How to Install a Garden Shed: Choosing a Base and Weatherproofing

A garden shed installed properly on a good base in a suitable location will give 20–30 years of useful service with minimal maintenance. One installed hurriedly on an inadequate base will develop rot, warping and door problems within 3–5 years. This guide covers everything from choosing the right location to weatherproofing the finished structure.

Planning: Size, Location and Regulations

Most garden sheds fall within Permitted Development Rights and don't require planning permission, subject to conditions:

• No more than 50% of garden area covered by outbuildings
• Maximum eaves height of 2.5m, maximum overall height of 4m (or 3m if within 2m of a boundary)
• Not in front of the house (forward of the principal elevation)
• Not in a Conservation Area, AONB or National Park without prior consent

Choose a location that is level (or can be levelled), has reasonable drainage, avoids overhanging trees (which drop debris onto felt and accelerate deterioration), and receives some sunlight on the southern face to help dry moisture from the timber.

Base Options

Concrete Slab

The most durable option. Lay as described in the separate article on concrete shed bases. A DPM under the slab prevents rising damp. The shed's floor bearers sit directly on the concrete — leave a small air gap around the edges for ventilation.

Paving Slab Base

A popular alternative — faster to lay and reversible. Lay on a well-compacted and levelled sub-base of MOT Type 1 hardcore (100mm depth). Position slabs carefully — they must be level with each other to within 3mm to prevent the shed frame racking. Butt slabs tightly together to minimise gaps that weeds can exploit. No pointing required for a shed base.

Timber Bearers on Gravel

Pressure-treated 100 × 100mm or 150 × 50mm timber bearers laid on a 50–75mm gravel bed provide good drainage and ventilation. The gravel drains water quickly and the treated timber resists rot. This is a quick solution but provides less long-term stability than concrete or slabs.

Erecting the Shed

Most purchased sheds come with panel-based assembly. Work through the manufacturer's instructions carefully, but the general sequence is: floor → two end panels → two side panels → roof panels → roofing felt → door and window fittings. Have at least two people for panel erection — timber shed panels can be 40–60kg each.

Before fixing any panels to the base, check the floor is square using the 3-4-5 triangle method (3m on one wall, 4m on the other, 5m diagonally = 90° corner). A square floor prevents door and window problems.

Weatherproofing

Roofing Felt

Most sheds come with mineral felt (also called bitumen felt). This typically has a 5–10 year lifespan, after which it cracks, lifts at the edges, and allows water in. Start from the bottom course and work upward with each course overlapping the previous by at least 50mm. Fix with clout nails and felt adhesive at overlaps. The top ridge felt should turn down onto each slope by at least 150mm.

For longer life, specify 3-layer felt (mineral surface reinforced felt) from a roofing supplier. Alternatively, fit EcoBase rubber roofing (EPDM) — a single-piece membrane that lasts 40+ years, costs £100–200 for a standard shed roof, and can be laid without specialist tools.

Preservative Treatment

Untreated timber sheds must be treated with exterior timber preservative (Ronseal Total Shed and Fence Treatment, Cuprinol 5 Star Complete Wood Treatment) on all external surfaces — including the base boards. Apply with a brush or garden sprayer. Many pre-treated sheds still benefit from an initial treatment on end-grain and cut sections, and annual retreatment.

Sealing Gaps

Panel joints and the junction between the floor and wall panels are entry points for wind-driven rain. Seal from the inside with exterior caulk or expanding foam. Check the door fit — gaps around the door are a significant source of draught and water ingress; fit a rubber threshold draught excluder and check the door latch alignment.

Ventilation

A shed without ventilation develops condensation — everything inside gets damp. Fit ventilation panels or fixed louver vents in the gable ends (high position) to allow airflow above stored items. Don't seal the shed completely — managed ventilation is far better than a sealed, damp interior.

Costs

• Pressure-treated timber shed (6 × 8ft): £400–900 delivered
• Concrete base materials (as separate guide): £120–200
• Paving slab base: £100–180
• EPDM roof membrane upgrade: £100–200
• Professional erection service: £200–400 on top of shed cost