100 mm rigid insulation board in extruded polystyrene (XPS)

Insulation buried beside foundations or covered by a floor must stand up to conditions that are hard to inspect in service. XPS is extruded polystyrene with a compact, closed-cell structure. It combines thermal insulation and low water uptake with a compressive strength specific to the grade. This makes it useful wherever moisture or loads place additional demands on insulation.

Closed cells restrict water penetration. On basement walls and foundations in contact with the ground, a suitable XPS grade helps the insulation retain its thermal performance in damp conditions. It works alongside the waterproofing. Using a board suited to the exposure is especially valuable where future access is difficult. Insulation at the wall-to-floor junction reduces heat loss around the base of the house and helps improve comfort on the ground floor.

Rigidity also matters below usable surfaces. A grade rated for the loads can be used in a garage floor, utility room or suitably designed roof. Rigid boards have defined dimensions, making it easier to plan layer depths. For surfaces carrying foot traffic or equipment, check the declared class of the particular board against its intended duty.

The uniform structure makes it easy to cut pieces for corners and changes in width.

Different surface finishes allow the board to be matched to adjoining layers.

Profiled edges on selected boards help align adjoining insulation joints.

Low weight makes boards easier to carry into excavations and basements under renovation.

XPS can insulate foundations in new homes or below-ground walls exposed during refurbishment. Other uses include ground-bearing floors and suitably designed inverted roofs. At a basement it helps limit heat loss to the ground. In a garage it forms part of a loaded floor assembly, and on an accessible roof it allows the insulation to work with the planned use of the surface. Moisture resistance matters near water, but the building still needs a separate watertight layer.

SteelProfil can compare board thickness, surface finish and declared strength for your foundation, floor or roof. Check current prices, promotions, batch grades and immediate availability against the quantities in your budget.