Overview
ISO 7728:1985 defines properties, characteristics and classification criteria for typical horizontal joints between an external wall made of prefabricated ordinary concrete components and a concrete floor. The standard addresses functional performance (thermal transmission, air permeability, sound insulation, condensation risk, durability and appearance) and gives a practical example solution for watertightness where standardized test methods were not yet available. It applies to public and private buildings (dwellings, offices, schools, hospitals) and can be extended to some industrial buildings with modified property requirements.
Keywords: ISO 7728, horizontal joints, prefabricated concrete, watertightness, air permeability, thermal transmission, joint classification
Key topics and technical requirements
- Purpose: specify characteristics of horizontal joints affecting building physics and functional performance (thermal, acoustic, airtightness, water/snow tightness, condensation and appearance).
- Watertightness: no formal test method in the standard; an example joint detail is proposed based on laboratory and field experience.
- Overlap: outer lip must overlap inner lip; minimum overlap height h = 50 mm.
- Capillary break: gap between lips (width g) must be > 5 mm and surfaces bounding it must form an angle α with vertical between 0° and 20° to provide drainage.
- Airtightness: jointing material placed in the upper part; air permeability shall not exceed 0.2 m³/h/m at 1 Pa (measured per ISO 6589).
- Slope at foot of inner lip: upper surface of lower component should slope outwards to drain moisture.
- Performance considerations also include prevention of condensation, control of sound transmission (measured per ISO 140/4 and ISO 717/1), emission of odours/toxic fumes in fire, and maintenance/replacement of degradable jointing materials.
- Classification criteria cover the wall’s structural role (loadbearing, self-supporting, supported, bracing), floor thickness and joint position relative to reference planes.
Applications and who uses it
- Intended for building designers, façade and structural engineers, architects, precast concrete manufacturers, contractors and building inspectors concerned with:
- Designing and detailing horizontal wall-to-floor joints for prefabricated concrete systems
- Ensuring airtightness, drainage and basic watertight detailing in façades and floor junctions
- Specifying maintenance and replacement regimes for joint materials
- Classifying joint types for modular coordination and production tolerancing
Related standards
- ISO 2444 - Joints in building: Vocabulary
- ISO 2445 - Fundamental principles for design
- ISO 6589 - Method of test for air-permeability of joints
- ISO 140/4 and ISO 717/1 - Sound insulation measurement and rating
- ISO 6511, ISO 7729 and others referenced for modular coordination, vertical joints and related tests
This concise reference helps professionals apply ISO 7728 requirements when detailing horizontal joints in prefabricated concrete construction to manage thermal performance, airtightness and moisture control.