9 Suspended floors for heated buildings
9.1 Heated underfloor space
This clause applies to foundations for which Hf < H0.
The same procedures as for slab-on-ground floors, using the values of the parameters in clause 8, can be used for suspended floors in which the underfloor space is either unventilated and airtight or ventilated by the internal air, provided that:
- the walls of the underfloor space are insulated, with thermal resistance at least Rv as given in Table 2, and this insulation is continued below ground as specified in 8.6;
- Rf, taken as the sum of the thermal resistance of the suspended part of the floor and that of the insulation on the base of the underfloor space, does not exceed 5,0 m2·K/W.
Ensure that the foundation walls are properly sealed to restrict air leakage.
9.2 Underfloor space ventilated with outside air
9.2.1 General
The foundations may be designed either without ground insulation according to 9.2.2 or 9.2.3 (as appropriate), or with ground insulation according to 9.2.4, subject to the following restrictions.
- 1) The width of the building, B, is at least 4 m.
- 2) The average internal air temperature in each month in all parts of the building is not less than 17 °C.
- 3) The thermal resistance of any insulation on the ground surface at the base of the underfloor space does not exceed 0,5 m2·K/W.
- 4) The thermal resistance of the suspended part of the floor does not exceed 8 m2·K/W (without ground insulation) or 5 m2·K/W (with ground insulation).
- 5) The thermal resistance of the foundation wall above the outside ground level is not less than the appropriate value in Table 6 when the bottom of the floor construction is situated at a height not more than 0,6 m above the outside ground level.
If the bottom of the floor construction is situated higher than 0,6 m above the outside ground level, this thermal resistance is to be increased such that the total heat flow rate passing through the foundation wall above the outside ground level does not exceed that of a 0,6 m high wall having the thermal resistance specified in Table 6.
- 6) Vertical edge insulation of thermal resistance at least that specified in Table 6 is applied to a depth of at least 0,6 m if there is no ground insulation, or to the lower surface of the ground insulation if ground insulation is present.
- 7) The ventilation rate of the underfloor space does not exceed 2 m3 per square metre of floor slab per hour.
NOTE A method of estimating the ventilation rate is given in EN ISO 13370, Thermal performance of buildings — Heat transfer via the ground — Calculation methods.
If any of the above conditions are not met, either design the foundations as for unheated buildings in accordance with clause 10 or undertake numerical calculations in accordance with annex B.
| Fd K·h |
Rv m2·K/W |
| Fd ≤ 5 000 | 0,5 |
| 5 000< Fd ≤ 10 000 | 0,8 |
| 10 000 < Fd ≤ 20 000 | 1,0 |
| 20 000 < Fd ≤ 30 000 | 1,0 |
| 30 000 < Fd ≤ 40 000 | 1,0 |
| 40 000 < Fd ≤ 50 000 | 1,2 |
| 50 000 < Fd ≤ 60 000 | 1,4 |
| 60 000 < Fd ≤ 70 000 | 1,6 |
9.2.2 Foundations with no ground insulation : long buildings
A long building is one whose length is more than three times its width.
Depending on the design freezing index, the maximum ventilation rate of the underfloor space, and the thermal resistance of the suspended floor, the foundation depth shall be:
- at the walls, at least that in Table 7;
- near the corners for a distance Lc from the corners, at least the greater depth given in Table 8;
where values of Lc are given in Table 5 as a function of the design freezing index. Linear interpolation may be used in Tables 7 and 8 for other values of Rf.
| Design freezing index Fd K·h |
Ventilation rate m3/m2h |
|||||
| 1 | 2 | |||||
| Rf m2·K/W |
Rf m2·K/W |
|||||
| 2 | 4 | 8 | 2 | 4 | 8 | |
| Fd ≤ 5 000 | a) | a) | 0,50 | a) | 0,40 | 0,55 |
| 5 000< Fd ≤ 10 000 | a) | 0,45 | 0,70 | a) | 0,55 | 0,80 |
| 10 000 < Fd ≤ 15 000 | a) | 0,55 | 0,85 | 0,45 | 0,70 | 0,95 |
| 15 000 < Fd ≤ 20 000 | a) | 0,65 | 0,95 | 0,50 | 0,80 | 1,15 |
| 20 000 < Fd ≤ 25 000 | 0,35 | 0,75 | 1,10 | 0,60 | 0,90 | 1,25 |
| 25 000 < Fd ≤ 30 000 | 0,50 | 0,85 | 1,25 | 0,70 | 1,00 | 1,35 |
| 30 000 < Fd ≤ 35 000 | 0,60 | 1,00 | 1,40 | 0,80 | 1,20 | 1,60 |
| 35 000 < Fd ≤ 40 000 | 0,70 | 1,15 | 1,60 | 0,90 | 1,35 | 1,80 |
| 40 000 < Fd ≤ 45 000 | 0,75 | 1,25 | 1,75 | 1,00 | 1,50 | 2,00 |
| 45 000 < Fd ≤ 50 000 | 0,85 | 1,40 | 1,90 | 1,10 | 1,65 | 2,20 |
| 50 000 < Fd ≤ 55 000 | 0,90 | 1,50 | 2,05 | 1,20 | 1,75 | 2,35 |
| 55 000 < Fd ≤ 60 000 | 0,95 | 1,60 | 2,20 | 1,25 | 1,90 | 2,50 |
| 60 000 < Fd ≤ 65 000 | 1,05 | 1,70 | 2,35 | 1,35 | 2,05 | 2,60 |
| 65 000 < Fd ≤ 70 000 | 1,10 | 1,80 | 2,50 | 1,45 | 2,15 | 2,70 |
| a) indicates less than 0,35 | ||||||
9.2.3 Foundations with no ground insulation : short buildings
A short building is one whose length is not more than three times its width.
The foundation depth shall be at least that given in Table 8 all round the building.
NOTE The greater depth is needed all round short buildings because, for a given width, these have greater loss (per square metre of floor area) through the ground and through the walls of the underfloor space, compared with a long building, resulting in a lower temperature in the underfloor space.
short buildings and corners of long buildings
| Design freezing index Fd K·h |
Ventilation rate m3/(m2·h) |
|||||
| 1 | 2 | |||||
| Rf m2·K/W |
Rf m2·K/W |
|||||
| 2 | 4 | 8 | 2 | 4 | 8 | |
| Fd ≤ 5 000 | a) | 0,40 | 0,55 | a) | 0,50 | 0,65 |
| 5 000< Fd ≤ 10 000 | a) | 0,55 | 0,80 | 0,45 | 0,70 | 0,90 |
| 10 000 < Fd ≤ 15 000 | 0,45 | 0,70 | 0,95 | 0,55 | 0,85 | 1,10 |
| 15 000 < Fd ≤ 20 000 | 0,50 | 0,80 | 1,15 | 0,65 | 0,95 | 1,30 |
| 20 000 < Fd ≤ 25 000 | 0,60 | 0,90 | 1,25 | 0,75 | 1,10 | 1,45 |
| 25 000 < Fd ≤ 30 000 | 0,70 | 1,00 | 1,35 | 0,85 | 1,25 | 1,60 |
| 30 000 < Fd ≤ 35 000 | 0,80 | 1,20 | 1,60 | 1,00 | 1,40 | 1,80 |
| 35 000 < Fd ≤ 40 000 | 0,90 | 1,35 | 1,80 | 1,15 | 1,60 | 2,05 |
| 40 000 < Fd ≤ 45 000 | 1,00 | 1,50 | 2,00 | 1,25 | 1,75 | 2,25 |
| 45 000 < Fd ≤ 50 000 | 1,10 | 1,65 | 2,20 | 1,40 | 1,90 | 2,40 |
| 50 000 < Fd ≤ 55 000 | 1,20 | 1,75 | 2,35 | 1,50 | 2,05 | 2,50 |
| 55 000 < Fd ≤ 60 000 | 1,25 | 1,90 | 2,50 | 1,60 | 2,20 | 2,60 |
| 60 000 < Fd ≤ 65 000 | 1,35 | 2,05 | 2,60 | 1,70 | 2,35 | 2,70 |
| 65 000 < Fd ≤ 70 000 | 1,45 | 2,15 | 2,70 | 1,80 | 2,50 | 2,80 |
| a) indicates less than 0,35 | ||||||
9.2.4 Foundations with ground insulation
The foundation depth (all round the building) shall be at least that given in Table 9.
The data apply for Rf 5 m2·K/W. Ground insulation of width bg 1,0 m is applied all round the building, having thermal resistance Rgw along the walls, and Rgc at the corners and for a distance Lc from each corner, where values of Lc are given in Table 5.
| Rgw (m2·K/W) | 0,0 | 0,5 | 1,0 | 1,5 | 2,0 | 2,5 | 3,0 |
| Rgc (m2·K/W) | 0,0 | 0,7 | 1,4 | 2,1 | 2,8 | 3,5 | 4,2 |
| Fd K·h |
|||||||
| Fd ≥ 20 000 | 0,80 | 0,35 | a) | a) | a) | a) | a) |
| 20 000 < Fd ≤ 25 000 | 0,90 | 0,50 | a) | a) | a) | a) | a) |
| 25 000 < Fd ≤ 30 000 | 1,00 | 0,70 | 0,35 | a) | a) | a) | a) |
| 30 000 < Fd ≤ 35 000 | 1,20 | 0,90 | 0,60 | 0,35 | a) | a) | a) |
| 35 000 < Fd ≤ 40 000 | 1,35 | 1,15 | 0,90 | 0,60 | 0,35 | a) | a) |
| 40 000 < Fd ≤ 45 000 | 1,50 | 1,35 | 1,10 | 0,85 | 0,55 | 0,35 | a) |
| 45 000 < Fd ≤ 50 000 | 1,65 | 1,45 | 1,25 | 1,00 | 0,75 | 0,50 | 0,35 |
| 50 000 < Fd ≤ 55 000 | 1,75 | 1,55 | 1,35 | 1,15 | 0,90 | 0,65 | 0,45 |
| 55 000 < Fd ≤ 60 000 | 1,90 | 1,65 | 1,45 | 1,30 | 1,05 | 0,85 | 0,60 |
| 60 000 < Fd ≤ 65 000 | 2,00 | 1,80 | 1,60 | 1,40 | 1,20 | 0,95 | 0,75 |
| 65 000 < Fd ≤ 70 000 | 2,15 | 1,90 | 1,70 | 1,50 | 1,30 | 1,05 | 0,90 |
| a) indicates less than 0,35 | |||||||
