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Playgrounds Designs

Space Requirements
Design of a playground differs from design of other recreational facilities in one very important respect: the first decisions which must be made are the types of equipment that will be installed. Until these decisions are reached, it is impossible to adequately determine how large the facility must be to permit safe use. If the available space is limited, then the playground planner is obviously limited in the type and size of equipment to be installed.
 
The minimum space which must be kept clear of hazards around a piece of equipment to allow for safe play is referred to by the U. S. Consumer Product Safety Commission (CPSC) as the "no encroachment zone." Because different kinds of playground equipment require different zones, the first step in laying out a playground is to determine what equipment will be installed. After the equipment choices are made, a scaled layout should be prepared to provide for safe movement of pedestrian traffic around the equipment.
 
The best source of information on the necessary clearances between pieces of playground equipment is the CPSC "Handbook for Public Playground Safety." The authors recommend consulting this handbook before laying out any public playground facility.
 
It is also important to consult with manufacturers of playground equipment for their recommendations on minimum safe distances and other factors relating to playground safety.
 
18.2b Surfacing Materials
 
Playground surfacing material is meant to do three things:

1. To provide a barrier separating the feet of playground users from the soil layer beneath
2. To allow surface water to drain easily through the profile and quickly reach an installed drain system or a naturally porous sub-base that will channel it away.
3. To safely absorb the shock of falls by kids using the facility.

Table 18.1 is based on a CPSC chart with recommended depths of surfacing material required to protect users falling onto the surface from variously-sized playground equipment. Understanding this chart requires the planner to determine the maximum height from which a user could fall in using each piece of equipment, then to find the depth in inches of material needed for proper shock absorption.
 
Table 18.1. Minimum Surface Depth for Various Falling Heights (from CPSC)
 
Almost all suppliers of surfacing material can provide information on how much each product will settle and/or compact in use. This information will help the planner make appropriate buying decisions regarding the amount of material required.
 
Shredded Wood
The most common surface material used on playgrounds today is shredded wood. (For our purposes, we will refer to all of the wood products listed in Table 18.1, as "shredded wood.") The deeper the layer of shredded wood, the greater the ability of the surface to absorb the shock of falls (see Table 18.1).
 
With effective subsurface drainage under the material, wood loss through decomposition is minimal, but it will still be necessary to make occasional additions to the shredded wood layer. Frequently check the surface layer for both thickness and sogginess. If the bottom of the wood layer is usually waterlogged, it probably indicates that the drainage system is not adequate. Be aware that freezing temperatures reduce the cushioning ability of shredded wood surfaces.
 
Sand
In some areas, sand is a popular alternative for playground surfacing. Sand has some attractive qualities as a playground surface material: sand is soft, it does not rot, and it cushions falls fairly effectively. However, wet sand sticks to shoes and clothes and tracks all over. Also, sand without fine (coarse sand) is unstable to walk or run across, and displaces easily out of the area. Check Table 18.1 for minimum sand thickness required.
 
Like shredded wood surfaces, sand loses its cushioning properties in the presence of moisture and freezing temperatures.
 
Pea Gravel
Pea gravel is another material sometimes used for playground surfacing. However, this material never stabilizes, which makes it difficult to walk or run across, and consequently less desirable as a playground material. Pea gravel is also somewhat abrasive, creating the safety concern of scrapes among playground users. Probably the best use of pea gravel for a playground would be to install a layer of it as a drainage material under a shredded wood surface layer, although some disagreement about this method remains (see Section 18.2c below.)
 
Rubber Chips
One of the new products of the recycling movement is rubber chips for playground surfacing. This material is soft and easy to work with, and it does not rot. The disadvantage of rubber chips is cost--at this writing, three to five times the cost of shredded wood. However, given the fact that the rubber does not rot, the cost of replacement material is eliminated. So if the price of rubber chips declines, the economics of using this material will look better and better.
 
Ask the manufacturer for the minimum depth of rubber chips to install for the maximum falling height of the equipment being used.
 
Rubber Mats
Interconnecting rubber mats are also available for playgrounds. In addition to their advantages under swings and slides, these mats should also be considered for any areas that will be used by children with disabilities. Rubber mats are sometimes installed over asphalt beds, and are also used for indoor play areas, such as those becoming popular at fast-foot restaurants.
 
As with rubber chips, ask the manufacturer for the maximum falling height, and for recommended drainage specifications.
 
18.2c Planning for Effective Drainage
 
Whichever surfacing material is chosen for a playground, virtually all authorities agree that it is important to plan the facility to provide effective drainage. There is also general agreement that it is important to isolate the playground against runoff from adjacent areas by using swales and/or catch basins. However, there is substantial disagreement about how to achieve drainage underneath the surface material when it is placed over a nonporous sub-base.
 
For example, one common way to construct playgrounds with a shredded wood surface is to install pipe drains in cloth-lined trenches 12" deep in the subsurface. The pipe is covered with pea gravel to subsurface level, then filter cloth is laid over the entire playground. A layer of pea gravel is then installed with an additional layer of filter cloth on top of it. (The filter cloth keeps the materials from infiltrating each other.) Finally, the shredded wood is placed in a uniform layer on top of the gravel. Many playgrounds around the country have successfully used this design to achieve a dry and well-drained facility.
 
However, soil scientists point out that this layering of materials is a technique that is considered to result in a perched water table, which would hold water in the surface layer until it becomes fully saturated. To prevent this condition, these experts say that the only way to achieve effective drainage under the surface material is to contour the surface and the subsurface to allow positive runoff.
 
Those who construct the layered playgrounds, however, counter that relying on contouring alone has created conditions in which water lays in the surface materials, resulting in excessively wet areas and, in some cases, rotting of organic surface materials accompanied by an unpleasant odor.
 
If the planner is concerned about the possibility of a perched water table, one alternative method would be to omit the gravel layer, and to install strip drains in the sub-base, then to place the surfacing material directly on the sub-base. This method would also offer cost savings through the elimination of the pea gravel and through the substitution of less costly strip drains. If shredded wood is used as the surfacing material, the installer would need to backfill the strip drains with coarse sand. But if the surfacing material is inorganic (sand or gravel), that surfacing material itself can be used for the backfilling process. (See Chapter 8 for details on the use of strip drains.)
 
Whichever of these methods is used, the process of laying out a playground for effective drainage should begin with a topographic survey to solidify the planners' understanding of how water moves around the surface of the area. Then develop a set of proposed elevation to isolate the playground from that surrounding water movement. In most cases, playgrounds can be laid out on a fairly level plane, sloping 1% or less in any direction.
 
Where subsurface drain systems will be installed, pipe drains or strip drains on 20-foot centers will normally provide for adequate removal of surface water resulting from inclement weather.
 
Of course, one problem area on most playgrounds is mud puddles in the depressions under each swing or slide. An effective installed drain system will prevent this problem by draining away moisture before these mud puddles can develop. Also, rubber mats can be installed to prevent the formation of these depressions.
 
It has become common in some areas to build playgrounds "aboveground"--to construct wooden or plastic forms around the perimeter of the playground and fill the enclosure with surfacing material. Many planners have ended up with soggy, poorly draining facilities because they assumed that an aboveground facility will by definition drain quickly and easily. The truth is that the forms can turn into a sort of artificial lake in wet weather unless the sub-base is porous, or some sort of installed drain system is provided.
 
A drain system should be laid out at the same time as the playground equipment, to make sure drains will adequately serve trouble spots like those under swing sets, slides, etc. Smaller "tributary" drain lines can be run to serve these areas.
 
As mentioned above, catch basins can be a valuable tool for keeping the playground playable by channeling away surface water from the surrounding terrain before it reaches the playground. Catch basins also serve as the junction boxes of installed drain systems. Aim to leave 15 to 20 feet between the edge of the playground and the catch basins. Use small grate openings to prevent tripping and bicycle tire damage.