Fences, screens and walls are fundamental aspects of landscape design and construction, defining borders, creating spaces and providing various degrees of privacy and protection from the elements – here are some considerations from BRANZ regarding materials and building techniques
A myriad of fencing options are available, from simple post and wire fences, to prefabricated metal or timber palings or lattice work, to walls of stone, brick or concrete block.
Timber post and rail fences
Use H4-treated or naturally durable timber for all in-ground material. Using H4-treated timber (or equivalently durable timber) for the bottom rail of a fence is desirable, where it is likely that the rail will be covered by or in contact with mulch.
Posts should be placed 100mm into the ground for every 300mm above ground.
Ensure the excavation is filled with rodded concrete (preferably) or thoroughly rammed earth. Limiting fence height to 1m is recommended when rammed earth is used to fill post holes.
Keep timber rail spans smaller rather than larger. The longer the span, the greater the potential for sag in the completed fence – for example, limit the span of a 100x50mm rail on edge to less than 2.4m.
Other factors to consider for timber-framed fences are:
Ensure fixings holding trellis panels together will be durable. Staples should be stainless steel for external use.
Keep fibre-cement and profiled steel fence panels clear of the ground.
Select fittings such as gate hinges and catches that are durable. Stainless steel fittings are preferable to zinc-plated fittings, which are not suitable for external use on treated timber.
Ensure the spans of fencing panels are in the limits set by the manufacturer – typically 600mm maximum for fibre-cement.
For profiled steel claddings:
Don’t use unfinished zinc/aluminium alloy-coated steel in corrosion zones D or E.
Ensure factory coatings are undamaged.
Use colour-matched fixings suitable for the corrosion zone.
Limit spans (supporting framing spacing) to 1200mm.
Avoid use where the surface will not be regularly cleaned by rain.
For fibre-cement:
Use hot-dip galvanised fixings in corrosion zones B and C and stainless steel in zones D and E.
Paint for durability.
Limit spans (supporting framing spacing) to 600mm.
Figure 1: Steps for installing fence posts embedded into the ground.
Brick and concrete block fences or walls
Ensure there is a solid bearing.
Provide a concrete foundation beam to lay the wall over.
Ensure the base of the wall is sufficiently into the ground, anchored to a footing or has structural piers/columns or returns to prevent overturning. In some cases, concrete piles under each column may be required to extend deep into the ground to provide a firm footing. The advice of an engineer should be obtained.
Reinforce as for a concrete block foundation wall.
Keep trees a sufficient distance away from the fence or wall to prevent roots affecting it.
Cap the wall to restrict water entry.
Steel or Aluminium fencing
Embed posts into the ground as detailed for timber.
Cap the tops of posts to prevent water entry and accumulation in the post (a known cause of accelerated deterioration).
For steel, hot-dip galvanise, powder coat or protect with a specialised coating system.
For aluminium, uncoated use is acceptable in most environments.
Avoid coating damage during transport, handling and installation.
Match fixings to the material.
If using a proprietary system, follow the manufacturer’s installation instructions.
Stone walls
There are a number of design and construction options for stone walls. They can be:
Free-standing.
Used as a veneer or facing to a concrete or concrete masonry structural wall.
Used as a veneer to the polystyrene formwork of a reinforced concrete retaining wall.
Solid stone structural walls (usually limited to low height), laid with mortar or without (dry stone).
Built with incorporated piers or columns, either structural or for decorative purposes.
Constructed from uncut stone, where adjoining sides of the stone are not at right angles (such as river boulders or quarry stone), or ashlar, where the adjoining sides have been cut or dressed at right angles to each other.
Coursed, where some effort is made to align horizontal and/or vertical joints, or random, where a stone is either cut to fit or selected for the space available.
For coursed work, there are a number of combinations:
Random squared (or dressed) stone, also called random coursed ashlar, to a general arrangement of courses.
Broken ashlar, where no attempt is made to course the work – each stone is cut for a specific location. where the adjoining sides have been cut or dressed so that they are at right angles to each other.
Coursed, where some effort is made to align horizontal and/or vertical joints, or random, where a stone is either cut to fit or selected for the space available.
Ashlar, where cut stones are laid in continuous horizontal courses with plumb vertical joints. Options include:
Regular pattern using stones of a consistent size, laid stretcher bond (coursed ashlar).
Variable course height (although stonework is of a consistent height and length in each course) with stretcher bond vertical joints.
Variable course height (although stonework is of a consistent height in each course) using stones of different lengths to give random vertical joints (blocked course ashlar).
Coursed random uncut stone, where some effort is made to produce a coursed effect.
Broken coursed (in quarried stone).
Random uncut stone (in river stones and boulders).
Considerations include:
The wall height and the width available to build the wall in.
The availability of suitable stone.
The time available for laying – for example, broken ashlar is a time-consuming laying method.
The construction method – whether it is being constructed as a dry stone wall without mortar to bed the stones or mortared.
The foundation detail.
What will prevent the wall from overturning.
Whether the wall is retaining soil – if so, it must be designed for the loads.
This article was first published in BRANZ’s Landscape Construction book, Second Edition and is reproduced with permission.
The book covers the design, building and planning rules as they apply to landscape construction and provides guidance on design and construction to ensure good practices are followed. It can be purchased at www.branz.co.nz.