Material for the foundation perimeter.

A blind area is a special waterproof covering constructed around the perimeter of a building adjacent to its foundation. The main functional purpose of the blind area is to drain rainwater and meltwater away from the foundation and plinth of the building, preventing their flooding, reducing the load on the foundation’s waterproofing, and lowering the risks of frost heave of soils in close proximity to the structures. In addition to its purely utilitarian hydrotechnical function, the blind area plays an important role in shaping the architectural appearance of the building, creating a visual transition from the walls to the landscape, and also serves as a convenient pedestrian walkway for facade maintenance. Structurally, a classic blind area is a multi-layered “pie” that includes a preparatory base, a drainage layer, waterproofing, insulation (in some cases), and a finish coating. Each of these layers requires careful selection of materials depending on the soil type, climatic conditions, architectural features of the building, and planned loads.

Historically, blind areas were made from simple local materials: compacted clay, crushed stone, cobblestone. In modern construction, the approach has become much more technological and differentiated. The choice of material for the blind area, especially for the lower, invisible layers, determines the durability of the entire structure and the effectiveness of its protective functions. Incorrectly selected or laid material can lead to subsidence, cracks in the finish coating, water stagnation near the foundation, and, as a result, dampness in basement rooms, foundation deformations, and even cracks in load-bearing walls. Therefore, the process of selecting material for the blind area should be based on engineering calculations and an understanding of the physical processes occurring in the soil and in the structure itself.

Particular importance is given to the material for constructing the so-called “bedding layer” or “cushion.” This layer is the foundation for the entire blind area and performs several key tasks. First, it replaces the heaving or weak soil in the immediate vicinity of the foundation with a more stable and draining material. Second, it provides the required slope of the blind area (usually 2-10% from the building wall) for effective water runoff. Third, it evenly distributes loads from the overlying layers and possible pedestrian or vehicular impacts, preventing local subsidence. Depending on specific conditions, the bedding layer may consist of one or several materials: sand, crushed stone, gravel, clay, lean concrete, or profiled membranes. The choice between them depends on the groundwater level, type of base soil, presence of site slope, and project budget.

In addition to the bedding layer, a critical element in regions with cold climates is the insulation layer. Its task is to prevent soil freezing under the blind area and, accordingly, minimize frost heave forces acting on the foundation. Extruded polystyrene foam (XPS) is most often used as insulation, having almost zero water absorption and high compressive strength. Sometimes expanded clay is used, but its thermal protection properties are significantly lower, and the required thickness is greater. Thus, the material for the blind area is a comprehensive concept covering an entire system of interrelated components, the choice of which determines not only the durability of the blind area itself but also the well-being of the entire building. In this article, we will examine in detail each type of material, their properties, areas of rational application, and working technologies.

Classification of Materials for Blind Area Base Construction

Materials used for creating the base (cushion) of a blind area can be classified by their main functional purpose, origin, and physical-mechanical properties. The main division is into materials performing a drainage function and materials performing leveling and stabilization functions. The first group includes materials with high water permeability, whose main task is to quickly drain water that has penetrated through the finish coating or seeped from the sides, away from the foundation. The second group includes materials that create a dense, level, and stable base for laying the finish coating, be it paving slabs, paving stones, asphalt, or concrete. In practice, these functions are often combined, and the blind area cushion is created from several alternating layers.

The classic and most common drainage material is crushed stone. It is an unrounded bulk material obtained by crushing rocks (granite, limestone, gravel). In the context of a blind area, its fraction (grain size) and flakiness (grain shape) are important. For the lower layers of the cushion, crushed stone of fraction 20-40 mm or 40-70 mm is usually used. A coarse fraction ensures high water permeability and is economically advantageous. Finer crushed stone (5-20 mm) is used to create an upper leveling layer under paving slabs or for backfilling on top of the main drainage layers. Important parameters are the strength grade (not lower than M600-M800 for critical structures) and frost resistance (F50 and above). Gravel, unlike crushed stone, has a rounded shape and smooth surface, which worsens its interlocking in the layer, but is also widely used due to its availability. Sand is an indispensable material for creating leveling and drainage layers. In blind areas, mainly coarse or medium river or washed quarry sand is used, which does not contain clay and silt particles that can clog the drainage.

Sand-gravel mixture (SGM) or enriched sand-gravel mixture (ESGM) is a ready-made composition combining the advantages of sand and gravel. SGM is used to create a universal base combining drainage and stabilization. However, the proportions of sand and gravel in natural SGM are unstable, so for responsible work, it is preferable to use ESGM with a standardized gravel content (usually 70%). Clay, paradoxically, can also be used in the blind area structure, but in a completely different capacity. Fat clay serves as an excellent natural waterproofing agent. In traditional constructions of the so-called “clay castle,” a layer of compacted clay was laid directly at the foundation, creating a barrier against capillary moisture suction. In modern conditions, clay is sometimes used as a lower waterproofing layer in areas with low groundwater levels, on top of which a drainage cushion of crushed stone and sand is then poured.

Modern materials for the base include geotextiles and profiled drainage membranes. Geotextile (dornit) is a synthetic nonwoven material laid between layers of sand and crushed stone. It performs the function of a separation layer, preventing the mixing of materials and clogging of crushed stone with sand particles, thereby preserving drainage properties throughout the service life. Geotextile also distributes loads evenly. Profiled membranes made of high-density polyethylene (HDPE) are sheets with a studded surface. They are laid with the studs facing down, creating channels for water drainage even under significant loads. Such membranes can replace a crushed stone layer or work in tandem with it, significantly improving drainage efficiency. To strengthen weak base soils, soil-cement is sometimes used—a mixture of local soil with a small percentage of cement, which after compaction forms a hard layer. However, this method requires precise dosing and is used less frequently.

Thus, the choice of material for the blind area base is not a matter of preference but an engineering decision depending on hydrogeological conditions. On dry sandy soils, a simple sand cushion may suffice. On loams and clays prone to heaving, a powerful drainage layer of crushed stone wrapped in geotextile is required. Under conditions of high groundwater levels, the installation of a full-fledged wall drainage integrated with the blind area may be necessary. Understanding the properties of each material allows the designer or builder to form an optimal and economical structure that will serve for decades without loss of its functions.

Sand: Types, Properties, and Application Technology in Blind Areas

Sand is one of the fundamental materials in construction, and its role in constructing a blind area cannot be overestimated. It is used as a leveling, drainage, and cushioning layer. However, not all sand is suitable for these purposes. The key characteristics of sand that determine its suitability for a blind area are: fineness modulus (grain size), filtration coefficient (water permeability), presence of impurities (clay, silt, organic matter), and void content. By origin, sand is divided into river, quarry, marine, and quartz sand. For blind areas, river or washed quarry sand of medium and coarse fraction is most preferable. River sand, due to natural water processing, has rounded grains and minimal content of clay and silt particles. This ensures good water permeability and layer stability after compaction.

Quarry sand, extracted by open-pit mining, usually contains a significant amount of clay and silty particles. In its untreated form, it compacts heavily, poorly transmits water, and is susceptible to frost heave. Therefore, for responsible work, quarry sand must be washed or sieved. Washed quarry sand approaches river sand in its properties. Marine sand is also clean but may contain salts, limiting its use near metal structures due to corrosion risk. Quartz sand has a high cost and is rarely used in blind areas, mainly for decorative purposes or as part of dry construction mixtures for upper layers. The fineness modulus of sand for the blind area bedding layer should be at least 1.5-2.0 mm. Fine and silty sands (fineness modulus less than 1.0 mm) are not suitable for these purposes, as they have low water permeability and heave strongly when frozen.

The technology for using sand in a blind area is strictly regulated. After removing the vegetative layer and excavating soil to the required depth (which depends on the design thickness of all blind area layers, usually 30-50 cm), geotextile is laid on the bottom of the trench. This prevents clogging of the sand with soil particles. Then a layer of sand is poured. The layer thickness after compaction is usually 10-20 cm. Sand is poured in layers, each layer 5-10 cm thick is thoroughly watered and compacted with a vibrating plate or manual tamper. Watering is a critical stage, as it allows the sand to achieve maximum density by filling the voids and causing the sand grains to settle into the most stable position. Compacting dry sand is practically useless. After compaction, the sand layer should have a level surface with the specified slope away from the building wall.

Sand performs several functions in this layer. First, it creates a level and dense base for laying crushed stone or directly the finish coating. Second, thanks to good drainage properties, it allows water that has seeped through the joints of the finish coating (e.g., tiles) to pass into the lower drainage layers or into drainage pipes. Third, the sand layer acts as a damper, absorbing deformations from frost heave of the base soil and preventing these deformations from being transferred to the rigid finish coating. In the case of constructing a soft blind area (made of crushed stone, gravel, lawn), the sand cushion is the main load-bearing and leveling element. It is important to note that sand has virtually no tensile resistance, so it cannot work to strengthen slopes or resist sliding. Other materials or geosynthetics are used for this. Also, sand, being a bulk material, requires mandatory lateral confinement to prevent spreading. For this, curb stones, concrete curbs, or formwork are used, which are installed before sand backfilling and compaction.

Crushed Stone and Gravel: Comparative Analysis and Application Features

Crushed stone and gravel are the main stone materials used to create the drainage layer in a blind area structure. Despite external similarity, they have fundamental differences in origin, shape, and properties, which directly affect their behavior in structures. Crushed stone is obtained by mechanically crushing hard rocks (granite, limestone, dolomite) or recycling construction waste (concrete, brick). As a result of crushing, crushed stone grains have an irregular angular shape with a rough surface and many chips. This shape provides excellent mechanical interlocking between grains and with surrounding materials. A compacted crushed stone layer forms a rigid framework with high load-bearing capacity and good water permeability due to large voids between grains.

Gravel, on the other hand, has a natural origin. It is fragments of rocks formed as a result of natural weathering and processed by water in rivers, seas, or glaciers. Gravel grains have a rounded, smooth shape. This makes them less prone to mutual interlocking. A compacted gravel layer also has good water permeability, but its load-bearing capacity and resistance to horizontal shear are lower than those of crushed stone. Gravel compacts more easily to a denser state, leaving fewer voids. The choice between crushed stone and gravel for a blind area depends on specific tasks. If a powerful, stable drainage layer is required that will withstand loads from pedestrian traffic or possible parking of a passenger car, crushed stone is unquestionably preferable. Its angular grains create a strong framework. Gravel is more suitable for decorative soft blind areas, where aesthetics are important, or in conditions without significant loads, where the main task is drainage.

The most important characteristic of both materials is the fraction—grain size. The following fractions are used for blind areas:

• Coarse fraction (40-70 mm, 40-100 mm): used for the lower layer of the cushion on weak, water-saturated soils. Creates a powerful drainage layer that passes water well. Requires mandatory backfilling with finer fractions on top for leveling.

• Medium fraction (20-40 mm): the most universal and commonly used size. Provides a good combination of drainage capacity and load-bearing characteristics. Can be used as an independent layer or on top of coarse crushed stone.

• Fine fraction (5-20 mm, 3-10 mm): used to create an upper leveling layer for laying paving slabs or paving stones. Also used as a finish coating for soft blind areas.

The strength grade of crushed stone matters if increased loads are planned on the blind area. For ordinary conditions, grade M600-M800 is sufficient. Frost resistance should be at least F50, and in northern regions—F100 and above. Flakiness (content of flat and elongated grains) is a parameter especially important for crushed stone. A high content of flaky grains (Group V) worsens layer compactibility and reduces its strength. For blind areas, it is better to use crushed stone of cubical shape (Groups I or II). The installation technology for crushed stone and gravel is similar. The material is poured in layers 15-20 cm thick onto a prepared base (compacted sand or geotextile). Each layer is carefully leveled and compacted with a vibrating plate. Compaction is carried out until grain movement stops and a footprint from shoes appears. To improve drainage properties and prevent clogging, it is recommended to enclose the crushed stone/gravel layer in a geotextile “envelope”: the material is laid on geotextile and also covered with it before sand backfilling. This is especially important on clayey soils.

Comparative table of crushed stone and gravel for blind areas:

Geosynthetic Materials: Geotextiles and Drainage Membranes

Modern construction is unthinkable without the use of geosynthetic materials, which radically improve the reliability and durability of engineering structures, including blind areas. These materials perform functions of separation, reinforcement, drainage, and filtration, allowing to significantly reduce material consumption and improve base characteristics. The leading role among them in blind area construction is played by geotextile. Geotextile (dornit) is a roll material made from polypropylene or polyester fibers by needle-punching or thermal bonding. It has high tensile strength, resistance to chemical and biological influences, and does not rot. In a blind area structure, geotextile performs several key tasks.

The first and main function is separation. Geotextile is laid between the base soil and the sand cushion, as well as between layers of sand and crushed stone. It prevents intermixing of materials, which is especially critical on clayey soils. Without a separation layer, clay particles over time rise into the sand and crushed stone, clogging the drainage layer and depriving it of water permeability. Geotextile, however, freely passes water but retains solid particles. The second function is reinforcement. Due to high tensile strength, geotextile absorbs tensile forces and redistributes the load from overlying layers, preventing local subsidence into weak soil. This allows reducing the overall thickness of the cushion. The third function is protective. Geotextile protects waterproofing membranes (if used) from damage by sharp edges of crushed stone.

The technology for laying geotextile is simple but requires care. The sheets are rolled out with an overlap (15-20 cm) on the prepared and leveled trench bottom. The edges of the material are temporarily fixed. A layer of sand is poured onto it, which is then leveled and compacted. It is important that during work the geotextile is not damaged by sharp tools and is not subjected to significant tensile forces. In addition to classical nonwoven geotextile, woven geotextile (geofabric) is sometimes used for blind areas, which has even higher strength and elastic modulus, and is used mainly for reinforcement on particularly critical sections.

Profiled drainage membranes (geomembranes) represent another type of high-performance geosynthetics. These are sheets of high-density polyethylene (HDPE) with protrusions (studs) 8-20 mm high, covered on one or both sides with a layer of geotextile. When laid with the studs facing down, the membrane creates a continuous channel for water drainage even under soil pressure and loads. Water entering this layer easily flows down the slope into the drainage system. The geotextile attached to the studs performs a filtering function, preventing soil particles from clogging the drainage channels. The use of such a membrane in a blind area allows radically solving the problem of draining water away from the foundation and often replaces a thick layer of crushed stone, which is especially relevant with limited trench depth or the need to reduce load on the soil.

Drainage membrane installation is carried out on top of compacted soil or a thin layer of sand. The sheets are laid overlapping, and the joints are glued with special tape or sealed. The top of the membrane is backfilled with sand, which fills the space between the studs, creating a level base for the next layers. The combination of geotextile and drainage membrane creates an ideal system: geotextile separates layers and filters, and the membrane ensures guaranteed water drainage. The use of geosynthetics, although increasing initial costs, pays off many times over due to increased blind area service life, absence of frequent repairs, and prevention of much more costly foundation problems.

Insulation for Blind Areas: Necessity, Types, and Installation Technology

Insulating a blind area is not a whim but a crucial technological measure for buildings constructed in regions with seasonal or permanent soil freezing, especially on heaving bases (clays, loams). The main goal of insulation is to stabilize the temperature regime of the soil in the foundation zone, preventing it from freezing. When freezing, water contained in the soil turns into ice and increases in volume by approximately 9%. This creates powerful frost heave forces that unevenly affect the foundation base and side walls, leading to its deformations, tilting of the entire building, and cracks in walls. An insulated blind area expands the zone of non-freezing soil around the house, pushing the freezing boundary beyond the foundation and making its performance more predictable and safe.

Only a limited range of materials is used as insulation for blind areas, which must meet strict requirements: have almost zero water absorption (so as not to lose insulating properties when wet), high compressive strength (to withstand loads from overlying layers and possible pedestrian traffic), biological resistance, and durability. Extruded polystyrene foam (XPS) fully meets these requirements. This is a material with a closed-cell structure, having one of the lowest thermal conductivity coefficients among insulations (0.028-0.034 W/(m·K)), water absorption of no more than 0.2-0.4% by volume, and compressive strength from 200 to 700 kPa depending on the grade. For insulating blind areas, XPS boards with a density of 35-45 kg/m³ and compressive strength of at least 300 kPa (marking T or TK) are usually used.

Expanded polystyrene (EPS, white foam plastic) is poorly suited for insulating blind areas due to high water absorption (up to 4%) and low strength. When wet, it quickly loses its properties, and under load, it crushes. Expanded clay is a traditional bulk insulation also used for insulating blind areas, but its effectiveness is significantly lower. The thermal conductivity coefficient of expanded clay (0.1-0.18 W/(m·K)) is 3-6 times worse than that of XPS. To achieve a comparable effect, the expanded clay layer must be very thick (30-50 cm), which is not always possible or economically justified. Moreover, expanded clay is hygroscopic and requires very reliable waterproofing. Polyurethane foam (PUR) in the form of boards or spray has excellent characteristics, but its cost is high, and spraying requires special equipment, so it is used less frequently.

The technology for laying XPS insulation in a blind area is as follows. After constructing and thoroughly compacting the sand cushion, insulation boards are laid on it. Installation is carried out close to the plinth, starting from the building corner. The boards are laid in a single layer, but in regions with harsh climates, two layers with staggered joints may be required. Joints between boards are preferably glued with special tape or filled with mounting foam to prevent cold bridges. It is important that the surface under the boards is as level as possible, without differences and sharp protrusions that could compress and damage the material. A layer of geotextile is necessarily laid on top of the insulation as a protective-separating layer, and then a layer of crushed stone or sand for load distribution. If the finish coating is concrete, then polyethylene film is laid on top of the insulation for compensation of thermal expansions, followed by reinforcement mesh and concrete mix.

The width of the insulated blind area should be not less than the design depth of soil freezing in the given region, but in practice it is often limited to 0.8-1.2 meters due to economic considerations. The thickness of the insulation layer is calculated by thermal engineering calculation. For central Russia, a 50-100 mm thick XPS board is usually sufficient. Insulation of the blind area is especially critical for buildings with heated basement floors or basements, for shallow strip foundations, and foundations of the UShP (insulated Swedish slab) type. Properly executed blind area insulation in combination with plinth and foundation vertical waterproofing creates a reliable thermal circuit that protects structures from the destructive effects of frost, reduces building heat loss, and, consequently, heating costs.

Waterproofing Materials for Blind Areas

Although the main function of a blind area is water drainage, waterproofing materials may also be required in its structure. Their task is to create an additional barrier against capillary and surface moisture, especially in cases where the groundwater level is high or the house is located on a slope. Waterproofing in a blind area is not always used, but in a number of cases it becomes a necessary element that increases the reliability of the entire foundation protection system. Waterproofing materials for blind areas can be divided into several types: roll (adhesive), coating, penetrating, and membrane.

Roll waterproofing materials are traditionally used in construction. These include roofing felt, glass isol, hydroisol, modern polymer membranes on a bitumen base (e.g., Technoelast). They are laid on a prepared base (compacted sand or concrete preparation) with an overlap on the plinth to a height of 15-20 cm. The sheets are rolled out with an overlap of 10-15 cm, and the joints are coated with bitumen mastic or heated with a torch (for weldable materials). A protective screed of lean concrete or a layer of sand is installed over the waterproofing, after which the installation of the remaining blind area layers continues. The disadvantage of roll materials is the risk of damage when laying crushed stone and the relative difficulty of ensuring joint tightness. However, they provide a continuous, reliable barrier.

Coating waterproofing is represented by bituminous, bitumen-polymer, polyurethane, and cement-polymer mastics. They are typically applied to the vertical surface of the plinth and the horizontal surface of the blind area junction with a brush or trowel. Bituminous mastic is a classic, inexpensive option, but over time it can crack. Bitumen-polymer mastics (with latex, rubber additives) are more elastic and durable. Cement-polymer compositions (penetrating waterproofing) are applied to concrete surfaces and work by forming insoluble crystals in the concrete pores that block capillaries. This is a very effective but expensive method, usually used for waterproofing the foundation itself, not the blind area.

Profiled drainage membranes with geotextile, mentioned earlier, also perform a waterproofing-drainage function. They do not so much retain water as actively drain it away from the structure. In modern practice, this approach is increasingly used: instead of creating a barrier, water is intelligently diverted. Another modern material is bentonite mats. They consist of a layer of bentonite clay granules fixed between two layers of geotextile. Upon contact with water, bentonite swells, forming a dense gel that self-heals minor damage and creates an absolute waterproofing screen. The mats are laid overlapping, and the joints are simply sprinkled with granules. This is an expensive but very effective solution for complex hydrogeological conditions.

The choice of the necessity and type of waterproofing depends on specific conditions. If the house stands on well-draining sandy soil with low GWT, and the blind area is correctly constructed with a slope, additional waterproofing may not be required. If the soils are clayey, GWT is high, or the basement floor is residential, then the use of a waterproofing layer in the blind area structure (most often in combination with roll material on top of the cushion and coating on the plinth) will be a justified measure, insurance against extreme weather events. It is important to remember that waterproofing is always only part of a comprehensive system, which includes drainage, storm sewer, and properly designed roof overhangs.

Concrete and Lean Concrete for Base Preparation

Concrete, as a material for blind areas, is more often associated with the finish coating. However, it is also used for constructing the so-called “preparation” or “sub-base” — a leveling and strengthening layer under the main coating. This layer of lean concrete performs several important functions, especially when installing rigid blind areas made of monolithic concrete, asphalt, or paving slabs on cement-sand mortar. Lean concrete is concrete with a reduced cement content (usually B7.5-B10, strength class M100-M150) and an increased content of coarse aggregate (crushed stone). It has low strength compared to structural concrete but significantly exceeds a compacted sand cushion in stability and load-bearing capacity.

The main task of the lean concrete layer, 5-10 cm thick, is to create a rigid, level, and immobile base for laying the finish coating. This prevents local subsidence, especially under dynamic loads (walking, wheelbarrow movement). Moreover, concrete preparation serves as an additional waterproofing barrier, as concrete, even lean, has much lower water permeability than sand or crushed stone. This is important if it is necessary to completely exclude the penetration of surface moisture to the insulation or foundation. Also, it is convenient to lay roll waterproofing or insulation boards on a level concrete surface. The technology for constructing the preparation is simple: concrete mix is placed on a compacted layer of sand or crushed stone, leveled with a rule according to pre-set guide rails considering the slope, and compacted with a vibrating screed or manually. After setting (1-2 days), further work can proceed on this base.

For the blind area itself as a finish coating, structural concrete of classes B15-B22.5 (M200-M300) is used. Such a blind area is called rigid. It is very durable (if properly constructed), withstands significant loads, but has significant disadvantages: prone to cracking from thermal deformations, requires the installation of expansion joints, has not the most aesthetic appearance, and is difficult to repair. Concrete for the blind area must be frost-resistant (not lower than F100), with a low water-cement ratio to increase water resistance. Reinforcement with a mesh made of wire with a diameter of 4-5 mm and a cell of 100-150 mm is mandatory, which is placed in the upper third of the slab thickness. It is critically important to install expansion (temperature) joints every 1.5-2.5 meters, as well as a compensation joint along the building wall, which is filled with an elastic material (polyethylene foam, bitumen mastic).

Thus, concrete in the context of a blind area can act in two capacities: as a material for the preparatory layer (lean concrete) and as a material for the finish coating (structural concrete). Using lean concrete for preparation is a sign of a quality, capital approach to construction, which pays off on complex soils and with high durability requirements. However, it increases the cost and labor intensity of work. In many cases, especially for a private house on good soils, a carefully compacted sand-crushed stone cushion can suffice, which will also perfectly perform its functions if constructed correctly.

Criteria for Selecting Material for Blind Area Depending on Conditions

The choice of the optimal composition and structure of the blind area bedding layers cannot be template-based. It must be based on a comprehensive analysis of the specific conditions of the construction site. Several key factors can be identified that have a decisive influence on the decision-making. The first and most important factor is the type of base soil. On strong, non-heaving soils (coarse sand, gravelly deposits), the requirements for the cushion are minimal. A layer of compacted sand 10-15 cm thick for leveling and creating a slope is sufficient. On loams and clays, which are characterized by low water permeability and high heaving, a powerful drainage layer is necessary. The standard solution: geotextile, then a layer of crushed stone fraction 20-40 mm, 15-20 cm thick, geotextile again, and on top a layer of sand 10-15 cm. This will prevent clogging of the crushed stone and ensure rapid water drainage.

The second factor is the groundwater level (GWL). If the GWL is high (above the depth of the cushion laying), or the site is prone to flooding, the drainage function of the blind area becomes paramount. In this case, it is advisable to use a profiled drainage membrane laid with a slope towards a drainage well or ditch. The third factor is climatic conditions, namely the depth of soil freezing. In regions with deep freezing (more than 1.5 m), insulating the blind area becomes almost mandatory. In this case, insulation (XPS) is laid on top of the sand preparation, and waterproofing is spread under it if necessary. The width of the insulated blind area should be at least the depth of freezing. In southern regions without negative temperatures, insulation is not required.

The fourth factor is the type of finish coating. Under soft coatings (crushed stone, gravel, lawn grid), especially high-quality base preparation is required, since the coating itself is not rigid. The sand cushion here must be perfectly compacted, and the drainage layer must be as efficient as possible. Under paving slabs or paving stones laid on sand, a stable and level layer of sand or cement-sand mixture on top of a crushed stone base is needed. Under monolithic concrete or asphalt, preparation from lean concrete or very densely compacted fine-fraction crushed stone is desirable. The fifth factor is the expected loads. Will only walking occur on the blind area, or is passenger car access possible? For pedestrian zones, a standard structure is sufficient. For vehicular loads, the crushed stone layer needs to be increased, and possibly a geogrid for reinforcement should be used.

The sixth factor is budget and material availability. In some regions, crushed stone may be expensive or unavailable, then options using local gravel or even brick rubble (only for lower, non-critical layers) can be considered. However, saving on the quality of the cushion material can result in quick repairs and foundation problems. The seventh factor is the presence and condition of the building’s drainage system. If an effective drainage pipe in crushed stone backfill is already laid around the house’s perimeter, the blind area may perform more of a decorative and protective function against surface water, and the requirements for its drainage layers may be reduced. Thus, the choice of material for the blind area is always a balance between technical necessity, climatic challenges, architectural intent, and economic feasibility. A competent design that considers all nuances is the key to creating reliable and durable protection for the foundation—the basis of the entire house.