Note: Descriptions are shown in the official language in which they were submitted.
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AN ISOLATED LOG ELEMENT
The present invention relates to a wooden log element which
is intended to be stacked with similar log elements to form
a wall structure while using a so-called corner jointing
technique.
Log cabins are generally constructed from solid logs which
are provided with corner jointing recesses at both ends
thereof, wherein the logs are placed one on top of the other
and timber-jointed at the corners of respective cabin walls.
Cabins that are built of logs that are "dovetailed" at the
corners of the cabin walls have an attractive, rugged
appearance and consequently many people wish to use this
construction technique when building weekend cottages and
like occasional dwellings. However, the overall coefficient
of heat transfer of walls that are comprised of "dovetailed"
natural timber is much too high to afford adequate
insulation. The thermal insulation of such corner-jointed
log structures is a serious problem, particularly when the
builder desires inner wall surfaces that have the appearance
of old-fashioned timber walls with the logs clearly visible
from inside the building, for the sake of appearance.
In order to improve the insulating properties of the log
elements while retaining their mechanical strength, bearing
capacity and torsional resistance, the Swedish Patent
Specifications 440 250 and 457 456 propose the use of log
elements having wooden outer parts whose inwardly facing
surfaces are provided with grooves which extend in the
longitudinal direction of the log element. These outer
parts are held spaced from one another with the aid of
spacers and the empty space between these outer parts are
filled with a heat-insulating material, preferably
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polyurethane, which when cured fixes the outer parts and the
spacers in position. The outer parts of these known log
elements are exclusively load-absorbing or, in coaction with
the spacers, only partially load-absorbing, and to this end
have a rectangular cross-sectional shape formed by a single
panel element or a number
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of mutually joined panel elements.
one problem with these known insulated log elements is that
a wall constructed therefrom will dry-out and contract in
time, therewith lowering the height of the wall. In the case
of a wall of circa 2 metres in height, the extent of this
contraction may be as high as 5 cm. These dimensional
changes, which continue for from one to two years, occur
transversely to the fibre direction, which means that the
wood loss in the vertical direction of the outer parts of
each of the aforesaid known log panels will result in a large
loss for the wall as a whole when taken together. Consequent-
ly, it is necessary for a wall constructed from these log
elements to be given enough time to settle before any
internal decoration work can be commenced, resulting in long
construction times and higher costs.
It has been found in practice that the shape or form of these
log elemehts never ceases to change completely, due to the
fact that they are subjected constantly to changes in
atmospheric humidity. Because the air present in the house
is warm and dry during those periods of the year when the
relative humidity of the outside air is at its highest causes
the wood to dry in different directions from the outside and
the inside of the log walls. This results in very high
stresses and therewith in pronounced changes in shape or form
of the log elements. Consequently, wall panels or like
furnishings fitted on the inner surface of the log walls will
tend to bend or crack.
Accordingly, one object of the invention is to provide a log
element which will exhibit minimum contraction in a vertical
direction in comparison with hitherto known insulated log
elements, and which has the shape of a naturally round log
and whose outer parts are shape-locked in all directions with
the aid of spacers in a manner to eliminate the danger of the
log element changing in shape.
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A further object of the invention is to enable surface wood
or bark to be used in the construction of the inventive log
element. By surface wood is meant the outermost pieces sawn
from a log and having so much wane that it is considered
uneconomical to process these pieces for use in wooden
structures for instance and which are therefore normally
chipped.
These objects cannot be achieved with hitherto known log
elements. According to the present invention there is
provided a wooden log element (1) adapted to be stacked with
other log elements to form a wall structure while using so-
called corner jointing techniques, said log element
including surface parts (3) having inwardly facing surfaces
which are provided with grooves (12, 15, 15') that extend in
a longitudinal direction of the log element (1), and further
including spacers (4) which function to hold the surface
parts (3) in supported mutually spaced relationship, wherein
an empty space between the surface parts is filled with a
thermally insulating material (5), which when cured will fix
the surface parts (3) and the spacers (4) in position,
characterized in that the log element (1) has the form of a
natural log where the surface parts (3) disposed on each
side of the thermally insulating material (5) have an
arcuate cross-sectional shape and are formed by a plurality
of mutually joined panel elements (2) with the spacers (4)
disposed therebetween in mutually spaced relationship along
the full length of the log element (1) and essentially
enclosed by the thermally insulating material (5), wherein
for the purpose of shape-locking the outer parts (3)
together in all directions, the spacers (4) have a square
frame construction in which mutually intersecting outer end
parts (13, 13') project out from the corners of the frame
construction and are fixed together at said corners, wherein
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the end-parts of said outer end parts (13, 13') are received
in the grooves (15, 15') that extend longitudinally in the
inwardly facing surfaces of the outer parts (3).
The invention will now be described in more detail with
reference to a non-limiting exemplifying embodiment thereof
illustrated in the accompanying drawings, in which
Fig. 1 is a perspective view of mutually joined inventive
log elements, of which the top log element is shown
partially in section, with one end-piece of the log element
being shown separated from the remainder of the log;
Fig. 2 is a cross-sectional view of one end-part of the
inventive log element; and
Fig. 3 is a cross-sectional view of one end-part of an
alternative embodiment of an inventive log element.
The log element 1 shown in Fig. 1 has an outer layer in the
form of a plurality of surface panels produced from panel
elements 2 and planed to a particular shape which enables
the elements to be joined, e.g., glued, to surface parts 3
which, in section, have the form of arcuate parts of a
hollow cylindrical log. In order to make the log element 1
self-supporting, spacers 4 are disposed in suitable mutually
spaced relationship inside the log element, along the full
length thereof. These spacers 4 are intended to take-up
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forces and to stabilize and shape-lock the outer parts 3
formed by the panel elements 2. In order to enable the log
elements to be stacked one on the other while obtaining an '
essentially continuous insulating layer throughout the entire
stack, insulating material 5 extends through the entire log,
i.e. from the upper side to the lower side of the log and
along the full length of the log. In this regard, the
underside of the log includes a longitudinally extending
recess 6, while the upper side of the log has a shape which
is complementary to the shape of the recess 6.
The inventive log elements 1 can be joined together with the
aid of a known corner locking technique and by optionally
bracing stacked log elements with the aid of tension rods
extending through a constructed wall. For instance, to enable
the log elements 1 to be joined together, each log may be
provided with a necked part in the vicinity of each end
thereof or at locations at which logs are to be joined to the
logs of an intersecting wall structure, i.e. may be provided
with opposing recesses on each side of the log. Alternative-
ly, the upper log element of the meeting wall structure may
be provided with a recess 8 which has a depth corresponding
to half the thickness of said log element, or to the radius
of a round log element, and which corresponds in shape to the
shape of the upper surface of an underlying log element, as
shown in Fig. I. This enables an upper log element to be
fitted readily to a lower log element, as indicated in Fig.
1. Irrespective of the corner jointing technique used,
however, the insulated layer 5 will always extend to the
upper and the lower side of each recess, therewith fully
insulating the walls in the absence of cold bridges at the
corners of the structure, while the insulating material
functions to provide a completely sealed corner joint when
Y
the log elements are joined together in the manner shown in
Fig. 1.
Fig. 2 is a cross-sectional view of a first embodiment of the
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inventive log element i, wherein each panel element 2 in the
log element 1 has an outwardly facing, visible outer surface
9 and an inwardly facing surface provided with longitudinally
extending grooves, said panel element 2 being curved appro-
5 priately to obtain a round log element. In order to enable
the panel elements 2 to be fitted together to form parts of
a round log and therewith ensure that the panel elements will
be connected stably with one another, one longitudinal edge
of the panel elements 2 is provided with a longitudinally
extending tongue 10, whereas the other longitudinally
extending edge of said panel elements is provided with a
corresponding longitudinally extending groove 11. The tongue
10 of respective panel elements is intended to be brought
into engagement with a corresponding groove 11 on one side
of an adjacent panel element 2 , whereas the groove extending
along the ether side of the panel element is intended to
receive the tongue of an adjacent panel element. In addition
to the stabilizing effect thus obtained, the tongue-and-
groove arrangement is also intended to prevent the ingress
of water. The inwardly facing surface of the centre part of
each panel element 2 is also provided with a longitudinally
extending slot 12 which functions to prevent twisting of the
panel elements 2 prior to assembly.
When machining the panel elements 2, the outwardly visible
surfaces of the panel elements are given year rings which
follow the curvature of the log in a natural way, such that
when assembled a finished log element will have the appear-
ance of a log taken from a tree trunk. The outer parts 3
formed by the panel elements 2 are held spaced apart, braced
and kept together by means of spacers 4. These spacers each
have the form of a square frame structure having vertical and
horizontal mutually intersecting frame parts, which are fixed
together and have outwardly projecting end portions 13, 13'.
In one practical embodiment of the invention, each of the
spacers includes at least four wooden spacer members 14, 14'
arranged in a square frame construction 14. The spacer
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members extend vertically and horizontally so as to intersect
one another and are appropriately joined together and have
outer ends 13, 13' which project out from their points of
intersection at right angles to one another.
'
The outwardly projecting end portions 13, 13' of the square
spacers 4 are received in longitudinally extending grooves
or slots 15, 15' provided in the inwardly facing surfaces of
respective panel elements 2. As will be seen from Fig. 2,
when the outer parts formed by the panel elements are
assembled, the outer parts will be held together by virtue
of the projecting outer ends 13, 13' of the spacers being
received in the grooves or slots 15, 15', said outer ends
being glued in said slots, for instance. This arrangement
ensures that the outer parts 3 of the finished log element
1 will be shape-bound to one another in all directions in a
manner which will prevent the outer parts from being separat-
ed from one another, e.g. from being pulled apart. In order
to take-up the forces and loads to which the log element is
subjected, at least two of the wooden spacer members 14 will
preferably extend generally vertically and at least two of
said spacer members 14' will extend generally horizontally.
So that the Load-bearing capacity of the inventive log
elements 1 can be utilized to the best effect, it is impor-
tant that the spacers 4 of each log element are disposed
essentially in the same vertical plane when the log elements
1 are stacked one upon the other. When a load is applied to
the upper edge of a wall constructed from the inventive log
elements 1 with the spacers so arranged, the force exerted
by an applied load will be transmitted through the spacers
structure down to the underlying surface on which the wall
rests. The number of spacers 4 used, their dimensions and
positioning are determined primarily by the desired strength
of the structure built with log elements 1, although the
number of spacers 4 used will be as small as possible, since
they form cold bridges.
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One important feature.of the present invention is that the
force-absorbing and load-transmitting spacers 4 are enclosed
essentially in the insulating polyurethane foam 5. This is
of particular importance in the aforesaid practical embodi-
s 5 went of the invention in which the spacers 4 are constructed
from four wooden spacer members 14, 14' disposed in the form
of a square frame structure which must be kept from contact
with the ambient atmosphere, in order to avoid shrinkage. It
is also important that the fibres of the wooden spacer
members 14, 14' are orientated in the longitudinal direction
of the spacer members, so as to further reduce the risk of
shrinkage or contraction. As a result of this enclosure of
the load-transferring spacer members 4, shrinkage of the log
element 1 in its cross-direction will be extremely small or
practically non-existent.
Before describing the manufacture of the inventive log
element, it should be mentioned that a suitable adhesive is
applied to all jointing locations prior to the log elements
being fitted together, although this will be obvious to one
skilled in this art.
The inventive log element 1 is manufactured in the following
way. Two panel elements 2 are joined together through the
medium of their respective grooves 11 and tongues 10 on each
side of the bottom half of an internally round mould which
can be divided at a location corresponding to half the height
of the mould, the dimensions of which correspond to the
dimensions of the finished log element 1. The panel elements
2 are fixed in position in suitable space relationship with
the aid of the spacers 4, the spacing of the spacers being
dependent on the desired mechanical strength of the log
element. The thus formed unit is then lifted from the mould
J
wherein the still only partially formed outer parts of the
unit will fall slightly outwards from the upper part of the
mould half, wherein each outer part can now be completed by
joining each of the two remaining panel elements 2 to
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respective partially formed outer parts 3, through the medium
of their grooves 11 and tongues 10.
It will be understood in this regard that the "impossible"
form-bound locking of the panel elements in all directions
resulting from the mutual coaction of the spacers 4 and the
outer parts 3 enables the outer parts to be formed by a
plurality of mutually joinable panel elements 2 whose tongues
and grooves 11 engage in one another while permitting
10 limited but still sufficient movement to enable the log
elements 1 to be fitted together.
After having closed the mould, by placing the upper mould
half on top of the lower mould half and sealing the ends of
the mould, the mould is filled with a curable foam 5, e.g.
polyurethane foam, which fills the mould cavity and binds the
log element components together. When the foam has set or
hardened, the formed log element is removed from the mould.
The underside 6 of the log element 1 is then recessed to
provide a log element of circle-segmental cross-section and
the upper side 7 of the log is given a shape which is
complementary to the underside of the log, as shown in Fig.
1, so that the upper side of the log element be received in
the recessed bottom side of an overlying log element when
assembling the wall.
As will be seen from Fig. 1, the ends of respective logs are
cut-out and fitted with end-pieces 16. These end-pieces are
comprised of solid end covers that have been cut from natural
timber logs and turned on a lathe to fit into the cavity
milled in the end of the log element 1. The end-pieces 16
form end plugs which ensure that the insulating material 5
will be fully enclosed in the respective log elements 1 of
a wall structure. The end-plugs 16 extend into respective
ends of a log element 1 and are glued and pinned thereto. The
end-plugs 16 are provided with grooves to prevent shear
tendencies.
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Although not shown, an elastic sealing device, e.g. a rubber
strip, can be placed between the log elements 1 so as to
obtain a watertight connection. Alternatively, the upper
panel element of the panel elements 2 that lie adjacent a
- 5 region between two contiguous log elements 1 may be provided
with a longitudinally extending water-conducting groove.
Fig. 3 is a cross-sectional view of a further embodiment of
an inventive log element 1, in which in addition to the
recess 6 provided on the underside of the log and the
complementary shaped upper side 7 of said log, the upper side
of the Iog is provided with a continuous, longitudinally
extending guide strip 17 while the underside of the log is
provided with a corresponding longitudinally extending slot
18 at each edge part of the recess 6. This ensures that the
log elements will be fixed in position when placed one on top
of the other to form a wall section.
It is conceivable within the scope of the present invention
to give the stock element 1 a different cross-sectional shape
to that shown in the illustrative embodiment, and to produce
the log element from a different material. The recesses
provided in the log elements 1 for the purpose of jointing
the same in a wall structure may, of course, be given a shape
different to that illustrated. It is also possible to produce
the log elements 1 without insulation and to apply a continu-
ous insulating layer to a wall structure built from the log
elements 1. It will also be understood that the afore-
described spacers 4 may be made of an appropriate material
other than wood, for instance a suitable plastic material,
aluminium or like material, and also that the panel elements
may be disposed adjacent one another in a manner which will
impart the form of a continuous circle to the log element
when seen in cross-section.
