Landscape Detailing Volume 2

Surfaces

Michael Littlewood

• Publisher: Routledge
• Year: 2012
• eBook ISBN: 9781136154058
• Edition: 3
• Topic: Architecture
• Subtopic: Architecture General

As a ready reference for landscape designers and as an indispensable time-saving tool, Landscape Detailing is an essential for the design office.Each section begins with technical guidance notes on design and construction and then provides a list of points against which specifications can be checked. This is followed by a set of drawn-to-scale details sheets. These details can be traced for direct incorporation into the set of contract drawings. A list of relevant British Standards, references, bibliography and a list of associations and institutions indicate where further guidance can be obtained.

PEDESTRIAN PAVING

GUIDANCE NOTES

Paving patterns

Patterns for large units such as paving slabs should be kept as simple as possible, as a heavy pattern is only attractive when used to fulfil a particular function. Do not mix colours and too many different surface finishes. When introducing a texture into the paving, consider the function of the area, i.e. wheeled traffic or street furniture. When introducing an infill into a large area of smooth paving, make sure the overall design and pattern of the infill are not in conflict. In selecting colours of paving, first ensure that they blend with the building or surroundings.

Large complex patterns are difficult to design as they suffer foreshortening when seen obliquely from the ground, making them difficult for the pedestrian to comprehend. Small units such as bricks offer a variety of patterns. Setts, either granite or concrete, offer even more flexibility, such as curved and circular patterns, but their use in an area should be very carefully considered. Cobblestones, depending upon their shape, are used either as a deterrent surfacing or for walking upon. They can be used to infill corners when creating paving patterns with other materials or on their own for a path if properly laid.

Choice of materials

Hard surfaces should retain their interest throughout the year. A limited range of materials should generally be used to give coherence to a scheme, but surfaces should not become monotonous, particularly in the winter months.

The materials selected should complement each other and be suitable for the shapes they are covering. In-situ concrete and gravel are better for awkward or rounded shapes than square or rectangular units which require extensive cutting. The best guide to selecting appropriate paving materials is by observation; those derived from natural materials are obvious choices. New materials using, and blending with, the colours of these materials, provided they are laid correctly, generally look right.

It is preferable to reflect the local vernacular, as this creates a sense of place. The separation of pedestrian from vehicular surfacing provides an opportunity to create a far more interesting design. Where it is necessary to provide for pedestrians as well as vehicles, a mixture of materials can be used, or the same material (in a different colour) can be used for vehicles but with the appropriate increase in foundation thickness.

The main aim is to keep the areas of each material as large as possible and ensure a smooth transition from one to another. The stronger the pattern, the larger the area must be, and considerable care must be taken not to introduce too many colours. Some paving colours clash violently with the foliage of plants. Keeping the elements as natural as possible, such as granite setts, gravel and cobblestone, is one method of producing a harmonious design.

Weathering

All materials weather, but at different rates. Natural stone paving and natural materials accept moss and lichen easily. The subtle variations in light, shade and dampness are expressed by these growths, quickly giving the material a ‘mature’ look. Bricks, pavers; tiles and concrete lose their manufactured finishes less quickly, retaining into old age a crispness not in itself unpleasing.

Weathering can be encouraged by selecting rough textured materials, or by applying organic solutions to encourage the growth of moss and lichen. The latter is not always desirable as it makes the surface damp and slippery.

Paving materials

Different paving materials should be used logically to indicate different usage of areas, changes of use, and as direction indicators.

Drainage gutters and changes in level can often be picked out in different materials to good advantage. Small-scale unit materials relating to pedestrian scale can be contrasted with more monolithic paving in areas used by vehicles. Careful choice of materials can produce an interesting and satisfying floorscape.

At a functional level, paving surfaces should not be slippery, be resistant to erosion, have a reasonable life expectancy and require limited maintenance.

Sub-grade, base and sub-base

To ensure that any surface paving material retains its final laid position, it is essential that both the surface and base materials be prepared thoroughly. Paving usually has a base and sub-grade underneath, and both of these must be thoroughly compacted.

Sub-grade

This should be well compacted either by hand or by mechanical means. The required contour of the paving is obtained by shaping the sub-grade.

Base

The base is usually of hardcore, compacted by a 3-tonne roller or a 508 kg vibrating roller.

Design of sub-base

The design of the sub-base is dominated by two factors:

1. The bearing capacity of the sub-grade, expressed as its California Bearing Ratio (CBR). Table 10 (derived from Table 3 of Road Note 29) shows the CBR values for typical British soils. Note that the depth of water table affects the results. Sub-soil drainage should be provided if the water table is less than 600 mm below formation level.

2. The load carried in the design life of the paving. For pedestrian areas design is usually on a rule of thumb basis. Table 11 shows the thicknesses of sub-bases required for typical pavings, for a given CBR of sub-grade.

TABLE 10. ESTIMATED CBR VALUES FOR BRITISH SOILS

TABLE 11. SUB-BASE THICKNESSES

Foundations on firm dry sub-soil, where light pedestrian use can be ensured, may not be required for paving units more than 500 mm square and in-situ concrete paving. Where small paving units are to be used, a concrete base should generally be laid, except for brick and concrete blocks, which may be laid on a flexible foundation with a sand laying course.

Base or laying courses of mortar or sand are used to bed unit materials such as blocks, bricks and paving stones to obtain finished levels. Base courses are used for flexible surfaces like tarmacadam or cold asphalt, which may be thin or made with small particles, and have little cohesion without a base.

Choice of materia...

Table of contents

• Cover
• Halftitle
• Title
• Copyright
• Contents
• Foreword
• Acknowledgements
• Introduction
• Tables
• Vehicular Paving
• Pedestrian Paving
• Steps and Ramps
• Margins, Edges and Trims
• Kerbs
• Drainage Channels
• Appendix A. References
• Appendix B. Bibliography
• Appendix C. British Standards
• Appendix D. Manufacturers and Suppliers
• Appendix E. Institutions and Associations
• Appendix F. Standard graphic symbols
• Appendix G. Conversion tables