Abstract <p>Due to modification, there is a significant improvement in the mechanical and operational properties of wood, which significantly increases the scope of application of this structural material in construction. The paper presents a method for increasing the fire resistance of solid wood by its thermochemical modification with a water-based fire retardant, consisting of oxyethylidene diphosphonic acid and monoethanolamine. The advantages of the proposed method are the simplicity of its implementation under production conditions and the achievement of complete impregnation of solid wood. In turn, the proposed protective composition is environmentally friendly and belongs to the foam-forming type of fire retardants, the principle of which consists in the splitting off of gaseous substances with the subsequent formation of a fire-protective layer that prevents the effects of open fire and thermal radiation on the upper layers of wood, while maintaining its strength characteristics. Gluing fire-retarded wood with phenol–formaldehyde resin of the cold-curing brand SFZh-093 ensures the formation of strong adhesive joints, leads to an increase in mechanical properties of the material, as well as its resistance to water and other aggressive environments. The triethanolamine (tris(2-hydroxyethyl)amine) salt can be adsorbed on the surface of the resin, creating a protective layer that reduces the penetration of moisture and other substances into the material, thereby increasing the durability and stability of the adhesive compounds.</p>