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Installation of insulated monolithic slab with underfloor heating

This article gives an overview of how to install an insulated monolithic slab with underfloor heating, a cost-effective and energy-efficient solution for home heating and cooling. The insulated monolithic slab is made of foam boards fixed together with steel plates to enclose the slab. This construction ensures excellent thermal insulation and reduces heat loss, resulting in reduced energy consumption. The article explains that the installation of the slab requires advanced techniques and it should be done by a professional contractor. Moreover, the insulation should be properly maintained afterwards, in order to ensure maximum energy efficiency. Additionally, this setup offers many advantages such as improved indoor air quality and an overall reduction of energy costs.

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More and more high-quality modern houses are being built on the slab foundation of the USP or UFP. Today, our site of advice will consider how appropriate such a decision is, in which cases it makes sense to put a house on a slab, and also give basic instructions for building a monolithic slab foundation with insulation.

Installation of insulated monolithic slab with underfloor heating

Benefit from a slab foundation

In individual construction, laying a building on a slab foundation is practiced in two cases:

  1. When a heavy structure is erected on a weakened soil, with a high ground level or pronounced heaving. Slab helps reduce ground pressure and is the most stable type of foundation.
  2. When building a house with a low thermal balance. Such a foundation helps to minimize heat loss to the ground and allows floor heating to be used as the only heating method.

In the second case, a definite plus is getting rid of heating devices and pipelines. In addition, when properly processed, slab foundations provide an excellent base for fine floor coverings. The possibility of laying communications in the slab presented as an advantage is not such: it is much easier to lay water supply and sewage pipes with a strip foundation with backfilling.

The slab foundation copes well with the movement of soil both vertically and horizontally. A monolithic base can be installed in areas where terracing or planning with filling was carried out, time for soil shrinkage is not required.

The only danger for a monolithic slab is uneven soil compression, provided that an area with soft or mobile soil occupies more than 40% of the slab area. In view of this, conducting hydrogeological surveys for the development of a construction project is strictly mandatory.

Installation of insulated monolithic slab with underfloor heating

Slab foundation construction

The slab follows the contours of the outer walls of the building with a projection from 50 to 80 mm. This tolerance is necessary to compensate for the torsion of the formwork and the curvature of the walls so that they do not hang over the foundation in any place..

The thickness of the slab is selected according to the required bending load capacity. Serious calculations should be carried out only when constructing buildings over two floors, including basement. The standard slab thickness of 35 cm is quite enough even for brick buildings, especially if the foundation is made using Finnish technology and has stiffeners at the edges..

Installation of insulated monolithic slab with underfloor heating

The 35 cm thickness is considered standard for a simple reason. Protective concrete layers for the upper and lower belts of reinforcement are 50 and 70 mm, respectively. The remaining 230 mm is the optimal distance between the reinforcing meshes, necessary for the correct perception of tensile and bending loads.

In most cases, the strength of such a board is excessive. If there is a desire to save money on concrete and reinforcement, or to reduce the pressure on the ground due to its high subsidence, a careful calculation can be made. There is no single standard for insulated monolithic slabs, but you can use the following documents when developing:

  • SNiP 2.02.01โ€“83 โ€œFoundations of buildings and structuresโ€ โ€“ basic information on the calculation of foundations and the development of their structure;
  • SP 50-101-2004 โ€œDesign and construction of foundations and foundations of buildings and structuresโ€ โ€“ the most relevant set of recommendations for the construction of foundations;
  • SP 20.13330.2011 โ€œLoads and Impactsโ€ โ€“ information on how to calculate the bearing capacity of the foundation for the limit states;
  • SP 52-101-2003 โ€œConcrete and reinforced concrete structures without prestressing reinforcementโ€ โ€“ will help to correctly develop the reinforcement cage and the shape of the concrete product.

When calculating loads, the configuration of the load-bearing walls must be taken into account. If all of them are located along the perimeter, the slab will experience a combined twisting effect along the lenticular plot. If the house has internal load-bearing walls, the load will be distributed more evenly, and if the foundation is thick enough, the torsion moment can be neglected. It is possible to lighten the weight of the slab without loss of strength by means of a cross system of reinforcing ribs. They are made up to 40-50 cm high, the width is equal to the thickness of the slab.

Foundation preparation

The slab foundation must necessarily rest on a cushion of sand and gravel, which protects against frost heaving and erosive action of groundwater. After geodesy and marking, it is necessary to remove the sod layer from the site or excavate the soil to the depth of occurrence of sufficiently dense sedimentary rocks. The dimensions of the pit exceed the design dimensions of the slab by 50โ€“70 cm on each side. The bottom is compacted with a vibration method and is planned with a tolerance of 3-5 cm.

Installation of insulated monolithic slab with underfloor heating

Drainage filling is carried out to a height of 30โ€“35 cm. This is a fairly large volume of gravel, but it is necessary to distribute loads in case of uneven soil compression. Without this, the insulation will experience concentrated loads exceeding the limit of reversible deformation. The top layer of backfill, 40โ€“60 cm thick, is made with clean sand without clay inclusions and is separated from the gravel with a needle-punched geotextile. The sand cushion will provide the most even distribution of the load and protect the waterproofing from pushing through.

Installation of insulated monolithic slab with underfloor heating

Installation of insulated monolithic slab with underfloor heating

Installation of insulated monolithic slab with underfloor heating

The gravel pad should be poured in stages, in layers of 8โ€“10 cm with intermediate compaction. It is optimal to use crushed stone of fraction 20-40 for this, but mixed road gravel is also suitable. Quite often, sanding is replaced with a footing. This solution is especially beneficial in unfavorable hydrogeological conditions and the construction of a slab on collapsible soils..

Constructive decisions

There are two options for arranging a foundation slab suitable for arranging a heated floor. One type is usually called Finnish, the other โ€“ Swedish, about which our site has already written many times. The main difference is that the first option implies the location of thermal insulation on top of the supporting base, while the Swedish plate lies on a layer of expanded polystyrene, which has a sufficiently high compressive strength.

The Finnish slab is more complicated in the device: the base is quite thin โ€“ up to 15 cm with one reinforcement belt. For reinforcement, the slab is equipped with 20ร—15 cm stiffening ribs, located with a step of 130โ€“150 cm. After the building box has been erected, a slab insulation is attached to the slab and an 80 mm thick reinforced screed is poured, inside which there are communication channels and floor heating elements. One of the main advantages of such a foundation system is that the thermal bridge along the contour of the abutment of the walls to the slab is almost completely excluded.

Installation of insulated monolithic slab with underfloor heating

The last problem in the Swedish version of the foundation is solved by complex insulation of the basement of the building. Industrial grade expanded polystyrene is used as thermal insulation, which can withstand increased loads. Since the main thermal protection belt is located completely under the foundation, the slab itself belongs to the warm contour of the building and provides increased thermal inertia.

Installation of insulated monolithic slab with underfloor heating

One of the features of the Swedish slab is protective flanges along the contour on the lower side of the foundation. They perform two functions: they insulate and protect the insulation from the lateral pressure of the soil and strengthen the perimeter of the slab, where the main load from the walls falls. It is recommended to do flanging regardless of whether the slab has stiffening ribs. The width of the ledges is 30โ€“35 cm, the depth is up to 50 cm, depending on the type of soil and the annual amount of precipitation. In general, we can say that it is the Swedish version of the flanged plate that is most suitable for operation in the climate of Siberia and Eastern Europe..

Formwork installation

Slab casting formwork consists of two parts: bottom and side.

The lateral formwork is performed with panels knocked down on the basis of a frame made of square pine timber with a side of 60โ€“80 mm, depending on the massiveness of the slab. A frame up to 2 m long and a height equal to the actual height of the foundation is knocked down from the timber. The frame must be reinforced with jumpers made of the same timber every 40-50 cm. On one side, each deck is sheathed with OSB or moisture-resistant plywood 10-12 mm thick.

Installation of insulated monolithic slab with underfloor heating

The installation of the formwork is performed accompanied by leveling. The upper boards are set to a common horizon, to adjust the decks in height, they are screwed to wooden stakes driven into the ground to a depth of 50 cm. In the optimal version, the stakes are installed opposite each partition of the formwork frame. Between themselves, the shields are twisted directly through the timber, and in both directions.

Strengthening the formwork to resist the mass of concrete is carried out by resting it on the adjacent soil. With a step of 1 meter and an indent from the shields of 50โ€“70 cm, stakes from a bar of 100ร—100 mm are driven into the ground to a depth of 30โ€“40 cm. Sections of boards of 50ร—100 mm, placed vertically on the edge, are abutted into these beams. On the reverse side, the boards are screwed to the shield frame. All spacers must be connected by a common cross bar. Sometimes, for additional reinforcement, horizontal struts are also installed, with which the stakes are connected to the bottom of the formwork, but such a move is required only when the slab height is over 40 cm.

The lower part of the formwork is a properly prepared foundation pit. Since the mass of concrete is high, and it itself does not have strength before solidification, even the slightest pushing of the soil can become a serious problem. This is why it takes so much effort to prepare a gravel pad..

Installation of insulated monolithic slab with underfloor heating

Styrofoam slabs are laid on top of the preparatory layer or foundation, while the waterproofing along the perimeter of the future slab is tucked inside the sides and nailed to them with staples. It is advisable to purchase insulation of such a thickness that it can be placed in two layers, shifting the joints for dressing.

There are two types of bottom formwork configuration. In the first case, square boxes with a side of 130โ€“150 cm are laid on top of the slabs, which form the formwork of the stiffeners. After gaining strength for 3 days, the boxes are removed and the gaps between the ribs are filled with gravel of fraction 20 or expanded clay. After that, a reinforcing mesh is tied to the anchors protruding from the edges and the top plate is poured with a thickness of 100-120 mm.

Installation of insulated monolithic slab with underfloor heating

In the second version, there are no stiffening ribs, but there is a lower flange. Western builders form it by using special-shaped polystyrene products: ordinary flat plates are laid in the central part, and foam trays are placed at the edges. At a domestic construction site, they often do it in a different way: remove the top layer of the gravel cushion around the perimeter, and put insulation 150-200 mm thick in the center. In this case, a trench is formed along the perimeter, in which reinforcement is mounted in the form of a square frame 200ร—200 mm.

Reinforcement and concrete pouring

The main problem of pouring a slab with insulation is the high risk that the expanded polystyrene can float, or due to a leaky formwork, mass leakage will occur and the estimated amount of concrete will not be enough. You need to order concrete with a margin: from 0.3 to 0.5 m3 for losses in the mixer and pump, plus 3% of the total volume.

Installation of insulated monolithic slab with underfloor heating

Concrete work is carried out in two stages. At the first stage, concrete of the M100 grade is prepared at the place, which is poured into all existing gaps from the outer side of the formwork. At the same time, the mixture is prepared as thick as possible..

After sealing the formwork, the reinforcement cage is assembled. The first row of mesh is laid on spacer plugs providing a 30 mm bottom protective layer. The first row of reinforcement is intended for the perception of secondary loads, therefore it is made of thin reinforcement, but the mesh has a more frequent spacing. U-shaped clamps are tied to the lower reinforcement, which regulate the gap between the meshes. It is chosen in such a way that the upper concrete layer is not less than 40 mm. The reinforcement is used with a thickness of 14 mm, while the laying spacing can be from 160 to 300 mm. The content, thickness and location of reinforcement are determined depending on the mass of the building and hydrogeological conditions, almost any online calculator will help to cope with this task.

Installation of insulated monolithic slab with underfloor heating

To prevent the extrusion of polystyrene foam with concrete, the slab is poured starting from the center. Filling is carried out in the same way as for a monolithic overlap โ€“ by pumping through the boom. The drop height should be 60โ€“80 cm, the boom boom should be no more than 5 meters. If the mass gains too much speed, it can break the reinforcement cage. At the same time, feeding too slow will cause voids in the bottom layer..

The slab is poured in one stage, but at the same time the break between the portions of concrete allows it to cure before the final filling of the form, which is used as the main way to prevent the insulation from floating up. When the central part of the slab is completely filled, the mass begins to be dropped from the edges into the flange. After the final filling of the form, the concrete is compacted with submersible vibrators, if necessary, adding the mixture in the places of formation of holes.

The leveling of the slab surface is done in two stages. Immediately after pouring and shrinking the mixture, the surface is stretched out with wide scrapers, removing footprints and leveling out large nodules. After 21 days of curing, the concrete is wet-sanded, forming an almost ideal horizontal plane, which serves as a finished sub-floor.

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Comments: 5
  1. Avalon

    Can you provide more information about the process and benefits of installing an insulated monolithic slab with underfloor heating?

    Reply
    1. Joshua Clark

      Installing an insulated monolithic slab with underfloor heating involves pouring a continuous concrete foundation with integrated insulation. Underfloor heating pipes are then laid on top before finishing the surface with flooring material. This system offers several benefits. Firstly, the insulation provides excellent thermal efficiency, reducing heat loss and energy consumption. This results in lower heating costs and increased comfort. Secondly, the even heat distribution provided by underfloor heating ensures a uniform temperature throughout the space, eliminating cold spots. This provides a more comfortable and pleasant living environment. Additionally, this system eliminates the need for radiators or baseboard heaters, freeing up wall space for furniture and enabling greater design flexibility. Overall, an insulated monolithic slab with underfloor heating is a modern and effective solution for achieving energy efficiency, comfort, and design versatility in a building.

      Reply
      1. Oliver Robinson

        Installing an insulated monolithic slab with underfloor heating involves pouring a continuous concrete foundation with integrated insulation. Underfloor heating pipes are then laid on top with flooring material. This system offers several benefits, including excellent thermal efficiency which reduces heat loss and energy consumption, resulting in lower heating costs and increased comfort. The even heat distribution eliminates cold spots, providing a more comfortable living environment. This system also frees up wall space by eliminating the need for radiators, allowing for greater design flexibility. Overall, it is a modern and effective solution for energy efficiency, comfort, and design versatility in a building.

        Reply
      2. Elijah Quinn

        Installing an insulated monolithic slab with underfloor heating is a cost-effective and energy-efficient way to provide comfortable heating throughout a building. The integrated insulation minimizes heat loss, reducing energy consumption and lowering heating costs. The underfloor heating system ensures even heat distribution, eliminating cold spots and creating a consistent temperature in every room. This system also allows for more design flexibility by eliminating the need for bulky radiators or baseboard heaters, freeing up wall space for furniture and dรฉcor. Overall, an insulated monolithic slab with underfloor heating is a modern and effective solution for achieving warmth, comfort, and design versatility in a building.

        Reply
  2. Josiah Brooks

    Can anyone share their experience with the installation of an insulated monolithic slab with underfloor heating? What are the steps involved in the process? How effective is it in terms of energy efficiency and comfort? Any tips or advice for someone looking to install this type of flooring system? Thank you in advance!

    Reply
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