Principles of Pallet Storage Design
A Guide To Pallet Storage Design In The Context Of Industrial Storage And
Materials Handling
One of two no-nonsense guides to safe
storage from Redirack
THE PRINCIPLES OF
PALLET STORAGE DESIGN
A guide to the basic principles of pallet storage design,
in the context of modern
industrial storage and materials handling
CONTENTS
Foreword
Page 4
What is a store?
5
How wide?
8
Which pallet?
9
How high?
12
Pallet rack layout
15
Which pallet, which rack?
18
How much can be stored?
19
Alternative pallet storage layouts
22
FOREWORD
Increases in the cost of square footage, the high cost
of building materials, higher labour charges, expensive
equipment, and stiff penalties for late deliveries and
damaged goods. The key to success in the storage and
materials handling business is, to a great part, knowing
how to get over these hurdles.
The science of storage and materials handling is a fastgrowing science. New systems and techniques come thick
and fast. But a close look at the ‘science’ will reveal a basis
of simple fundamentals and good oldfashioned commonsense.
The title of this booklet, ‘The Principles of Pallet Storage
Design’, may sound much like that of a complicated
textbook. Far from being complicated, it is like the science
it is about, mostly common-sense. Although only a very
concise guide to basic principles, this booklet will provide
you with the basic formulae necessary either for designing
a working storage installation, or for improving an existing
one.
It won’t, of course, turn you overnight into a leading
storage and materials handling expert. But it will, we
hope, help you over some of those hurdles that exist in the
business of building and operating a successful storage
installation.
WHAT IS A STORE?
Before we can begin to analyse stores, storage
methods, materials handling and so forth, we must
know what a store is. And we must identify the
unique characteristics which make it a store.
To help us arrive at a definition, let us take a
simple store, found in every household. The most
common storage item in a house is the cold water
storage tank, found normally in the roof space.
Water comes into the tank from the mains,
the water is held in the tank and is then drawn off
through various taps.
Immediately we can see three of the basic
characteristics of a store - water comes IN (goods
come in) the water is HELD (goods are stored), the
water goes OUT (goods go out).
IN
HELD
OUT
The next distinguishing features of a store is
why the water is held.
Let us look at what happens when we draw
water off. Sometimes no water is drawn off. One
may turn on a tap. A toilet is flushed, and somebody
runs a bath. These things can happen individually,
at any time, or all together, or, one single demand
can be combined with any other demand. In other
words, the demand for water in a household varies
from nothing, to all taps running at the same time.
However, water comes in from the Main at a
constant rate. So it would be impractical to expect
the water from the Main to meet this widely varying
demand. At times, if all taps were being used, the
pressure would be very low and each user would get
very little water.
So the water tank acts as a BUFFER between
the fluctuating demands for water, and the rate
of supply of water. Notice we have built up the
definition of a store - A STORE HOLDS GOODS
AS A BUFFER BETWEEN THE FLUCTUATIONS IN
SUPPLY OF THE GOODS AND THE DEMAND FOR
THE GOODS.
Stores throughput
Although the function of a store is to hold goods, the
way In which goods flow through a store affect the
method in which they are held. In particular, goods
come in and go out in the following manner:
BULK IN
INDIVIDUAL IN
SETS IN
BULK OUT
INDIVIDUAL OUT
SETS OUT
Any alternative in the way the goods come in,
shown in the first column, can be combined with
any alternative in the way goods go out, shown
in the second column. To make matters more
complicated, in any store there can be several of
these combinations operating at once.
Take for example, a factory where at the end of
the production line, coils of wire are stacked on to
a pallet of half a ton or one ton capacity. They are
moved into the store on a pallet, so we have BULK
IN. Ideally despatches to customers are made in
pallet loads, so we get BULK OUT.
BULK IN
BULK OUT
However, there are times when an individual coil
has to be despatched to a customer, and this is a
case of BULK IN - INDIVIDUAL OUT.
Take another factory where pneumatic tools are
assembled. Bulk supplies of components come in
from suppliers. In the stores different components
are selected and put together on to a tray to make
up a completed tool, so here we have BULK IN SETS OUT.
If we consider a pallet racking beam or a pallet
racking frame as one item, then at the end of the
production line individual items are transferred to
the store where they are put together to meet an
order, so we have INDIVIDUAL IN - BULK OUT.
Of course some items are either too large or
too valuable to be moved other than in individual
form, e.g. large diesel engines that go into mining
equipment. These are moved into, and out of store
individually.
Under normal circumstances it is rare to get a
SETS IN - BULK or INDIVIDUAL OUT. This most
common occurrence of sets is in the outward
movement, but the above is theoretically possible.
The one exception to these definitions of flow is
when the holding operation is the prime function
and the flow through is insignificant. An example
of this is where the goods are held for an aging
process, where for example, whisky may be kept in
store from five to fifteen years.
‘Measuring’ performance
There are four criteria we can use in measuring the
‘performance’ of a store.
1. Use of volume.
2. Ease of selection.
3. Ease of handling.
4. Preservation of the quality of goods.
The ‘Use of volume’ is a statement of how much
cubic capacity is effectively being used out of the
total amount available, i.e. the volume of the goods
stored compared with the volume of the building
length x breadth x height.
‘Ease of selection’ - indicates all those factors which
go to the identification of the location of the goods
stored, both for putting away into the stores, and for
getting them out to meet despatch requirements.
‘Ease of handling’ describes those factors that
affect the handling of goods, whether mechanical
handling is required, whether double handling is
involved, the speed of handling, etc.
‘Preservation of the quality of goods’ relates to
deterioration of the goods, either by accidental
damage, age, as with vegetables for example, or
deterioration because goods go out of style, e.g.
fridges, cookers (which although fairly robust in
themselves do have changing styles ).
Now these factors are all inter-related. Any
action to improve one factor will most likely
adversely affect the others.
A simple theoretical example can demonstrate
this. Imagine you have a simple cubic building
with one door into it. If you fill this building up
completely, you will make excellent use of volume.
However, if you have more than one type of item
stored in there, then it would be extremely difficult to
select the item you want. So what happens?
Do you start creating gangways to improve the
selection of goods? This will immediately reduce the
use of the volume.
If you require mechanical handling the
gangways need to be even wider, reducing the
volume, and there is always a danger that with
mechanical handling the rate of damage to goods
increases.
Of course, you might find that by block stacking
the lower items will be crushed, so you may decide
either to store only one-high with the consequent
reduction in volume, or put the goods on racks,
which also reduces the amount of volume effectively
used.
The most common plea from someone
investigating an efficient store is that he needs
more space. In practice this is rarely so. There is
usually enough volume to cater for the goods he
stores. It is more likely that the requirement is in
fact, for improved handling, improved selection of
goods (whether putting away or despatching), or for
increased protection of the goods. This is why great
care must be taken to identify the more important
factors relating to the optimum efficiency of the
store.
For a simple example relating to the use of
volume, imagine a building 30 m long by 14m wide
by 7m high to the inside of the ceiling obstructions,
that is 2940 cubic metres.
Storage capacity of layout:
1 block 22 pallets x 6 pallets x 4 pallets high
= 528 pallets
2 blocks 10 pallets x 5 pallets x 4 pallets high
=400 pallets
TOTAL:
928 pallets
Each pallet uses 1.5 cubic metres.
Therefore 1392 cubic metres of storage is utilised
in 2940 cubic metres available.
=47.35% usage!
That allows only 42 different lines to be stored and
assumes every single space can be used, which will
not be the case in practice.
PALLET AND LOAD
DETAILS
HOW WIDE?
When considering storage equipment to be used
with uprights we need to go back to basics. The
function of Adjustable Pallet Racking is to store
goods on pallets. Therefore, the physical parameters
of the pallets affect the racking used. The weightcarrying capacity of pallet racking is a specific
instance of a general principle. The affects of the
weight of the load can be traced through all the
structural members of the racking down to the floor,
and every structural member must be considered as
follows:
GENERAL PRINCIPLE
PALLET RACKING
LOAD
LOAD
SHELVING
PALLETS
BEAMS (IF USED)
BEAMS
UPRIGHTS
FRAMES
FLOOR
FLOOR
gap between the top and bottom decks is usually
100mm.
When used in conjunction with racking, pallets
normally rest on beams (they of course could rest on
solid shelving but this would be an expensive way
of carrying the load). Consequently the underside
of the pallet, which is the interface between pallet
and beam, is most important. Pallets are frequently
described as two-way or four-way entry, which
means that the forks can either enter on two sides or
four, as the sketch shows.
At this stage we are considering wooden pallets
only. Pallets are objects which permit goods to
be moved mechanically by fork lift trucks. These
goods may be single units or a multiple of items,
but normally the load is such that it cannot easily
be carried manually, and the use of a fork lift truck
effects cost savings.
A pallet must have a deck on which to carry goods,
a space into which forks can enter, and a support
on the ground. Because the thickness of forks
entering the pallet is of the order of 50 mm the
In the following section, WHICH PALLET?, we take
a closer look at pallets and pallet types, the choice
of which will ultimately dictate to a larger extent, the
width of racking to be used.
WHICH PALLET?
Pallet components - standard terms and
definitions
TWO-WAY ENTRY
Here the bearers permit the entry of forks or fingers
from two opposite directions only. The sides through
which the forks enter are called “entry sides”.
FOUR-WAY ENTRY
The bearers (or blocks) permit entry of forks or
fingers at each end and at each side. The sides
through which the load wheels of a pallet truck can
pass without leaving the ground are known as “free
entry sides” . The other sides, where the load wheels
have to pass over the bottom slats are termed
“restricted entry sides”.
BEARERS
Members under the top deck or separating the top
and bottom decks, which provide a space for the
entry of forks or fingers. They may consist either of
longitudinal members or distance pieces (usually
known as blocks).
CHAMFER
A rebated angle in the structure of a pallet, in
particular on the edges of the bottom deck, to
facilitate the passage of the load wheels of a
pallet truck.
(a) Through chamfer
(b) Stopped chamfer
STANDARD SIZES FOR FLAT PALLETS
The British Standards Institution has selected the
following plan dimensions for standard pallets:
800 mm x 1200 mm, 1000 mm x 1200 mm,
1200 mm x 1200 mm, 1200 mm x 1800 mm
(B.S. 2629 1967)
The International Organization for Standardization
has also recommended the above sizes and
proposed the following plan sizes as international
standards for maritime use:
DECK
The top or bottom flat surface which may be solid or
otherwise.
ENTRY MEMBERS
Members forming the outside edges of decks on the
sides in which the forks or the fingers enter.
STRINGER
A horizontal member connecting the bearers and
supporting the deck.
ENTRY
Space permitting the entry of forks or fingers in a
particular direction.
WINGS
Those parts of the deck or decks which project
beyond the bearers.
1200 mm x 1600 mm and 1200 mm x 1800 mm
These standard plan sizes take into account the
majority of transport vehicles and are designed
to give the best practicable loading on general
purpose vehicles, provided the pallets themselves
are loaded to capacity.
TWO-WAY ENTRY, SINGLE DECKED
A pallet with only a top deck. Suitable for items
which can withstand the concentrated loads
imposed by the bearers, during stacking, e.g.
wooden boxes and drums. Also used where little
stacking is required and for storing unit loads in
pallet racking when the bearers are supported by
the rack framework. Shown here with an Open
boarded (slotted) deck.
TWO-WAY ENTRY, REVERSIBLE
A pallet with similar top and bottom decks, either
of which will take the same load. This gives even
distribution when stacking. Shown here with a
Close-boarded deck. Note: Not suitable for use with
pallet trucks.
TWO-WAY ENTRY, PERIMETER BASE
The bottom slats are so arranged as to present a
level bearing surface, thus giving a less concentrated
load distribution when stacking. Shown here
(inverted) with a Close-boarded deck.
TWO-WAY ENTRY, NON-REVERSIBLE
For multi-tiering. The bottom slats add to the
strength of the pallet and provide a larger surface
area, therefore giving a less concentrated load
distribution. Shown here with an Open-boarded
(slotted) deck.
FOUR-WAY ENTRY, PERIMETER BASE
Four-way entry, having the bottom deck so arranged
as to present a level bearing surface compatible
with hand pallet truck usage, and giving a less
concentrated load distribution when stacking. Shown
here (inverted) with a Close-boarded deck.
TWO-WAY ENTRY, REVERSIBLE, WINGED
The decks extend beyond the outer bearers for lifting
purposes, e.g. by crane with spreader-bar slings.
Similar top and bottom decks either of which will
take the same load. Even load distribution when
stacking. Shown here with a Close-boarded deck.
Note: Not suitable for use with pallet trucks.
FOUR-WAY ENTRY, CRUCIFORM PERIMETER BASE
The ‘cruciform’ design of the bottom slats adds
to the strength of the pallet and improves load
distribution when stacking. The most widely used
type of four-way entry pallet. Shown here (inverted)
with a Close-boarded deck.
FOUR-WAY ENTRY, NON-REVERSIBLE
A pallet having bearers which permit the entry of
forks or fingers from either side or end. This can
be of advantage in block stacking operations.
Only suitable for items which can withstand the
concentrated load imposed by the bearers when
stacking. Shown here with a Close-boarded deck.
FOUR-WAY ENTRY, REVERSIBLE
A pallet with similar top and bottom decks, either
of which will take the same load. Gives even load
distribution when stacking. Shown here with an
Open-boarded deck.
Locating uprights on the beams as shown in Sketch 2
permits the pallets to be enclosed within the perimeter
of the rack. However, the width of the beam is only
50 mm so if the fork lift truck driver fails to put the
pallet fully into the rack there is a danger he will miss
the back beam, causing the goods to be dislodged,
or if he puts the pallet 50 mm too far in he will miss
the front beam level, again causing the goods to be
dislodged. One can visualise the damage that would
ensue to the racking.
Note: Not suitable for use with pallet trucks.
TWO-WAY ENTRY, NON-REVERSIBLE, WINGED
A normal two-way entry pallet but with the deck
extending beyond the outer bearers for lifting
purposes, e.g. by crane with spreader-bar slings.
85% of all wooden pallets in the UK measure 48
in x 40 in (1219 mm x 1016 mm, or the European
standard equivalent, 1200 mm x 1000 mm).
The next 10% of pallets are 40 in x 40 in (1016 mm
x 1016 mm, or the European standard equivalent
1000 mm x 1000 mm). In the former case with the
fork entering the 1200 mm side, 95% of all pallets
enter into the racks with 1000 mm dimension front
to back.
Shown here with an Open-boarded (slotted) deck.
FOUR-WAY ENTRY, REVERSIBLE, WINGED Similar
top and bottom decks either of which will take the
same load. Even load distribution when stacking.
Both decks extend beyond the outer bearers (blocks)
for lifting purposes, e.g. by crane with spreader-bar
slings. Shown here with Close boarded deck.
Note: Not suitable for use with pallet trucks.
Consequently considering the two methods of
loading pallets into racks as detailed before, the
required beam centres are shown as follows. It can
be seen why the 900 mm and 750 mm wide frames
have been established as standards.
The advantages of storing pallets with the front to
back runners resting on the beams enables the front
and rear, left to right cross members to act as a
locking device so that pallets cannot be accidentally
dislodged. However, it does mean that the front to
back members must be substantial, which virtually
eliminates four-way entry pallets.
HOW HIGH?
To determine the height of the rack, one has to
combine factors relating to the fork lift truck, the
goods, the pallet and the building.
Fork truck capability
Below is a sketch showing the height of the lift as
generally described by fork lift truck manufacturers.
The thing to note is that they define the height of
the lift as the height to the top of the forks, when the
mast is fully extended, down to the ground.
Let us translate this into practicalities. The pallet sits
on the forks. The forks support the underside of
the top timbers, thus there is a 125 mm of pallet
hanging below the top of the forks. In addition,
allowance must be made to clear the beams. This
allowance increases with the beam height. The
actual amount to be added on can be seen in
column B on the chart on page 18.
This means that the sum produced must be taken
off the truck manufacturers maximum lift height to
calculate the height at which you can put in the top
beam.
However, fork lift trucks have parts extending above
the height of the forks. The forks are supported by
the mast. Sometimes there are load guards fitted
on top of the mast to prevent accidentally dislodged
good falling back onto the driver. Loads rarely
exceed the height of the parts of the fork lift truck
extending above the top level of the forks. When
working out a layout careful note must be made
as to whether the pallet and its load is higher than
those parts above the forks.
Trucks with extending masts
Many fork lift trucks have extending masts, usually
denoted by the term double or triple mast, or duplex
or triplex mast. They also have what is known as
‘free lift’, when used with these masts. What this
means is the forks travel up the mast for some
height before the mast starts extending.
Now it is possible that a user may have a fork lift
truck with a double or triple extending mast, but is
using it in a comparatively low ceiling situation. On
these occasions it is quite possible that the mast itself
will be higher than the load and care must be taken
about this point.
Most fork lift trucks used with pallet racking are
either reach-trucks or narrow-aisle trucks (which
are based on the reach-truck construction). In
conjunction with pallets care must be taken when
calculating the clearance from the ground to the
underside of the first beam level. When the mast
is retracted the pallet must sit on top of the wheel
casings, so it is already above the ground at this
point. As the mast is extended forward to put the
Of course, it is possible for the forks to be
extended with their load in the gangway, before the
pallet it placed within the rack. This increases the
width of the gangway because in effect the truck is
being used as a conventional counter-balance
truck. The whole point of the reach truck principle is
lost on these occasions. Normally increasing the
height from the ground to the underside of the first
beam level is a most cost effective way of using the
available space.
LOAD + PALLET
BEAM
CLEARANCE
FLOOR TO BOTTOM BEAM
PLAN VIEW SHOWING PALLET
SITTING ON WHEEL CASING
load into the rack the pallet will travel at this height
above the ground. It is not until the pallet is fully
enclosed within the rack that the forks can be
lowered to the ground. So, in addition to the
clearance between the top of the load and the
underside of the beam, clearance must be allowed
for the wheel casing, plus the height of the pallet
above the wheel casing, as shown in the sketch.
SIDE ELEVATION SHOWING PALLET
SITTING ON WHEEL CASING
LOAD + PALLET
BEAM
CLEARANCE
HEIGHT OF WHEEL CASING SAY -
Resultant
Beam
850mm Height
90mm
75mm
1015mm 1050mm
850mm
90mm
75mm
400mm
1415mm 1425mm
Door sizes
The height of doors through which trucks will travel
is obviously critical. Frequently, even when the
forks are in a closed position, the height from the
ground to the top of the mast can be in excess of
2,400 mm. Many doors are only 2,000 mm or
2,100 mm high.
Roof heights
The other factor that must be considered in
choosing the height of the top beam, is the building
itself. There must be a clearance beneath the roof,
the roof truss, or any obstruction such as steam
pipes, lights etc, and the top of the pallet load. This
clearance is not only required in the racks but also
in the full width of the gangway. Clearance required
is shown in column B of table on page 18. Errors
are frequently made here - the following sketch
shows what can happen.
The other clearance in the roof needed is that
required for the sprinkler system. Normally,
insurance companies like the top of the goods
to be at least 300 mm clear beneath the bottom
of the sprinkler head. They estimate that with this
clearance, water can be thrown far enough to put
out any fire. Failure to meet this means that the
insurance premium can be increased significantly.
If you are measuring up a partially completed
warehouse, remember that sprinkler systems, steam
pipes, electric trunking etc, all tend to be among
the last of the services put into a building. So it’s
possible that when you measure up the building
these services will not yet have been installed. (These
comments apply to control boxes located on walls
and columns, too.)
And on lower beam levels, 75 mm min. clearance
is required between the top of the pallet and load to
the underside of the beam above.
So how high?
If a survey was carried out on all the fork lift trucks
available it would be found that the height of the lift
for fork lift trucks with a simple, single mast, would
be in the range of 3 m to 4 m, the trucks with a
double or duplex mast would be in the range of 5 m
to 6 m and trucks with a triple or triplex mast would
be in the range of 7 m to 8 m. However, before
one can determine the height of racks one has to
consider the load and the building.
Unless a building has been purpose-made for
warehousing it is rare indeed that the height to the
eaves is greater than 5 m. During the post-war
boom in industrial building the standard height was
about 4 m. In practice, over 95% of all buildings
used for storage are less than 5 m high, and the
majority of these are less than 4 m high to the
eaves. Assuming that a load plus the top of the
pallet is about 1 m high, and that we use a simple
mast truck, the height to the top of a fully lifted load
will be in the order of 4 m to 5 m. So it can be seen
that depending upon the height of the load, the
most common height to the top shelf is 2.4 m, 3 m
and 3.6 m.
PALLET RACK LAYOUT
In any rack layout there are four components:
1. The space occupied by the goods and the
equipment on which they may be stored, with the
necessary clearances.
2. The aisleways between the goods, for direct
access to the goods.
3. The gangways, at the right angles to the
aisleways.
4. Any other areas, devoted to such things as
marshalling of goods, loading and unloading
of lorries, fire escape routes, clearances round
heating systems etc.
Aisleway widths
The width of the aisleway is the clearance between
the pallet, goods or rack, whichever clearance is the
smallest:
Width of aisleway is determined by the turning
circle of the fork lift truck. This is usually given by
the manufacturer assuming a 1200 mm x 1000
mm pallet is being used. But check, sometimes they
assume a 1000 mm x 1000 mm pallet.
If the pallet being used by the customer is larger, a
bigger aisleway is required.
Normally, the goods are stored within the perimeter
of the pallet. If not, the comments about pallets will
apply to the area occupied by the goods.
ALWAYS INCREASE THE MANUFACTURER’S
RECOMMENDED AISLEWAY BY AT LEAST
200mm.
Why?
Warehouse layouts invariably involve a
compromise between the use of the available space
and the speed of materials handling. Working to
the manufacturer’s minimum aisleways is similar
to parking in a very tight parking space. It can be
done, but it takes time, and there is considerable
wear and tear on both the vehicle and the driver.
(Imagine how fatigued you would be after 8 hours
spent maneuvering in an out of tight parking
spaces). It is reasonable to expect between 20 and
30 pallet movements per hour. This throughput will
be halved with restrictive aisleways.
When calculating minimum aisleway widths
forktruck manufacturers assume that pallets will be
located as far back as possible on the fork.
pallet, can be used e.g.
Aisleway + 2 pallets
+ Clearance = Module
2500mm + 2 x 1000mm + 100mm = 4600mm
THIS
WIDTH OF ROOM ÷ MODULE =
NUMBER OF AISLEWAYS FLANKED BY SINGLE
ENTRY RACKS
NOT THIS
EXAMPLE:
37 METRES ÷ 4,600 = 8 Aisleways
(or two single entry and seven double entry racks i.e 16 x
single entry racks)
And that pallets have been placed on racks
accurately.
THIS
Gangways
Gangways are used to gain access to aisleways.
The absolute minimum width of one gangway
should be 1800 mm. This permits only one fork lift
truck at a time to use it. Although this is more than
sufficient for the truck to drive down, the space is
needed for turning in and out of aisleways.
If more than one fork lift is being used on the above
the gangway should be 3000 mm.
NOT THIS
Quick Method of Assessing Layout
For calculating the number of runs of pallet
locations that can be positioned into the width of
the room, a module consisting of one aisleway +
two pallets + the clearance between the back of the
Gangways are basically dead space. They should
be kept to a minimum. Consequently, the best
utilisation of space is usually achieved when the
racks run in the same directions as the longest
dimension of the space. This rule holds true in 90%
of cases.
The number of gangways is frequently determined
by the requirements of the Fire Officer and Fire
Escape routes, e.g. the optimum layout may be:
It is possible, of course, to convert a gangway into
an aisleway like this:
The number of gangways required - (which then
determine the length of the racks) is determined by a
number of factors such as the amount of access
required, number of forklift trucks in use, position of
marshalling-area. However, it is desirable that the
racks should not exceed 30 metres length. Longer
than this the fork lift truck drivers’ effectiveness
decreases, caused by things such as difficulty in
locating pallet positions, greater distance penalties
for choosing wrong aisleways etc.
This would be rejected because there are aisleways
with access from one end only, causing dead ends
or blind alleys. Thus there should normally be
gangways at the end of aisleways.
The beam length is determined by number of pallets
per beam x left-to-right dimension of pallet, plus at
least 75 mm clearance between each pallet, and 75
mm clearance between pallet and frame.
So taking the most common pallet sizes used in this
country, 48 in (1219 mm) x 40 in (1016), and its
European equivalent 1200 mm x 1000 mm, two
pallets side by side.
2 x 1219 = 2438 + 3 x 75 mm clearance.
= 2438 + 225 = 2663 mm.
2 x 1200 = 2400 + 3 x 75 mm clearance.
= 2400 + 225 mm.
= 2625 mm
Our STANDARD is 2650 mm
The length of the rack is determined by adding the
width of the upright + clearance to the length of the
beam x number of bays + one upright (add 90 mm
to beam length for our SD uprights, 110 mm for our
HD uprights).
e.g. 4 bays, SD Uprights, 2650 beam
90 + 2650 = 2740 x 4 = 10960 + 90
= 11050, overall length of run.
WHICH PALLET-WHICH RACK?
Width of frames, clearance between back-to back
loads, pallet overhang, height clearances. These
are all key considerations in planning a rack.
Fortunately, the SEMA Code of Practice provides an
easy way of calculating the necessary dimensions.
They’re tried and tested
recommendations, and you should be surprised if
your supplier suggests anything different. If he does,
and he hasn’t got a convincing reason for doing so
- use these tables to work it out for him...
Pallet locations end elevation
2 WAY ENTRY
typical dimensions
x
y
z
750
600
100
900
700
100
1000
750
150
1200
900
150
4 WAY ENTRY
x
y
z
750
700
75
900
800
75
1000
900
100
1200
1100
100
x - overall depth of pallet
y - dimensions over outside of beams
z - back to back clearance between pallets or loads
Pallet locations front elevation
typical dimensions
BEAM
HEIGHT
a
b
3000
75
75
6000
75
100
9000
100
125
12000
100
150
Beam Height is the dimension from floor to top of
beam
a - clearance between adjacent pallets or loads, and
pallet/load and upright.
b - clearance between underside of beam and top
of load or pallet where no automatic height
selection is used.
HOW MUCH CAN BE STORED?
The illustrations on the following pages show layouts
and capacities for various types of storage systems
with different types of fork lift trucks.
The table on page 21 shows the theoretical and
practical capacities of goods stored in each of these
layouts. These are based on a building 60 m long
by 32 m wide by 7 m headroom (clear).
When considering the practical capacity of a store
one must bear in mind the criteria for measuring the
performance of a store (see page 5). These are:
1. Use of volume
2. Ease of selection
3. Ease of handling
4. Preservation of the quality of goods (quality
preservation)
To get an exact answer to the question: ‘how
much can be stored?’ one would have to consider
all the factors relating to a specific warehouse.
The notes below are designed to help you apply
the generalised facts and figures to your specific
application. In some cases they cover in detail points
made earlier in the text.
Ease of Selection
As we’ve said, it is impossible to operate a store
assuming 100% use of available capacity.
Normally it is desirable that goods of different
types are not mixed together. Pallets of item B should
not block access to pallets of item A. Therefore when
assessing the practical capacity of a store for say drivein racking, or for block-storage or live storage, one
has to assume that the lane of storage is for one item
only. Thus, in a drive-in or block-storage situation, four
pallets deep front to back, by four pallets high, then all
the 16 pallets should be of one type of goods.
If the goods are mixed, all that is happening is the
cost space and storage equipment is being transferred
to the cost of selection handling and quality
preservation. Obviously if one has to remove and
replace two or three pallets to get at the item required,
then it can be seen handling will take considerably
longer. There is a very good chance that the goods to
be selected will be hidden by other items, so selection
would take longer, and every time goods are moved
the likelihood of damage increases.
‘LIFO’ and ‘FIFO’ are terms that you will come
across in warehousing, they mean ‘Last In, First Out’
and ‘First In, First Out’. If deterioration in the quality
of goods is important then a warehouse normally
has to operate under FIFO principles, consequently
block storage and drive-in storage are not practical
because their use tends to be restricted to a LIFO
situation.
If the principle of non-mixing goods is adhered to,
then the variety of goods that can be kept will depend
upon the number of distinct different storage locations
available. In layout 5, showing block storage, the
theoretical capacity is 5076 pallets. However, there
are only 94 lanes so that particular store can accept
only 94 different types of goods or lines. To establish
whether the extra capacity would be useful, one
should ask ‘How often would we get a situation
where all 94 lines will each fill every single space
available?’ On our table of capacities of the various
layouts we have shown the number of ‘picking
locations’ available against each lane.
Picking Locations
‘Picking locations’ is an important term, which
needs explaining.
Basically there are two ways of locating stock.
One can either locate goods that come in into
the first available space, i.e. Random Location, or
specific locations can be allocated for certain types
of goods, i.e. Specific Location.
In Specific Location the item numbered 1 will go in
the first location and the item numbered 2 will go into
the second location, and so on. By using the item stock
number obtained from a catalogue or
computer printout the location holding the stock of that
item can be found. The potential disadvantage of such
a location system is where the size of the goods stored
varies considerably. It is used extensively for example
in certain sub sections of mail order warehouses, e.g.
shirts, pyjamas, dresses etc. are packed in boxes all of
roughly the same size. However, in sayan engineering
spares or service store, item 1 could be a complete
tractor engine, and item 2 a 12 mm washer. Here
it can be seen that variation of size can cause great
wastage of space if a Specific Location system is used.
As a consequence most stores do tend to work on
a Random Location system. Unfortunately it often
happens that no systematic method of enumerating
the locations is used and these warehouses tend
to rely on the memory of a storekeeper as to the
location of a particular item A systematic method of
pin-pointing a location is to use a numerical or alpha
numerical system of the first digit numbering the rack,
the second digit numbering the bay and the third digit
numbering the shelf level. So working on a six digit
code, a location might be numbered as follows: 05
1402, which means the fifth rack, the 14th bay and
the second location from the floor assuming goods
are stored on the floor, i.e. first shelf level. All that is
needed now is for the warehouse keeper to record on
a card where he is putting the goods using this
numerical location system and when the goods are
called for despatch they can be located very easily.
This brings us to the term ‘Picking Location’
which is one frequently used in mail order and
wholesale operations which tend to store goods on
a Specific Location basis. When a storekeeper is
assembling a multi-item despatch order he walks
around the various locations and picks the goods
required, hence the term Picking Location. The
corollary of that term is ‘Putting Away Location’.
Ease of Handling
If a fork lift truck has to drive down a narrow aisle
it will go slowly. It is for this reason that installations
using narrow aisle trucks have guide rails so that the
speed of the fork lift truck operation can be increased.
However, guide rails are not normally supplied with
drive-in installations or block storage installations so in
these cases speed of operation is reduced dramatically.
The smaller the number of aisleways and gangways
the smaller the number of fork lift trucks that can be
used to operate the warehouse. So in the warehouse
where there is fast movement of the goods this can be
a disadvantage.
Where the border between the aisleway and the
goods is not clearly defined this will lead either to an
increase in the damage to goods or to slowing of
handling.
As mentioned before if different types of goods
are mixed together this automatically slows down the
handling. One of the most important principles that
should be applied to handling and particularly to the
place where goods are kept is Pareto’s rule:
“In any series of elements to be controlled, a
selected small fraction in terms of numbers of elements
almost always accounts for a large fraction in terms of
effect. This tendency has also been expressed as the
concept of the ‘vital few and the trivial many’ and is
commonly known as the ‘80-20 Rule’” . This means in
warehouse terms that 20% of the lines account for 80%
of the volume of goods despatched, volume of space
taken up, volume of goods coming in. Ideally therefore
if these can be identified they should be located near
to the goods inward and despatch areas to reduce the
amount of fork lift truck travel.
In block storage and drive-in it is essential that the
width of the fork lift truck is smaller than the width of
the pallet, otherwise extra space has to be allowed to
accommodate the fork lift truck in the storage lanes.
Use of Volume
Another term one comes across is ‘Lead Times’.
This is the time taken from the order being placed
to the delivery of the goods. Usually sufficient goods
have to be stored to accommodate the despatch
demands during the lead time. In other words, if
it takes four weeks for goods to be delivered after
ordering, it is advisable to have at least five weeks
stock, to ensure that after the purchase order has
been placed demands on the store can still be
met. This of course has a serious consequence on
practical use of volume.
If goods go out on an average of one pallet a
day and the lead time is 20 working days, then
goods would be re-ordered normally when there
is 25 working days stock. At that stage there are
25 pallets in stock. However, by the time the fresh
supplies of goods have arrived this stock holding is
down to 5 pallets. So one can see that on average
during this time one has 15 pallets in stock.
If the minimum quantity that can be ordered is
say 30 pallets then at the end of four weeks the
stock holding is 35 pallets.
Consider the consequence on the effective use of
volume on bulk storage systems such as block stacking
or drive in. When the purchase order is delivered 35
to 40 pallets are in stock, so 35 to 50 spaces must be
available. Just prior to that delivery only 5 pallets are
in stock. This is a situation that is repeated throughout
a warehouse, but with different phasing. On average
therefore there are 23 pallets occupying 40 pallet
spaces, or 57.5% of the usable space.
This is a situation that will apply in all warehouses
using the Specific Location system, and, because of the
constraints of not mixing goods bulk storage systems
must operate to a Specific Location system. Basically,
on average, in the examples given in the bulk storage
situations (drive-in, blockstacking, and live storage). it
is estimated the practical use of the space available is
just over 50%.
Now of course this problem will not apply to
Random Stock location systems because as stocks go
down in one item the space freed can be filled with
different goods. It has been known that a Random
Stock selection system has been operated up to a 92
or 93% efficiency, but this demands extensive systemscontrol of the warehouse. For practical purposes a
figure of 80% should be used.
The amount of money tied up in stock would be
exorbitant if on every single occasion any customer
placed an order it could be met out of stock
immediately. Most warehouses aim to achieve a
90% satisfaction level. In other words in any 10 items
ordered 9 will be in stock.
By judicious use of the Pareto’s rule, and ensuring
that the 20% popular lines meeting the 80% demand
are always in stock a 99% customer satisfaction level
can be achieved.
General
It tends to be treated as a bit of a platitude, but
the situation is that the only constant in business is
change and that any warehouse or store designed
for today’s business is likely to be obsolete next year
or the year after. Frequently warehouses are
2184
2016
4428
2. Reach Truck APR
3. Counter Balance
APR
4. Drive-In
2538
1269
2 High
1 High
4000
4160
3700
2528
6. PMPR
7. PMPR
8. Live Storage
9. Narrow Aisle
4 High 300 mm
4320
3807
3 High
Pallet Converter
5076
4 High
5. Block
2342
No. of
Pallets
1. Reach Truck APR
Layout
3792
5550
6240
6000
6480
1904
3807
5711
7614
6642
3024
3276
3513
Cubic
Metres
28.75
41.3
46.4
44.6
48.2
14.2
28.3
42.5
56.7
49.4
22.5
24.4
26.1
% Use of
Cube
Theoretical Capacity
80
56
80
80
54
54
80
80
80
% Use of
Storage
Equip.
2022
2072
3328
3200
2333
1685
1371
2056
2741
2391
1613
1747
1874
No. of
Pallets
3033
3108
4492
4800
3500
1028
2057
3084
4112
3587
2420
2621
2811
Cubic
Metres
22.57
23.13
37.1
35.7
26
7.7
15.3
23
30.6
26.7
18
19.5
20.9
2528
148
4160
4000
94
82
2016
2184
2342
Picking
% Use of Locations
Cube
Practical Capacity
Comparative Storage Capacities (see diagrams on pages 22/26)
designed to allow for the maximum of flexibility to
meet changing conditions even if this means a loss
in the use of volume.
Bearing this in mind an optimum warehouse
for any particular business would normally contain
a conglomerate of different types of storage
equipment, be it block stacking, conventional
racking, drive in, live storage or powered mobile.
ALTERNATIVE PALLET STORAGE
LAYOUTS
1. Reach Truck
2. Reach Truck
3. Counter Balance Truck
4. Drive-in
5. Block Storage
6. Powered Mobile
7. Powered Mobile
8. Live Storage
9. Narrow Aisle
10. Pallet Converter
N.B. Uprights encroach on pallet space thus
reducing capacity
Plan view
Redirack Limited, Wharf Road, Kilnhurst, Mexborough, South Yorkshire. S64 5SU.
Tel: +44 (0) 1709 584 711 Fax: +44 (0) 1709 589 821 Web: www.redirack.co.uk