Why Use Pressure-Treated Timber for Outdoor Builds

Autumn is the perfect season to start thinking about how your outdoor timber structures will cope with the coming wet, windy and cold months. If you’re planning a fence, deck, shed base, pergola, or anything exposed to the elements, pressure-treated timber should be high on your list. In this post we’ll explain what pressure-treated timber is, when it makes sense to use it, the benefits (and trade-offs), plus examples of what Ryedale Timber offers and other good options.

What Is Pressure-Treated Timber?

Pressure-treated (or “tanalised”) timber has preservatives forced into its fibres under high pressure. This process gives timber enhanced:

• Resistance to rot, fungal decay & wood-boring insects
• Durability when in contact with soil or moisture
• Longer useful lifespan outdoors

5×2 C24 Tanalised Timber (4.8 m)

C24 grade, treated / tanalised
£9.50 – £14.50

Best Used For:
Joists, bearers, outdoor frames that need structural strength and weather resistance.

When Should You Choose Pressure-Treated Timber?

Use pressure-treated timber in these situations:

• Ground contact — e.g. fence posts, sleepers, pergola uprights, where timber meets soil.
• Regular exposure to moisture — decking bottoms, fence-board bottoms, gates, shed bases.
• Structural outdoor builds — rafters, joists, bearers that support weight and will face weather.
• Where maintenance will be minimal — less painting, fewer inspections or treatments.
• Harsh local weather (North Yorkshire & East Yorkshire) — wet autumns, frosts, damp shadowed spots under trees etc.

If the timber will remain dry, sheltered, indoors, or under a big overhang, untreated timber might sometimes be adequate — but often treatment gives safety net.

6X2 C24 Tanalised Eased Edges

C24, treated, eased edges
£11.50-£16.00

Best Used For:
Deck frames, steps, external load-bearing work where edges matter (less splintering).

Benefits vs Things to Watch Out For

Benefits:

• Much longer lifespan outdoors, especially in damp conditions
• Better resistance to rot, fungal attack, insect attack
• Safer for structural and ground contact applications
• Often more cost-effective over the lifespan of the build (less replacement / repair)

Things to consider:

• Cost is higher than untreated timber
• Appearance: treated wood often has a greenish hue, or may look different; may need painting or staining
• Chemicals: though modern treatments are much safer than older ones, you should use treated wood properly (e.g. don’t burn it, don’t use for food contact without safe coatings)
• Maintenance still matters: even treated timber benefits from sealants, good design (avoid damp traps), regular checks

4×2 C24 Tanalised Timber

Standard thick section, treated
£8.50-£10.95

Best Used For:
Structural frameworks, fence rails, gates

Best Practices for Using Pressure-Treated Timber

To make sure your build lasts, follow these guidelines:

1. Check the treatment class — is it intended for ground contact, above ground, or both? Select appropriately.
2. Choose the right strength grade – (C16, C24) depending on load and structural need.
3. Protect cut ends — apply preservative or end grain sealant wherever you saw or notch timber.
4. Ensure drainage & ventilation — elevate timber where possible; avoid sitting in water; allow airflow under decks and between boards to avoid build-up of moisture.
5. Finish and maintain the surface — even treated wood benefits from a stain, oil or sealant to keep appearance and reduce surface degradation.
6. Avoid direct soil contact unless certified — for long durability, use posts with post-anchors, concrete footings, or suitable sleepers.

If you’re building or repairing anything outdoors—decks, fences, pergolas, roofs—pressure-treated timber from Ryedale Timber is a smart investment. The up-front cost is higher, but the protection, durability, and reduced maintenance make it worth it long term. With Ryedale’s stock of C16 & C24 tanalised timber, planks, posts and boards, you can build with confidence knowing your timber is fit for the autumn and winter ahead.

6×1 Tanalised Fence Boards

Strong and sturdy
£1.95 – £2.70

Best Used For:
Durable, weather resistant garden fences and screens.