Difference between revisions of "Fence"
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Revision as of 14:29, 18 September 2017
There are various types of fence, each with their own strengths and weaknesses.
This article considers the construction and repair of different kinds of fence.
A new fence must comply with all applicable rules for fences. These can include covenants on you property as well as planning law and permissions. Timber fences marking boundaries between properties are exempt from the Party Wall etc Act 1996, but permanent structures like brick walls do fall within its remit. A DIYer should be extremely cautious if contemplating replacing a timber fence with a wall, and certainly obtain all necessary permissions before starting work.
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.
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.
The featheredge fence is built entirely from timber: posts, horizontal rails and overlapping featheredge boards, and ideally with the boards resting on timber boards along the bottom. This type of fence is strong and durable, and impact damage can often be repaired by renewing only the affected boards. It is also straightforward to build a custom installation to negotiate obstacles, and if the ground is difficult you have a free choice of post spacings. Conversely the material cost is higher and the fence is slower to construct compared to panel fencing.
Rails can be arris rails or cant rails. Arris is triangular and more common in Britain; cant is rectangular with a sloped top to let water run off. You can use metal brackets to fix the rails to the posts, but tapering the ends of the rails to fit into notches in the posts will make for a stronger job. The top rail should be rather lower than the top of the boards to make climbing over the fence less easy.
Featheredge boards require an overlap of 12 mm or more as a precaution against shrinkage. You can use a block of timber to achieve a consistent overlap, but remember to use the spirit level from time to time to make sure the boards are upright and not tending to lean one way or the other during assembly.
The usual width for the boards is "5 inch" (now sold as 125 mm) but there are many other widths. If you are building a new fence, be aware that some featheredge boards are twice the thickness of others and will make for a stronger job. A row of timber boards along the ground at the base, attached to the fronts of the posts, makes construction a lot easier.
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.
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.
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 the 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 for fences come in 3- and 4-inch sizes. The 4-inch posts contain almost twice as much wood as 3-inch posts (16 against 9 square inches), are more durable and better surviving rot and high winds. They are also large enough to accept notches for the rails in featheredge and plank fences.
H-section timber posts exist. Panels are slotted in between the posts, as with some concrete posts. These posts offer good support to a panel, but they are weaker than a solid post of comparable dimensions. They work well with dense trellis panels, but may not be strong enough for a solid fence panel especially in an exposed location.
Round posts are available with a point on one end. These are mostly used in agriculture, where the farmer will use machinery to drive them into the ground.
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.
uPVC sleeves are available to drop over a structural steel or timber post.
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 in weak ground the post can be wobbly.
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.
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.
Occasionally its difficult to get a sound fixing at the base of the post due to for example there being a weak wall under the posts, which wont hold the fence against strong winds. If there's a suitable wall nearby, posts can be fixed at the top instead, using a crosspiece.
- Nail it in place. Nails can pull out in severe winds
- Slot panels into slotted posts. Easy, but panels can be removed easily by vandals or strog winds
- Screw it into place. Better pullout resistance than nails
- Fence clips (pictured). Stronger fixing than nail or screw, but more cost
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 an 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 almost no support.
Another option where appearance isn't critical is to ram a second short post into the ground next to the original, then screw or 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, nailing or bolting a new treated strip on can fix it. A bowed panel can generally be straightened the same way.
The featheredge fence is a surprisingly strong construction, and a major impact can leave damage needing only a minor repair where a panel fence would need one or more complete new panels. If you are buying a few replacement boards, take one of the old ones with you to the timber yard. Boards vary in profile and especially thickness, and it is possible to rip down wider and thicker boards to create new boards to match the profile of the originals.
Featheredge boards will rot at the bottom if they are touching the ground. The options are a full replacement, replacement of a few worst affected boards, 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.
Cut wires can be fixed to the nearest post and missing sections replaced.
Trellis 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 temporary filling.
The thin iron wire can 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.