Timber Structure Inspection

According to EN 14081, structural timber must be strength graded (visual or machine) and bear CE marking. Common classes: C16, C24, C30 for softwood. Glued laminated timber according to EN 14080 (GL24h, GL28h, GL32h). Moisture content at installation should be <=20% for most applications according to NP EN 1995-1-1 Service Class 1 and 2.

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

2. Confirm that the class matches the design specification

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

4. For glued laminated timber, check the class marking and inspect for delamination

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

- Ungraded timber used for structural purposes

- Moisture content too high at installation — leads to shrinkage and cracking

- Delamination of glued laminated timber due to manufacturing defect or moisture exposure

- Timber strength class lower than the design requirement

According to NP EN 1995-1-1 Section 8, timber connections must be designed for the specific fastener type (nails, screws, bolts, dowels or proprietary connectors). Minimum spacings, edge and end distances according to NP EN 1995-1-1 Tables 8.2–8.6. Metal connectors must be corrosion resistant for the service environment.

1. Check that the connection type and fastener size match the design

2. Confirm that minimum edge and end distances are respected

3. Check bolt tightening and washer dimensions in bolted connections

4. Inspect metal connection plates (joist hangers, angle brackets) — correct size and fixing

5. Confirm that 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 that do not allow for hygroscopic timber movement

According to NP 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 according to EN 350. Preservative treatment according to EN 351 when natural durability is insufficient. Structural timber in contact with the ground (UC4) or water (UC5) requires treatment or a naturally durable species (e.g. oak heartwood). In Portugal, special attention must be paid to the risk of termites, particularly in older urban areas.

1. Check that the Use Class assigned to each timber element corresponds to its exposure

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

3. Check preservative treatment certificates when required

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

5. Confirm that construction details avoid moisture accumulation (good drainage, ventilation)

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

- Timber in contact with the ground without treatment or barrier

- Poor detailing that traps moisture — end grain exposed to weather

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