Timber Structure Inspection

According to EN 14081-1 (strength-graded solid timber), EN 14080 (glued laminated timber), EN 1995-1-1 and NTC 2018 (Chapter 4.4 and Chapter 11.7), structural timber must be strength graded and bear the CE marking. The moisture content must be compatible with the intended service conditions (service classes 1, 2, 3 according to EN 1995-1-1).

1. Check the CE marking of structural timber elements and the Declaration of Performance (DoP).

2. Verify the strength class (e.g. C24, GL24h) and compliance with the design specifications.

3. Measure the moisture content with a resistance moisture meter, verifying it is compatible with the service class (typically < 20% for classes 1 and 2).

4. For glued laminated timber, check the manufacturer's certificate (factory production control system - FPC).

5. Check the visual quality of the timber: absence of excessive defects (knots, splits, grain deviation) not permitted by the grading class.

6. Verify compliance with the requirements of NTC 2018 Chapter 11.7 for wood-based materials.

- Structural timber lacking CE marking or strength grading.

- Excessive moisture content at the time of installation.

- Strength class lower than that required by the design.

- Visual defects (splits, knots) exceeding the limits of the declared class.

- Incomplete or missing manufacturer documentation.

According to EN 1995-1-1 (Section 8) and NTC 2018 (Chapter 4.4), connections in timber structures must be made with fasteners conforming to product standards (EN 14592 for nails and screws, EN 14545 for connectors, EN 1912 for bolts). Minimum edge and spacing distances must comply with Eurocode 5 requirements.

1. Check the type, diameter and length of fasteners against the construction drawings.

2. Verify edge distances, end distances and spacings between connectors according to EN 1995-1-1 Tables 8.2–8.5.

3. Check bolt tightening with a torque wrench and the presence of adequately sized washers.

4. For metal plates, check thickness, dimensions and corrosion protection.

5. Check for the absence of splitting in the timber near connections.

6. For glued connections, verify the adhesive type (conforming to EN 301 or EN 15425) and bonding conditions.

- Insufficient edge distances causing timber splitting.

- Bolts not tightened or lacking washers with adequate bearing area.

- Metal plates not protected against corrosion in humid environments.

- Pre-drilling not performed when required to prevent splitting.

- Connections not conforming to design details in type or number of fasteners.

According to EN 1995-1-1 (Section 2.3) and NTC 2018 (Chapter 4.4), the durability of timber structures must be ensured by selecting species with adequate natural durability (EN 350) or by applying preservative treatments (EN 351). The use class (EN 335) determines the risk of biological attack and the required level of protection.

1. Verify the use class (EN 335) assigned in the design based on exposure conditions.

2. Check that the timber species used has adequate natural durability according to EN 350 for the intended use class.

3. If preservative treatment is specified, verify the treatment certificate, product type and penetration/retention according to EN 351.

4. Check construction details that promote durability: water drainage, ventilation, separation from the ground.

5. Inspect surface protection (impregnation, painting) and its compliance with specifications.

6. Check the protection of element end grains, which are particularly vulnerable to moisture absorption.

- Timber species with insufficient natural durability for the use class.

- Preservative treatment not conforming in penetration or retention.

- Construction details that promote water ponding (missing drip edges, insufficient slopes).

- Timber elements in direct contact with the ground or masonry without an impermeable barrier.

- Surface protection missing or deteriorated on exposed parts.