Is it possible to make a flat roof from aerated concrete for a one- or two-story house?

Because of their streamlined appearance and effective use of available space, flat roofs are a choice that is growing in popularity for contemporary homes. To build these roofs, many homeowners are experimenting with various materials in an effort to strike a balance between affordability, longevity, and insulation.

Homeowners and builders alike are interested in aerated concrete because of its insulating qualities and lightweight nature. With its many advantages, this material might be the best option for building flat roofs on one- or two-story homes.

We’ll explore the viability of utilizing aerated concrete for flat roofs in this post, looking at its benefits and possible drawbacks. You can decide on the best course of action for your building project by being aware of the characteristics of aerated concrete and how it functions in a flat roof configuration.

Question Answer
Can you make a flat roof from aerated concrete for a one-story house? Yes, it"s possible to use aerated concrete for a flat roof on a one-story house. It provides good insulation and is lightweight, making it suitable for smaller structures.
Can you make a flat roof from aerated concrete for a two-story house? Yes, but with extra considerations. Aerated concrete is lightweight and insulates well, but additional support and proper waterproofing are necessary to handle the load and prevent leaks.
What are the benefits of using aerated concrete for a flat roof? It offers good insulation, is lightweight, and can be easily shaped and cut to fit various designs.
What are the drawbacks of using aerated concrete for a flat roof? It requires careful waterproofing to prevent leaks and may need additional structural support, especially for larger buildings.

What kind of structure is this?

An example of an enclosing structure in a building or structure is a roof composed of aerated concrete, which is created from cellular artificial stone materials that have either been autoclaved or naturally hardened.

The roofing components are laid separately on top of the supporting base in the first instance, either as slabs or beams. In the second instance, however, the roof can be cast directly at the installation mark in a pre-made formwork, or it can be combined with the floor slab.

If the strength calculation is done correctly, an aerated concrete roof can function as a base for a roofing protective pie, act as a roof slab, and withstand operational and snow loads.

What types can be made of aerated concrete?

Though aerated concrete of any kind places several limitations on horizontal building envelopes, it can be applied to the following kinds of roofing components:

  • Aerated concrete has found its widest application for flat roofs with a soft waterproofing coating. In the presence of reinforcement with steel or composite meshes or rods, and free spans up to 2.5 – 3.0, as well as with support on 4 sides, such structures can be cast on the assembly horizon.
  • Monolithic aerated concrete can also be used as a screed on top of a reinforced concrete roof slab on a building.
  • Aerated concrete blocks can be laid on top of a solid supporting base, or in spans between pre-assembled beams, as thermal inserts or elements of permanent formwork. This technology is actively used in Western European countries.
  • Installation of autoclaved aerated concrete blocks on top of a solid slab or beam base on single-pitch or gable roofs, provided that the slope is no more than 15 degrees.
  • Installation of aerated concrete fully prefabricated or small-piece elements as enclosing structures of a pitched roof, provided there is sufficient load-bearing capacity of the rafters and purlins.

Pitch roofs require stops for rows of aerated concrete blocks in addition to the distribution slab because doing so prevents the weight of the blocks from concentrating at the level of the eaves beams, greatly simplifying the design.

When is such a roof appropriate??

In the following situations, a roof composed of monolithic cellular material or aerated concrete blocks is recommended:

  • If the load-bearing or enclosing vertical structures of a private house have high heat transfer resistance.
  • In the presence of a combined roof, which is also an enclosing structure for the exploited internal space. Such roofs are often used in the absence of an attic or technical floor.
  • If the exploited terrace of the building is located above the living quarters of the lower floors.
  • For garages, provided that the room is heated and insulated along the entire contour.

This type of roof is impractical if the building has a technical floor. This also holds true for any wooden homes or buildings with expansive windows and a metal framework for support. If the arrangement of the wall structures results in a low energy efficiency index, using such a roof will incur unnecessary costs without producing the desired results.

The aforementioned enclosing structure lowers the building’s winter heating expenses dramatically and serves to isolate the closed, exploited space.

For what types of buildings is it suitable?

Aerated concrete roofing is a relatively new technology that is only now starting to gain popularity in our nation. These days, the following building types most frequently employ this constructive element:

  • Single-story buildings for technical purposes with a special temperature and humidity conditions.
  • Low-rise private residential buildings of modern construction with flat roofs above the last usable floor.
  • Townhouses as part of blocked residential buildings with flat roofs, or subject to a slope of up to 15 degrees.
  • Loft-style premises, which are often located in modern apartment buildings, where the covering slab is combined with the roof above the living space.

This kind of roof is also occasionally found on multi-story apartment buildings, but only in those cases where the roof is covered by a disc of reinforced concrete that is a part of the structure’s rigid frame.

In these cases, cellular blocks are simply arranged to the necessary thickness and serve as both thermal insulation and a foundation for the portion of the roof that is utilized, allowing you to set up a walking terrace in the event that the building contains penthouses.

Requirements for walls

The following materials are used to construct load-bearing, enclosing walls of buildings and room partitions in the presence of aerated concrete roofs:

  • Aerated concrete blocks, provided that their density is at least 600 kg/m3, and the support bed for the floor slab is from 300 mm or more.
  • Monolithic reinforced concrete walls, pylons or columns, if there is a horizontal beam above them for rigidity and creating a support bed for the slab along the contour.
  • Stone masonry made of small-piece materials, which is equipped with an armored belt along the entire perimeter in the upper edge of the walls.
  • Steel frame made of profile elements, provided that in the upper part it forms a beam cage of the main and secondary span load-bearing structures suitable for bearing the load from the aerated concrete roof.

These kinds of roofs are therefore best suited for stone buildings, as the wooden walls of frame-panel or log homes are not strong enough to support weight.

Properties and characteristics of the roof

The physical and mechanical characteristics of roofing made of monolithic cellular materials or aerated concrete blocks are as follows:

  • High compressive strength of the material, which ensures the reliability and durability of the roof (from B4 and more).
  • Increased thermal insulation properties of enclosing elements.
  • Minimum hygroscopicity and moisture absorption rate (not less than W4).
  • Increased resistance to the seasonal temperature difference through zero mark (from F25 and above).
  • The coating thickness, as a rule, is from 250 – 300 mm or more, to ensure the required strength simultaneously with heat-insulating properties.
  • Fire resistance of elements is from EI60 and higher, which prevents the destruction of coating elements within 60 minutes after the start of the fire.

The density of the material structure, the quantity and size of voids, and the thickness of the layer enclosing the structure all influence the aforementioned properties.

A one- or two-story home’s flat roof can be constructed with aerated concrete, which has advantages like superior insulation, lightweight design, and ease of handling. To avoid problems like water seepage or structural weakness, it is essential to guarantee adequate structural support, waterproofing, and routine maintenance.

Material requirements

Not all aerated concrete products are suitable for roofing because they are subject to the following legal limitations and regulations:

  • Only structural aerated concrete with the D900 – D grade is used for the coating
  • When organizing an enclosing structure made of aerated concrete as part of a roofing pie, it is allowed to use structural and thermal insulation material (grade D600 – D800).
  • The vapor permeability of blocks or monolithic structures made of cellular concrete for roofing should not exceed 0.15 mg / (m * h * Pa).
  • In the presence of a combined roof over residential buildings, the sound insulation of products should be from 46 dB and more.
  • If the frost resistance of products is less than F25, they should be protected by vapor barrier and waterproofing membranes to prevent destruction from aggressive environmental influences.
  • When using monolithic non-autoclaved aerated concrete, its shrinkage should not exceed 2 mm / m.

The manufacturer of the material and ingredients for it cannot guarantee the longevity of the enclosing structure while it is in use if the property owner disregards these requirements.

Preparation rules

When preparing concrete in a factory or on a construction site, there are a few guidelines that need to be followed:

  1. When preparing in factory conditions:
  2. Ingredients are dosed using electronic scales, which ensures the closest technical characteristics specified in the quality passport of each product.
  3. The solution is formed using special dosing devices.
  4. After laying the solution of the required consistency, vibration of the aerated concrete structure is ensured using special tables with eccentrics.
  5. After molding and compaction, the products harden in an autoclave – special steam ovens with a water vapor temperature of up to 120 o C, at high pressure.
  6. After the folding of forms and the extraction of finished products, the geometry of the selective samples of each batch is monitored by the geometry of the geometry. The maximum deviation from any of 3 geometric parameters does not exceed 0.3%.
  7. When preparing at the construction site:
  8. To knead the solution, it is better to purchase the finished mixture used in the preparation of aerated concrete in advance.
  9. Given that hardening occurs in natural conditions, the strength characteristics of the mixture should be higher than in the factory, which compensates for a partial violation of the technology.
  10. When mixing the mixture with a mixer, or in a concrete mixer, pure water is added portioned until the material receives mobility P2 (the sour cream-shaped mass of a light gray shade).
  11. After mixing, before laying aerated concrete in forms or in a flanging, it is necessary to wait up to 5 – 15 minutes for the chemical reaction to occur with the release of gas molecules to form pores.
  12. After placing the concrete in the form, it is necessary to ensure its compaction with an internal vibrator with a mace so that all air molecules come out. In such situations, the formation of pores continues in the structure of the material until the binder component sets.
  13. After molding and pouring, it is necessary to provide heating and a humid environment for the aerated concrete to gain strength, which will affect its physical and mechanical properties.
  14. Before laying liquid concrete, it is necessary to lubricate the forms with oil, which eliminates increased adhesion of two dissimilar materials. Thus, when removing the sides, the safety of all edges will be ensured and there will be no delamination of the material.

It is advised to use specialized adhesive compositions that are also highly porous in order to successfully install a roofing pie made of individual blocks. This will help to prevent the formation of cold bridges.

How to calculate the required quantity?

When building a roof, a straightforward algorithm made up of multiple arithmetic operations should be used to determine the necessary amount of aerated concrete (using an example):

In a private residential building, the volume of an aerated concrete covering slab in addition to the roof’s thermal insulation material must be ascertained. The way the slab is positioned is because there is a terrace with an exit from the room above the utilized area.

The room measures 4 by 5 meters. Four load-bearing beams are positioned in the transverse direction, each with a step of 1 meter. A fiberglass composite mesh with a 100 x 100 mm cell pitch and a 6 mm rod thickness is used to reinforce the slab.

In order to determine the strength, the slab’s minimum thickness should be 240 mm, accounting for the application of 180 kg of snow per square meter and 300 kg of operational load per square meter.

Heat engineering calculations require that the structure’s thickness be at least 320 mm (at a density of 800 kg/m3), taking into account the coldest five-day period for climate zone II, which is -28 o C.

The slab’s thickness, which is 320 mm, is the maximum of the necessary values.

The room measures 4 by 5 meters, with wall structures ranging in thickness from 400 to 600 mm. A 250–300 mm sufficient support area is needed for such a slab with beams.

Hence, the floor slab’s overall measurements are 4.6 by 5.6 meters.

The volume of aerated concrete needed to install a roof over the concerned room is 5.6 x 4.6 x 0.32 m = 8.24 m 3.

Given that waste generation is an inevitable part of the process of producing aerated concrete, it is advised to account for the stock of materials for each ingredient when performing calculations. This means that the best course of action would be to prepare a solution for the structure in question that would require 8.8 to 9.0 m³.

Equipment and devices for creating

The following collection of instruments, gear, supplies, and devices will be required by the master in order to construct an aerated concrete roof:

  1. For marking and taking measurements:
  2. Level for determining differences in elevation marks of the installation horizon.
  3. Laser rangefinder for determining the dimensions of the roof plane.
  4. Ruler with a steel sheet for measuring the thickness of the future ceiling and roofing cake.
  5. Angle for construction work to determine the orthogonality of the formwork sides.
  6. Nylon cord with rod fasteners.
  7. Laser or bubble level.
  8. For preparing the base:
  9. Tool for cleaning the slab plane.
  10. Mater for applying the bedding on top of the distributing belt of the walls.
  11. Rule, installation profile for setting the horizontal level of the reinforced belt of the masonry.
  12. Plumb line with a load to determine the uniformity of marks at each point of the support area.
  13. Heat-insulating or elastomeric gaskets, if necessary, to set a vibration-absorbing gap between the supporting structures – beams, walls and the future coating.
  14. For the device of factory-made blocks:
  15. Drill with mixer attachment for mixing glue.
  16. A grinder with an abrasive disk or a hacksaw with a small tooth for cutting material.
  17. Winper with a cable, or a crane with a chalk for puffing the material on the mounting horizon.
  18. Rubber hammers to adjust the position of the blocks.
  19. For a monolithic device aerated concrete:
  20. Elements of sewing, laminated plywood, racks, tripods, forks and crossbars for collection of formwork coating.
  21. Brushes and machine oil for processing the inner plane of formwork.
  22. Mixer to knead the liquid mixture.
  23. Libra for the dosage of water and other ingredients.
  24. Deep vibrator for sealing the mixture.
  25. Thermal gun to ensure the necessary hardening conditions.
  26. Rule for smoothing of the laid ambitious concrete.

A roof is a multi-layered structure that requires vapor barriers, waterproofing, and other structural components in addition to the above-mentioned tools and supplies. The working project dictates how much material is needed and in what order for various types of roofs.

Step-by-step instructions: how to do it right?

Aerated concrete roofing is a responsible, labor-intensive process that calls for specialized knowledge and expertise. Making contact with experts would be the best course of action in this regard. In the event that the home craftsman is confident in his skills or that this is not feasible, he must adhere to the process maps that are outlined in more detail below.

Nuances for the garage

An aerated concrete garage roof installation requires consideration of several significant functional and technological details, including:

  • Blocks or non-autoclaved aerated concrete must be reliably protected by a layer of vapor barrier, which simultaneously impregnates the absorption of harmful fumes from the operating internal combustion engine.
  • If there is a pitched roof over the garage, before laying the first elements of the roof, it is recommended to install a cross beam-purlin to organize the support.
  • Monolithic concrete is cast on formwork that has temporary supports that prevent deformation during the installation period.
  • The mobility of the mixture for a garage with a slope of more than 5% should be no more than P2 to avoid uneven redistribution of thickness.
  • Non-autoclaved aerated concrete for garage roofing is recommended to be cast in the form of reinforced slabs with a span width of no more than 1 m, which are subsequently mounted between the load-bearing cross beams.
  • It is not allowed to install monolithic aerated concrete over the entire span of the garage, since the distance between the walls in the transverse direction for such buildings is at least 2.8 – 3.2 m.
  • The material is pre-mixed on the basis of Portland cement and sand with water until the desired consistency is achieved, after which caustic soda, lime and soot are added to it. The ingredients are dosed until bubbles appear in the structure of the liquid solution, indicating the release of gas and the formation of spherical pores.
  • It is recommended to install a monolithic non-autoclaved aerated concrete slab at a temperature of +10 o C and above.
  • Aerated concrete can be reinforced with road or masonry meshes, as well as composite rod materials with a selected equivalent strength.
  • Considering that aerated concrete has a brittle structure, the use of rods without distribution frames is not allowed in order to exclude the formation of a degree of freedom due to the loss of concrete compression forces.
  • After installing liquid concrete in the formwork, it is necessary to ensure that the material is covered for at least 48 hours.
  • Stripping of the structure is allowed no earlier than after 6 – 7 days.
  • During the strength gain, it is recommended to provide conditions of high humidity and heating of the concrete in order to get as close as possible to the environment obtained in an autoclave. This will minimize the shrinkage of the material structure.
  • Monolithic aerated concrete refers to amorphous structures, which can cause unpredictable and uneven settlement of the structure. In this regard, as it hardens, it is necessary to periodically monitor the elevation mark of the installation horizon with a level.

It’s also important to remember that the garage is one of the buildings that produces more toxic and harmful gases than other types of structures. It is advised to consider in advance whether to use a mechanical or natural exhaust ventilation system for the roof’s outlet.

For a bathhouse

Nearly every interior space in the bathhouse is an exploited space with a unique humidity and temperature regime. The most comfortable functioning is guaranteed by the insulation of all surrounding structures for the bathhouse.

To create a roof of such a structure from aerated concrete, it is necessary to perform the following steps:

  • For the device of aerated concrete roofing, it is recommended to install in advance the distributing supporting slab of the roof.
  • When installing such a roof over a log house, the best solution would be to use autoclaved individual structures, which are laid out on top of load-bearing wooden beams with a cross-section of at least 100 x 200 (H) mm.
  • Installation of individual elements should be carried out by filling each seam with fast-polymerizing adhesive compounds with a high porosity coefficient in order to avoid the occurrence of cold bridges.
  • Considering that aerated concrete roofing is a heat-insulating structure, during its installation it is necessary to exclude the formation of a dew point in the body of the material, which requires the installation of an organic polymer membrane that will not melt when a high temperature is reached in the steam room.
  • If cracks are detected on the plane of the slab, it is recommended to install alabaster beacons for several days to exclude the risk of their opening and ensure proper monitoring of the progression of the defect.

When the bathhouse is used extensively and for extended periods of time, a significant amount of water vapor builds up in the under-roof area. This requires the owner to install breathable waterproofing that is both layered beneath the base of the enclosing structure and as part of the top coating.

Several control strategies and safety measures are discussed above when building an aerated concrete roof. This can be attributed to the material’s low mechanical strength, which has a safety factor significantly lower than that of heavy concrete. This raises the risk of using such a roof in the event of an unintentional technology violation.

Possible difficulties in the process

Beginners may commit several major errors and infractions when building a roof out of aerated concrete, which could have detrimental effects.

  • The appearance of cracks in aerated concrete elements. It is recommended to purchase only high-quality blocks, slabs or components to create a monolithic porous structure. Before choosing a material, it is recommended to request certificates of conformity for each component from the seller.
  • Uneven settling of the material. The aerated concrete roof should be used and loaded only within the limits of the load-bearing capacity of the material declared by the manufacturer.
  • Destruction under the influence of moisture. Any porous material after installation must be protected from water vapor and precipitation by special vapor barrier and waterproofing membranes.

The material exhibits shrinkage cracks with an undesired opening width after casting. Aerated concrete components must all be combined strictly according to the prescribed recipe, and the master must create ideal conditions for hardening and strength gain after the concrete has set.

It is advised that, prior to beginning work, you familiarize yourself with video tutorials and master classes that experts frequently post in the public domain, discussing a variety of nuances and secrets, in order to eliminate the challenges and errors outlined above.

Advantages and disadvantages

Ax concrete roofs from last year are becoming more and more common. Due to the existence of several benefits, small real estate object owners include:

  • Increased thermal properties of the material.
  • High absorption rate of sound waves.
  • Low dead weight, which eliminates the load on supporting structures and the use of reinforcing elements.
  • Some modifications of the material are characterized by a high level of hygroscopicity, which also affects the frost resistance index.
  • Ease of cutting ready-made autoclaved materials.
  • Fast polymerization and strength gain of monolithic aerated concrete.
  • Excellent adhesion not only to the steel reinforcing mesh, but also to composite reinforcing elements.

However, because these structures have a number of drawbacks, they frequently cause issues for their owners.

  • Low mechanical strength and susceptibility to brittle destruction.
  • When the material delaminates due to physical wear, dust is formed, which can negatively affect the respiratory tract.
  • If the structure is saturated with water vapor, it begins to collapse.
  • This material cannot act as an independent span structure, since it has virtually zero deformability, which requires preliminary construction of load-bearing elements – beams, capitals, the main roof slab.

Aerated concrete blocks and regular concrete roofs differ in a number of ways, both in terms of technology and design:

  • Aerated concrete is significantly more expensive than ordinary heavy concrete.
  • Monolithic or precast reinforced concrete always requires the construction of a heat-insulating and waterproofing pie, since it does not have the necessary heat transfer resistance.
  • Heavy concrete can always be used as a load-bearing span structure and a rigidity element of the building frame.
  • Not every craftsman can properly work with monolithic aerated concrete and ensure proper care for it during hardening.

It is advised to carefully consider all the advantages and disadvantages, as well as how the future structure will operate, before deciding to use aerated concrete for the roof.

Average costs for materials and work

Aerated concrete blocks and other cellular concrete products are widely available in the market and are priced as follows:

  • Ready-made blocks of different sizes, autoclaved, with a density of 600 kg/m3 – from 5,000 to 7,500 rubles. per 1 m3 .
  • Ready-made blocks of different sizes, autoclaved, with a density of 500 kg/m3 – from 4,000 to 6,500 rubles. per 1 m3 .
  • Aerated concrete adhesive with high specific resistance to heat transfer – from 15 to 30 rubles. per 1 kg of dry matter.
  • Dry mix for the preparation of monolithic aerated concrete with caustic soda, lime, slag and ash – from 450 to 600 rubles. per 1 bag of 25 kg.

Additionally, there are a tonne of businesses on the Internet that provide owners of both private residences and commercial buildings with the option to install aerated concrete roofing.

Regardless of the Russian Federation’s region, the average price level for work is roughly the same due to the increased level of competition among these organizations:

  • Device of aerated concrete blocks on a flat surface – from 350 – 550 rubles. for 1 m 2 .
  • The device of aerated concrete blocks on an inclined coating up to 15 degrees – from 450 – 650 rubles. for 1 m 2 .
  • The device of aerated concrete blocks on the pitched coating – from 700 – 1200 rubles. for 1 m 2 .
  • Creation of monolithic aerated concrete in beams – from 2000 – 2500 rubles. per 1 m 3 .
  • Creation of monolithic aerated concrete on shield formwork – from 2500 – 3500 rubles. per 1 m 3 .

A thorough estimated computation will be necessary to ascertain the ultimate cost of the materials and labor needed to construct an aerated concrete roof. This calculation will comprise all the information from the specifications, basic costs, and several corrective coefficients that depend on both direct and indirect factors.

It is feasible to construct a one- or two-story house’s flat roof out of aerated concrete. This material is a sensible option for building flat roofs because it provides good thermal insulation, is lightweight, and is simple to work with. Aerated concrete has cost-effectiveness and the ability to lessen the overall load on the building structure.

However, when employing aerated concrete for flat roofs, it’s imperative to guarantee adequate waterproofing and drainage systems. Because this kind of concrete is porous and absorbs water, improper management could result in structural problems. Maintaining the integrity of the roof requires using waterproof membranes and making sure the slope is sufficient for water runoff.

Even though aerated concrete is a feasible option, it’s crucial to follow best construction practices and speak with experts. A long-lasting and energy-efficient flat roof that improves the comfort and appearance of your house can be achieved with careful planning and installation.

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Marina Petrova

Candidate of Technical Sciences and teacher of the Faculty of Construction. In my articles, I talk about the latest scientific discoveries and innovations in the field of cement and concrete technologies.

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