# 10 Unheated buildings

## 10.1 General

This clause applies to foundations for which Hf < H0 and to:

• a) buildings which are unheated;
• b) buildings in which the monthly average internal air temperature in any month of the year may fall below 5 °C.

NOTE The data given apply to climates for which the average annual air temperature is not less than 1°C. For annual average air temperature in the range 0 to 1°C, frost insulation can be designed by undertaking numerical calculations in accordance with annex B.

## 10.2 Without ground insulation

If ground insulation is not used, the foundation depth (including any layer of material that is non- susceptible to frost beneath the foundation) shall be at least the maximum frost depth in undisturbed ground, in accordance with clause 7.

## 10.3 With ground insulation

The foundation depth may be reduced to less than that required in 10.2 by having a continuous insulation layer beneath the foundations and extending to each side of the foundation. If frost heave will damage the floor, the insulation layer should continue under the whole floor. See Figure 6.

NOTE 1 The insulation is continued beneath the foundations to prevent them acting as a thermal bridge.

Key

• 1 Ground insulation
• 2 Foundation wall
• 3 Foundation base
• 4 Slab-on-ground
• 5 Foundation wall
• 6 Column
Figure 6 — Width of ground insulation for unheated buildings

The necessary thermal resistance, Rg, and width, bg, of the insulation depends on:

– the design freezing index, Fd;

– the annual average external air temperature, ;

– the foundation depth.

Determine the width bg from Table 10 according to the design freezing index, Fd. Linear interpolation may be used for intermediate values of Fd.

Table 10 — Width of ground insulation for unheated building
 FdK·h 10 000 20 000 30 000 40 000 50 000 60 000 70 000 bgm 0,75 1,20 1,60 2,00 2,40 2,75 3,10

For small foundations and near corners of larger foundations, the insulation shall extend at least bg from the foundation. For whole buildings, or for strip foundations of length at least 3 m, the insulation width may be reduced to 0,75 bg at distances greater than bg from the corner or end of the foundation: see Figure 6.

Determine the minimum thermal resistance of the ground insulation, Rg, from Table 11 for foundations at least 0,4 m deep, or from Table 12 for foundations at least 1,0 m deep. Linear interpolation may be used in these tables for intermediate values, and linear interpolation may also be used between Tables 11 and 12 for foundation depths intermediate between 0,4 m and 1,0 m.

NOTE 2 The same value of Rg applies along walls and at corners.

NOTE 3 Values of thermal resistance greater than 5,0 m2·K/W in Table 11 have been put in brackets to indicate that it will usually be a more viable option to increase the foundation depth.

NOTE 4 If Fd 60 000 K·h, a foundation depth of 0,4 m is not sufficient and should be increased.

Table 11 — minimum thermal resistance of ground insulation, Rg (m2·K/W) for unheated buildings with Hf = 0,4 m
 FdK·h °C 1 2 3 4 ≥ 5 10 000 – – – 1,1 1,1 20 000 – 1,8 1,6 1,5 1,3 30 000 3,5 2,9 2,5 2,1 1,9 40 000 4,5 3,8 3,3 2,8 – 50 000 (5,6) 4,7 4,1 – – 60 000 (6,7) (5,7) – – –

Table 12 — minimum thermal resistance of ground insulation, Rg (m2·K/W) for unheated buildings with Hf = 1,0 m
 FdK·h °C 1 2 3 4 ≥ 5 ≤ 10 000 – – – 0,0 0,0 20 000 – 0,7 0,5 0,4 0,4 30 000 1,8 1,3 1,1 0,8 0,6 40 000 2,3 1,8 1,5 1,2 – 50 000 3,1 2,4 2,0 – – 60 000 3,9 3,0 – – – 70 000 4,8 – – – –

Protect the insulation layer as follows:

a) place a layer of well-drained material that is non-susceptible to frost at least 100 mm thick beneath the insulation;

b) above the insulation, arrange a protective cover consisting of:

• under the foundations and within the building, at least 50 mm of concrete or similar;
• outside the building, at least 300 mm of soil, unless covered by paving in which case the soil thickness may be reduced to 200 mm;

c) place the insulation above the maximum level of the ground water Table.

## 10.4 Additional material that is non-susceptible to frost beneath insulation

The minimum thermal resistance of the ground insulation, Rg, specified in 10.3 may be reduced by having a layer of material that is non-susceptible to frost beneath the insulation of thickness greater than 100 mm.

Rg may be reduced by 0,2 m2·K/W per 100 mm increase in the thickness of this layer above 100 mm.

## 10.5 Additional soil cover above insulation

The minimum thermal resistance of the ground insulation, Rg, and its minimum width, bg, specified in 10.3 may both be reduced by having a layer of soil above the insulation of thickness greater than 300 mm.

Rg may be reduced by 0,1 m2·K/W per 100 mm increase in thickness of soil cover above 300 mm.

bg may be reduced by 0,1 m per 100 mm increase in thickness of soil cover above 300 mm.

NOTE The increase in soil cover can be limited by the requirement to keep the insulation above the water Table (see 10.2).

ISO 13793-2001 Thermal performance of buildings Thermal design of foundations to avoid frost heave