ISO 17738-3:2019

Overview

ISO 17738-3:2019 - Thermal insulation products - Exterior insulation and finish systems (EIFS) - Part 3: Design requirements establishes design requirements, material selection and application guidance for EIFS used as exterior wall cladding. It is intended for building designers, code officials, product manufacturers and contractors to help sustain installed performance and durability of EIFS assemblies. The document complements ISO 17738‑1 (materials) and ISO 17738‑2 (installation) and applies to new and retrofit EIFS installations. Note: it primarily addresses adhesively fastened systems (Annex A discusses mechanical fasteners) and does not replace regional codes or specify substrate structural design.

Key topics and technical requirements

• Planes-of-control: design is organized around five control layers - water-shedding, water-resistive, thermal, air and vapour barriers - each with distinct functions and required continuity across assemblies.
• Material compatibility: all EIFS components must comply with ISO 17738‑1 and be matched to the substrate and adjacent materials.
• Critical interfaces and terminations: drawings and specifications must detail continuity and flashings at key locations (foundations, window/door sills, heads and jambs, roof‑to‑wall interfaces, parapets, balconies, dissimilar cladding interfaces, penetrations, drainage joints, etc.).
• Drainage and WRBA performance: the water-resistive barrier assembly (WRBA) must provide a clear gravity drainage path, be continuous with adjacent claddings and windows, and incorporate flashings to direct water out of the drainage cavity. Liquid-applied WRBs that double as air barriers must meet air barrier continuity requirements.
• Thermal control: EIFS is intended as a continuous thermal barrier. Minimum insulation thickness is 50 mm, with a limited exception to 30 mm for aesthetic reveals tied to the drainage cavity geometry. Designers should limit thermal bridging (refer to ISO 14683 guidance).
• Slope and drainage of projections: EIFS mouldings and horizontal reveals require minimum positive slopes (typically 1:2) to shed water unless protected by flashing or overhangs.
• Substrate requirements: substrates must have adequate strength and rigidity to support the EIFS, wind and other loads; existing buildings require structural assessment before retrofit.

Applications and users

• Who uses it: architects, façade engineers, building envelope consultants, code officials, EIFS manufacturers, and installers.
• Practical uses: specifying EIFS assemblies in construction documents, developing interface details for windows/doors and adjacent claddings, ensuring WRBA and air/vapour control continuity, designing EIFS for retrofits, and coordinating EIFS requirements with energy and moisture control strategies.

Related standards

• ISO 17738‑1 - EIFS: Materials and systems
• ISO 17738‑2 - EIFS: Installation
• ISO 7345, ISO 9229 - related thermal and terminology references
• ISO 14683 - guidance on thermal bridging (referenced)

Keywords: ISO 17738-3, EIFS design requirements, exterior insulation and finish systems, water-resistive barrier, air barrier, thermal insulation products, EIFS installation, building envelope design.