Pressure-Treated vs Dip-Treated Timber, and How to Look After a Shed

By Craig Davison, Director, Lichfield Garden Buildings · 14 years selling garden buildings and involved in more than 1,000 sales

When two sheds of the same size are very different prices, the timber treatment is often the reason. It changes how long the shed lasts, how long the guarantee is and how much work you'll do each year. Here's the plain-English version.

Dip-treated timber

The timber is dipped in a preservative at the factory. It gives the shed its colour and some protection, but the treatment sits near the surface.

• Pros: lower price, wide choice of sizes, ready to go.
• Cons: needs re-treating every year, and guarantees often depend on it.

For example, Power Sheds sheds are factory dip-treated with a preserver and wax additive. Their 10-year guarantee against rot, decay and insect attack requires the timber to be re-treated inside and out every year, and the shed to stand on a firm, level base.

Pressure-treated (tanalised) timber

The timber goes into a sealed tank, and preservative is forced deep into the wood under pressure. "Tanalised" is a common name for the same thing.

• Pros: long-lasting protection against rot and insects, less upkeep, usually a longer guarantee.
• Cons: costs more, and the surface still weathers and greys without a finish.

For example, Suresheds buildings use fully pressure-treated Scandinavian redwood, with an anti-rot guarantee of 10 years on 12mm cladding and 15 years on 16mm and 20mm. Some other ranges offer a tanalised option on the product page.

Side by side

Other finishes you'll see

• Untreated. Many log cabins arrive untreated, or with only the floor bearers treated. Treat them inside and out as soon as they're built.
• Basic factory treatment. Some ranges have a light treatment that must be topped up soon after installation. On Shedlands buildings, for example, the standard treatment needs re-coating within 3 months, unless you choose the painted finish.
• Factory painted. Some ranges offer a painted finish, applied before the building leaves the workshop. You'll only need to touch it up when it starts to crack or flake.

Always read the care and guarantee notes on the product page, because each maker's rules are different.

Which treatment to use

We sell the Protek range of British-made wood treatments. As a rough guide:

• Protek Wood Preserver ++ is a water-based preservative that protects against rot, mould and wood-boring insects and also works as a primer for a top coat. It covers around 6 to 8 square metres per litre.
• Protek Shed & Fence is a wax-enriched stain in 14 colours for sheds and large garden buildings. It covers around 10 to 12 square metres per litre, and more coats give deeper colour and more weather protection.
• For a longer-lasting coloured finish, look at Protek Wood Stain & Protect or Protek Royal Exterior.

On a bare or untreated building, a common approach is a preservative first, then a coloured top coat. Some preservatives contain insecticides that harm cats, bees and pond life, so always read the label.

How much will I need?

Work out the area of each wall (length x height), add them together, and double it if you're doing two coats. As a rough example, an 8ft x 6ft shed with walls about 2m high has around 17 square metres of outside wall. At 10 to 12 square metres per litre, that's roughly 1.5 to 2 litres per coat, before the gables and doors.

A simple care plan for a timber shed

When it's built

• Treat the timber, including the bottom edges of the cladding and the underside of the floor if you can reach them.
• Make sure it sits on a firm, level base with air moving underneath. See what base do I need for a shed?

Every spring or summer

• Re-treat dip-treated sheds. Check pressure-treated sheds and refresh the finish when rain soaks in instead of beading.
• Choose a dry, mild spell with a few dry hours after you finish.

Every autumn

• Check the roof felt for tears and lifted edges, and clear gutters.
• Pull soil, leaves and plants away from the walls. A gravel strip stops rain splashing back.
• Oil hinges and locks.

All year

• Ventilate on dry days so moisture doesn't build up inside.
• Leave a gap between stored items and the walls.
• Don't store wet cushions or tools without drying them first.

Our timber garden building care guide covers roofs, condensation and winter jobs in more detail. If you'd rather avoid treating altogether, see metal vs wooden vs concrete sheds.

Ready to choose? Browse our garden sheds, or read what size shed do I need?

FAQs

Is pressure-treated timber better than dip-treated?

For long-term protection, yes. Pressure treatment forces preservative deep into the timber, so it resists rot for longer and needs less upkeep. Dip treatment only protects the surface, so it needs re-treating every year, but it keeps the price down.

How often should I treat a dip-treated shed?

Every year, inside and out if the maker asks for it. Some guarantees depend on it, so keep a note of when you treat it.

Does a pressure-treated shed need treating?

It needs less, but not nothing. Pressure treatment protects against rot, but sun and rain still weather the surface, so a stain or finish every few years keeps it looking good and adds water protection.

What is the best time of year to treat a shed?

A dry, mild spell, usually late spring to early autumn. The timber needs to be dry, with a few dry hours after you finish. Check the tin for the right temperature.

Is shed treatment safe for pets?

Some preservatives contain insecticides that are harmful to cats, bees and pond life. Read the label, keep pets away while you work and while it dries, and don't use them near beehives or ponds.