 m 3.
Knowing the volume of one product, you can also calculate the cube of the timber, that is, determine how many of its units (pieces) are in 1 m 3. To do this, you need to divide 1 cube by the cubic capacity of one product already calculated or taken from the reference tables (in this example, 0.18 m 3):
1 / 0.18 \u003d 5.55555 ... pcs.
In the same way, the amount of this type of timber is calculated for any volume.
The nuances of calculations - how not to make mistakes and not let yourself be deceived
As follows from the above methodology and calculation examples, it is very easy to calculate the required volume of timber in pieces or cubic meters. However, it must always be remembered that in 1 cubic meter there is not an integer number of these products. For the example given in the example with dimensions of 150x200 and a length of 6 m - 5.55555 ... pcs. Unscrupulous, most often retailers of timber cleverly take advantage of this.
For example, you need 1 cube of this material from the example. The seller, of course, releases 5 products, but takes the amount as for a whole cube. The overpayment will be the cost of half a bar.
And let's say that the same 49 bars from the example are needed to build a house. And if the seller considers according to the following scheme, then you will have to significantly overpay for the timber received:
- 1 cube - 5 products 150x200 6 m long;
- 49/5 = 9.8 cubes payable.
This is a divorce of the purest water for 5 units of timber. They are superfluous and not needed, however, they will be paid, but not received. Above, in the calculation examples, the data of 49 products have already been translated into cubes - this is 8.82 m 3. That is, a "particularly enterprising" seller will deceive an inattentive buyer by:
9.8 - 8.82 \u003d 0.98 m 3 timber,
which is 0.98 / 0.18 \u003d 5.44444 ... pcs. this lumber (0.18 - the volume of one product calculated above).
Therefore, it would be most correct to calculate in advance exactly the number of units (pieces) of the material, and only then, using these data and the dimensions of the timber or board, calculate their actual cubic capacity.
That is, in the case of purchasing one cubic meter in the above example, you must first decide how many bars you really need to take - 5 or 6. And then we consider their cubic capacity:
0.15 ∙ 0.2 ∙ 6 ∙ 5 (or 6 pcs.) \u003d 0.9 (or 1.08) m 3.
And for 49 units of this timber:
0.15 ∙ 0.2 ∙ 6 ∙ 49 \u003d 8.82 m 3.
Then you will have to pay exactly for these 0.9 (1.08) or 8.82 cubic meters, having received exactly 5 (6) or 49 products. Moreover, both the quantity in pieces and the volume in m 3 must be indicated in the invoice for the timber sold by the seller.
Other features of calculating the cubature of lumber
Another important feature that you should know for the correct calculation of the cubic capacity of timber or boards when purchasing them. The actual length of lumber usually always slightly exceeds the standard or declared by the manufacturer of this product. So, instead of 6 m, the average length of the considered timber, as a rule, is 6.05 m. This is due to the fact that the ends of the lumber are not processed after it has been cut, because of which they may turn out to be uneven, go at angles, and be different or simply be dirty. Of course, these 5 cm do not need to be paid. But some cunning sellers, although quite rarely, still try to take into account even this when calculating cubic meters, which is pure deception.
And regarding the calculations for grooved and profiled timber. The presence of spikes, grooves, and other protruding or turned places should not be embarrassing. The calculation of the cubic capacity of such materials is no different from determining the volume of ordinary products that are even on all sides. For grooved and profiled lumber, the rule applies that only the main part (working width) of the product is measured and taken into account, and all structurally necessary and / or decorative elements are not taken into account in the calculations. This provision applies to absolutely all types of timber.
Purchase of large volumes of materials - calculation of storage and dense cubic meters
When it is necessary to purchase a large amount of timber, their cubic capacity is calculated somewhat differently than discussed above. For example, a timber and a board are needed for the construction of an impressive spacious house, as well as various other outbuildings near it. In this case, the necessary lumber, for sure, will be of different sizes in cross section and length. To measure and calculate each type of required material with similar purchase volumes is an occupation that can take more than one day.
For such cases, there is a specific calculation method. It is based on two important concepts:
- 1. Dense cubic meter of wood. This is the name of the volume occupied only by wood and not having voids in it, as well as gaps. It is determined by measuring individual timber pieces, and then subsequently calculating their total cubic capacity.
- 2. Folding cubic meter. This is the name of the volume occupied by the lumber stacked as tightly as possible and having voids, as well as gaps between individual wood products. It is determined by measuring the stack, and then multiplying the dimensions of the latter. Moreover, in such a package, the main amount of material should have approximately the same length, and the remaining products may be shorter, but not longer. It is allowed to have short lumber in piles, which should be tightly stacked one after another.
In order to quickly calculate the large volume of required purchased lumber, which is already prepared and stored in the form of a stack, the latter is first measured, and then its cubic capacity is calculated. This will calculate the folding cubature. Then its value must be multiplied by a special conversion factor. The result will be the volume of only wood (a dense cubic meter), that is, exactly those materials that are bought and will be paid for.
The value of the conversion factor is regulated by a number of standards for lumber: GOST 6782.2-75, 6782.1-75, 6564-84, OST 13-24-86 and others. For timber and boards, depending on their moisture content and the type of wood from which they are made, it is in the range of 0.74–0.82.
We consider the required cubic capacity of timber for building a house
- The height of the outer walls, measured from the level of the foundation. Let's denote it as H.
- The height of the internal partition walls, if any, and should be made of timber.
- The length of the outer and inner walls.
- The number and length of the beams used in the truss system, as floor beams and, as well as in its other structures - if provided for by the project.
Then we select the thickness of the material for each of the above structural elements. For external and internal load-bearing walls, depending on the purpose of the house being built and the region where it is being built. For non-bearing partitions - at your own discretion. The plinth (lowest) crown of the outer walls is usually slightly thicker than the rest of the timber for them. For the remaining elements of the structure, the thickness of the material is selected based on the conditions of its operation, as well as the required strength of the structures in which it is used. In a well-designed project, by the way, the thickness of the beam used for walls, the basement crown, and other building structures should already be indicated.
Now only pure arithmetic remains. First, we calculate the perimeter of the house - we add up the length of all its external wall structures. For a simple rectangular or square structure, you just need to add up its width and length, and multiply the resulting value by 2. Then we calculate the cubature of the base crown:
V C = T C ∙ Z C ∙ I, where
V C - total cubic capacity of basement lumber, m 3;
T C - thickness of the basement, m;
Z C - its width (height), m;
I - the perimeter of the outer walls, m.
Calculate the remaining height of the outer walls, m:
h \u003d H - Z Ts, where
H - total height, m.
We calculate the area of external wall structures without a basement crown, m 2:
If the thickness of the material of the basement crown is the same as that of the entire wall, then the area of \u200b\u200bthe latter, m 2:
We calculate the area of \u200b\u200bthe inner walls, the thickness of the lumber in which is the same as that of the outer ones, m 2:
S В1 = H В ∙ L В1 , where
H B - the height of the internal walls, m;
L B1 - the total (total) length of the internal walls, the material thickness of which is the same as that of the external ones, m.
We calculate the area of \u200b\u200bthe internal walls, the thickness of the timber in which is different, m 2:
S B2 = H B ∙ L B2 , where
L B2 - the total length of the internal walls, the material thickness of which is different, m.
We calculate the cubature of the main lumber - for external walls and internal partitions from the same timber, m 3:
V S = (S Н + S В1) ∙ Z S , where
Z S - selected thickness of the product, m.
We determine the volume of material for internal partitions from another timber, m 3:
V B = S B2 ∙ Z B, where
Z B - selected material thickness for these partitions, m.
The results obtained (V C, V S and V B) are divided by the length of the purchased lumber and its selected width (height). Get the amount of material in pieces. We round this value to an integer value, and then we recalculate V Ts, V S and V V, as described in the second chapter.
To save on lumber, you should calculate the total areas of window, door and other openings for the corresponding walls. Then their values \u200b\u200bshould be subtracted from S H, S B1 and S B2, respectively. After that, we calculate V S and V B using the same formulas. Then we increase the obtained values by 10-20% - so that there is a margin just in case.
The cubic capacity of the timber for the rest of the elements of the house in which it is used is calculated even more simply. Its total length is calculated, which we multiply by the thickness and width selected for the material.
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