Loose-fill insulation in walls and attics

- How varying moisture conditions influence density

Summary

This report describes material behaviour that significantly influences the settling of loose-fill insulation materials. The specific application presented here is the loose-fill insulation material filled in walls and used as insulation in attics. This is the second of two reports related to the same programme. The first report is By og Byg Documentation 011.
Filled in a 0.1 m thick, 2.4 m high and 1.0 m wide gypsum wall, cellulose loose-fill material with a minimum density of 48 kg/m³ was found not to settle if kept at a constant relative humidity of 50 % and at a temperature of 23 °C. A minimum density of 53 kg/m³ is necessary if the thickness of the wall is increased from 0.1 m to 0.3 m. If the constant environment is changed from a relative humidity of 50 % to 80 %, a minimum density of 63 kg/m³ is necessary. Furthermore, if the wall is exposed to a temperature of 23 °C and an alternating relative humidity of 50 % and 80 %, the necessary density is increased to 73 kg/m³. Assuming that the material maintains its elastic capability the density can be reduced to 69 kg/m³. Results are shown in Figure 1.

Model

The report describes a method that can be used for determining the necessary density of a loose-fill insulation material filled in walls. The necessary density is determined from characteristics describing the wall, the loose-fill insulation material and the moisture conditions that the loose-fill insulation material will be exposed to. In addition, the settling of loose-fill insulation materials used as insulation in attics can be determined. And the settling is determined from characteristics describing the loose-fill insulation material and the moisture conditions that the loose-fill insulation material will be exposed to. The method includes both constant and alternating moisture conditions.

Tests

The loose-fill materials tested were both new and conventional materials sold on the Danish market and used as thermal insulation. They were various types of loose-fill material such as: mineral wool, cellulose, wood fibre and granulated flax.
Creep has been described for all the investigated materials. Tests were carried out at a constant temperature and included three load cases of approximately 80, 150 and 300 Pa, respectively, with an alternating relative humidity of 50 % and 80 % for each case.
For a limited number of materials and wall materials the friction coefficient is determined from tests.
Fill in tests of loose-fill insulation material filled in walls were carried out. Two different fill in procedures have been tested. For one fill in procedure, the local density and the overall density of the filled in loose-fill insulation materials have been documented. The used fill in procedure have been used on two fundamentally different types of walls; One was built as a closed box with a wooden frame and sides of gypsum boards; the second was built as a closed box with a wooden frame and sides of gypsum boards with horizontal laths added. At 0.6 m intervals, laths was placed against the gypsum boards. A vapour retarder was placed between the laths and the gypsum board of the second type of wall.
Full-scale walls and boxes simulating attics were used to verify the method.

Calculations

A large number of calculations were performed by applying the presented method. Calculations show that the necessary density and settling of loose-fill insulation materials can be determined by using the method presented.
It was found to be possible to determine analytically a stable density of loose-fill insulation material as a function of stress exposed to alternating moisture conditions.

Conclusion

A method for determining the necessary density and settling of loose-fill insulation materials is presented. The necessary density in a wall can be determined from characteristics describing the wall, the loose-fill insulation material and the environment that the material will be exposed to during its lifetime. And the settling of loose-fill insulation material in attics can be determined from characteristics describing the loose-fill insulation material and the environment the material will be exposed to during its lifetime. The report describes material behaviour, thus providing a better understanding of the material behaviour of loose-fill insulation materials.
This method can be used to calculate the density needed for a given granulated loose-fill insulation material to stay in a volume-stable state.

Figure 1. Calculated necessary density as a function of wall thickness to prevent settling of cellulose loose-fill material in a wall. Calculations are performed for a 0.1 m wide gypsum board wall with a relative humidity of to 50 % and 80 %. In addition, the calculated necessary density is shown for an alternating relative humidity of 50 % and 80 %. Data from Ekofiber vind are used. The calculated volume-stable state is related to RH 50 % and 23 °C. The curve for RH 80 % is based partly on extrapolated data. The curves for an alternating relative humidity are either based on the assumption, 1) that the cellulose loose-fill material does not keep its reversible strain or 2) that the cellulose loose-fill material keeps its reversible strain.

By og Byg Documentation 030. Torben Valdbjørn Rasmussen.

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