A shed that is insulated stays warmer in winter and cooler in summer, making it genuinely usable as a workspace, home office, or gym rather than just a storage space. The limited wall and roof depths of typical shed construction mean rigid foam insulation boards are the most practical choice, providing the best thermal performance per unit thickness.

Choosing the Insulation Material

Rigid PIR or polyurethane foam boards provide the highest thermal performance per millimetre of thickness and are the best choice for shed walls and roofs where depth is limited. A 50mm PIR board achieves a similar thermal resistance to 100mm of mineral wool, making it practical even in shallow wall depths. Mineral wool batts are also suitable where there is enough depth, and are easier to cut to fit around complex shapes. Expanded polystyrene (EPS) boards are a budget alternative with lower thermal performance per millimetre than PIR.

Insulating the Walls

Most timber sheds have a framework of vertical studs with the cladding boards fixed to the outside. The gap between the studs is the available depth for insulation. Measure the stud depth and cut rigid insulation boards to fit snugly between the studs, pushing them in firmly. Fix in place with construction adhesive if needed. If there is a gap between the insulation board and the inner face of the studs, fill this with thinner boards or fold-out mineral wool to avoid thermal bridging through the timber.

Line the inside of the insulated walls with plywood, OSB, or plasterboard to protect the insulation and provide a finished surface. Seal all edges and joints with acoustic sealant or tape to prevent cold air penetrating around the insulation boards.

Insulating the Roof

The roof of a flat or pent roof shed can be insulated by fitting insulation boards between the rafters from inside. Fit the boards tightly between the rafters and line with boards for a finished ceiling. For a pitched apex roof, insulate the sloping roof sections between the rafters in the same way. A vapour control layer on the warm side of the insulation reduces the risk of condensation forming within the roof structure.

Insulating the Floor

A bare concrete or timber floor loses significant heat through ground contact. For a timber floor on joists, fit rigid insulation between the joists from below if accessible, or fit boards directly onto the existing floor surface. For a concrete floor, a layer of rigid insulation with a structural deck over the top is the most effective solution, though it raises the floor level and requires adjusting door heights accordingly.

Summary

Insulate a shed with rigid PIR foam boards cut to fit between wall studs and roof rafters, lined with boards for protection. Insulate the floor with rigid boards under a deck layer. Seal all gaps around doors and windows to prevent draughts. A vapour control layer reduces condensation risk in the roof. Rigid foam boards provide the best thermal performance in the shallow depths of typical shed construction.