Settling of loose-fill insulation materials in walls
Summary
The report describes material behaviour, which significantly
influences the settling of loose-fill insulation materials. The
specific application presented here is loose-fill insulation material
injected in walls as thermal insulation.
The physical formulation of the issue to be discussed is that the mass
is kept in position in the cavity by frictional forces, which
counteracts the settling but complicates injection. The purpose of this
study is to investigate whether there is a possibility that decreased
friction will be able to release settling.
Cellulose loose-fill material injected in a 0.1 m thick and 1 m wide
gypsum wall with a minimum density of 48 kg/m3 was found not
to settle if kept at a constant relative humidity, RH 50 %. 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 changing the constant
environment from RH 50 % to RH 80 % a minimum density of 63
kg/m3 is necessary. Results are shown in figure 1.
Furthermore, results so far show that cellulose loose-fill material
spread on the attic floor will have a density after settling of 48
kg/m3 for a constant RH 50 %, corresponding to 43
kg/m3 dry material. The results were found by using a model
and tests.
Model
The report describes a theory that can be applied to estimate the
settling of loose-fill insulation materials. Settling is determined
from characteristics describing the wall and the relative humidity of
the loose-fill material and the density of the loose-fill material in
the wall. In addition a model describing the creep of the loose-fill
material is presented.
Furthermore, it was found that injection procedures for loose-fill
materials can be evaluated. When evaluating the injection process, the
relationship between stresses and the distance from the injection point
must be calculated for each wall and insulation material. From these
calculations the injection procedures can be optimised to achieve an
almost homogeneous distribution of the insulation material in the
wall.
Tests
The friction coefficient is determined from tests for a combination
of 3 - 4 wall materials and 7 loose-fill materials. The loose-fill
materials tested are both new and conventional materials sold on the
Danish market and used as thermal insulation. The various types of
loose-fill material include; mineral based, cellulose, mineral
granulate, woodwool and granulated flax.
The ratio between the horizontal pressure and the vertical pressure is
determined for all the materials. The ratio is difficult to measure but
it was nevertheless done with success. The test method is described in
the report.
For a number of the materials, creep has been described. Tests were
carried out at a constant temperature. Tests include three load cases,
including 80 Pa, 200 Pa and 500 Pa, with different combinations of
loose-fill density and a relative humidity of either 50 % or 80 %.
Furthermore, creep tests were carried out using a constant temperature
and a constant load level for RH ranging from 50 % to 80 %.
Two full-scale walls were used to verify the model.
Calculations
A large number of calculations were performed by applying the
presented model. Calculations show that stresses in loose-fill
materials can be determined.
It was found to be possible to determine creep analytically with good
agreement with test results.
Conclusion
A model is presented which considers stress analysis for loose-fill
materials to remain in a stress-stable state, and the creep of the
material. From stress analysis it was found to be possible to set up
equations to estimate stresses in granulated insulation materials as a
function of the height of a wall. These considerations are combined
with theories describing creep of a material, thus providing a better
understanding of the material behaviour of loose-fill insulation
materials in walls.
In addition a method is presented for theoretically estimating the
necessary density of loose-fill insulation in walls in order to ensure
volume stability. This theory can be used to calculate the density
needed for a given granulated insulation material to stay in a
volumestable 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 wall with a relative humidity equal to 50 % and 80 %. Data from Ekofiber vägg are used. The calculated volume-stable state is related to RH 50 % and 23 oC. The curve for RH 80 % is partly based on extrapolated data.
By og Byg documentation 011. Torben Valdbjørn Rasmussen.
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