All buildings benefit from foundations – the better the foundations, the sturdier the building will be. Even though a shed can be comparatively light in weight, proper foundations will ensure that it stays level. An exception is a small plastic tool store which could be placed on soil or grass.
The best foundations are a specially laid concrete float, or paving stones on a base of hardcore and mortar of around 75/100mm. My own shed is on a professionally laid flag base with the shed supported by 100mm x 50mm lengths of rough sawn timber placed edge down and running the length of the shed.
The shed’s cross bearers are then placed on these supports. All supporting timber needs to be treated with preservative, but an alternative is to buy tanalised timber. Remember that any cut edges need to be treated. Otherwise 2 or 3 coats of high quality preservative should suffice. It is not worth using cheap water based fence paint as a preservative – Cuprinol is widely available and is of good quality. A solvent based preservative is better, as it is generally absorbed further into the timber, but is less environmentally friendly than water based preservatives.
Placing the shed base on longitudinal timbers ensures an element of air circulation under the shed which should assist residual water lying on the concrete or paving base to dry out. Metal and plastic supports are also available.
Not having a proper base may ultimately shorten the useful life of the shed, causing out of alignment ends and/or sides that may cause the door to jam. It is even more important to have a solid base for a greenhouse as even a slight twisting of the building may cause glass panes to crack.
