The foundation is a structure that has essentially nothing to do with aesthetics, design, or style. And it is practically invisible. That is why future homeowners sometimes pay so little attention to it. And in vain…

The cost of constructing a foundation is 15-20% of the total cost of the project (if there is a basement or ground floor – up to 30%), and the cost of violations of the zero cycle, even at first glance insignificant, can ultimately exceed all conceivable percentages. It is worth, literally worth it for the owner, even if very far from the construction theme, to devote time and effort to delve into a number of important points of this stage of construction at the basic level.

The question is – what basics?

Soils, waters and frosts (“national characteristics”)

The main thing is to adapt the project to local conditions, namely – geology and climate. We are overcome by cold, difficult soils and high groundwater. The most reliable and durable – rocky – soil, which practically does not require deepening, is very rare. There are more places with detrital soil, requiring a depth of about 0.5 m. It is even easier to find areas of sandy soil with a sufficient depth of 0.4-0.7 m. This soil is strongly compacted and subsides, but does not retain water and freezes weakly. However, the resource of “sandy areas” is drying up before our eyes with the current rapid construction.

There are expanses of all kinds of sandy loams, loams, clays, not to mention swampy areas, where you can’t do without spending money on drainage work. Such soils are not only easily compressed and washed away, but also rise, heave at sub-zero temperatures, pushing out the foundation. That is why they are called heaving.

The most important parameters that you need to know when developing a site: the depth of soil freezing and the groundwater level (GWL) in a given place. They determine how well the project corresponds to the area and dictate what kind of foundation it is advisable to lay here. The first parameter has its own “regional standards”. For example, in the Moscow, St. Petersburg, Voronezh or Veliko-Novgorod regions, the established freezing depth is 1.4 m. However, there are always local peculiarities, so it is extremely useful to obtain information from the nearest, professionally developed areas.

The groundwater level cannot be even approximately standardized. You can only trust the results of competently conducted engineering and geological work in a given place. But with the results of preliminary studies in hand, the customer has no sin in making general calculations himself – and this is not difficult. And if it turns out that the groundwater level is higher than the freezing depth, do not skimp on the appropriate measures to protect the foundation. The cost of the most expensive “prevention” is incomparably lower than the losses on “treatment”.

Engineering and geological studies. These include studies of the composition and properties of the soil taken from boreholes drilled on the site, and chemical analysis of the water. When building wooden houses, the depth of such boreholes should be 5 m, for brick and stone houses – 7-10 m. At least four boreholes are required, at least in the corners of the future house.

In the case when you plan to buy a finished cottage, it would be a good idea to find out how “correct” its foundation is, that is, to make an effort to obtain the results of a previously conducted examination and to take samples of the foundation masonry itself in order to compare them.

It makes sense to indicate a few more important aspects related to the depth of the foundation. Thus, the standard depth can be reduced under certain thermal conditions of the building, since in heated rooms the heating of the soil largely depends on the design of the floor and its materials.

The depth of the foundation also depends on the specifics of the relief, and for a building without basements – on the planned underground utilities, the nature and magnitude of the loads.
Strip, columnar, pile… Is there a choice?

In a finished project, the type and design of the foundation correspond to the main material of the house – wood, brick, reinforced concrete blocks, frame, etc. – and its number of storeys. However, soil conditions and the relief of the site can make “forced” adjustments towards strengthening – and therefore increasing the cost – of the house support or, conversely, allow for pleasant savings. It is worth taking the time to discuss the issue with professionals. And, first of all, you cannot succumb to the well-known prejudice that it is better to build a foundation as deep and massive as possible.

The foundation is “combined” from the selected type of structure (strip, solid, columnar, pile) and the laying technology (prefabricated, monolithic). Accordingly, if the laying is carried out to a depth of 5 m, the foundation will be considered shallow, and if deeper than this mark, then – deepened. Here we note that when using an excavator, it is better to initially make a trench for the foundation approximately 20 cm higher than the approved depth for subsequent careful finishing (cleaning, leveling) manually.

This approach significantly improves the quality of the foundation sole. These preparatory stages (moving out the axes, excavation and compaction of the soil) usually make up from 5 to 25% of the total cost of the foundation.

The type of foundation is determined primarily by the weight of the house, the presence or absence of a basement and cellar, and the properties of the soil. A two- or more-story cottage with heavy structures on sufficiently strong and dry soil is usually placed on a strip foundation, prefabricated or monolithic.

On heaving soil with active groundwater dynamics, a slab foundation is optimal. The latter is essentially a combined one, since the same strip foundation is laid on top of reinforced concrete slabs (solid, precast-monolithic or monolithic-cross) like on a raft. This design is optimal on any soil for buildings made of light frame structures.

Make sure that the topsoil is removed before digging trenches or pits over the entire area of ​​the building, including the blind area, to avoid possible subsidence and rotting.

Foundation formwork. Advanced professionals install reusable metal formwork in the pit, rather than the “obsolete” wooden formwork, into which reinforcement is placed and concrete is poured. Such formwork provides the foundation with a smoother and more even, and therefore more durable and cold-resistant surface. A true professional also makes a concrete ingot with the pouring date and gives it to the customer complete with a concrete passport, certificate and receipt from the receipt order.

There is a well-known problem of choosing between prefabricated strip foundations and monolithic strip foundations. Supporters of the former rely on many years of construction experience, on the reliability, durability and cost-effectiveness of structures made of reinforced concrete blocks, on the fact that such foundations have proven their effectiveness in the northern regions, in places with high groundwater levels and highly heaving soils.

However, a prefabricated foundation, although cheaper than a monolithic one (approximately 20%), requires more skill and professionalism (specific placement of blocks, their adjustment at the corners, filling seams and gaps, installing more reliable waterproofing), as well as special equipment and a site for its installation.

A monolith, almost universally used in the West, requires less engineering and technological costs and hassle with waterproofing. Practice also shows that monolith is optimal when there are heavy load-bearing walls in the project and, in addition, only it is suitable in conditions of excessive soil heaving. Important points that the customer should monitor himself: ramming of the sand and gravel cushion at the bottom of the pit (for sandy and sandy loam soils, a gravel cushion is enough) should be carried out using a vibrating electric plate, and not manually, and each layer separately; waterproofing before laying the reinforcement should be protected with ascent or slate; there should be no pauses in the process, especially before pouring concrete, to avoid loosening and crumbling of the soil under the influence of rain and changes in air humidity. There is a well-known problem of choosing between prefabricated strip and monolithic strip foundations. Supporters of the first rely on many years of construction experience, on the reliability, durability and cost-effectiveness of structures made of reinforced concrete blocks, on the fact that such foundations have proven their effectiveness in northern regions, in places with high groundwater levels and highly heaving soils.

However, a prefabricated foundation, although cheaper than a monolithic one (by about 20%), requires more skill and professionalism (specific placement of blocks, fitting them to corners, filling seams and gaps, installing more reliable waterproofing), as well as special equipment and a site for its installation.

A monolith, almost universally used in the West, requires less engineering and technological costs and hassle with waterproofing. Practice also shows that a monolith is optimal if the project includes heavy load-bearing walls and, in addition, only it is suitable in conditions of excessive soil heaving. Important points that the customer should monitor himself: ramming of a sand and gravel cushion at the bottom of the pit (for sandy and sandy loam soils, a gravel cushion is enough) should be done with a vibrating electric plate, and not manually, and each layer separately; waterproofing before laying the reinforcement should be protected with cement or slate; There should be no pauses in the process, especially before pouring concrete, to avoid loosening and crumbling of the soil under the influence of rain and changes in air humidity.

In any case, on heaving soil, the strip foundation must be a solid frame created by a rigid system of intersecting strips. In addition to concrete, other, quite economical materials suitable for small one-story houses are used to lay shallow foundations. On dry, non-heaving soils, sand with additional layers of gravel, crushed stone and broken brick, as well as brick, are often used. The latter requires additional measures to protect against moisture. Rubble foundations, record-breakingly strong and durable, are laid from large boulders and stone fragments, seized with cement mortar. Rubble concrete foundations, constructed in formwork or a trench with vertical walls, consist of a solution with a filler of small crushed stone and gravel.

Columnar foundations (the range of materials for them is very wide) are optimal for the construction of wooden and frame houses without basements and cellars on heaving soils with a large freezing depth, as well as in cases where the soil serving as the base lies at a depth of 3-5 m. The fundamental limitation for these foundations is sites with a difference in height, where laying them is contraindicated.

Foundations of this type are very economical: in terms of material consumption and labor costs, they are almost twice as cheap, and when laid deep, sometimes five times cheaper than strip foundations. But there is one significant problem: the need to install a so-called backfill, a connecting wall between the pillars made of brick, concrete or rubble masonry for insulation and protection of the underground space. Finding craftsmen who know how to do it correctly is, alas, sometimes a difficult task.

A type of columnar foundations are pile foundations. They are becoming increasingly common in projects for one- and two-story houses, as they are very effective in weak soils and high groundwater levels. Piles are either used ready-made, or they are made directly in drilled wells. They use pillar piles, whose bases reach solid soil, or hanging piles, which create support due to soil compaction and friction. Pile foundations are considered the most environmentally friendly in terms of their impact on the soil landscape of the area. Moreover, they are increasingly considered the most progressive. However, the same problem remains – a shortage of professional personnel. Therefore, when including a pile foundation in a project, it is important to enlist the support of specialists.
Filizols, acrylics, styrenes … What to insulate with?

Waterproofing is akin to the human immune system. And it is important not only for the “health” of the building itself, but also to a large extent – its owners. In the structure of foundation costs, it takes 5-10%.

With a serious approach, waterproofing is “built” in three lines of defense of the house. The first is internal. As a rule, it is necessary only in houses with basements. The second is external, directly on the wall surface. The third is also external, with special soil treatment.

The main types of waterproofing used in construction with soil separation along the perimeter of the building are coating, painting, cast, adhesive, fused, injection, penetrating. Which ones should be used in a particular case, only a specialist can advise.

The most progressive types are coating-penetrating and injection types of insulation. Among the first, mastics based on chlorosulfonated polyethylene and polyurea, applied to the surface of the foundation under pressure, show very high efficiency. These materials, developed in Russia, are extremely resistant to the aggressive effects of natural factors, do not decompose and, as a result, are extremely durable. Other advantages: the quality of such insulation is easy to control, it can be applied to freshly laid concrete, and it can be used in winter at temperatures down to -15C.

Another very promising Russian development deserves special attention – natlen, a bulk material based on activated bentonite clay. When in contact with water, it forms a kind of gel barrier that holds it back. It has been shown that at a pressure of 40 atmospheres, water penetrates into the thickness of natlen by no more than 2-3 cm. Thus, a 4-centimeter layer of natlen (with or without formwork) is quite sufficient for reliable protection of the foundation.

Penetrating insulation technologies are actively developing. Special compounds are applied to the wet foundation surface and, thanks to moisture, are absorbed into microcracks and pores, plugging them, and then, drying, pass into a solid crystalline phase. When new cracks form and soil moisture naturally enters them, the process is resumed, spreading to new areas: the insulating material “lives”, improving the foundation surface.

In a certain sense, this technology is akin to the method of injecting the soil adjacent to the foundation (and basement walls, if any). In this case, wells are drilled from the surface of the earth or directly from the basement through the foundation body to a standard depth and reinforcing waterproofing materials are injected into them under high pressure. Thus, a kind of protective “sarcophagus” is created around the underground part of the building. The composition of the injected solutions is determined depending on the engineering-geological and filtration parameters of the soil, as well as the type and condition of the foundation. The most widely used materials against flooding today are those based on epoxy, polyurethane and acrylic resins. Technologies for protection against rising capillary moisture by low-pressure injection have also been developed.

Roll materials, such as hydrostekloizol, filizol and others, are still widely used. They have their advantages, and their installation technologies have long been developed, but with the available choice of materials, their disadvantages are beginning to come to the fore. They decompose relatively quickly. Control of seams is quite difficult. The “human factor” plays too much of a role in their installation — technology violations are often allowed.

Remember the importance of the initial planning of the entire site with the obligatory installation of a slope to drain surface water from the house. And also — the enduring waterproofing role of the blind area, which completes the zero cycle of construction.

The “topic” of groundwater should be supplemented with another problem that may arise already during the pouring of the foundation. When the soil is saturated with water, to avoid silting of the cushion, it is necessary to treat it along the contour with binders or by covering it with a polymer film.

Blind area. It should be up to 1.5 m wide and is made in three layers: first – soft, well-compacted clay, then – broken brick or crushed stone, and on the outside – cement mortar or asphalt. It is better to lay the last layer a year after laying the first two. By the way, the blind area is the only “designer” part of the zero cycle.
Thermal insulation

This area of ​​protective technologies lives by its own traditions and priorities. This area of ​​protective technologies lives by its own traditions and priorities. Technologies in it are rapidly developing, introducing new brands to the market. However, in most cases, the base, arranged directly on the plane of contact between the soil and the house structures, remains the long-used expanded clay placed on sand. The expanded clay layer must be protected with the so-called cement milk. A concrete screed is arranged on top. On it, if there are no basements or ground rooms, there are reinforced concrete floors. If there is a basement, expanded clay is used much less often. In this case, the most common technology remains pasting the internal walls of the basement with foam plastic (20 mm) on bitumen mastic, which is then plastered over a chain-link mesh.

Among the progressive materials, the main ones are basalt wool (brands ROCKWOOL, ISOROC, PAROC, etc.), staple glass fiber (URSA, ISOVER), extruded polystyrene foam (in particular URSA XPS, PENOPLEX). Basalt wool is durable, does not shrink, does not burn (it is also used as fire insulation!), and is environmentally friendly. We recommend using this insulation with water-repellent impregnation, and also protecting it from the inside with a vapor barrier material.

Staple glass fiber is also very effective, resistant to chemical influences and possessing antimicrobial properties. It is also recognized as the best sound insulator. At the same time, like basalt wool, it should be protected from steam and water (special solution plus foil).

Extruded polystyrene foam is durable, withstands sudden temperature changes, is moisture-resistant and therefore is especially suitable for insulating foundations and basement rooms. It is usually glued to a layer of waterproofing to avoid areas that conduct cold into the room – “cold bridges”. At the same time, it protects the waterproofing from freezing and mechanical damage. It is only important to protect it from direct “impact” of sunlight before use, otherwise the material may crumble.

According to various estimates, the cost of thermal insulation for different types of foundations ranges from 5 to 15% of the total cost of its construction.

In conclusion, we draw attention to a number of fundamental construction details subject to customer control. It is better to carry out the work in the summer, under favorable weather conditions. It is unacceptable to pour a shallow foundation on a frozen base. You cannot succumb to the old misconception that the foundation needs to settle before erecting the walls. It is necessary to put the cottage box before the ground freezes and begins to actively push out the unloaded foundation. It is important at the beginning of construction to look into the pit yourself together with a specialist and make sure that all embedded elements – for sewerage, cold water supply, grounding – are not forgotten, are introduced and introduced correctly. Finally, when choosing a contractor, it is worth betting on a company that already has experience in construction in this area.