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New method of drainage of basement walls
Edvardsen, K. I.; National Research Council of Canada. Division of Building
Research
I
,
Title:
Author:
Reference:
Translator:
NATIONAL RESEARCH COUNCIL OF CANADA TECHNICAL TRANSLATION 1603
New method of drainage of basement walls
(Ny metode for drenering av kjellervegger)
Knut I. Edvardsen
By g g mest ere n , Oslo, 4 4 (18): 2 4 - 2 7, 1 9 7 0
D. A. Sinclair, Translations Section, National
The traditional practices employed in designing and installing peripheral drainage systems around sub grade con-structions have not been entirely successful, particularly where the basement space is to be finished. The Division of Building Research became aware of the development of improved practices in the Scandinavian countries. This is a translation of a study of these new approaches carried out by the Norwegian Building Research Institute which have particular application in Canada.
The Division is most grateful to Mr. D. A. Sinclair, head of the Translations Section of NRC, for translating this paper and to Mr. J. K. Latta of this Division who checked this
translation.
Ottawa
September 1972
N. B. Hutcheon Director
NEW METHOD OF DRAINAGE OF BASEMENT WALLS
Although in future we shall see other less conventional methods of laying foundations used to a greater extent in small house construction, there is nevertheless reason to believe that basement foundations will continue to be appropriate wherever the soil and terrain conditions are right for them.
In all foundation wall constructions, moisture is the principal cause of damage. The damage may take the form of a precipitation of salt, which can dislodge the plaster or other coating both on the outside above the ground and inside, or frost cracking and the spreading of mildew. In sills resting on foundation walls and higher up in half-timber walls, rot can set in. Damage can also occur in the floor joists over the basement and in basement services.
Even for basement constructions above the groundwater table i t is important to take into account the various moisture condi-tions that may occur.
In recent years there has been growing interest in the utilization of basement areas for purposes other than storage space. As the interior climate is greatly influenced by the moisture and temperature conditions at the boundary surfaces of the basement, i t is necessary to ensure that no excessive liquid water or vapour will be released from the foundation walls and that there is satisfactory thermal insulation. This applies
also where there is space for permanent occupation which is partly below ground level, and where there has previously been a need for a clearance at the walls which are in contact with the ground. It is therefore important to develop solutions that can give
optimum conditions in these areas. Since in many places good backfilling materials are expensive or hard to get, i t is also desirable, to find alternative methods of execution.
In the Building Specifications of August 1, 1969, Chapter 42:1 i t is stated that:
"The soil beneath the building and the ground around i t
shall be treated and landscaped so that no moisture will develop
in the building and the foundation wall is not exposed to earth
pressure or frost pressure greater than the pressure for which
i t is designed. Care shall be taken to ensure that surface
water cannot reach the building."
Chapter 42:3 reads:
"Exterior basement walls
"Exterior basement walls shall satisfy the heat insulation
requirements in Chapter 54:3. The walls shall be constructed
so that water cannot penetrate into the basement."
And in the same chapter, No.5:
"Draining
"Buildings with floors below ground shall be drained if
the ground is not self-draining. Other buildings shall De
drained when necessary.
"The drainpipe size depends on the amount of water that
has to be carried away.
"The drainpipe shall be laid at least 200 mm below the top
edge of adjacent floor, measured from the bottom of the inside
of the pipe. If the floor is raised, calculate from the lower
edge of the elevated part. The drainpipe must have a slope of
not less than 1:200 and empty into a creek running through the
ground or a basin connected to the sewerage system, as decided
by the Building Council. The drainpipe must be covered with
f i l l . The refilling must be so executed that no water pressure
can occur on the wall of the foundation.
"If the basement is laid at so Iowa level that i t cannot
be drained, i t must be waterproofed."
It is evident that the sections dealing with basement walls
and drainage are generally formulated from the functional point
of view. Specific requirements for the execution such as were
- 5
-This means that i t is now possible to use new and uncon-ventional methods for protecting basement walls against moisture. The same applies to finished space for prolonged occupation
where the need for a clearance at walls adjacent to the ground has disappeared.
The methods currently being employed are essentially as follows:
(a) Corrugated slabs of asbestos cement;
(b) Plastic panels with projecting knobs or ridges to ensure clearance between the panels and the foundation wall; (c) Mineral wool on the outside of the foundation wall; (d) Combinations of (a) with (b) or (c).
Methods (a) and (b) have already become common practice. Corrugated asbestos cement is used in one layer (upright) outside ordinary basement walls, while they are used alternately in
vertical and horizontal double layers to provide clearance.
Mineral wool, from all appearances, besides having a
draining and capillary disrupting effect, can be used for outside insulation of basement walls that are sufficiently
pressure-resistant. Certain types of mineral wool can also be used as filters over drainpipes.
These alternatives will undoubtedly prevent the build-up of water pressure on the walls, assuming that no plugging occurs and that there is a potential for flow to the drainpipe.
Investigation of Glass Wool as a Draining and
Capillary-disrupting Layer Against a Basement Wall
For some time, now, the Norwegian Building Research Institute (NBI) has been working on various foundation-laying methods for small houses, studying, among others, problems connected with the moisture-proofing of basement walls.
-
6
-In this connection i t was desirable to test the present alternatives for draining basement walls under controlled
laboratory conditions. As an assignment for Glavaprodukter AS, the Institute had an opportunity to test glass wool for this type of application.
The test arrangement, shown in Figure 1, comprised a poly-ethylene vessel with interior dimensions of 1240 x 995 x 925 mm. The vessel is braced with a steel frame. At one end in the
bottom an outlet is provided for a 3" drainpipe laid along the test wall of the vessel with a drop of approximately 1:100.
A sheet of polyethylene 1240 x 200 mm is welded vertically along the centre of the floor. Six glass tubes are secured along one of the long walls to act as gauges for reading the water pressure.
Parallel to one long side, inside the vessel, a perforated steel plate (hole diameter 3 mm) is mounted. The bottom 200 mm of the plate is not perforated. At the bottom of the pocket thus formed between the plate and the side of the vessel a tapping cock is installed.
A wire mesh box 1000 x 600 x 150 mm is suspended in the middle of the vessel. This is covered with tightly woven cloth, mesh
size 0.0497 mm, to prevent passage of fine particles. Over the box a float is installed which enables the water level inside to be kept constant.
The water passing through the drainpipes is collected in two vessels fitted with floats. The rate of flow is indicated on a recorder. Silt was used as a backfilling material with a layer of sand about 0.1 m thick in the centre of the forward part to produce a faster rate of flow.
The grain-size distribution curves of the sand and silt are shown in Figure 2.
The test apparatus is designed to give an extremely large moisture load on the draining material, so that the s i l t is kept at a constant and high pore water pressure. If the drain material does not conduct the water to the drainpipe fast enough, water
-
7
-pressure will be exerted against the wall. Another reason for
choosing s i l t as the filling material was that this kind of soil
is more likely to plug the draining and filtering materials.
In the test setup three variants were investigated with glass
wool. These are shown in Figure 3.
the product studied was a mat of glass wool having a bulk
density of about 50 kgjm 3• The nominal thickness of the mat was
10 mm. Two layers of i t were placed against the wall inside the
vessel and without any joints going all the way through. In
setup 2 the corrugated asbestos cement slabs were assembled so
that a pair of them against the f i l l made a horizontal and a
vertical joint.
For the sake of comparison, a conventional arrangement with
a sand filling of 0.20 m against the wall and a sand filter over
the drainpipe was also tested (Setup 4, Figure 3).
Observations
For each test setup the water levels in the gauges were
checked regularly. The time when the water penetrated through
the perforated wall in the vessel was observed visually.
Wherever this occurred the amount of water was measured.
The tests were continued until there appeared to be stable
drain conditions in the box, and the rate of flow through the
drainpipes was measured every day with the aid of a recorder
con-nected to a float system.
On filling with water at the beginning of the test in setup 1
i t was noted that a few drops had passed through the glass wool
at the end of the vessel. Subsequently, during the course of
the test no water passed through the perforated plates in the
vessel. In setups 2 and 3 no water penetrations were observed.
No water pressure was shown by the gauges.
The mat was then dug up and examined visually. Only the
outermost 1 to 2 mm of glass wool, where i t was in contact with
mat was wet. Fine particles had penetrated to some extent into
the outer 5 mm of glass wool, but i t was by no means clogged.
At the sand layer the penetration was somewhat greater, but did
not reach the inner mat.
The part of the mat which had extended into the layer of
sand at the bottom of the vessel or was placed over the
drain-pipe was wet through.
It also appeared as though a "crust" of fine particles had
been deposited on the mat.
On digging up setup 2 i t was found that s i l t had collected
between the corrugated plate and the mineral wool at a level of
about 100 mm on one side and about 200 mm on the other. This
s i l t must have passed through the horizontal joints in the
asbestos cement slabs or underneath them.
The traditional filling (setup 4) performed less favourably
than the other setups. An hour after starting up, a pressure
of 20 mm Hg was measured in the gauges. This decreased steadily
to 0 in the course of a day. The water began to seep through
the perforated wall almost immediately at a rate of about 20
litres/hour. This stopped after a day, but the perforated wall
remained damp to a height of about 450 mm from the bottom of the
vessel during the entire 67 days of testing.
In all the tests only very small amounts of s i l t collected
in the drainpipes or in the collecting vessels.
Evaluation
When we compare the flow curves for the four setups
(Figure 4), we see that from the beginning the rates of flow for
setups 1 and 2 are much lower than for the other two. Similarly,
the first two setups appear to attain a stable flow more rapidly.
As far as setup 1 is concerned, the explanation is that the plastic
film laid horizontally forced all the drainage to occur through
the vertically placed mineral wool mat; none at all passed
- 9
-In setup 2 the plastic sheet was removed, but the vertical
part of the glass wool was covered with slabs of corrugated
asbestos cement. The accumulation of s i l t on the backs of the
slabs indicated that some of the water had found its way through
the joints between the slabs or around the lower edge of the
bottom slab. Most of the runoff, however, must have gone directly
through the glass wool which covered the drainpipe.
Conditions such as compactness of the s i l t or variations
in its grain-size distribution may have affected the flow rate,
but the differences between the two pairs of curves, 1 and 2,
on the one hand and 3 and 4 on the other, are in any case so
pronounced as to make i t obvious that a better runoff is obtained
by placing a draining material against the basement wall than
an impervious one, the purpose of which is merely to interrupt
the capillary connection between the damp soil and the basement
wall.
The reason why the flow curve for all four setups shows a
steep drop at the very beginning is, apparently, that as the s i l t
in the box is consolidated channels inevitably form through which
the water can escape rather easily. After a comparatively short
time (when the s i l t gets thoroughly wet) these close up, so that
a more uniform runoff is obtained. The carrying-away of fine
particles will thus eventually result in the s i l t being further
consolidated, and i t appears as though this transporting of
fine particles has resulted in the formation of a comparatively
compact layer of s i l t on the side of the mats. As a consequence
of these processes, the runoff finally became stabilized for the
first three setups at approximately the same level.
In the case of setup 4 with sand f i l l , the runoff remains
greater than the other three variants over the entire test period.
This may be due to the properties of sand as a filtering and
draining material, but possibly also because the water in this
case has a shorter distance to go through the s i l t than in cases
1, 2 and 3.
However, sand was much less effective than glass wool in
Glass wool is resistant to moderately acid and moderately yet been published, but appear to be positive.
No water
This is something When the mat is compressed to 10%
It is thought that rock wool will act
The stability of glass wool covered by soil In the other three setups tne wall remained
The results of these long-term experiments have not
the transverse direction. the entire test.
ment wall.
By comparison, silt has a permeability coefficient of 10-4 to 10- 7 em/sec.
The NBI preferred not to test how remote pressure and external insulation.
lateral pressures affect glass wool and walls. dryas far as i t was possible to judge visually. pressure was recorded.
In Sweden, tests were carried out with rock wool as an
of its original thickness, the permeability is reduced to 0.2
em/sec. The compression is carried out with a load of 1 to 2 kg/cm2 • simultaneously as a capillary disrupting layer against tae
base-alkaline solutions.
that has to be studied by means of practical field tests. It appears, however, that construction with mats of glass wool is every bit as good as a conventional construction.
Tests at the Norwegian Geotechnical Institute show that the permeability of a glass wool mat with a bulk density of 50 kg/m 3 is 0.2 em/sec in the longitudinal direction and 0.4 em/sec in
water came through the perforated wall and i t remained damp during
was not tested at the NBI, but field studies at the Agricultural college(2) indicate a satisfactory stability.
Glass wool of the same quality is used in agriculture as a filtering material over drainpipes. In both laboratory(l) and field(2) tests i t was found that glass wool has satisfactory properties with respect to drainage and danger of being plugged with mud, compared with conventional materials.
The permeability of sand varies from 10-4 em/sec to 1 em/sec for coarse sand. As far as their permeability is concerned,
- 11
-Figure 5 shows a practical setup for draining with glass
wool mats.
Conclusion
According to the Building Specification (Chapter 42:5),
filling next to basement walls must be executed so that no water
pressure can occur against the wall. It is also desirable for
the draining material to have a capillary disrupting effect.
According to Chapter 42:1 care should be taken in building
foundations to prevent surface water from draining towards the
building. Some of the surface water will also seep down into
the ground. This moisture, together with the capillary-bound
water in the soil, must be prevented from forcing its way to
the basement wall. The backfilling must also be able to conduct
the water downward from the walls above during rainy weather or
intentional watering of plants, and/or must be able to prevent
such water from exerting pressure against the wall.
It is assumed that the drain (weeping tile drain) around
the house will keep the ground water table at a sufficiently low
level, i . e . , below the basement floor.
Laboratory tests at the NBI indicate that glass wool mats
should make a suitable draining and capillary disrupting layer
against a basement wall, provided that, as always, satisfactory
draining around the foot of the foundation is provided.
Laid in two layers and without continuous joints, the glass
wool mats used in the NBI test setups showed better properties
than the conventional executions they were compared with. No
water penetration was recorded, and the mats showed no particular
signs of plugging.
The UBI hopes to be able to test several other ways of
draining of basement walls so that different solutions for
different applications can be recommended.
Section through test apparatus J drain pipe .; -Po1vethv1ene vessel _ _--Jl-_Sand Silt Fig. 1 References
Hove, Peder, Laboratorieforsok med grofrematerialer. Voliebekk 1964. (Norges landbrukshog-skole, MeIdinger, b. 43, nr, 10.) HariIdstad, Erling. Dekkmateri-aIer for dreneringer. Vol lebekk 1968. (Norges landbrukshog-skoIe. Meldinger, b. 47, nr. 11.) [ 1] [2] Constant water level
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±f=,==3
Wire mesh..: : . ｾ vessel
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glass tube1
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- 13
--- Mechanical composition of silt ---- Mechanical composition of sand
Silt Sand Gravel
1=l fraction fraction fraction
0
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<Il <Il.j.I til til til
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--- -2 em glass wool
---1
' . . .' .' _:-.:...- 2cm glass wool ':=H _+__ Corrugated slab of asbestos cement ＮＮＺＮＮＮＮＭﾷＮ｟Ｎｾｉ - Si It IｴｾＧ
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ＭＧｾＭ
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--..1---1---Sand I ｾ. I ｉｾ I I·
. I II ｾ II·
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--
ｾＭ］ＫＭ Sand1---
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i
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15
-r
Setup 1ｾＭＭｾ Setup 2
..--..
---10 15 20 25 30 35 40 45 so 55 6J
Days from start
Earth excavated and backfilled
Fig.
4
Runoff curves for the different setups - mean values
Mould --+-__- _
... : t,
i. ": .. :
I ,t 1'\ , . , t • , 1 f, .
Fig. 5
Suggestion for practical design. The basement wall is poured directly on the basement floor lying directly over
a consolidated supporting soil of suitable material
