Water and external systems · Decks & Paving
Fence and Gate Boundary System
A reference account of the fenced boundary as one continuous structure, of the gate as a differently loaded part of that structure, and of the ground line where such assemblies commonly fail first.
Educational reference entry. How this system behaves depends on climate, jurisdiction, loading, substrate, the adjacent systems it meets, how the building is used, the manufacturer's instructions and qualified professional design.
Overview
What fence and gate is
A fence resists wind at its posts and their bases, not at its panels. This is the distinction from the masonry boundary wall, which states its own purpose as enclosing a space with a permanent masonry element 'rather than with fencing or planting', and which resists wind by weight and buttressing. That sentence draws a boundary around the wall entry, and this system is what sits on the other side of it.
The line is a single structure rather than a repeated detail. Rails, arris rails or straining wires connect the posts so that wind on one bay is shared along the run, and the ends, corners and straining points are where that continuity is anchored. A post in the middle of a run is doing a different job from the post at the end of it, even where the two look identical.
A gate is part of the line and is not the same problem. Its weight acts at a distance from the hanging post, it is repeatedly accelerated and stopped, and the closing post has to still be where the latch expects it after all of that. The two gate posts are therefore loaded quite differently from the line posts on either side, and they are commonly the parts of a boundary that stop working first.
The ground line runs through the whole assembly and is where it usually fails. That band is alternately wet and dry, it holds the post against overturning, and it is where the line has to negotiate sloping ground by stepping down or raking with it. What happens in that band is decided by the post material, the base, the ground and the treatment together.
Terminology
Common names and aliases
These names describe the same assembly. The encyclopedia keeps one entry per system so that a trade term or a regional name never becomes a second, thinner page.
- fencing system
- boundary fencing
- perimeter fencing
- post and rail fencing
- fence line and gate
Purpose
What this system is intended to do
The job the assembly exists to perform, conceptually. An intention is not a guarantee that any particular build achieves it.
- Mark, enclose or screen a boundary with a line that resists wind through post fixity rather than through weight.
- Share the action on any one bay along the run through rails, wires or a continuous frame.
- Carry a gate within the line without the leaf's weight and movement being taken by an ordinary line post.
- Follow sloping or uneven ground while keeping the infill doing what it was chosen to do.
- Protect the part of each post that sits in the alternately wet and dry band at the ground line.
Composition
The roles this system is made of
What each part does in the assembly and what it depends on — never a product, a thickness, a fixing or a determination that anything is adequate for the role.
Order is not meaningful in this system. These roles interact as parts of one whole rather than stacking up in a sequence, so the list below is not a build-up and nothing should be read into the order it appears in.
- Primary supportLine posts and their bases
The elements that hold the line upright and carry wind action into the ground, whether set into a surround, bolted to a base or driven. What resists overturning is the post and its base together, so neither can be considered without the other.
- AttachmentRails, arris rails or straining wires
The horizontal members connecting posts into a continuous run. They carry the infill and they share action between neighbouring posts, which is why a run behaves differently from the sum of its bays.
- ProtectionThe infill
Panels, boards, mesh, wire or slats filling between posts and rails. It is what the boundary is for - screening, containment or demarcation - and it is also the surface the wind acts on, which makes an appearance decision a loading decision.
- Primary supportStraining, corner and end posts
The posts at the terminations and changes of direction, loaded along the line rather than across it. A wired or tensioned line pulls on them continuously, and they hold the continuity that every intermediate post is relying on.
- Primary supportHanging post and closing post of the gate
The pair of posts a gate lives between. The hanging post carries the leaf's weight at a distance from itself as well as the force of the gate being swung; the closing post has to remain where the latch and the stop expect it. Neither is an ordinary line post.
- AttachmentGate hardware
Hinges, latch, stop and any drop bolt or ground socket. These are where the repeated action of a gate being opened and shut is delivered into the posts, and they are the parts adjusted most often and understood least.
- Edge and terminationGround-line profile: steps, rakes and level changes
How the line follows the ground - stepping down in bays, raking with the slope, or being made up at the bottom. It decides what happens to the infill at each change and where gaps open at the base of the line.
- ProtectionTreatment of the post at the ground line
What is done where the post passes through the alternately wet and dry band: preservative treatment, a sleeve, a metal spur, a raised base or a change of material. It is the zone where the assembly most commonly fails first, and where the failure is invisible until the post moves.
Interaction
How the parts work together
The reason this is a system rather than a list of parts: what depends on what, and what stops working when one part is changed.
Change the infill and every post and base sees a different action, although nothing about the structure looks different. A close-boarded or panel infill presents the wind with a solid surface where an open mesh or spaced rail let most of it through, so a boundary that was rebuilt with a more private infill has quietly been given a larger load on the same posts.
Continuity means a post is only as fixed as its base and its neighbours together. Rails share what lands on one bay along the run, so a single failed post is carried for a while by the ones beside it, and the line goes on looking sound until enough of them have gone for the run to move as a whole.
Hang a gate on an ordinary line post and it rotates out of plumb and stops closing. The leaf applies a turning action the line post was never asked to resist, and the first sign is not a structural one: it is a gate that drags, then catches, then needs lifting.
Step a line down a slope without rearranging the infill and gaps open at every step, because the panel is rectangular and the ground is not. Raking the infill instead keeps the base closed but changes what the infill has to be, so the ground profile is chosen at the same moment as the panel type rather than discovered afterwards.
Materials
Material families commonly met in each role
Commonly encountered, not recommended. Whether a material suits a given project depends on the whole assembly, the exposure, the manufacturer's documentation and qualified professional review.
Primary support
Posts are commonly encountered in these families, including concrete posts used with timber infill. What a post has to resist depends on the infill it carries and the exposure of the site, and is a structural question on tall or solid boundaries.
Primary support
Post bases and surrounds are commonly formed in these families. How a base resists overturning depends on the ground it is formed in as much as on the material, which is why identical bases behave differently across one site.
Attachment
Rails, fittings, hinges and straining hardware are commonly met in these families. Where two different metals meet, or where a fixing passes into treated timber, compatibility is a documentation question rather than an assumption.
Protection
Infill is commonly encountered in these families, from boarded timber to woven or punched metal to filled cages. How solid the infill is changes what the posts are resisting, so the family is not only an appearance decision.
Protection
Applied treatments of these kinds are commonly met on posts, rails and infill. What any of them does at the ground line, where the exposure is most severe, is set by the product documentation and by how the post was treated before it arrived.
Edge and termination
Gravel boards, plinths and kerbs at the base of a line are commonly formed in these families. They close the gap where the infill meets uneven ground and keep the infill clear of it.
Boundary
Where this system ends and meets another
The edge of this system. Everything above is inside it; each junction below is a condition at its boundary, where an adjacent system or an adjacent building condition takes over. Junctions are where most assemblies actually fail, so they are set out explicitly rather than left inside the prose. What resolves one is a detail designed for the specific building — not a rule of thumb.
A fence carried on or continuing from a masonry wall
Where a line is fixed to the top of a wall, or a run of fence continues from one, the wall is being asked to take a wind action it was proportioned for without the fence. The wall entry lists gates, railings and items fixed to it as something outside itself, which is precisely the junction this is.
Read about Freestanding Wall →A line crossing or meeting paving
A post set through a paved field interrupts the laying course and the perimeter restraint the paving depends on, and the paving returns the favour by making the post base hard to form and harder to replace. Which of the two was designed first is usually visible on site.
Read about Flexible Paving →A boundary standing at the top of a retaining structure
A fence along the head of a retaining wall places its posts inside the zone of ground the wall is holding, and adds a wind action above it. The two are commonly designed separately, and the retaining structure is the one that was not told.
Read about Gravity Retaining Wall →Where a boundary coincides with a change of level
Marking a boundary and guarding a drop are different duties with different requirements, and a line that does both is being asked to satisfy the guarding requirement. Which requirement governs, and what it asks for, varies by jurisdiction and is not settled by the fence looking substantial.
Read about Guarding System →Buried drainage and services in the line of the posts
A boundary is a straight line of holes dug to a consistent depth, which is exactly where drains, ducts and supplies commonly run beside a building. Establishing what is in the line is a question asked before the first post base, not after.
Read about Buried Drainage Network →A line passing through a rooting volume
Post holes within a rooting volume cut roots and compact ground that was deliberately left uncompacted. Where a boundary has to cross one, how the line is founded there becomes an arboricultural question as much as a structural one.
Read about Tree Pit System →The legal boundary and the neighbouring land
Which side the posts and rails face, whose ground a base occupies, how far a gate swings and whether the far face can be reached to maintain it are questions of ownership and of local convention rather than of construction. They are settled before the line is set out, and they vary by jurisdiction.
Considerations
Topics worth discussing
Which topics genuinely apply to this system and what to raise about them. Measured values, classes and ratings come from a qualified professional's design for the specific building, not from a reference page.
- Durability
- The ground line is the part that decides how long the assembly lasts, and it is the part that cannot be inspected. What the post is, how it is treated, and what it passes through in that band are worth more attention than the infill that everyone is looking at.
- Movement
- A line stands in ground that swells, shrinks and freezes, and it carries a gate that moves by design. Whether the run is expected to stay in one plane, and what is acceptable where it does not, are worth stating rather than assuming.
- Moisture
- Water reaches this assembly from above, from splash at the base, and from the ground itself. Keeping the infill clear of standing ground, and letting the ground line drain, is the recurring theme of every long-lasting boundary.
- Buildability
- The line is set out on ground that is rarely level and rarely straight, and the setting-out decides where the steps fall and whether the gate opening lands where it is wanted. Access to both sides of the line during construction is commonly the constraint nobody raised.
- Maintenance and access
- Gates need adjusting, timber needs recoating, and posts fail one at a time. Whether both faces of the line can be reached, and who has the right to reach the far one, determines what upkeep is actually possible.
- Interfaces
- Boundaries meet walls, paving, retaining structures, drainage and level changes along their length, and each of those junctions is designed by someone thinking about the other thing. The line is the element that crosses all of them.
Design
Questions the design has to answer
The decisions this assembly turns on. They are questions rather than answers, because the answer depends on the building.
- What is this boundary actually for - marking, screening, containing or guarding - and does the infill follow from that?
- Is the infill solid or open, and have the posts and bases been considered against that action?
- Where does the gate sit in the run, and are its hanging and closing posts different from the line posts?
- How does the line follow the ground: stepped, raked or made up, and what happens to the infill at each change?
- What is in the ground along the line, and who confirmed it before post holes were dug?
- Does any part of this line coincide with a change of level where guarding requirements apply?
- Which face of the line faces out, whose land does the base sit in, and how is the far face maintained?
Boundaries
Commonly misunderstood points
Distinctions that are easy to blur, and the places where a familiar term means something narrower than it sounds.
- A fence is not a lightweight masonry wall. The published boundary wall entry describes enclosing a space with a permanent masonry element 'rather than with fencing or planting', and a wall resists wind by weight while a fence resists it by post fixity; this system is the case that exclusion leaves.
- The panel is not what resists the wind. The infill collects the action and the posts and their bases resist it, so changing to a more solid infill increases the load on an unchanged structure without anything appearing to have been altered.
- A gate is not a hinged panel. Its two posts are loaded by a leaf that hangs away from the hanging post and is repeatedly swung, which is a different action from anything the rest of the line carries.
- A boundary line is not guarding. Where the ground falls away, guarding requirements apply on their own terms, and satisfying them is not established by the fence being tall or solid.
- The post does not fail where it is seen to break. Loss of section happens in the band at the ground line, and the break higher up or the lean that follows is the consequence rather than the cause.
Conversations
Questions for qualified professionals
Bring these to the relevant qualified professional, manufacturer or authority. Requirements vary by project and location.
- For a boundary of this height and this infill, has the wind action on the posts and bases been considered by anyone?
- What base arrangement is proposed for each post type, and how does it differ for the gate posts?
- How is the ground-line zone of each post being protected, and what is expected to happen there over time?
- What is known about buried services and drainage along the line, and how was that established?
- Where the line meets a wall or a retaining structure, who is checking what that structure is being asked to carry?
- Does any part of this boundary coincide with a change of level that brings guarding requirements into play?
- What access is needed to both sides of the line, for construction and for upkeep, and has it been agreed?
What this page does not do
- This entry describes how a fenced boundary is organised. It is not a specification, a design, or a substitute for advice from a qualified professional where the line is tall, solid, exposed or retaining.
- No height, post spacing, embedment, base size or wind action is stated here, and none can be inferred from this page.
- Boundary position, ownership, permitted height and rights of access are legal matters that vary by jurisdiction, and verify them against local requirements before work begins.
- Where a boundary also guards a change of level, the guarding requirements are separate from anything described here and are determined by the applicable regulations.
Related systems
How this system relates to others
Every link states what the relationship actually is, rather than leaving a bare list of related pages to be read as a suggestion.
Alternatives
Different systems answering the same need. Listing them together is not a comparison and does not suggest one is better — which, if either, suits a project is a design decision.
Applications
Building contexts this system is used in
The functional parts of a building this assembly is commonly met in. This is membership, not a ranking and not a recommendation: several systems answer any one context, and which of them suits a project is a design decision. A context appearing here does not mean the system is suitable, permitted or adequate for it.
- Boundary Structure · External works
- External Works · External works
Go deeper
Related Build Design Hub guides
Planning guidance behind the decisions this assembly involves.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this system comes up.
Decks, Paving and Hard Landscape Systems
External surfaces people stand on, plus the substructure, edge, support and guarding that make one usable, each decided by the layer beneath and the route its water takes.
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