Frame-beam ceiling in a private house

Recommendation points

• General specificity
• Carrying system device
• Laying of communications
• Ceiling decoration
• Rough floor

Frame-beam floors, which will be discussed this time, are successfully used not only in frame, but also stone houses. We will tell you about the main features of their device and describe in detail the installation process from the assembly of the supporting system to the installation of rough finishing surfaces.

General specificity

The construction of floors is considered one of the main difficulties in civil engineering. With the requirements for high strength, bearing capacity and high-quality sound insulation, monolithic and precast-monolithic technologies remain almost the only option. However, the installation of a concrete floor requires the use of heavy construction equipment, which is not only expensive, but also not always possible due to the lack of normal access roads to the construction site. In addition, during construction, a large amount of expensive steel and concrete is used, the load on the foundation and load-bearing walls increases, and formwork rental is required..

However, alternatives to concrete slabs exist, the most attractive being the use of a framing system on load-bearing beams. This type of overlap is successfully used in modern Finnish houses: in terms of performance, they are not inferior to concrete ones, but at the same time they have a consistent assembly technology that does not include rigging, are lighter and provide simple wiring of utilities.

At the same time, frame-beam floors have a number of disadvantages. The main one is the large thickness, forcing the increase in the height of the walls to maintain the design height of the ceilings. Another disadvantage is the reduced service life in comparison with reinforced concrete. Nevertheless, despite some overconsumption of material during the construction of walls, this type of overlap is still economically profitable, and the service life is reduced to only 50-70 years, which is quite enough for private housing construction.

Carrying system device

The supporting floor system is represented by beams, which can be one of the following structural elements:

1. Glued pine board 250-300 mm wide. The strength of solid wood is not compromised, so the density of the glued board beams is lower than in the case of other materials. There are also disadvantages: high cost and length limited to six meters.

2. Wooden I-beams have recently become a fairly common material on the domestic market. The relatively low flexural strength is compensated by the possibility of a tighter placement of the beams, which allows the relatively low cost of the I-beam. The main advantage is the significant length of the beams, which allows spanning spans up to 13 meters without joining. Preference should be given to an I-beam with LVL shelves and OSB ribs 10 mm or more thick.

3. Timber trusses can be self-assembled from available lumber. This is the most budget-friendly option for beams, in the manufacture of which pine beams 50–70 mm thick are used. The main disadvantage is the complexity of calculating the bearing capacity, which requires a significant margin of safety. In addition, it takes some time to assemble the trusses, which slows down the construction process..

3. LVL is considered to be the most authentic material of the Finnish floor support system. Advantages of the material: high strength, considerable molding length, resistance to fire and organic damage, the highest of the listed materials, the service life. Among the disadvantages, the most pronounced are the low prevalence and high cost of high-quality LVL..

In addition to the main load-bearing elements, the floor structure also includes additional ties that perform the function of positioning the beams and holding them in a position that is optimal from the point of view of the perception of loads. If the beams are made of glued board or LVL, they are fastened together with spacers made of the same material. Spacers are staggered to distribute indirect loads and facilitate fastening to the end of the tie through the beam body.

It is most convenient to fasten trusses and I-beams with horizontal bar inserts between the upper and lower chords. The trusses are preliminarily set up step by step and leveled, then temporarily fastened with boards laid diagonally in the upper and lower planes of the floor. Then the main connections are established and the temporary spacers are removed. A design option is also common, in which the role of additional ties is played by the flooring and the hemmed draft ceiling, however, this method of overlapping is technologically more complicated..

It is also necessary to pay attention to the joints of the floor to the wall. If we are talking about a stone building, a ledge with a width of at least a third of the beam height must be formed in the wall. At the same time, in buildings made of gas silicate blocks, an armored belt must be installed to distribute the load from the beams. The beams are fastened with cement mortar and masonry, the thermal bridge is removed by covering the beams with expanded polystyrene. It is also possible to overlap without the formation of a quarter, in which case the fastening is carried out through special shaped beam brackets. In frame houses, the pillars of the lower floor are covered with a massive bar that acts as a support crossbar for the floor beams and pillars of the upper floor. Beams are fastened through the transom from below.

Laying of communications

There is no difficulty in placing utility lines parallel to the load-bearing beams. With the right organization, this possibility allows you to lay up to 80-90% of all engineering networks without interfering with the design of the supporting system.

However, it is almost inevitable that there is a need to make passages in the beams. Beams can be drilled only if a number of conditions are met:

1. The hole diameter should not exceed 1/3 of the beam height.
2. The holes should be located at least 50 mm to the edges of the beam, ideally strictly in the center.
3. Holes cannot be made closer than 150 mm from the end of the beam or the extreme support point.
4. Between the holes in the same beam, a distance of 4 times the diameter must be maintained.

Observing these conditions, it is quite easy to lay the main communications in the ceiling: rough plumbing, electrics and low current. However, when it comes to ventilation ducts, usually more than 100 mm in diameter, the diameter of the holes exceeds the allowable limit. There are several solutions to this problem: arrange a technical cavity in the ceiling of the first floor, give preference to trusses instead of beams, or strengthen holes whose diameter exceeds 1/3 of the beam height. For this, reinforcing linings are installed at the place where the passage is made, which doubles the nominal section of the supporting beam. The length of the overlay should be sufficient to overlap the bonding area by a distance 5 or more times the width of the hole. As a rule, the linings are fixed with distributed fasteners: by drilling up to ten through holes for bolts or screw ties.

Ceiling decoration

Immediately after the completion of the laying of communications, it is necessary to carry out a preparatory finishing of the ceiling in order to then fill the ceiling cavities with sound-insulating material. At the same time, preparations are being made for the installation of the supporting sheathing to perform the sheathing of the rough ceiling.

The support of the slab filling material is required to eliminate pressure on the back of the suspended structure planking. To do this, a lathing made of a 25×50 mm lath with a step of 30–40 cm is nailed across the bottom of the beams. The specific size of the step of the laths is determined so that they have overlapping places of the vapor protection canvases. The film is hemmed from below and shot with staples, then a strip of tape is glued along the line of the fastener.

The installation of the supporting lathing under the sheathing is carried out either on a counter-lattice lined from the bottom along the line of the beams, or on straight suspensions and a galvanized profile. In both cases, it is required to first apply marks on the walls indicating the axial centers of the beams, or to be guided by the clearance through the film.

Rough floor

The filler (mineral wool) can be laid before the completion of the ceiling on the lower floor. Nevertheless, it is recommended to nail the vapor barrier in advance so that the cotton wool does not spill down during further work. If the density of the filler is high enough to place it on the spur, no additional support is required. However, often in ceilings, cheaper, low-density mineral wool is used, for laying it you first need to lay plywood or MDF board with a thickness of up to 5 mm on the battens.

After the overlapping cavities are completely filled, the entire cake is covered with dense geotextile on top. Laying is performed along the direction of the beams, the overlap is placed directly above the beams and nailed to them, having previously folded a double fold. Geotextiles are necessary to exclude the weathering of mineral wool particles during floor vibrations, therefore this barrier must have sealed joints and abutments.

From above, the ceiling is covered with a flooring made of edged boards or sheet materials with a total thickness of up to 20 mm. The hallmark of Finnish technology is the installation of a cement or semi-dry screed 50–70 mm thick over the subfloor. It is this version of the cake that provides the highest quality sound insulation between floors and a high bearing capacity, comparable to hollow slabs – up to 400 kg / m².