The scope of strip foundations is extensive.
This type of foundation can be used as a basis for massive brick walls, lighter walls built from cellular concrete, for wooden log cabins or frame houses. Strip foundations have a simple manufacturing technology, but at the same time they require a large amount of building materials, have a high labor intensity of production and are very massive.
It is necessary to start the construction of the foundation with a breakdown on the plan of the planned structure. The planned right angles of the future building are set using the so-called “Egyptian triangle”, which has an aspect ratio of 3-Ch-4-Ch-5, which is made of long boards, soft wire or rope. Be sure to perform a final check on the squareness of the planned foundation by measuring its diagonals (they must be the same).
The breakdown of the plan of pits and trenches for the foundation must be carried out taking into account the maximum permissible steepness of earthen slopes. Vertical walls of trenches or pits 1-1.2 meters high without formwork or additional reinforcement can only be left in loamy and dense clay soils in the complete absence of groundwater. In any other cases, it is necessary to temporarily equip earthen slopes with special poles, props, using slabs or undercarriages.
The construction of the foundation should be started immediately after digging holes and trenches, after removing liquefied soil and water from it.
The sole of the designed strip foundation should be located at least 20 cm below the freezing depth of the soil in the construction region. If the soil is sandy or dry, it can be laid above the freezing level, but, in any case, not less than 50 – 70 cm from the ground level. It is allowed to save building materials (as a rule, up to 50%), fill the bottom of the trench prepared for arranging the foundation with dry coarse sand, followed by thorough tamping. These foundations can be used in any type of soil, any humidity. In this case, the base of the foundation should be located at the estimated depth of laying, and the stone masonry is replaced with a sand cushion with a depth of about 40 – 60 cm. It is necessary to lay sand on the bottom of the trench in layers of 15 – 20 cm thick. Each such layer is poured with water and carefully compacted. After that, a layer of crushed stone or gravel about 10 cm thick is laid on the compacted layer of sand and poured with a cement-sand mortar on top. Next, the next layer is arranged, etc. A formwork of the required height is arranged above the surface of the earth and concrete mortar is laid in it. The entire surface of the foundation is carefully waterproofed in order to prevent capillary transfer of moisture from the soil through the foundation material to the walls. This option for the construction of a strip foundation will help save about 50% of concrete.
As a filler for a cement-sand mortar for the construction of foundations of this type, gravel, crushed stone, rubble stone, broken and burnt bricks can be used. When making brick foundations, it is more expedient to equip it on a high sand cushion, since this saves bricks and, to a large extent, improves the quality and reliability of the foundation. For its quick and efficient construction, it is recommended to use a prefabricated structure made of concrete blocks, which can be made in advance using a formwork from knocked down wooden boards.
During the construction of the foundation, it is necessary to bring the masonry above the designed zero mark, followed by leveling the upper surface of the slab with mortar.
After pouring the strip foundation, for its safety and durability, it is necessary to perform high-quality vertical and horizontal waterproofing. Horizontal waterproofing is performed using several layers (at least two) of bituminous roofing material. Horizontal waterproofing prevents the capillary transfer of moisture from the wall to the foundation, and will also be an excellent protection of the foundation from rain until the start of the erection of the wall structure. In addition, it is necessary to carry out vertical waterproofing of the foundation from surface water and moisture, which may be in the soil in contact with the foundation slab. Along the entire perimeter of the foundation, it is necessary to equip a blind area with a width of more than 1 meter. The blind area should have a slight slope from the walls of the foundation structure to effectively remove moisture from the house. The blind area must be carried out immediately after the completion of construction work on the arrangement of the foundation. As a blind area material, many experts recommend using greasy clay, laid in a prepared recess along the wall, on top of the clay is covered with a small layer of sand with fine gravel or gravel, lightly tamping.