Note: Descriptions are shown in the official language in which they were submitted.
'73~
"ROOF AND WALL COVERI~G"
~;PECIF ICAT IO~
The invention relates to a roof and wall
covering, in particular for heat-insulating house walls
or roofs, consisting of elongated hollow plastic sections
with several chambers having substantially the same
cross section throughout extending in longitudinal
direction therethrough. The plastic sections also having
tongue and groove cross sections at the edges thereof
insertable flush into each other.
In view of the need to conserve energy, heat
insulation of house walls and roofs is gaining more and
more in importance. Independent thereof, it is also being
recognized increasingly that the utilization of solar
energy to produce usable heat can very well be economical
even in regions with less sunshine, provided success is
achieved in keeping the installation required for the
purpose and t~e necessary maintenance costs for such an
installation small. Plate~shaped solar cells are already
being of~ered on the market which can be mounted on
terraces~ in the yard, on roofs or the like and which make
it possible in various ways to absorb solar energy in the
- form of heat and thus heat a heat carrier fluid which
. ~ .
transfers its heat in a heat exchanger to a water system
for use. The water system may be connected to various
heat consumer points in the home, in shops or the like.
Such installations are still expensive to pro-
duce and acquire, and they are also considered an eyesore
when mounted on terraces, in the yard, or on roofs.
''~' ~ ~
;
; '.' - - :
...
3~
It is an object of the invention to overcome
these difficulties and to provide a wall and roof cover-
ing which can be applied in particularly simple and
inexpensive manner in place of other coverings, at the
same time contributing considerably to the heat insula-
tion of the walls or roofs while at the same time per- ~
mitting effective utilization of solar energy for the ~;
generation of heat. ;
In essence, this problem is solved in that a
10 roof and wall covering consisting of elongated, hollow ;
plastic sections, each with several chambers having
; substantially the same cross section throughout extend-
ing longitudinally therethrough and with tongue and
groove edge cross sections insertable flush into each
other is used, and in that the so]ar energy, either
absorbed by the hollow sections themselves and trans-
formed into heat and/or the air layers heated on the
outside surface of such covering by the sun rays are
`~ utilized for the generation of heat, the chambers of
20 tlle hollow sections being used as a duct system.
Air or another gas, or also a fluid may be
used to advantage as a heat carrierO The heated heat
carrier is attracted by a pump and - possibly with the
interposition of a heat pump - is fed to a heat
exchanger so that heat is transferred to the circulating
fluid of a consumer heat circulation system preferably
equipped with a heat reservoir.
rr~ -2-
3~3
;
To start with, the hollow sections must per-
form the job of a conventional wall or roof covering.
They represent a weatherproof, easy-to-care-for, rugged
cover for walls or roofs. Due to their design as hollow
sections, the covering forms at the same time a highly
effective heat insulation for the wall or roof surfaces,
as far as both heat radiation from the outside and heat
emission from inside the building is concerned. The
covering thus performs at the same time an important
heat insulation function. Thirdly, the covering has the
additional important function of forming with the cham-
bers of the hollow plastic sections a simple, safe col-
lecting ancl conducting system for fluid transporting heat
gained from solar energy.
The hollow plastic sections can be installed on
appropriate wall or roof bases particularly simply,
safely and without any damage to the hollow sections by
means of special clamping elements. In view of the
multiple function of the covering, production and
installation as well as upkeep of the covering and the
related systems are extremely simple.
~ The invention is explained below in greater
`~ detail by way of several embodiment examples with
`~ reference to schematic drawings, of which
F~g. 1 is a perspective view of a portion of a
regular residential roof with a heat barrier constructed
according to the invention,
;
~ 3-
Fig. 2 in larger scale, partly in section and
otherwise in perspective view, illustrates several juxta-
posed hollow section parts of the roof covering according
to the invention,
; Fig. 3 is a detail in vertical section along a
chamber of a hollow section part of the new roof covering,
Fig. 4 ifi a view similar to Fig. 3 of a modified
embodiment of the heat barrier structure of the invention,
Fig. 5 is a cross section view illustrating the
connection between two adjacent hollow sections in a pre-
ferred embodiment of the covering of the invention,
Fig. 6 illustrates in various views, the clamp-
ing element used in Fig. 5 to connect the hollow section
parts,
Fig. 7 illustrates in vertical section, a roof
covering according to another embodiment of the invention,
Fig. 8 illustrates details of the roo covering
accordiny to Fig. 7 in cutout and in perspective view,
; Fig. 9 illustrates a preferred embodiment of
the elongated hollow section used in the covering o~ the
` invention and an extension or connection therefor,
.f' Fig. 10 illustrates in larger scale, a longi-
`:
tudinal section of a terminal or connecting section of
the structure of the invention,
Fig. 11 illustrates in cutout and perspective
view, a modified embodiment of the hollow section
covering of the invention,
; Fig. 12 illustrates a further modified embodi-
ment of the hollow section in cross section, and
: ` .:` -
3~
Fig. 13 illustrates in schematic representa-
tion, a heat pump space heater for the embodiment
example of the roof covering according to Fig. 7.
The roof 1 shown in Fig. 1 has a covering
according to the invention. The roof may be designed
in the usual manner with appropriate roof pitch and
have two roof surfaces inclined relative to each other,
one facing ~orth in the direction of arrow 2 and the
other South in direction of arrow 3.
The roof consists of rafters 4, a layer of
boards 5, on top of that a layer 6 of insulating
material and horizontally aligned furring strips 7
serving to fasten the actual roof covering 9. The roof
covering 9 consists of individual, elongated, plastic,
hollow section parts joined to each other mechanically
and in moistureproof structures by means of a tongue
and groove connection. The pitch line of the roof
surface 9 is indicated by the arrow 10, while the two
roof surfaces are covered jointly by a ridge section 11.
soth roof surfaces consist of the same
elongated, hollow section parts 8 so that the roof sur-
faces are of uniform appearance over their entire extentO
The design of the individual hollow section
parts is demonstrated best in Fig. 2. Each hollow section
part has upper and lower flat sides concaved towards the
outside (sic). This gives the plastic, hollow section
parts extraordinarily great stability, further supported -~
; by the division of the interior of each hollow section
;. ' ,:
-5-
,
~7~
part into several chambers extending in longitudinal
direction and being completely separated from each other
by webs in between them. The chambers have the refer-
ence symbols 17, 18, 19, while the section parts are
differentiated between by being numbered 15a to 15d.
Each section part has on one long edge two
lips 25, 26, designed as hollow sections and bounding
between them an engagement groove extending in longi-
tudinal direction for connection to a web-shaped tongue
section 27 extending along the other long edge of the
hollow sections and likewise designed as a hollow
section. The mutually facing inside surfaces of the
sections 25 and 26 limiting the groove have a lengthwise
oriented serration 2~3, 29, whereas the web-like tongue
is essentially smooth, merely having near its free end
on the top and bottom side one or two single fine teeth
30, 31 extending in lengthwise direction. D~ring
installation, the lower section 25 of the example
illustrated is nailed to the furring strips 7 by means
o a few nails hammered into part 25 in the manner
indicated by the dash-dotted line 35. Then the tongue
. ,;:
27 of the adjacent hollow section part is pushed into -~
the groove of the previously fixed section part9 the
parts 25 and 26 giving elastically during this assembly
operation so that the teeth 30, 31 snap into the
` appropriate serration of parts 25 and 26 in the final
engaged position. In this manner an adequate seal, also
against moisture, is assured for most applications. But
:` -,
~ -6-
' "' ~ '
`''' ~ ' .
if required, an additional packing may be inserted in
or assembled to the bottom of the groove to cooperate
with the face of the tongue 27 as a seal in assembled
condition. However, an elastic sealing lip assuming
the sealing function may also be molded to the bottom
of the groove when the hollow sections are produced.
The hollow section parts 15a to 15d of the
example illustrated consist of a highly impact resistant
plastic colored dark through and through, preferably
blackened with about 2 to 6% chemical carbon black, in
particular of highly impact and weather resistant poly-
vinylchloride. Practice has shown that such colored
plastics practically do not lose their color even when
constantly exposed to the atmosphere, specifically they
will not bleach out.
; The entire rooE surface is covered with the
hollow section elements shown, it being possible to
orient the covering parallel to the pitch line 10, as
shown in Fig. 1, or transverse thereto. In the latter ~ -
case, the hollow section parts are oriented so that the
tongue sides point upwardly. In such cases, additional
sealing is not required, even in extreme situations.
The entire roof surface roughly facing South,
or parts of this roof surface are at the same time
designed to generate heat by solar energy absorption.
- Experience in practice has proven that the black colored
plastic is capable to a considerable degree of absorbing
and converting into heat considerable amounts of solar
. .,
.~
--7--
- ~ :
~ ~t7~
energy, even in diffuse sunlight. In the example
illustrated, this heat is transferred to a fluid, in
particular water or water enriched by additives, which
is conducted through the chambers 17 to 19. The water
is introduced to the chambers 17 to 19 in a suitable
place and removed from the chambers in another
appropriate place.
If applicable, the fluid is conducted through
the chambers 17 to 19 not directly, but through ducts
20 to 22, inserted in turn into the chambers 17 to 19
loosely or by using a filler so that physical contact
between the ducts and the limiting walls of the
chambers sufficient for the heat transfer is provided.
The ducts 20 to 22 may go through all chambers of each
hollow section part on the sunny side o the roof surface.
But it is also possible to provide selected hollow section
parts only or selected chambers in one and the same hollow
section part with ducts. All suitable hollow section
chambers 17 to 19 in the example shown are equipped with
duct groups A, B and C. To be able to lead the ducts
several times over the length of the hollow section parts
without special connections or junctions, the hollow
parts may have at their ends, as Fig. 3 shows for section
part 40, or at any other point between their ends, a cut-
out 45 on the bottom side 42, through which a ~nee 46 of
tube 44 is led laterally from one hollow section part to
the next. 41 is the top side of the hollow section part
and 45 a-limiting web for the chamber shown.
:.,,'~'.
As shown at 58, the tube sections 57 may also
be led out of the roof plane downward through an appropri-
ate cutout 56 on the underside of the hollow section parts
50 by bending it, and be reintroduced in corresponding
manner into the next hollow section part through a U-bend,
or, as shown, be connected to a distribution or collecting
line 60. 51 is the outside of the roo~, 58 the tube knee,
53 a rung-like strip corresponding to strip 7 in Fig. 1,
54 the sheathing, 55 a heat barrier and 59 the tube con-
nection to the distribution or collecting line. sut
special connector sections to accept the rerouting or
connecting tube sections may also be provided at the end
of the roof. For instance, close-off plugs may be ultra-
sonically fused or cemented into the sections. They may
have at least one connector element for a tube connection.
I~ the preceding discussion involved plastic section parts
with chambers going through in loIlgitudinal direction,
this is to include also the case where the section com-
prises at least one single through chamber. -
It may be seen in the covering according to
Fig. 5 that the hollow sections 101 have cavities lOlb
separated by webs lOla and that they are concaved on
their top side 10~ and their bottom side 105. Through
nodal points the webs lOla are integrally joined to the ;
top and bottom walls~ The result of extensive testing
has been that the sections described so far meet
extremely high requirements as to impact s~rength, bend-
ing strength and weather resistance.
. ~
_g_
,
.~ , ' '~ ~' ' '
: -.
Each hollow section 101, of which the mutlally
joined long sides of two adjacent hollow sections 102
and 103 are illustrated, have on one long side each a
tongue-like section 111 which is provided on its top
and bottom side with, say, two mutually spaced, fine,
lengthwise teeth 116. Provided on the other long side
of the hollow section is a grooved section consisting
o an upper lip 113, a lower lip 114 and a groove 112.
The inner boundary walls of the groove are provided with
fillet-like recesses 115 running in longitudinal direc-
tion, to be engaged by the fine teeth 116, the dimensions
of the fillets and fine teeth being selected so that even
in the event of heat expansions transverse to the longi~
tudinal direction of the hollow sections, the fine teeth
will remain uniformly in the same fillet llS, i.e. ;
without jumping into the adjacent filletp which could
result in undesirable noises. OnLy one lengthwise tooth
116 may be provided on the top and bottom side. But two
mutually spaced teeth 116 help prevent a hinge effect at
the connecting point 110.
Each hollow section has on its concave under
side 105 two strip-shaped glide surfaces 106 and 107 in
the area of the side edge profile. These glide surfaces
106 and 107 lie in a common plane and form the support
for the respective hollow section on the seating surface
131 of a base 130. But in the example shown, the glide
surfaces 106 and 107 do not interact directly with the
seating surface of the base 130, but with the top side of
~r~
--10--
.. , ~ .. ~ . ,.. - . ........ . . .
a plate-shaped section 118 of a clamping element 117
which can be placed on the base 130.
Each clamping element has a clamping section
123 lanced out of the plate-shaped section 118, bent
up in hook form, and its free end bent away from the
plate-shaped section 11~, as indicated at 125.
In the example shown, the plate-shaped section
118 is rectangular in top view and has deformations in
the form of longitudinal ribs 120 and 121 to increase
, 10 the bending strength of the plate-shaped section, the
;~ ribs jutting out away from the base 130 in the example
shown. The lengthwise extent of the plate-shaped
section 118 is such that, in assembled condition, the
reinforcing ribs 120 and 121 of the plate-shaped section
118 protrude on both sides of the connecting point 110 `
beyond the glide surfaces 106 and 107 of the adjacent
hollow sections so that the glide surfaces 106 and 107
of the hollow sections 102 and 103 support themselves
on the ribs 120 and 121. The ribs thus form glide
supports for the ~lide surfaces 106 and 107, per~itting
a noiseless heat expansion motion of the hollow sections
transverse to as well as in longitudinal direction of
. . .
the sections.
The clamping elements may consist of plastic,
but preferably of zinc-plated sheet metal parts. -
To install the roof or wall covering, two or
more than two clamping elements 117 are pushed at
intervals over the upper lip 114 of the groove cross
. .
:
:
: ~
~73~
section of the hollow section 102 until the free face
of lip 114 stops against the foot section o~ the hook-
shaped clamping part 123. As the side view in Fig~ 6
shows, the clamping part 123 may be formed so that it
can be pushed over the lip 114 under a predetermined
; preload.
When pushing the clamping part over the lip
114, the glide surface 106 of the hollow section 102
will rest on the reinforcing ribs 120 and 121. As may
be seen from the top view of Fig. 6, the base portion
118 of the clamping element has several holes 127,
through which the clamping element can be nailed to the
base 130 by means of nails 132, as indicated in Fig. 5.
~ow the tongue-like section 111 of the adjacent hollow
section 103 can be pushed into the groove 112. The
depth to which it can be pushed in is limited by the
stop-like, formed portion 125 at the free end of the
; clamping part 123. This simpli~ie.s the installation
work considerably and assures that the visible joint
along the connecting point 110 is o~ the same size and
shape everywhere. When sliding in the section 103, the ~.
glide surface 107 of this section again rests on the
; rib-like reinforcements 120 and 121 of the clamping
element 117. Depending on the number and mutual spacing
of clamping elements 117 distributed over the length of ..
the hollow sections, it can be assumed that essentially
the narrow glide surfaces 106 and 107 of the hollow
sections only rest on the base sections 118 of the
. : .
~ -12-
clamping elements so that a direct contact with the
base 130 can be avoided. But this is not absolutely
necessary. After the installation, all hollow sections
can freely expand or contract in transverse as well as
longitudinal direction when temperatureschange, without
tensions occurring in the sections themselves. Expansion
noises are virtually precluded through this system.
Therefore, a stable, trouble-free roo~ covering o~ great
strength and high quality is thus obtained.
Shown in Fig. 7 is a roof and wall covering
according to another embodiment example o~ t~le inven~
tion. On a conventional base not detailed, of which
only nailing strips 202 are shown, the roof covering
201 has two roof surfaces 203 and 204, each ~ormed of
elongated, hollow, plastic sections. Each hollow sec- -
tion 205 again has a concave outside surface 206 and a
concave underside 207 according to Fig. 9, on which glide
surfaces 208 and 209 are provided. The chambers have
the reference symbol 210, the tongue-like edge cross
section 211 and the groove-like edge cross section
limited by two hollow lips 213 and 214 is marked 212.
It is again assumed in the example shown that
each hollow section consists of a plastic colored dark,
preferably black through and through, by means of a
filler.
The lower ends of the hollow sections are open,
preferably towards the external ambient atmosphere so
that the outside air can enter the chambers 210 at 220
in the area of the lower roof edge. The hollow sections
-13-
. :
~'73~
205 end short of the ridge line of the roof and are
cpen at these ends also. The open ends of the hollow
sections are enclosed in the ridge area by housings
222 which e~tend parallel to the ridge and bound on
air collection chamber 221. Provided on the long
edges of housing 222 are retaining sections 224 and
238, respectively, for elastic sealing strips 225 and
239 which rest elastically on the top and bottom side
of the covering and seal the air collection chamber ;
221 towards the outside and the inside without inter-
fering with the heat expansion motions of the hollow
sections 205.
The two air collection chambers 221 of the
two roof surfaces 203 and 204 are preferably separated
from each other and have separate nipples 236 and 237
for the connection of a suction line. The latter leads
to the intake side oE a heat pump connected to a space
heating system via a heat exchanger. This may involve
any known space heating system.
The air entering the profile chambers 210 at
220 is sucked at low velocity through the chambers 210
upwards into the collecting channels 221 and conducted -
to the heat pump. In the process, the air heats up
greatly, depending on the sunlight. Since practically
all chambers of all the hollow sections can be connected
to the heat pump, a great quantity of heated air is
available, from which heat can be gained via the heat
p~lmp and transmitted to the space heating circuit.
-14-
:
3~
The space heating circuit may also contain appropriate
intermediate heat storage facilities for cooler times
of the day.
It may be expedient in some cases to use
additionally a liquid heat carrier medium also, which
absorbs the heat from the hollow sections as in the
first embodiment example. In such a case, some of the
chambers 210 may be connected directly or through the
insertion of hoses or tubes ~45 (see Fig. 9) to the
circulation of a liquid heat carrier kept in motion by
a pump.
Instead of to the outside atmosphere, the
lower open ends of the hollow sections 205 may also be
in open connection to an inside room of the house in
order to conduct the inside air through the hollow
sections, thereby heating it by utilizing solar energy.
The hollow sections of all embodiment examples
can be used also in the same manner for a wall covering
instead of a roof covering. If the wall in question is
exposed to the sun's rays, the heat absorbed by the
hollow sections can be utilized by a heat pump via an
air circulation in the same manner as indicated in
~- Fig. 7.
It can often be observed tha sun rays will
greatly heat up an air layer located directly above the
outside of the roof or the outside of the wall and almost
resting on the roof or wall surface. In order to utilize
this heat also, the covering may be equipped with devices
to suck up the heated air layer.
-15-
i ' '
Sucking up the outer hot air layer is accomp-
lished in the embodiment example according to Fig. 7 by
a hood 231, disposed along and spaced from the ridge of
the roof, co~ering the outside of the roof surfaces 203
and 204. This forms an entry channel 233 for the hot air
; layer. In the example shown, the hood 231 is supported
by T-brackets 223 mounted or molded to the outer holders
224 of the housings 222. The outer flange 228 serves to
brace the hood 231 while the web 226 is provided with
holes 227 for the passage of warm air. A slide 229,
likewise equipped with holes 230 and oper~ble selectively
or automatically by temperature probes, may be coordinated
with the web 226. ~ir entry under the hood 231 can either
be opened up, throttled or shut off completely by means
of this slide. A collecting channel 234 for the hot air
sucked in from between the ~ebs 226 of the two housings
221. This collecting channel has a separate suction
nipple 235 which is connectable to the heat pump. If
separate valve flaps or similar valve mechanisms are
coordinated with each of the nipples 235, 236 and 237,
the slide 229 can be obviated. The adjustment of the
valve flaps permits optimal mixing of the air components
from the various suction areas prior to being supplied :
to the heat pump. The hood 231 may have a hinge-like
-` section 232 so that one and the same hood may readily
be adapted to different roof pitches.
To be able to connect the hollow sections 205
to each other in longitudinal direction or to equip them
with connecting nipples for a liquid heat carrier medium,
hollow slide sections 240 and 250, respectively, (see
. .:,'
-16-
73~38
Figs. 9 and 10) are provided, They have a center
section 241 and 255, respectively, whose contour and
profile are identical with the contour and profile of
the hollow sections. Protruding from this center
section at least to one side, preferably to both sides,
are plug-like sections 242, 243 whose contour and pro~
file correspond to the cross-sectional area of the
openings of the profile chambers. In this manner, the
ends of the hollow sections 205 can be plugged to the
plug-shaped sections with the interposition of a binder
so that a sealed, firm connection can be established.
The hollow terminal or connecting sections 240 and 250,
respectively, do not inter~ere with the flow in the
chambers.
If the sections such as section 240 serve only
to connect or extend the hollow ~;ections, the center
section 241 is designed narrow in longitudinal direction
only. But if the sections such as section 250 also
serve to make line connections, the center section 255 -
is designed correspondingly wide. As Fig. 10 shows, a
connecting nipple 258, 259 is inserted by means of a
tapped ring 257 into the lower wall of the hollow con-
necting sections at 256 so as to be sealing. By means
of plug-shaped extensions 255a dnd 255b, a hollow sec-
tion 251 and 253, respectively, whose chambers 252 and
, .
`~ 254 communicate with the hollow interior 256 of the
connecting section 250 can be plugged to the latter.
' ;,.
.` . ,
`~ -17-
, . ! '
. ' : .. '
', :, ;" , : .
But the connection section may also be closed off on
one side by a plug, such as indicated at 260 in Fig. 10.
To attract outside air directly above the out-
side of the hollow sections, the hollow sections them-
selves or also connecting sections such as the sections
240 or 250 according to Figs. 9 and 10 may be provided
with projections 263 jutting outwardly like a bay
window, such as indicated in the hollow section 261
according to Fig. 11. The bay window projections 263
of the hollow section 261 are located on the top side
262. The projections 263 rise tangentially ~rom the
surface 262 outwardly and terminate in an undercut face
262a. This undercut face 262 is provided with holes 26
or else with weakened wall areas of appropriate contour
which can either be pushed in easily or be cut out with
a tool to open up certain holes 264 selectively. The
holes 264 terminate in hollow chambers o~ the projection
263 and are in flow connection with the chambers 265 of
the hollow section 261.
In this manner, a certain portion of the air
layer resting directly on the outside o the hollow
section can be sucked into the interior of the hollow
section.
It has been proven to be particularly advan-
tageous for all embodiment examples if each hollow
section is made of plastics having diferent ray
absorption powers. One example of this is shown in
Fig~ 12. In essence, the hollow section 270 has the
~'
-18~
3i5~
same cross-sectional area as the hollow section
according to Fig~ 9. The top surface 271 and the
underside 272 are both concaved. The wall 275 forming
the top surface 271 consists of a plastic with but poor
ray absorption power. This may involve a PVC of notice-
able or good light transmittance. The lower half of
the section consists of a well-absorbing plastic such
` as a PVC colored dark, in particular black, by fillers~
The border line between the two wall areas 274 and 275
10 of different ray absorption power may, as indicated by
a dash-dotted line at 273, for instance, run along an
essentially horizontal plane bisecting the chambers.
In this~embodiment the solar energy is absorbed mainly
in the lower area of the section and transmitted to the
heat carrier (air or fluid). In this process, the out-
side wall 275 heats up relatively little. The same
applied to the air layer on the outside surface 271.
~,~; . ,
Fig. 13 shows schematically the layout of a
; room heating system designed by using the new roof or
20 wall covering. At 280 is shown a roof or wall covering
assembled of several hollow, plastic sections 281a to
. ~
281c in which air can enter the chambers of the hollow
sections at 232. At the other end of the hollow sections
the air is sucked off, collected and conducted through
line 283 to the intake of a heat pump 284 driven by an
electric motor 285, ~or example. The heat thus generated
is transmitted in a heat exchanger 286 to a circulating
heat carrier while the originally attracted air is led
:~
--1 9--
.. ..
~' :
3~3~
into the open or removed for further use at 287. The
heat circulation may contain a heat reservoir 2887 It
belsngs to the space heater 291~ The heat carrier, such
as a fluid heat carrier, is kept circulating by the pump
289 and flows through the radiators 290. After leaving
the radiators 290, the heat carrier flows back to the
heat exchanger 286 again.
But the heat ~enerated and emitted by the heat
pump 284 may also be transmitted to the air of an air
space heater.
When hollow sections are used which are clear
or transparent on the outside it may be expedient to
employ as heat carrier a fluid coLored dar~, in particular
black. This applies in particular to the arrangements
where hoses or tubes to conduct the heat carrier are
inserted in the chambers of the sections. The heat
absorptivity and with it the efficiency of the arrange-
ment can yet be considerably improved by coloring the
`~ heat carrier dark~ Since the heat carrier is circulated
` 20 as a rule, it need be colored dark practically once only.
