Many who are just planning the arrangement of the site are lost and do not know which foundation for the bath is better to choose. In this article, we will try to answer the most popular questions.

Types of foundations  

There are 5 types of bases that are used in the construction of a bath: 

• tape;
• slab;
• columnar;
• pile;
• pile-screw.

The tape type of foundation has become widespread and recognized among professionals and beginners. The creation of such a monolithic base-tape under the load-bearing walls is quite costly since it requires a large number of building materials. However, the relative ease of work without the involvement of special equipment compensates for the investment. To create a strip base, rubble concrete, precast or monolithic concrete are used. 

A slab foundation is a rational solution for owners of sites with “problem” soil. The use of a significant amount of building materials will require financial costs, but it will pay off with the reliability and durability of the bath. A monolithic slab is poured onto a “pillow” of waterproofing, sand, and crushed stone. The minimum permissible thickness is 20 cm.

A columnar foundation is one of the most budgetary options. An easy-to-erect system of supports, the minimum size of which is 50×50 cm. It is possible to use various building materials: brick, stone, reinforced concrete, metal, asbestos-cement pipes, etc. The distance between two supports, as a rule, does not exceed 2.5 m. corners of the building. An important point: the obligatory deepening of the support is 20 – 25 cm below the maximum depth of soil freezing.

The pile foundation involves the installation of piles up to 8 m high, which are made of steel, reinforced concrete, or wood. Driven and bored piles are distinguished by construction technology. The main road from the building is transferred to denser soil layers, although it is not necessary to dig a pit or trenches, fill up and remove the soil. 

The pile-screw foundation is created from all-metal hollow piles with an 8 – 15 cm diameter and a pointed end and blades. Such a device ensures optimal screwing into the ground and the reliability of the base. The piles are immersed to a depth of 1.60 – 3 m, but this figure may vary depending on the site’s specifics. Installation of elements is carried out along the perimeter of the future bath at a distance of 2 – 2.5 m from each other. Work can be done both manually and using special equipment. 

Strip foundation 

It got its name due to its specific design and appearance: a continuous tape of concrete runs along the structure’s load-bearing walls. It is created based on cement mortar with gravel, rubble, crushed stone, broken brick, or sand.

There are several types of strip base:

• monolithic (one-piece reinforced concrete block, poured at the construction site and fastened inside with a metal belt);
• prefabricated (prepared concrete products are connected to each other by welding, and the seams are filled with cement mortar).

A shallow foundation will be the best option if the building site is characterized by solid soil, which is not subject to deformation under heavy loads and freezing. The recessed type is required if the soil is mobile, easily deformed, or changes volume at low temperatures. 

The decision to use a particular type of strip foundation should be based on its inherent advantages and disadvantages. 

The indisputable advantages include:

• relatively low cost;
• simple design;
• strength;
• the ability to withstand heavy loads;
• fast erection.

The disadvantages of strip foundations are:

• the need for mandatory soil analysis and accurate calculation of deepening;
• large mass. 

Slab foundation 

A rigid structure and strict reinforcement around the entire perimeter are the main principles for creating a slab foundation. The load is distributed evenly. This property is especially important if the soil on the site is moving.

A one-piece slab of concrete goods is laid on a sand backfill or a leveling layer of concrete; additions in the form of polypropylene thermal insulation are rarely required.

In the case of building a bath with an impressive area or an intricate configuration, it is necessary to lay expansion joints. By splitting the base into separate sections, you will reduce the risk of deformation passing from one piece of land to another.

Among the advantages of the slab type of foundation, it is worth noting:

• reliability;
• long service life;
• versatility;
• finding above the depth of soil freezing;
• excellent load distribution;
• fairly simple construction;
• resistance to ground movement. 

However, a monolithic slab should not be considered an effective solution to problems because it also has disadvantages. Note:

• high cost;
• impossibility of use in areas with a slope;
• the laborious process of arranging a basement and laying communications;
• difficulties of work in winter.

Column foundation 

When creating this type of foundation, pillars are used, which are buried in the ground and connected by special beams made of reinforced concrete. The low consumption of materials largely determines the minimum financial costs and, as a result, popularity among the owners of private houses and summer cottages.

The columnar base can withstand a two-story building with light walls. If your plans are to build a bathhouse based on a wooden frame, then pay attention to this type of foundation.

A variety of materials can be used to create the pillars:

• concrete, pine or oak wood when building a small bath;
• brick, concrete during the construction of a brick bath;
• natural stone in the construction of a structure based on bricks and heavy reinforced concrete floors.

Any building structure has pluses and minuses. The columnar base is no exception.

Strengths worth mentioning:

• high speed of construction;
• budgetary cost and economical consumption of materials in comparison with analogues;
• no need to attract additional labor or special equipment;
• the possibility of using in areas with unstable soil and a large depth of freezing. 

Weak sides:

• exclusion of the option of arranging the basement and basement floors;

• the tendency of the structure to move horizontally;
• use only in the case of the construction of light structures.

Pile-screw foundation

The presented foundation is ideal for erecting a building of significant area and weight on too weak, damp, or subsiding soil. Here it is more expedient than ever to connect special equipment.

If you decide to start arranging the pile-screw base yourself, it will be difficult to avoid mistakes without a certain level of qualification and sufficient experience. Installation of piles at different depths, refusal from concreting supports, or deviation from the vertical plane – all this threatens to significantly reduce the technical characteristics of the foundation and its service life. 

Nevertheless, giving preference to the pile-screw foundation, focus on the following advantages:

• there is no need for preparatory work related to the layout of the construction site and the arrangement of access roads;
• the possibility of building a foundation at any time of the year, regardless of climatic conditions and the geographical location of the object;
• high functionality even on problematic soil types;
• construction speed (often only 3 days are enough to build a solid foundation);
• no shrinkage;
• simple repair or extension if necessary, etc.

Despite the impressive number of positive qualities, the pile-screw foundation has several disadvantages. For example, he cannot:

• for a long time to resist the effects of chemically aggressive substances, which are sometimes in the structure of the soil (service life – 50 years);
• used together with solid multi-storey buildings;
• serve as the basis for the basement;
• provide sufficient resistance to bending loads;
• resist the effects of corrosion (the only salvation is the processing of piles with a special resin and concreting from the inside).

Results: how to make the right choice?

Before deciding on a certain type of foundation, you must consider:

• material for building a bath; 
• maximum loads on the base; 
• type of soil;
• the degree of soil freezing;
• the presence of groundwater. 

The wrong choice can lead to all sorts of problems, including the destruction of the building.

Based on building experience and individual cases, the following rules can be derived:

• For compact baths, the area of ​​which does not exceed 4×4 or 4×6, a strip or columnar foundation is suitable.
• For a small building made of timber or logs, the most economical and practical solution will be the columnar type of base.
• A frame bath (even 2 floors high) will not require you to build an expensive strip foundation. For a long service life, a columnar one will be enough, which is made of plastic or asbestos-cement pipes, or a pile foundation.
• The brick building has a very large weight, for this reason, we recommend paying attention to the strip foundation.
• The construction of a bath with a drain involves preliminary and careful planning of the entire structure. If you want to drain directly into the ground below the structure, then a concrete base will not work. Provided that a full-fledged sewer system is organized , it is worth choosing a foundation, starting from the characteristics of the building itself and the soil.
• For a bathhouse being built on a slope, the best solution would be a bored pile type of foundation. 
• A pile foundation is required for the construction of a bathhouse on swampy or waterlogged soil, in places where landslides and ground movements are possible.
• The pile-screw foundation is irreplaceable on soft soils (swampy soils, quicksands, peat bogs, high groundwater levels).