Author: Brian October 31, 2012

I have previously posted about the Heat Loss from a Slab Floor so how does that compare with a suspended timber, or particle board, floor?

Well its not as bad as you might think because the the space under the floor acts as a Buffer Zone between the room and the external temperature. (Unless you have got a pole house or a Queenslander.)

The main considerations are:

1. The amount of external wall compared with the area of the floor, ‘ Perimeter to Area Ratio’ (PAR).
2. The height of the floor above the ground (the calculations below are based on this height being 0.5m or less)
3. The amount of ventilation expressed as m²/ m length of perimeter wall.

Heat loss Calculations

Perimeter to Area Ratio.

For a 10m x 10m house the PAR = 40/100 = 0.25

For a 20m x 5m house the PAR = 50/100 = 0.5

Ventilation

Low ventilation = 0.0015m²/ m length of perimeter wall

High ventilation = 0.003m²/ m length of perimeter wall.

The  table below provides some values of ‘U’ for the floor .

PAR	.2	3	.4	.5	6	7	8	.9
‘U’ low ventilation	0.4	0.51	0.59	0.66	0.72	0.77	0.82	0.86
‘U’ high ventilation	0.42	0.53	0.62	0.7	0.76	0.81	0.86	0.9

So for a typical single storey house of 20m x 10m

The PAR = 60 / 200 = 0.3

From the table ‘U’ is 0.51 -0.53 depending on ventilation

The heat loss from the slab = Area x ‘U’

= 200 x (0.51 -0.53)

= 102 -106 watts/degree C

The heat loss for this floor is 4 – 8% higher than the same sized slab on ground. The suspended floor will however have a lower thermal mass.

 

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