Difference between revisions of "Fence"
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Broken panels can be lifted out and new ones slotted in.
Broken panels can be lifted out and new ones slotted in.
Revision as of 13:03, 11 August 2009
A Fence gives privacy, a useful degree of security, and some noise reduction. It also helps establish boundaries.
There are various types of fence, each with their own strengths and weaknesses.
Ready made fencing panels are attached to timber posts or slotted between concrete posts. This is a fast way to install fencing, but the durability of the lightweight panels does not compare well with post & rail types. Panel fencing is probably the most popular type in Britain. Panels are widely available in 4', 5' and 6' heights.
Where panel ends are screwed or nailed to walls, drilling a clearance hole avoids the chance of the thin timber splitting, but takes a little longer. Splits reduce strength and encourage rot.
Various types of fencing clip are available to attach panel to timber post. No clips are required with concrete posts, the panels just slot in. But with these its possible to pop a panel out with enough force, so they aren't ideal for containing rowdy teenagers. Its also possible for severe winds to blow panels out.
Where the fencing run is not a multiple of panel size, panels are sometimes mounted sideways to change post spacing. Another option is to cut a panel and reattach the panel edging.
Fence panels have a thin strip of wood along the top to reduce rain penetration at the fence top. When the panel is mounted sideways this strip should ideally be removed and refixed to the new top of the panel.
Posts, horizontal arris rails and overlapping featheredge boarding create a strong and durable fence. However the material cost is higher, and they're slower to construct compared to panel fencing.
Its easy to space posts at custom distances, making going round objects (eg large trees) and curved fences eaiser than with panels.
Either arris or cant rails can be used. Cant is rectangular with a sloped top to shed water, arris is triangular. Metal bracets can be used to fix the rails to the uprights. The top arris or cant should be fixed well below the top of the fence for maximum board rigidity, and to make climbing over the fence less easy.
Featheredge boards require a minimum overlap of about 10-15mm, as they can shrink. Using a small piece of timber to achieve this is much quicker than measuring each one. Boards should be fixed with a nail in the centre, if 2 nails are used into each rail they can split as the timber shrinks.
A string line can be used to keep the tops of teh boards in line when fitting.
A tough robust alternative to featheredge is to use 1" sawn plank. Buying wany edge plank from a sawmill keeps costs down. This weight of wood is good for fences prone to vandalism.
Adding intermediate posts connecting the planks together (but not fixed in the ground) toughens the result up considerably, and assembling with screws instead of nails makes it even more durable.
Concrete panels can be slotted in between concrete posts. Each gap takes several low height panels. The result is heavy and vandal resistant, but not pretty.
Picket fences were developed in the US for their low cost, and are a type of post & rail fencing. The fences are of low height, and the vertical boards are spaced to give an open fence. Traditionally the top ends are decoratively shaped and the fence painted white. This is a low security decorative type of fence well suited to the fronts of properties, as it looks good, doesn't block view, and discourages undetermined intruders.
Post & Rail
The simplest post & rail fence is posts plus just one horizontal rail, usually at waist height. This marks a boundary, and can guide casual passers by in the right direction, but achieves little else.
The horizontal rails may be positioned like this
rather than this
to reduce susceptibility to rot.
There are 2 main types of wire fence.
Wire meshes are stapled to timber fence posts to create a see through barrier fence. There are various weights, mesh sizes and mesh patterns available, the best known of which is chicken wire.
Some amount of tension should be applied. Cut mesh ends can be wrapped most of the way round the posts to avoid finger injury.
Plastic coated mesh is an alternative to the more common galvanised, and gives a softer appearance. Galvanised posts are an alternative to timber.
Fencing wire is run horizontally, tensioned and stapled in place. These fences establish boundaries and discourage walking, but since they consist of nothing but posts and a few wires they don't offer any privacy or noise reduction. These are a minimum cost fence mainly used for stock control and boundary marking, and discouraging casual intruders. With 3 wires they aren't quite as easy to get through as simple post & rail, so have better deterrence.
A diagonal supporting post is added at the ends and corners of fence runs to support the final uprights, which must handle significant side load.
Fencing pliers can tension the wire, cut it and hammer in the staples.
Posts and heavy duty trellis create an open fence that allows sunlight through. These can be used for light climber coverage. Rails should be used for durability. The lack of rigid edged panels means several fixing points are recommended for good durability.
Low trellis is often added to the top of fence panels for decoration, and to encourage climbing plants.
Timber fencing roll
These consist of thin vertical wood canes closely spaced and tied together with iron wire. These are simply unrolled and stapled to fence posts & rails. The appearance is more informal and softer than panel fencing. The rolls may be made of various small timber, including sometimes bamboo.
These rolls are available in varying weave densities from open to closed, and differing weights of timber and durabilty of species.
Thin flexible stems can be woven between closely spaced posts (eg 6"). However the thin posts succumb to rot more quickly. These are suitable where lots of thin cut branches are available, and children can participate in building them. However the high labour input makes them not often used.
In some areas this is traditionally done with living hedge plants, each one is partly cut through, bent over and woven between neighbouring stems. These fence-hedges are pretty but slow to construct.
There are several rot prevention strategies
Soaking in preservative is more effective, and is more practical with lower cost preservatives such as oil & paraffin and smaller parts such as posts. A soaking bath can be made from sheet plastic restrained by blocks, or plastic wrapped round the workpiece and tied can also be used. Check the plastic isn't attacked by preservative before use.
Post connectors that hold the post off the ground move the posts away from the biggest cause of fence post rot, wet ground.
Decorative tops on the posts keep most of the rain off the exposed top end grain, delaying top end rot.
These low concrete fence boards, usually a foot high, sit under the timber panels to keep the wood panels away from wet ground and rain splash. The much drier timber panels last longer. Gravel boards are low cost, and their extension of panel life is significant. Despite this they are more often omitted to minimise initial cost.
6" boards are liftable by one person, a 12" board takes 2 people.
Timber boards can be used the same way as gravel board. These will rot eventually, but are fairly easily replaced. They're much cheaper to buy and far easier to install than concrete boards.
Mounting fence panels a couple of inches up from ground level avoids contact with wet soil, and allows ventilation, much reducing rot. It also allows mice, birds etc to escape from cats. The disadvantages are it encourages dogs to burrow under the fence, and allows weeds to grow under the panel from one side to the other.
A line of bricks under the panels acts in a similar way to a gravel board, but is less effective as the height is low. It is however an improvement on putting the panels on the ground. Its not as effective as mounting the panels off the ground with a gap, so is used when a gap at the bottom is unwanted.
Durable woods such as red cedar can be used, but are relatively expensive.
Coating the bottom section of the fence post with tar delays rot. This must be done before the post is installed, its not effective to just coat what shows afterward.
Square timber posts come in 3x3 and 4x4 sizes. The larger posts are more durable, better surviving rot and high winds.
Round 6" posts are also available with a point on one end. These are mostly used in agriculture, and are much tougher animals.
H shaped timber posts also exist. These are formed by nailing 2 planks onto a square section post. Panels are then simply slotted in between the posts. These offer better support to the panel outer frames in high wind areas, but require more material & labour to construct. but have little else to commend them. Water is trapped between the nailed pieces, accelerating decay. Stopping the planks several inches above ground level avoids accelerating ground level decay.
Good quality concrete posts can survive over half a century, though their appearance is not always liked as well as wood. Budget posts can fail as quickly as timber.
Concrete posts are very heavy, and take a minimum of 2 people to install.
With H section concrete posts, fence panels can simply be slotted in to place.
Galvanised steel posts may be used with wire mesh. The mesh is tied to the post with galvanised iron wire.
The writer has no experience with these, but its hard to believe they'll be very strong.
The most important thing is to get the posts accurately upright and correctly spaced. This is done using a fence panel, or a strip of wood cut to size & spirit level. A fencing sprit level can be attached to the post being driven, or posts can simply be checked for level after every couple of whacks.
Misaligned metal post sockets can be adjusted to some degree. Their angle can be corrected a little if necessary by hammering wedges into the post socket, and the post position can be moved a small amount by shaving a little wood off one side of the post where it sits in the socket.
Several post fixing options exist.
Hammering pointed posts direct into soil is an option, but can sometimes lead to wobbly and wonky fences.
A post rammer is the tool for the job. If a sledge hammer is used, the post top should be protected with a piece of scrap wood to minimise damage. Stony ground can make insertion difficult or impossible, and weak ground can make the post wobble.
A hole is dug for the post, and filled with concrete to support the post. This is a very robust type of fixing, and is low cost. The concrete mix is often put in dry; damp in the soil slowly sets the mix, and until set the mix acts as ballast to support the post. Its not necessary to use a high strength concrete mix.
A downside of this fixing type is that the post hole fills with water, encouraging post rot.
A no-fines concrete mix won't trap water as much, and can improve post life to some extent.
A hole is dug for the post, and filled with ballast (stone) for support. This is less robust than concrete, but is often sufficient. The limited ventilation provided by the ballast results in less wet conditions than with concrete fixing, which can delay post rot to some extent.
Round smooth stone is not suitable, only angular stone will lock together when compacted.
Metal post connectors
Bolt down connectors are used to attach posts to large masonry on the ground, such as large concreted areas. These connectors are no use for attaching to small pieces of masonry such as bricks, as the masonry must provide enough stability to withstand high winds.
Spiked connectors are hammered into soil. A timber stub (or fence post) should be used in the socket when hammering to avoid damage, and care is required to get them upright.
Adjustment of spiked connectors is not possible once inserted. Stony soil can make these impossible to keep upright. Making a pilot hole before insertion with a metal bar and sledgehammer has been reported to help with alignment.
Post connectors that keep the fence post an inch or 2 off the ground reduce the amount of rot in the post, giving a longer lived fence.
These metal post sockets have a base that hammers into the rotted base of an old post. They are used to avoid digging out a concrete fixing, and allow re-use of the old post with its rotted end cut off. A timber post with rot already set in won't last so well though.
Domestic fences are rarely required to be movable, but when they are the posts can be mounted in planting tubs filled with ballast, concrete or earthcrete.
Removing concrete fixings
Removing old concrete fixings can be done by digging around the lump and pulling it over sideways, preferably using the post if still attached. If the post has come away, an iron bar can be inserted and used to move the lump. The post is pulled one way and stones are put under the lump, then its pulled the other way and more stones put under. Repeating this gradually lifts the concrete out of its hole. An SDS chisel can break the lump up for disposal.
Rot of the fence post base is a common problem. Post replacement is a good option, but in many cases householders don't want to do the work.
Bar & ballast support
Where the post is near a wall and in a sheltered position, top fixing or ballast support are simpler fixes. A horizontal post is run from fence post top to wall, and
- either fixed to the wall with metalwork
- or rested against the wall, and the other side of the post restrained with a bag of ballast.
Although these are less than perfect repairs, they are effective, can survive storms in sheltered areas, and the appearance is acceptable for many situations. The ease of repair makes these approaches attractive, and can put off full fence replacement for many years.
A metal post holder with a spike can be used in non-stony soil. Hammer it in, keeping it aligned, and fit the timber post to it.
Bolt down metal post holders can be used to attach the remaining post to a substantial piece of masonry. These are only effective where the masonry in question is stable enough to prevent fence movement, sometimes they're seen bolted to little pieces of masonry that offer no significant support.
Another option where appearance isn't critical is to ram a second short post into the ground next to the original, then bolt the 2 together.
Repair of rotting panels is not usually worthwhile, panels are readily replaced.
If the panel has come apart but is not rotting, fixing it back together is generally quicker than getting a new panel, and ensures a colour match.
Where one strip of timber has broken but the rest is ok, bolting a new strip on can fix it. A bowed panel can generally be straightened the same way.
Featheredge tends to rot at the bottom. The options are full replacement, replacement of a few worst affected strips, or fixing a couple of additional horizontal strips across the bottom. Keeping soil clear of the bottoms much improves longevity.
Broken panels can be lifted or smashed out and new ones slotted in.
Damaged parts are readily replaced.
Post & Rail
If rot at the post tops is a problem, the posts can be trimmed down a bit and re-railed. However fitting new posts is likely to give much longer life expectancy.
Wire mesh gets cut by vandals and burglars sometimes. It may be sewn back together with iron wire.
Cut wires can be fixed to the nearest post and missing sections replaced.
Trelllis is usually used to support climbers, and by the time the plants are established, partial rot of the trellis has little effect, the plant providing additional support and visual cover. Thus trellis tends to be left until badly rotted, by which time replacement is the only option.
If the climber is robust and established, 2 or 3 horizontal wires may be enough to support it instead of new trellis. This minimises plant disruption.
Timber fencing roll
The thin posts tend to rot at the base. New posts of any diameter can be fitted and the fence tied to them.
Bits of wood can come out of the fence; new trimmings can be woven in. The new wood need not match, and soft dried stalks are usable as short term filling.
The thin iron wire may break. Sharp ends should be tucked out of the way, and new wire can be woven in to cover the break and a few stems each side. However by this time this is happening, more breaks are likely to occur. The fence may be re-tied or stapled to the horizontal rails using a close spacing to enable further service time.
New pieces of timber can be woven in, softer material can be used to fill gaps, or a climber can be planted early in the fence's life to fill any gaps later. Woven hedges will cover themselves with foliage each summer, and grow new wood to fill themselves.
Party Wall etc Act
Fences marking boundaries between properties are covered by the above Act, and failing to follow the measures outlined in the act can leave a DIYer liable for significant costs, and in extremis criminal prosecution for a minor offence. Following the letter of the Act can incur significant costs if the 2 owners proceeed without agreeing on the work, and such costs are usually judged not worthwile for small domestic fences.
Many repairs and replacements are done on the basis of verbal agreement. However this exposes the DIYer to the risks of costs of reinstatement, legal fees, and in extremis criminal prosecution for this minor offence. It is thus generally best to carry out work only after written agreement has been obtained in line with the Party Wall etc Act.