Balcony insulation: how to insulate the floor

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Although for the most part glazed balconies do not have insulation, the presence of thermal insulation on the floor significantly increases the comfort of being in the fresh air during the cold season. It is very important not to overload the balcony console and at the same time achieve high-quality thermal protection. How to do it – read our instructions.

Balcony insulation: how to insulate the floor

Floor insulation structure

Since the balcony is supported solely by the structural strength of the reinforced concrete slab, only lightweight materials are chosen for glazing and insulation systems. It should be remembered that in addition to warming, the purpose of arranging the floor on the balcony is its high-quality leveling, because usually the balcony console is slightly tilted outward.

To level the floor, a cross log system is used. It can be either adjustable screw lugs or a simpler frame-type structure, which is assembled with manual adjustment in place. The main material is the use of 50×50 mm bars and boards of the same thickness. The width of the boards can vary widely (70-200 mm) depending on the required degree of floor elevation.

Balcony insulation: how to insulate the floor1 – balcony console; 2 – transverse lathing; 3 – longitudinal lathing, logs; 4 – insulation (mineral wool); 5 – sheet material as a sub-floor

Mineral wool with a density of 25-30 kg / m is used as a floor insulation3. In conditions of approximately the same temperatures between the balcony and the outdoor environment, it is practically not susceptible to condensation, while providing a sufficient degree of thermal protection even with a layer of 70–100 mm. If necessary, the insulation can be protected with a windscreen and vapor barrier. The rough floor covering is formed by moisture resistant sheathing.

How high can the floor be raised

On the one hand, the more insulation is put under the floor, the warmer it will be in the end. On the other hand, everything needs to know when to stop. Insulation with a thickness of over 100 mm for a glazed, but non-insulated balcony will not bring much benefit. The floor is not the main pathway for heat loss, three exterior walls with a continuous glazing front do just fine.

Balcony insulation: how to insulate the floor

In addition to the expediency factor, there are a number of more obvious limitations. Firstly, this is the height of the rise above the floor level in the apartment, the difference in levels of no more than 100-120 mm is considered comfortable in this regard. Secondly, if you raise the floor too high, the distance from the floor to the bottom of the sash will be much less safe. According to safety requirements, the parapet fence should not be lower than the ilium of the pelvis, for a person of average height this is equivalent to a height of 90-100 cm.

Also, do not focus on the height of the dividing threshold between the floor and the apartment – this part of the building structure is not responsible, and therefore can be partially removed or extended. However, with the balcony unit already installed, the upper limit for raising the floor will be the level of the door frame. Ultimately, the plane of the floor covering should be 25-30 mm below the edge of the raised bead.

Assembling and securing the support system

The balcony floor frame is represented by two lines of beams. In the first bottom line, the beams are located across the length of the balcony, they are designed to fix the entire supporting system to the concrete slab. In the second line, the beams are located along the balcony: due to the smaller number of them, it is easier to align, plus it becomes possible to cut sheet materials into more compact fragments along the width of the balcony for easy installation.

Balcony insulation: how to insulate the floor

Before starting work, the beams are impregnated with fire protection and sorted. Lumber with the greatest curvature and the number of defects is sent for cutting transverse logs, and 2-3 of the best quality beams are left for making longitudinal ones. Cutting beams into the bottom row can be carried out locally with a tolerance of 1-2 cm from each wall.

Transverse logs are placed with an equal pitch of 45-50 cm, pre-drilled with a pitch of no more than 80 cm and fastened to a concrete slab through the holes. Anchor bolts can be used as fasteners if the nuts and studs are guaranteed not to fall under the longitudinal lags. If there is such a risk, the fasteners are changed to a screw pin in a plastic stopper, while the head is hidden in a pre-drilled sweat. When fastening the beams, it must be borne in mind that dust accumulates 2–3 cm from the bottom of the hole, which may prevent the fasteners from entering to their full depth. It is also not worth making the holes too deep, there is a great risk of drilling the balcony console through. After fixing the beams, the floor must be thoroughly cleaned of dust, sawdust and other debris.

Balcony insulation: how to insulate the floor

The second row of the lag, represented by boards on the edge, performs the function of leveling and raising the floor to the desired mark. The easiest way to do this is with mounting wedges: first, the highest point of the floor system is determined by the slatted level, where wedges are not required, usually this point is located at the inner wall. Further from the highest mark, the starting log is laid at a distance of 5-10 cm from the parapet, the board is leveled in the longitudinal direction along the horizontal level. Along the starting lag, the lag of the other edge is leveled, set 10–15 cm from the inner wall. If the width of the balcony exceeds 1 m, an additional lag is mounted in the center, which is aligned along the two extreme.

Alignment can be carried out without mounting wedges, in this case the starting lag is laid along the line of the lowest mark. When the board is firmly laid on the transverse joists, a rack level is applied to its side, resting on the highest of the crossbars. A line is drawn along the horizontal level, which vanishes at the highest point of support. After that, the board is unrolled and the intersections with the bars of the lower row are drawn on it. According to the resulting marking, a hacksaw is used to make cuts to a depth limited by the horizontal marking line.

Balcony insulation: how to insulate the floor

When the lag is laid in place, it remains only to slightly adjust it with thin wood chips and fix it with self-tapping screws or mounting metal corners. The lags of the higher level are leveled in the same way, however, the horizontal marking line is preliminarily shifted upward by a distance corresponding to the transverse level difference. When the supporting floor system is installed, all the free space is cleared of debris and densely filled with mineral wool.

Balcony insulation: how to insulate the floor


As sheet materials for the subfloor, either one layer of chipboard 16 mm thick, or two layers of OSB (at least class 3) or moisture-resistant plywood of 9 mm are optimal. For ease of installation, the material is cut into square fragments with a side 2 cm less than the width of the balcony at the installation site. Please note that with multi-layer flooring, the elements are shifted to tie the joints.

Balcony insulation: how to insulate the floor

Before laying the sheets, it is necessary to mark the axial centers of the longitudinal logs on the walls. After that, all the fragments are cut and placed in place without fixing. The sheets are placed with a gap of 1–2 mm, which eliminates friction of the ends and creaking of the floor. When the fragments of the flooring are laid out, the lines of the centers of the lags are beaten off with a dye cord and the sheets are screwed to the supporting system with self-tapping screws 35–45 mm. When laying the flooring in two layers, it is not necessary to screw the first one, but it is necessary to insert spacer inserts between the sheets of the lower layer.

Balcony insulation: how to insulate the floor

Pay attention to some of the sheets located in the area of ​​the balcony door. In this area, it is required to install an additional element that overlaps the threshold, tightly adjacent to the door frame and at the same time resting on the back side on the extreme lag. To do this, in the sheets of the main flooring, a cut should be made in advance, which will make half of the log available for fixing the insert. When the entire floor covering is sewn up, the joints between the sheets and at the edges must be sealed with polyurethane foam so that when the floor vibrates, the mineral wool particles are not blown out into the room.

Laying the flooring and protecting the abutments

After the completion of the subfloor, the parapet and balcony walls are finished. In this case, the finishing panels hang over the edges of the floor about 20-30 mm, covering the foam seam. Subsequent installation of the floor covering creates a long labyrinth in the corner junction, preventing heat outflow.

Balcony insulation: how to insulate the floor

Any type of light coating is suitable for a balcony: linoleum is laid with a sticker, laminate – over a damper substrate. To compensate for linear expansion, a gap of about 2 mm for long walls and about 4–5 mm for short walls should be left. When the cover is installed, the skirting board segments are cut to size and installed in place, which is fixed to the finishing panels with a false wall dowel. In this case, the capital inner wall needs to be drilled a little with a perforator so that the dowel body can be inserted to its full length until it is spread.

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