8.7 Alternative foundation designs
The foundation design should comply with 8.6 and with one of the following alternatives.
8.7.1 Foundations with no ground insulation
The foundation depth should be:
- at the walls, at least Hf;
- near the corners and at limited unheated parts for a distance Lc from these places, at least the greater depth Hfc (if Fd > 30 000 K·h);
where the values of Hf, Hfc and Lc are given in Table 3 as a function of the design freezing index.
| Fd K·h |
Hf m |
Hfc m |
Lc m |
| Fd ≤ 30 000 | 0,35 | 0,35 | – |
| 30 000 < Fd ≤ 35 000 | 0,40 | 0,60 | 1,0 |
| 35 000 < Fd ≤ 40 000 | 0,50 | 0,80 | 1,0 |
| 40 000 < Fd ≤ 45 000 | 0,60 | 1,00 | 1,5 |
| 45 000 < Fd ≤ 50 000 | 0,75 | 1,30 | 1,5 |
| 50 000 < Fd ≤ 55 000 | 0,90 | 1,60 | 1,5 |
| 55 000 < Fd ≤ 60 000 | 1,10 | 1,80 | 2,0 |
| 60 000 < Fd ≤ 65 000 | 1,30 | 2,00 | 2,0 |
| 65 000 < Fd ≤ 70 000 | 1,50 | 2,20 | 2,5 |
8.7.2 Ground insulation only at corners
If Fd 30 000 K·h, ground insulation is not required.
For greater values of Fd, the foundation depth shall be at least Hf all round the building, and ground insulation shall be used near corners and at limited unheated parts for a distance Lc from these places, where the values of Hf and Lc are given in Table 4.
The thermal resistance of the ground insulation shall be at least 1,0 m2·K/W, and its width shall be bgc, values of bgc being given in Table 4. See also Figure 3.
| Fd K·h |
Hf m |
bgc m |
Lc m |
| Fd ≤ 30 000 | 0,35 | – | – |
| 30 000 < Fd ≤ 35 000 | 0,40 | 0,50 | 1,0 |
| 35 000 < Fd ≤ 40 000 | 0,50 | 0,50 | 1,0 |
| 40 000 < Fd ≤ 45 000 | 0,60 | 0,50 | 1,5 |
| 45 000 < Fd ≤ 50 000 | 0,75 | 0,60 | 1,5 |
| 50 000 < Fd ≤ 55 000 | 0,90 | 0,80 | 1,5 |
| 55 000 < Fd ≤ 60 000 | 1,10 | 0,80 | 2,0 |
| 60 000 < Fd ≤ 65 000 | 1,30 | 0,80 | 2,0 |
| 65 000 < Fd ≤ 70 000 | 1,50 | 1,00 | 2,5 |
8.7.3 Ground insulation all round the building
If Fd 30 000 K·h, ground insulation is not required.
For greater values of Fd, the foundation depth may be reduced to not less than 0,4 m by placing ground insulation all round the building.
If Fd > 30 000 K·h, ground insulation is necessary near corners and at limited unheated parts, for a distance Lc from these places as given in Table 5. Select an appropriate combination of thermal resistance, Rgc, and width, bgc, of ground insulation near the corners using Figure 4, according to the value of Fd.
If Fd > 37 500 K·h, ground insulation is also necessary along the walls. Select an appropriate combination of thermal resistance, Rgw, and width, bgw, of ground insulation along the walls using Figure 5, according to the value of Fd. Then use Figure 4 to determine the greater ground insulation needed near the corners and unheated parts. The corner insulation applies for a distance Lc as given in Table 5.
See also Figure 3.
Key
- 1 Limited unheated part (store room, porch etc)
Key
| 1 minimum bgc | 3 Width of ground insulation at corners, bgc |
| 2 minimum Rgc | 4 Thermal resistance of ground insulation at corners, Rgc |
Key
| 1 minimum bgw | 3 Width of ground insulation along walls, bgw |
| 2 minimum Rgw | 4 Thermal resistance of ground insulation along walls, Rgw |
| Fd K·h |
Lc m |
| Fd 30 000 | – |
| 30 000 < Fd ≤ 35 000 | 1,0 |
| 35 000 < Fd ≤ 40 000 | 1,0 |
| 40 000 < Fd ≤ 45 000 | 1,5 |
| 45 000 < Fd ≤ 50 000 | 1,5 |
| 50 000 < Fd ≤ 55 000 | 1,5 |
| 55 000 < Fd ≤ 60 000 | 2,0 |
| 60 000 < Fd ≤ 65 000 | 2,0 |
| 65 000 < Fd ≤ 70 000 | 2,5 |
8.8 Buildings with low internal temperature
For poorly heated buildings with 5° C ≤ θi,m < 17 °C, the values in 8.7.3 may be used if Hf is at least 0,6 m instead of 0,4 m.
Alternatively increase the values of Hf in Table 3 or Table 4 by 0,2 m.
If θi,m <5 °C in any month, the frost protection of the foundations shall be designed as for unheated buildings (see clause 10).
