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Workshop floor construction

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  • Workshop floor construction

    I am converting one side of a detached double garage for use as a workshop, and would appreciate some advice on floor construction.

    The anticipated floor construction sequence is concrete subfloor / polythene damp proof membrane / polyisocyanurate foam insulation (probably 45 - 70mm) / polythene vapour control membrane / 22mm flooring chipboard / top floor surface layer.

    Do I use treated timber battens to support the floor between the subfloor and chipboard, to take the load off the insulation? This seems often recommended, but I really don't like the idea of sandwiching wood between 2 damp proof membranes: if (when?) it gets damp, it cannot dry out! The compressive strength of the insulation appears adequate, for example Kingspan Thermafloor TF70 is rated 140 kPa at 10% compression and 125 kPa at 5%, or approximately 14 / 12.5 tonnes per square metre. I therefore assume a maximum practical load of say 5 tonnes/sq m.

    A typical relatively heavy bench having 6 legs, and of 300kg laden weight concrete flooring redding(100kg bench, 100kg machine, 100kg miscellaneous material ) then requires each leg to have the load spread over a minimum 10cm square of insulation. This spreading should be adequately provided by the 22mm chipboard layer.

    So is a fully floating chipboard layer resting on the insulation OK in respect of load bearing including machines on benches? This would be at variance to other recommendations seen for direct rigid mounting of machines to the concrete subfloor, but I am not anticipating machines weighing much over 100kg, or swinging very heavy unbalanced workpieces.

    Any recommendations for floor surface? I have seen laminate flooring at the local DIY shed priced as low as 5/sq m, for a tolerably acceptable appearance, smooth surface, heavy domestic / light commercial rating. I wonder also about use of a heavy industrial grade of PVC flooring, in sheet or tile form.

    Any opinions gratefully received, especially if they coincide with my own