Installing Floor Insulations


Floor insulation involves adding an insulating material beneath or over the concrete or timber floor. Basically, only the ground floor requires floor insulation, as floors above heated spaces don’t need insulating. Exceptions to this being any floor in your home above an unheated space, such as an extension over a garage. Floor insulation can be for the two types of floors: solid, concrete floors or suspended floors. For the ground bearing concrete slab solid floors, insulation can be above or below depending on whether you fitting the concrete floor or it’s an existing one. If below, then thermal capacity of the house is improved, allowing for the maintenance of an even temperature. If above, the building will heat up more quickly. It is common also to plus any gaps between the floor and walls to ensure draught removal. Raised timber floors should have subfloor access, with soil clearance of around 400mm below the lowest timbers. This provides sufficient access to install insulation. Foil or bulk floor insulation works well, but in either case care must be taken to ensure it is well supported and will not sag or fall down in time. Access by vermin also needs to be considered. Insulation board can be laid beneath floor finishes if there is no subfloor access. Concrete slabs are either suspended or slab-on-ground. Suspended slabs can be insulated in a similar way to raised timber floors. A suspended concrete slab with an in-slab heating or cooling system must be insulated underneath and around the vertical edge of its perimeter with insulation having an R-value of not less than 1.0. A concrete slab-on-ground with an in-slab heating or cooling system must have insulation installed around the vertical edge of its perimeter. The insulation must achieve a minimum R-value of 1.0 and a maximum R-value of 2.0. The floor insulation must be water resistant and be continuous from the adjacent finished ground level to a depth of 300mm or for at least the full depth of the vertical edge of the concrete slab-on-ground. To install slab-on-ground edge insulation, excavate a shallow trench around the slab edge but avoid excavating right down to the bottom of the slab as the foundation may destabilized. Install a 40mm closed cell polystyrene board and fiber cement cover board around the entire slab edge, up to the height of the wall cladding. Ensure the termite barrier remains intact.

For more effective performance, an additional fin of closed cell polystyrene board can be laid horizontally from the slab edge underneath paving, extending about 1–1.5m All forms of insulation save the homeowner money on fuel bills by preventing unnecessary heat loss. Both weather and age will degrade insulating materials over time but you should be looking at getting a few decades of life out of your insulating materials. One of the selling points of suspended floor insulation is that its guaranteed to last the lifetime of the building. See the performance details.

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