Foundation Slab for House by Yourself

For example, install a correctly built foundation slab around the house.

A foundation slab is a waterproof strip running along the building's external perimeter, encircling it. Its purpose is to protect the foundation from rain and floodwater. When properly built, it reduces pressure on the underground waterproofing layer, thereby increasing the overall lifespan of the structure. The most popular types of foundation slabs are:

• concrete,
• concrete and cobblestone,
• flexible (soft) foundation slab.

Materials Needed for Foundation Slab Construction

Required materials for a foundation slab include:

• sand,
• gravel, brick debris, or crushed stone,
• asphalt,
• concrete,
• cobblestones, and others.

Additional materials used are:

• insulation,
• geotextile,
• hydro-technical insulation (e.g., bitumen membrane),
• boards,
• expansion joint tape.

Proper Width Selection for the Foundation Slab

According to standards, the slab width must exceed the eaves overhang of the roof by at least 20 cm. Along the entire perimeter, drainage ditches are dug for water runoff, though special gutters may be used instead. If a lawn is planned, these ditches look better near it. Additionally, collected water flows into a stormwater pit.

Preparation for Foundation Slab Installation

Before installing the slab, choose the material and method. All foundation protection systems consist of two main layers. The first is the base layer, made of materials such as gravel, sand, crushed stone, or expanded clay. These are layered into a shallow trench dug around the house, with a slight slope (about 5°) away from the foundation.

The second main layer is the chosen surface material, whose composition and installation order depend on the selected type. Concrete is currently the most widely used.

The bottom layer is a sand cushion, thoroughly compacted by watering and tamping. Then gravel is added and a concrete mix is poured. Note that reinforcement bars must be used.

Guidelines for Building a Concrete Foundation Slab

To prevent cracks, the slab should not be attached directly to house walls. Instead, treated wooden boards are placed on edge every 2 meters to create expansion (thermal) joints.

Freshly poured concrete requires troweling: sprinkling dry cement and tamping with a trowel. This creates a strong, waterproof surface. Cover the slab with a damp sack, re-wet periodically for 2 days. Seal the joint between the slab and the foundation with sealant or bitumen.

Special Features of Slab Construction

If concrete slabs are used, the process simplifies: after laying, fill joints with liquid bitumen. If the house has a basement, cellar, or root cellar, the slab should be insulated with foam glass, polystyrene, or another thermal insulator.

The structure made of reinforced concrete slabs and insulation must be placed so that a 10 cm air gap remains beneath. The base is compacted crushed stone, impregnated with bitumen.

Thus, a correctly built concrete foundation slab consists of the following layers (from top to bottom):

• reinforced concrete with thermal joints,
• gravel base,
• sand base.

Building a Concrete-Cobblestone Foundation Slab

If you wish to decorate the slab with cobblestones, first cover the trench bottom with compacted clay, then add gravel, followed by a 50 cm layer of sand. Cobblestones are pressed into the sand base.

Flexible (Soft) Foundation Slab Solutions

In recent years, a soft-form alternative to concrete-cobblestone slabs has become popular. Begin by removing topsoil around the building, ensuring a slight slope away from the house. Then line the trench with a roll waterproof membrane, overlapping onto the foundation. Return part of the excavated soil to its original position. Fill the remaining space with gravel or pebbles, level the surface without slope.

This design offers not only ease of installation but also an added advantage: water is drained across the entire width of the membrane extending from the foundation. If used as a garden path, the slab must be reinforced, or it may erode and settle under water pressure.

Final Steps in Soft-Form Slab Construction

To reinforce the membrane, after placing it in the trench, lay a 5 cm layer of coarse sand, then overlap geotextile by 10 cm, followed by a 10 cm layer of gravel. Then lay another layer of geotextile and a final 10 cm layer of pebbles (crushed stone).

A walkway forms around the building, which can be enhanced. For example, replace pebbles with sand, then lay decorative paving. Pavers are pressed into the top layer using a rubber mallet, and gaps are filled with fine dry sand.