How to calculate the amount of insulation needed on a ground floor
Unlike roofs, walls and intermediate floors, U–value calculations for ground floors cannot be calculated with reference to the construction detail alone. Heat loss from ground floors depends upon a number of factors including the ratio of the exposed floor perimeter to the total floor area.
It also depends on the size of the floor area that you are covering. For buildings with relatively small ground floor areas (primarily domestic properties), if the ground floor is left uninsulated, the thermal performance will be poor. Complete insulation of the ground floor will improve the thermal performance. However for buildings with large ground floor areas (primarily non–domestic buildings), complete insulation of the ground floor may be unnecessary. Instead either insulating the perimeter strip or insulating the floor in vertical or horizontal strips may provide adequate thermal performance. If this is the case then we suggest you contact our technical department for more information about the required thickness of insulation.
To work out the amount of insulation required for a floor, first you need to calculate the Perimeter Area (PA) ratio. This is calculated by dividing the exposed perimeter given by the floor area.
Floor dimensions should be measured between the finished internal surfaces of the external walls. This should include non-usable heated spaces, such as ducts and stairwells, but not unheated areas outside of the insulated fabric, such as garages or porches. The exposed perimeter is the length of the walls that connect to unheated spaces, such as garages or the outside world. If you are calculating this for an extension to an existing building, the floor dimensions should be taken as those of the extension. The smaller the P/A figure the less insulation is required; for example, a large area with a small exposed perimeter will have less heat loss and, therefore, will require less insulation. For a PA ratio less than 0.1 we would suggest that the floor does not require insulating fully and our technical department will be able to provide more guidance with this.
Type of floor
The next consideration is the type of floor construction, which is likely to be one of several options.
- Suspended Timber
- Beam and Block
- Solid Concrete (insulation below floor slab)
- Solid Concrete (insulation below floor screed)
- Suspended Concrete Floor
Each of these different types of flooring has a different construction build up and gives a different U-value for a specified thickness of insulation. The building standards/regulations page on our website gives guidance on what this u-value should be.
The easiest way to work out the required thickness of insulation required to achieve the specifed U-value is by looking at the product information in the Kingspan Kooltherm K3 Floorboard brochure. This has tables of U-values for different thicknesses of board as well as a brief guide to fitting the insulation. When you have settled on the thickness of board required (and if you are still not sure you can contact our technical department for more guidance), then you can get the boards from a stockist.
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