Timber pergola maintenance

Pressure-treated timber resists rot. It still splits, twists and greys, and the post bases take the most punishment. Most of the work is a yearly check.

Read the guarantee first

Timber kit guarantees usually cover rot, under conditions. Forest Garden, for example, states a 15-year anti-rot guarantee on its Ultima pergolas. Guarantees often expect the product to be installed and maintained as instructed. Read the terms and keep the receipt.

Once a year, ideally late spring

• Post bases. Look and prod with a screwdriver where the post meets the ground or the spike. Soft timber there is the first sign of trouble.
• Fixings. Tighten bolts and screws. Timber shrinks and swells through the year.
• Splits. Fine surface checks in posts are normal. Splits that open right through, or run from a bolt hole, are not.
• Joints and rafters. Look for movement and water sitting on top surfaces.
• Plants. Climbers hold moisture and add weight and wind load. Cut back growth that wraps round fixings or pushes joints apart.

Treatment

Use a product meant for exterior timber and follow its instructions on drying times and coats. Some makers say new pressure-treated timber should weather before it is painted or stained. Check the kit maker's advice first, so you do not void a guarantee.

Keep water away from the posts

• Keep soil, bark and gravel from piling against post bases.
• Post spikes or bolt-down shoes keep the end grain off the ground, if the maker allows them.
• Fill around in-ground posts so water runs away from the timber, not into a hole round it.

When should I replace a timber post?

When the base is soft or the post moves at ground level. A post that has rotted at the base can fail without warning in wind. Replace it, or get someone who knows timber structures to look at it.

Can I add a roof to a timber pergola?

Only if the maker offers one for that frame. A roof adds weight and a lot more wind load than an open frame was designed for.