Foundation for a bath: strip, pile, screw, slab, sand

Never drying out swampy soil with moisture-loving vegetation that can be systematically moistened is not the most favorable place to build a house frame. The close location of groundwater creates seasonal fluctuations in soil, especially during spring warming. Modern construction technologies can solve the problem of how to organize a foundation in a swamp so that it can withstand the load of a house.

Soil research

Using a hand-held probe, you need to drill several wells in the construction area and take rock samples. It is best to do this in the spring, when the soil is most saturated with moisture. Since it is almost impossible to independently assess the condition of the soil, contact an engineering company for accurate readings.

Attention! Be sure to take into account the freezing depth! The foundation, located at a shallow depth, where the soil freezes, begins to collapse very quickly. This is due to the fact that water expands when it freezes, breaking the structure of the soil and foundation material.

For a small log building, the depth of the wells should be more than five meters, and for heavy structures, brick or stone, at least eight meters.

Based on the information obtained as a result of research, you can determine which type of foundation is best for you.

The foundation is the most expensive and labor-intensive part of the building, and if you decide to build a foundation that will be located in a swamp with your own hands, you should not skimp on materials and the services of professional geologists.

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Or maybe it’s still tape?

Often houses on loam are built on a strip foundation. You can build a shallow strip foundation (obvious savings), or a structure buried below the GPG. The last option is most often chosen when building a house with a basement. It is the most material-intensive and therefore not the cheapest. In general, it is advisable to build reinforced concrete strips in situations where geological exploration revealed that the soil layers lie evenly throughout the construction site. In such situations, you can count on the absence of serious uneven deformations during heaving.

Pile type foundation

The pile type of foundation is designed specifically for construction in “problem” areas.

This type of structure has a number of advantages over others.

1. Pile foundation is the least expensive.

2. This structure allows for significant site unevenness and uneven soil. The use of piles of different sizes makes it possible to smooth out strong slopes.

3. Special processing of piles in production makes them resistant to corrosion, which is extremely necessary when building a foundation in a swamp with your own hands, since they will be used in a rather aggressive environment.

4. Speed of construction. You will not have to make allowances for weather conditions, and the construction of a pile foundation itself will not take much time, since you do not have to wait for the concrete solution to dry and harden.

5. Strength and durability. Thanks to the peculiarities of its design, it will serve you for a very long time without strong shrinkage, even with such capricious and unstable soil.

To work in wetlands, piles of at least twenty-five meters in length are used. There are two ways to immerse them in the soil: by pressing and also by vibration immersion. For the first case, driven piles are used, and for the second, screw piles are used. The most important thing is that the base of the pile enters a stable area of soil, bypassing groundwater and sand. The lining of such a foundation is made with reinforced concrete supports.

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We build a strip foundation

Calculation of strip foundation.

Let's consider the three most popular methods of constructing a strip foundation:

Method 1: gravel and sand are poured into the trench in layers (15 cm each). Each layer is compacted and watered. When they reach the top, the trench is watered with liquid cement. Afterwards, a basement is erected from brick or rubble stone. The base is insulated from moisture with roofing felt.
Method 2: fill the trench with layers (15 cm each) of gravel and sand up to halfway. The surface of the backfill is leveled, then a row of bricks is laid on it. They make removable formwork from boards covered with slate. The wood is treated with an antiseptic, dried and covered with molten tar. The formwork panels are fastened in a vertical position with wooden ties.
Method 3: in dense soil, slate sheets are placed overlapping in the trench, while securing the upper ends with removable ties. The gaps between the walls and slate are filled with sand and compacted. Half of the gravel and sand are placed in the formwork, compacted again, and concrete is poured on top. Layers - less than 15 cm. Do not forget about thermal insulation. The best materials for the foundation are slag concrete and expanded clay concrete with heat-insulating filler.

Wait a couple of hours and cover the structure with wet materials (burlap, sawdust, shavings), water everything thoroughly. In summer, repeat this process every four hours for the first two days. Next, cover the base with polyethylene.

When the concrete has set, remove the formwork. Fill the sinuses with soil or clay. Make a blind area and lay a waterproofing material (for example, two layers of roofing felt).

Slab foundation

A slab foundation is indispensable if you decide to build a solid house made of stone, as it can withstand heavy loads and sudden temperature changes. It is, of course, much more expensive than all other structures, but its design is such that the uniform distribution of the mass of the entire building on the surface will not allow the structure to sag under the influence of various weather conditions (soil freezing), and the sand and gravel cushion located at its base will easily allow groundwater to pass through, below the structure itself, without harming it. Such monoliths are also called drift foundations. Before you start building such a foundation in a swamp with your own hands, you need to carefully prepare the place.

1. Clear the construction site of all kinds of vegetation, such as trees, shrubs, and windbreaks, if any.

2. Dig a pit for the future foundation. On marshy soils, it is not necessary to remove a large layer of soil. The construction of a basement is excluded.

3. Carry out work to drain the pit. If there is not too much water, you can use a drainage system, but if there is an abundance of moisture, sometimes it is necessary to use pumps.

4. Place a layer of sand at the bottom of the drained pit and compact it well. The sand is covered with a layer of gravel on top. This way, you will build a sand cushion that will prevent groundwater from eroding the foundation of your house.

5. Cover sand and gravel with two to three layers of waterproofing material, such as roofing felt.

6. Make formwork for pouring the concrete mixture. The size of the monolith should be commensurate with the perimeter of the future structure. To correctly calculate the thickness of such a foundation, contact a specialist. You should not act relying only on your own strength and knowledge.

7. Build a reinforcing frame from metal rods at least twelve millimeters thick.

8. Prepare the required volume of concrete solution and pour it into the formwork. Make sure that the concrete is poured evenly and avoid the formation of voids.

9. The resulting slab should harden well and dry for several days, under favorable weather conditions. After the slab has dried, dismantle the used formwork.

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About what kind of soil there is

The base can be either natural or artificial. To decide what to do, conduct a soil analysis.

On a natural strong basis, the foundation need not be strengthened. If the soil is unreliable, strengthening it artificially is simply necessary. Fine sand, peat bogs, and silt are unsuitable for building a bathhouse.

The first of them is covered with a bed of coarse sand. The land on which you are building a bathhouse must meet the following requirements:

do not slide;
do not swell;
do not sag;
have good load-bearing capacity;
have uniform compressibility;
it should not be subject to landslides;
should not be located in areas where groundwater flows.

Homogeneous soil

Reinforcement of strip foundation.

This type of soil is considered the most convenient base for a bathhouse. On homogeneous, dry and dense soil, you can make a columnar foundation by first laying natural stones at the corners of the future structure. Then you need to install the lower crowns on them.

By the way, it is better to pre-treat the wood with an antiseptic, coat it with resin or drying oil. It is recommended to arrange the stones in a continuous strip.

Next comes the matter of the waterproofing material.

Note. The blind area will protect the building from rainwater.

The trench formed after removing the layer of earth is filled with clay. It also fills the gaps between the cobblestones, the lower crown of the building and the soil.

The cheapest and easiest to implement option is a clay-crushed stone blind area. Its width should be approximately 20 cm greater than the roof eaves. Grooves must also be dug along the edges to drain water. On uneven surfaces with wet, heterogeneous soil, it is recommended to build a strip foundation.

Clay soil

Installation of columnar supports.

Foundations built on clay soils are prone to swelling. If you pour a foundation and leave it in the winter without erecting walls, floors, or a roof, there is a high probability that it will become deformed.

For clayey and loamy soils, the foundation is placed on a pre-compacted sand cushion 30 cm thick. In loamy soils, the underground part of the foundation can be made without formwork, and the above-ground part with it.

If you have no choice and you need to build a bathhouse on clay soil, then prevent the ground from subsiding in the summer and swelling in the winter (the structure can rise by ten centimeters, and this, in turn, will lead to cracks in the steam room).

To avoid such problems, lay the foundation below the frost depth. But that is not all!

Important! Since the bathhouse is a lightweight structure, the foundation must be equipped with anti-heaving protection: fill the trench around the base with fine gravel or simple sand.

Before this, cover the “system” with grease, machine oil and warm garden pitch.

Strip foundation type

It is also called shallow. If you decide to build a foundation of this type in a swamp with your own hands, you need to know that in comparison with the above structures, this is the most inexpensive foundation, but it is only suitable for light wooden buildings. Its effectiveness is due to its excellent drainage system and removal of excess moisture.

Having previously cleared the site for construction, we begin to lay the foundation.

1. In order to lay this type of foundation, proceed according to a scheme similar to that used to build a monolithic one, only instead of a foundation pit, you will have to dig a trench of the desired shape along the perimeter of the future building.

2. Just as in the previous case, a sand cushion is poured.

3. Formwork and reinforcing frame are constructed according to the shape of the trench.

4. Take care of effective water outflow and build drainage.

5. Pour the concrete solution and wait for it to dry.

6. After drying and dismantling the formwork, carry out the necessary waterproofing. The foundation in the swamp, made with your own hands, is ready, you can start building walls.

If you did everything correctly, observing all the necessary measures, then the saying: “my home is my castle” will come true for you. Good luck with your construction.

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Foundation structure

As an example, we can consider the step-by-step production of a foundation structure for a bathhouse, which will require asbestos-cement pipes with a diameter of 20 centimeters.

In order for the supporting structure of the bathhouse to be properly placed on the foundation, the pillars of the foundation structure must be located at all corners of the bathhouse. In addition, such pillars should be located under load-bearing walls, with a pitch of about 1.5 meters.

For example, you can take a bathhouse, which measures 4 by 4 meters and is made of a wooden frame. This size and type of bathhouse is considered the most common and practical, that is, the one that is required in order to organize a bathhouse in your yard.

Installation of column-type supports

In order to make holes in the ground for column-type supports, it is necessary to dig or drill appropriate holes, the diameter of which should be 25 centimeters.

You need to drill below the level at which the soil freezes in the winter. After the holes are ready, they must be filled with dry sand, 20 centimeters thick, spilled with water and compacted properly.

After this, you need to cut the required number of pipes of the required size. It must be taken into account that in addition to deepening the pipe into the ground, at least 40 centimeters of the pipe must remain on the surface.

In order to protect the pipe from the negative effects of water and soil deformation, it must be wrapped in roofing felt before lowering it into the hole.

After the pipes are lowered into the pits, they must be filled with fine crushed stone or gravel up to 50 centimeters along the edges.

Homemade “tire” foundation

This is necessary so that the pipe is firmly fixed in the hole, after which concrete mortar can be poured to a height of 50 centimeters. After this, the pipe must be lifted so that the solution flows out of it and forms a high-quality base.

Then the pipe needs to be pressed slightly into the concrete base. The next step is to reinforce the pillar. To do this, you need to insert 2-3 reinforcement rods into the pipe, after which the hole is filled with gravel or small crushed stone.

Now you can fill the pipe with ready-made concrete mortar and compact it. To do this, it is best to use a rod that will allow the air accumulated in the pipe to escape. After the columnar supports have dried, the foundation can be considered almost ready.

Basement superstructure

Asbestos cement pipes for pouring a columnar foundation

A base for a bathhouse is simply necessary, because it will protect the underground space of the building from the penetration of snow and cold wind, which will make the microclimate in the bathhouse uncomfortable.

In order for the foundation to breathe, it is necessary to make two vents in the base of the bathhouse, which should be located on opposite sides of the structure.

You can make a plinth using various methods, using various building materials such as brick, block or wood. When making a bathhouse from a log house, it is advisable to make a base from boards, which will give the building the integrity of its overall appearance.

In addition, flat sheets of slate can be used as plinth cladding.

Slate plinth

Flat slate sheets, which are made from asbestos cement, have a standard size of 300x150 centimeters.

In order to calculate the required number of slate sheets, you need to follow this example. Due to the fact that for example we took a bathhouse with dimensions of 4x4 meters, the total length of the foundation structure will be 32 meters.

The height of the basement superstructure was 40 centimeters. Due to the fact that the slate blank must be recessed into the cement mortar by 10 centimeters, it is necessary to cut off the slate strip with a height of 50 centimeters.

If you cut the slate correctly, without transferring the building material, then from 1 slate sheet you will get exactly 3 blanks for the plinth.

The total length of the foundation is 32 meters, which means that if we divide the length of the foundation by the length of the slate sheet (3 meters), we will get 11 strips of slate blanks. We received 3 blanks from each slate sheet, which means that we will need 4 sheets of flat slate for the entire base. Next, you should begin making the concrete lintel.

A concrete lintel is a mandatory element of a columnar foundation, despite the use of different building materials for the manufacture of the plinth.

In order to make such a jumper, it is necessary to dig a special trench between the columnar supports along the entire perimeter of the foundation. The width of the trench should be 10 centimeters greater than the width of the pillars, and the depth of the trench should be about 30 centimeters.

The bottom of the trench must be covered with a layer of crushed stone and compacted correctly so that the layer thickness is 15 centimeters.

Pile foundation

After this, it is necessary to fill the trench with concrete mortar and sink slate blanks into it, the upper part of which should be flush with the end of the columnar supports. The slate blanks must fit snugly against the columnar supports.

Before installing slate blanks, it is necessary to make special holes for vents in two of them. An asbestos cement pipe with a diameter of 15 centimeters should be used as an outlet.

Accordingly, the diameter of the holes in slate blanks should be 15.5 centimeters.

For high-quality fastening of slate blanks to columnar supports, it is necessary to use metal screws.

Before screwing in the screw, you need to drill holes that will be half the size of the screw. The hole will help the screw to screw properly into the pipe and concrete.

The upper part of the base must be equipped with piping. To do this, you can use a metal corner, the size of which should not be less than 2.5 centimeters. The corner should be located not only on the outside of the base, but also on the inside.

The joints of slate blanks must be closed. This can be done from scraps of various building materials that will remain after you build the bathhouse. The plinth must be made of two layers of slate blanks.

The inner walls of the base must be covered with film, and the inner space of the base must be filled with expanded clay, which will reliably insulate the foundation structure.

Slab foundation

To ensure that the expanded clay does not interfere with the laying of the pipe for the vent, this pipe must be installed in the finished hole before filling the internal space with expanded clay. On the outside of the plinth superstructure, the vent pipe should not extend beyond the level of the plinth.

In order to simplify the subsequent construction of walls, it is necessary to fill the upper part of the base so that the level is exactly at the horizon.

To do this, the expanded clay needs to be filled with concrete mortar not reaching 5 centimeters to the edge of the slate formwork. After the concrete has hardened, it is necessary to make a cement screed, which is checked by level.

Furnace foundation

In order to make the sauna suitable for use, you will need to build a sauna stove.

Such a stove needs its own foundation, which will not only serve as a support for the stove, but also protect the bathhouse from fire. The bathhouse can be equipped with two types of stove foundations.

The first type of foundation is designed for relatively light stoves (up to 150 kilograms), which are made of sheet steel.

When equipping a bathhouse with a heavier stove (about 450 kilograms), which can be made of brick, the second type of foundation structure is used.

Video

We bring to your attention a video about the features of the foundation of a house on marshy soil, what problems you will encounter and how to solve them.

Swampy soils are subject to seasonal fluctuations to a greater extent than other soils. They are oversaturated with fine particles and therefore often form floaters. In winter they freeze and swell, in spring they are washed away when groundwater rises. Laying a foundation in a swamp with your own hands is a difficult task, but quite solvable. The main thing is to study the soil and choose the right type of support and its depth.

Preliminary work

Soil research

It is imperative to establish the composition of the soil and its changes at different horizons, as well as determine the occurrence of water carriers and evaluate the terrain. You can conduct the research yourself, but it is better to involve specialists in this. To analyze the soil content, you will have to drill several wells at different points, or dig pits.

Drainage of the site

If the soil is not very swampy, it is enough to drain the area to avoid flooding of the future structure.

In some cases, the thickness of the peat layer is small and can simply be removed. Then the foundation is established on stable rock, which is located below. Its form is adopted taking into account other technological or financial considerations.

In other cases, you will have to choose from two options:

pile foundation;
monolithic slab.

The project is finally approved taking into account the design of the building and the total pressure on the foundation.

How to build a foundation in a swamp

Construction of a foundation in a swamp

A pile foundation allows you to go through unstable layers and rest on reliable soil that can support heavy loads.

Pile foundation in a swamp

Typically, several types of piles are used for construction:

Screw metal. Not very durable, since iron will quickly oxidize in an acidic environment;
Hammers. Their installation is expensive and requires the use of construction equipment, but access to the site can be difficult;
Bored. Installed on pre-drained soils. Creating a foundation using such piles involves a large amount of work and is also expensive.

Whatever type of supports you choose, a grillage is finally built on top of them. For wetlands, it is made in the form of a reinforced concrete floor.

A monolithic slab foundation is a universal tool for constructing the support of a house in swampy areas. It is expensive, but quite reliable. The base turns out to be floating, and the large area of the sole distributes loads well from all sides. This allows you to avoid deformations of the building and its individual elements.

How to make a slab foundation

Monolithic foundation

Step #1. Before pouring the slab, you need to prepare the soil underneath it. The top layer is removed by about a meter and a cushion of gravel, stones and sand is poured. Sometimes it is partially replaced with construction waste. Everything is thoroughly wetted and compacted. This sand and gravel backfill allows groundwater to move under the sole without being delayed, and to swell less in winter.

Step #2. A thin layer of cement mixture is spread over the pillow as a substrate. It should smooth the surface of the crushed stone. It will dry out within 48 hours and then the insulation can be installed. Typically, 10 cm thick foam or polystyrene foam boards are used for this.

Step #3. Several rows of rolled waterproofing material, such as roofing felt, are laid on top. It will not allow soil moisture to be absorbed through capillaries into the concrete base. It is even better to use polymer diffusion membranes. They not only protect concrete from water from below, but also, due to their vapor-permeable properties, remove moisture from it.

Step #4. The formwork is being installed. The removable fence is assembled from boards fastened with nails, but you can use permanent sheets of foam plastic, which will also serve as insulation.

Step #5. Reinforcement for a foundation in a swamp should be chosen with increased strength, with a rod diameter of 12–16 mm. A two-level mesh is formed with a cell size of 15x15 cm. Dressings are made with steel wire.

Step #6. Concrete is poured at one time so that no seams are formed inside, weakening the structure. The solidified mass is treated with a deep vibrator to remove air from it. Finally, the surface is leveled with a vibrating screed. The slab will dry and gain strength for at least a month. To ensure that the process proceeds evenly, the area is covered with PVC film and wetted from time to time. The readiness of the foundation can be determined using the same polyethylene: when condensation stops settling on it, the process is complete.

Step #7. The formed slab must be protected from moisture on the top and sides with coating waterproofing. It will protect the concrete from freezing and mechanical damage.

With a small budget, it is very difficult to build a foundation in a swampy area. Even on light and dry soils, pouring supports takes from 1/5 to 1/3 of the total cost of the house. Therefore, you need to decide on the type of foundation and building materials even before purchasing a plot of land, and for this you need to have complete information about it.

Is your home built on marshy soils? Tell us about its construction and the quality of the constructed foundation by leaving a comment on the article.

Video

We recommend watching a video about the construction of a monolithic foundation on a peat site.

Foundation for a bathhouse on a peat bog

Question:

Hello, can you tell me about the foundation for a bathhouse, the drawing is not very clear, we have a piece of soil that is mobile (a former peat bog), what kind of foundation for a bathhouse would you recommend? And the brick house also started to crack, we already bought this one, what should we do with the house and the foundation? Is it possible to rebuild it somehow? with minimal costs.

Anna, Nizhny Novgorod.

Answer:

Hello Anna from Nizhny Novgorod!

As my late father said, “there are two fools in the market, one sells and the other buys.” It's rough, but you can't say it more precisely. Before making expensive purchases, you need to inspect what you are purchasing ten times. Walk around, ask neighbors about what and how. And if this is not done, then you can run into various troubles, including a collapsing house, a failing foundation, and the like.

Areas of moving soil in former peat bogs are not the best option for laying the foundation for a future bathhouse. I always remember the construction of ten years ago, when I first encountered a similar situation, as in your case.

There is a plot of land with a small lake measuring 5 - 6 square meters, next to it there is a log bathhouse about 4/5 meters high and 2 meters high. Under the bathhouse there are reinforced concrete railway sleepers as a foundation. In one layer. The soil is peat covered with turf. Banya is fifteen years old. The sleepers sank as much as I don’t want them to. The lower crowns are already touching the ground. Accordingly, they will begin to rot.

The drainage grooves made around the bathhouse to remove the perched water do not cope with their task.

What to do next with such a bathhouse? It is more expensive to disassemble and move to another place. Strengthening the foundation by raising the bathhouse on jacks and placing additional sleepers will not help. After some time, the foundation will sink back into the soil. So this bathhouse stands, sinking deeper and deeper. While they are steaming in it, one can only guess what will happen next.

We were instructed to place a summer house 3/6.5 meters in size, 2.5 meters high and with a small attic, a few meters from the bathhouse, instead of a light gatehouse. We started laying a foundation of shallow concrete blocks, and immediately ran into a problem. When a crowbar was stuck into the soil, it fell through its entire length of one and a half meters.

Soft peat, you can't do anything with it. And the client insists on construction. They dug holes under the block supports and poured in as much sand as possible. The blocks were installed in three rows. After three years, the light frame house sank and began to warp. I had to dig a meter deep trench under the entire house along the perimeter of the walls. Make a reinforced strip foundation. Now the house rests completely on it, but it still “sausages”.

Hence the conclusion - there are places where building is completely contraindicated.

I told you all this so that you will think more than once whether it is possible to build a bathhouse in the place you want. You can, of course, use the services of designers familiar with the geology and geodesy of your area. But they too (but at a considerable cost) can say that one should not build on a peat bog. Or maybe they will give other recommendations. Without examining and inspecting your site, it is difficult for me to recommend anything.

The fact that your brick house is cracking on the walls does not inspire optimism either. The only practical advice is still the same. Walk around and check out similar buildings. How are things going with their foundations? Are there similar cracks in the walls? What are their inhabitants doing to repair and how effective is it?

If someone has encountered the same problem and was able to get out of it, then borrow their experience. So that you don’t end up throwing too much money into repairing the foundation, but it still won’t help.

For now, limit yourself to cosmetic repairs to the walls by plastering them. Maybe not everything is as scary as I described to you. And the cracks will not grow any further.

In any case, do not lose optimism and good luck to you!