Question 1

1. What is CLS timber?

Accepted Answer

CLS timber stands for Canadian Lumber Standard timber. It‘s a type of softwood timber that’s been specifically prepared for construction purposes, particularly framing in housebuilding. CLS timber is planed and usually kiln-dried, with eased edges. It’s commonly used for stud walls, partitions, and general framing.

Question 2

2. Is CLS timber treated?

Accepted Answer

CLS wood is typically kiln‑dried before being pressure‑treated with preservatives (e.g. copper‑azole or similar). Treatment penetrates deeply, giving resistance to moisture, rot and insects. Treated CLS timber is graded by Use Class: UC2 for internal use, UC3 for above‑ground external, and UC4 for ground‑contact or wet conditions. Product specs should list use class to confirm suitability.

Question 3

3. Can you use CLS timber outside?

Accepted Answer

CLS treated timber is suitable for external use when kept above ground or in sheltered situations. It resists rot, decay and insects when properly preservative‑treated (e.g. Use Class 3 or UC3 levels). Untreated CLS timber should not be used outdoors. For ground‑contact or highly exposed areas, choose UC4 timber rated for contact with soil or fresh water.

Question 4

4. Can I use CLS timber for decking?

Accepted Answer

While CLS timber can form the structural frame beneath a deck, this is only advisable if it is correctly pressure‑treated (UC3 or UC4). Standard untreated CLS timber will deteriorate rapidly outdoors. Use decking‑grade, ground‑contact‑rated timber for joists and sub‑frame for long term performance.

Question 5

5. Is CLS timber the same as studwork timber?

Accepted Answer

Most of the time, yes. Studwork timber (also known as stud timber) refers to timber used for building internal partitions and structural wall frames. In the UK, CLS timber is commonly sold and used as stud timber because it matches the tolerance class, smooth finish, and strength grading needed for stud wall construction.

So CLS timber is a type of studwork timber. It's also the most commonly used type in modern construction. While not every stud wall timber product is CLS, all commonly stocked CLS timber is intended for studwork use.

CLS timber

CLS Timber FSC 38 x 63 x 2400mm

CLS Timber PEFC 38 x 89 x 2400mm

Bsw Home Grown C16 Cls 50 x 100mm x 3.0m

38mm x 89mm CLS Studwork Timber C16 (4" x 2") 2.4m

50x100 Homegrown CLS 2.4m

50x100 Homegrown CLS 4.8m

CLS Timber FSC 38 x 63 x 3000mm

CLS Timber PEFC 38 x 89 x 3000mm

Bsw Home Grown C16 Cls 50 x 75mm x 3.0m

50mm x 100mm x 2.4m CLS C16 Home Grown

38mm x 89mm CLS Studwork Timber C16 (4" x 2") 4.8m

50x75 C16 Kiln Dried CLS 4.8m

Homegrown CLS UC3 Green 100 x 50mm (89 x 38) 4.8m C16 FSC

50mm x 75mm x 2.4m CLS C16 BSW Home Grown