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To keep the subfield dry, ventilation of the foundation is necessary. It can be done in two ways – using ventilation holes in the basement of the building (air vents or vents) or by bringing the exhaust pipe to the roof and making several holes for air flow from different sides of the foundation.
Why ventilate the underground
If ventilation is not provided in the non-insulated foundation, humidity quickly increases in the subfield, which sooner or later turns into condensate. Moisture in the form of steam enters through the ceilings from the house, as well as from the ground. Since there is no ventilation of the foundation, it is not possible to remove it, it accumulates in the soil under the house, in the walls of the basement, settles on the floor beams, on the subfloor boards and / or filing materials. In the same place, where there is a positive temperature and high humidity (under a heated house, even in severe frosts, the temperature is always above zero), bacteria, fungi always multiply very actively, and materials rot. As a result, very unpleasant odors penetrate the house, the materials are destroyed.
The second reason why underground ventilation is necessary is radon gas, which is released from the soil, and, sometimes, in considerable quantities. It is a natural radioactive gas. Without ventilation, radon accumulates in the upper part of the underground space, gradually seeps into the house. It is probably not necessary to tell what the presence of radioactive gas in residential premises can lead to. So this is another good reason why you need to ventilate the subfloor.
There are two ways to ventilate the underground space:
- Make vents in the foundation (also called vents). In this case, moisture is removed due to a draft – ventilation holes are located in opposite walls.
- Arrange for air extraction from the underground – bring the ventilation pipe to the roof, and air intake – through the grates in the rooms. In this case, they do not make ventilation in the foundation, but it is necessary to make a thorough insulation of the outer foundation + basement + blind area. Then cover the soil inside the subfloor with waterproofing.
The second solution makes it possible to improve the aesthetics and not to dry out the subfloor due to drafts, but it requires significant material investments. This option is suitable if you are going to build an energy-efficient, well-insulated house. In all other cases, it is more appropriate to make foundations.
What should be the vents in the foundation and how to arrange them
Ventilation holes in the foundation are made of round or square section. If desired, it can be triangular or any other shape. If only they were sufficient in area to effectively remove moisture from the underground.
dimensions
The dimensions of the ventilation holes in the foundation are regulated by SNiP (SNiP 31-01-2003). Paragraph 9.10 says that the area of the vents must be at least 1/400 of the total area of u8bu9bthe subfloor. For example, if you have a house measuring 72 * 72 m, the area of u400bu0,18bthe subfloor is 18 sq. m. Then the total area of vents in the foundation should be XNUMX/XNUMX = XNUMX sq.m. or XNUMX sq. cm.
In the same paragraph of the standard, the minimum area of u0,05bu25bthe air is prescribed – it should not be less than 20 sq.m. If translated into dimensions, it turns out that rectangular holes should not be less than 50 * 10 cm or 25 * XNUMX cm, and round ones should have a diameter of XNUMX cm.
They do this in multi-storey buildings, but in private ones such holes look too large. Usually they are made two times smaller, while increasing the number of vents so that the total area of uXNUMXbuXNUMXbthe products is not less than recommended.
How to arrange
They make air in the foundation 15-20 cm below the upper edge of the tape. If the base is low, a recess is made in front of the vent – a pit. But ventilation of the underground is required.
The vents in the base are evenly placed on all sides of the foundation opposite each other. This is necessary in order for the ventilation of the foundation to work properly. The wind, “flying” into one hole, will fly out into another, taking water vapor and radon with it.
The distance between two adjacent air vents in the basement is about 2-3 m. If there are any piers inside, at least one vent is needed for each “room”. In the partitions themselves, it is also necessary to make vents – to allow the air masses to move and form a draft. This is exactly what we need. In order for the movement to be more or less free, the area or number of holes in the internal partitions should be larger and better if it is 2-3 times larger. You can make several holes of the same size as in the base, or you can make one, but wide. The second option, by the way, is preferable – the resulting passages can be used to service the underground.
Vents in the foundation of any format must be closed with bars – so that living creatures do not penetrate into the underground. It is desirable that the gratings are metal, and the holes are small. For mice, plastic is not a problem, and it is easier to prevent them than to deal with them later.
How to make puffs
Vents are formed at the stage of foundation manufacturing. If we are talking about a tape monolithic foundation, then the embedded parts are laid and fixed after the installation of the reinforcing frame. To organize round ducts, plastic or asbestos-cement pipes are laid. Their edges are brought flush with the outer edge of the formwork, well fixed. If plastic pipes are used, sand is poured into them, the edges are closed with plugs. This is necessary so that the mass of concrete does not flatten them during pouring. These mortgages are not removed after demoulding.
Rectangular vents are formed from boards, knocking down a box of the required size. It is also installed in the formwork, but after the concrete has set, the wood is removed.
If the plinth is built of brick, you can periodically cut the bricks or put a half instead of a whole. In the plinths of concrete blocks, they take several pieces with two large holes, make them through. Install instead of one of the “normal”. If the foundation and basement are built of reinforced concrete blocks, the vents are made at the joints.
About the same way, vents are organized in columnar, piled (screw, bored, TISE) foundations. When the gaps between the supports are closed with the selected material, the required number of holes are left, the total area of u1bu400bwhich is equal to XNUMX/XNUMX of the subfloor area.
How to fix the situation
What to do if there is a foundation, but they forgot to make air vents or their sizes are insufficient for normal ventilation – a fungus, high humidity and other “charms” began to multiply in the underground. There are several ways to solve the problem:
- Enlarge existing ones or drill new ones. Drilling a monolithic foundation is not an easy task. Do this or with the help of a crown of a suitable size. If there is no crown, you can take a long drill with a large diameter, drilling many small holes with it around the perimeter of the vent. Then the remaining gaps are drilled, and the uneven surface is then either polished or simply covered with a grate. Another way is to order diamond drilling. In this case, special equipment is used, holes are drilled much softer, without shock loads.
Diamond drilling in the basement of a building - If there is no possibility or desire to make new or expand old vents, you can improve traction by bringing one or more pipes from the vent to the roof. Due to the pressure drop, the draft will be better, the humidity will decrease.
- Make forced ventilation. In order not to turn it on / off manually, you can set a timer or a differentiated thermometer. It will turn on the fan when the temperature in the underground is higher than outside (condition for condensation).
- Reduce the amount of moisture entering the subfloor. The most common source is soil, especially at high groundwater levels. It is covered with a vapor barrier. A thick plastic film is suitable (thickness from 150 microns). It is laid so that one canvas overlaps another by 10-15 cm. The joints are glued with double-sided tape (you can do it twice – at the beginning of the “overlap” and at the end). The film is brought onto the walls by 20-30 cm, fixed with a plank. So that during further operation the film is not damaged, a layer of sand is poured on it or a skinny screed 3 cm thick is made. If there is no insulation, condensation will form on the film. By making a slope in some direction, moisture can be collected and removed from the subfloor. This option is worse, but it works.
- For ventilation of the underground in a bathhouse (heated) or houses with stove heating, there is another solution – put the stove so that the air is drawn from under the floor (make a blower below the level of the finished floor).
Ventilation of the foundation by means of air intake into the furnace from the underground - No subfloor – no ventilation needed. To realize this axiom, the entire space from the ground to the subfloor is filled up. The most affordable material with good heat-insulating properties is used. Usually it is expanded clay. Its disadvantage is that it is hygroscopic and is able to “pull” water from the soil. With a high level of groundwater, if you do not make high-quality waterproofing on the ground (a film with access to the walls), you can only make it worse. There is a second suitable material with the best thermal insulation characteristics and completely non-hygroscopic – granulated foam glass or its breakage. This material appeared relatively recently and few people know about it. For this case, it’s a great choice. True, it costs more than expanded clay, but it is also many times warmer and safer (expanded clay is often environmentally unsafe).
Close the vents for the winter or not
There are two points of view on whether to close the ventilation holes in the underground for the winter or not. If they are left open, moisture will not accumulate. And this is good, but in return we get a cold floor and increased heating costs. The way out is enhanced floor insulation so that ventilation does not affect its temperature and does not require enhanced heating.
If the ducts are closed for the winter, moisture accumulates in the soil. Warm moist air from the house enters the floor, falling on cold surfaces, and in winter it is the basement walls, moisture condenses, flows into the ground. This means that later, in the summer, it will evaporate from there, increasing the humidity in the basement.
Foundation ventilation without ventilation (vent)
This is a complex set of works, which begins with the installation of a drainage system. Water must be diverted from the foundation so that it does not seep into the building due to the hygroscopicity and vapor permeability of concrete. By the way, it can be reduced several times by using a primer for deep penetration concrete with polymers.
The next stage is the waterproofing of the foundation and basement, their insulation. Waterproofing can be coated or built-up. Insulation – for this case, EPPS is recommended – extruded polystyrene foam. It is ideal for these conditions: in addition to excellent thermal insulation characteristics, it is not hygroscopic, does not let water through either in liquid or gaseous state, insects and animals do not like it, it does not rot, microorganisms do not multiply in it.
The blind area is insulated with the same material, because without this the soil in the underground can freeze.
After that, it is necessary to minimize the flow of moisture from the soil – cover it with waterproofing material. You can use any material with suitable characteristics – from a polyethylene film (with a density of 150 microns) to modern diffusion membranes that will not interfere with the steam coming out of the underground, but will not let the steam inside. The panels are laid with one on top of the other by at least 15 cm, the knocks are glued with double-sided tape. Also, the waterproofing film is wound on the walls – by 20-30 cm, where it is fixed with a clamping bar (fasten with dowels or nails, depending on the material of the base).
Next is the ventilation system. One or more pipes are brought out to the roof (depending on the volume of the subfloor), several supply holes are made in the floor, preferably from non-residential premises. From the side of the house they are closed with ventilation grilles.