Timber Structure Inspection

In accordance with EN 14081, structural timber must be strength graded (visually or mechanically) and CE marked. Common classes: C16, C24, C30 for softwood. Glued laminated timber per EN 14080 (GL24h, GL28h, GL32h). Moisture content at installation must be <= 20% for most applications, per EN 1995-1-1 Service Classes 1 and 2. DTU 31.1 and DTU 31.2 specify execution requirements for timber framework and timber-frame construction.

1. Check that timber bears CE marking and strength class stamp (e.g. C24)

2. Verify that the class matches project specifications

3. Measure moisture content with pin-type meter — must be <= 20% (Service Class 1: <= 12%)

4. For glulam, check class marking and inspect for delamination

5. Inspect for defects exceeding class limits — knots, splits, wane, bow

- Ungraded timber used for structural purposes

- Moisture content too high at installation — causes shrinkage and cracking

- Glulam delamination due to manufacturing defect or moisture exposure

- Timber class lower than required by design

In accordance with EN 1995-1-1 Section 8, timber connections must be designed for the specific fastener type (nails, screws, bolts, dowels or proprietary connectors). Minimum edge, end and fastener spacings per EN 1995-1-1 Tables 8.2-8.6. Metal connectors must be corrosion resistant for the service environment. DTU 31.1 and DTU 31.2 supplement these provisions.

1. Verify that the connection type and fastener dimensions match the design

2. Check that minimum edge and end distances are respected

3. Verify bolt tightness and washer sizes at bolted connections

4. Inspect metal connectors (joist hangers, angle brackets) — correct size and fixings

5. Ensure connections allow for timber movement (shrinkage/swelling)

- Nails or screws too close to edges causing splitting

- Bolted connections over-tightened crushing the timber

- Joist hangers missing or incorrectly sized

- Connections not allowing for moisture-related timber movement

In accordance with EN 1995-1-1 Section 2.3.1.3 and EN 335, timber durability depends on the Use Class (UC1-UC5) and the natural durability of the species per EN 350. Preservative treatment per EN 351 is required when natural durability is insufficient. Structural timber in ground contact (UC4) or in water (UC5) requires treatment or a naturally durable species (e.g. oak heartwood). NF B 50-105-3 specifies use classes in France.

1. Verify that the Use Class assigned to each timber element matches its exposure

2. Check that the timber species is suitable for the Use Class or has been treated

3. Verify preservative treatment certificates where applicable

4. Inspect for signs of decay, wood-boring insect attack or fungal growth

5. Ensure detailing avoids moisture traps (good drainage, ventilation)

- Untreated timber used in high-moisture locations (UC3, UC4)

- Timber in ground contact without treatment or barrier

- Poor detailing trapping moisture — end grain exposed to weather

- Fungal decay in concealed locations (behind cladding, in roof spaces)