OSB panels can be installed over concrete slab floors in both commercial and residential settings. Sleepers can be applied to the concrete slab over rigid foam insulation and the OSB panels can then be installed directly onto the surface.
There is a variety of different methods and factors to be considered with this type of installation. The efficacy of these methods is reliant on the proper utilisation of an appropriate 6 mil (0.150mm) polyethylene vapour barrier. These are used to prevent any moisture, within the concrete slab, from transferring to the flooring installation above.
WOOD FLOORING PANELS ON CONCRETE
In order for the installation to be successful, the concrete slab must be level and without flaws. A topping layer of gypsum concrete or lightweight concrete can be poured over the concrete slab to ensure that the floor is even. When using this method, it is important to allow sufficient time for curing before the flooring is installed.
The flooring system can be glued directly to the concrete slab, providing that adequate pressure is applied during curing. Where vapour barriers are installed over concrete slabs, mechanical fasteners must be used to attach the flooring system to the concrete slab. When it comes to this type of installation, it may be the case that the expense becomes prohibitive.
With new construction, install a 6 mil polyethylene vapour barrier under the concrete. If it is unknown whether a barrier exists under the concrete, allow the concrete to completely dry (this may take from 6 to 18 months). Be sure to then use a vapour barrier with the new floor.
WOOD FLOORING PANELS OVER SLEEPERS
Placing OSB flooring panels over 2×4 sleepers is a superior method in terms of cost-effectivity. With this method, the vapour barrier can be placed over pressure-treated sleepers or underneath untreated sleepers. Here the sleepers must be attached to the concrete slab with the use of mechanical fasteners and/or a construction standard compliant adhesive.
Insulation can be incorporated in between the sleepers. By installing sleepers so that they are level, flaws in the concrete slab can be overcome to provide a straight, even surface for the flooring system.
If using this method it is essential to ensure that there is adequate spacing in between individual panels as well as in between panels and walls. This ensures that wood panel expansion in varying moisture conditions is accommodated for. Adequate panel spacing is of great importance as it can reduce or even eliminate panel issues and uneven flooring. This is particularly important for below-grade slabs where moisture presents a larger concern.
WOOD FLOORING PANELS OVER RIGID FOAM INSULATION
Applying OSB flooring over rigid foam insulation (must be at least 1 inch thick) helps to keep flooring even as well as providing excellent insulation. If using a single layer of panels, it is possible to prevent differential deflection and potentially crushing the foam by backing the square edges of panels with splice plates. An alternative to using splice plates is to install a double layer of square-edge panels with joints and seams offset or using T&G sub-floor panels to distribute the loads.
Overdriving mechanical fasteners will crush the foam insulation and potentially damage the concrete below and so this should be avoided. Where foam is compressed under fasteners, over time nail popping may occur which results in squeaky floors.
Pressure-treated timber must be used where it will be in direct contact with concrete.
WOOD STRUCTURAL PANELS OVER ABOVE-GRADE CONCRETE FLOORS
Concrete slabs can take 6 to 18 months to properly cure. When installing wood structural panels onto concrete that is still ‘green’, use the methods discussed above.
Installing wood flooring panels over sleepers is the recommended installation method. It provides multiple benefits and is also an economical choice. Always provide adequate panel spacing, always use an appropriate vapour barrier and use pressure-treated wood below any vapour retarder.
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