Which Post Support Do I Need? Complete Guide

The right post support depends mainly on what you are building, the surface or ground conditions, the size of the timber post and the loads the structure needs to withstand. For a lightweight fence in suitable ground, a post spike may be sufficient. For a pergola, canopy or heavier timber structure, an H-post support or another heavy-duty support anchored into concrete will usually be more appropriate.

Choosing the correct post support is important for both the stability and durability of a timber structure.

Do not choose a post support based on the post dimensions alone. A 90x90 mm post used for a lightweight fence is subjected to very different loads from a 90x90 mm post supporting a pergola.

Quick answer:

Lightweight fence in suitable ground: post spike.
Timber post on an existing concrete base: bolt-down post support.
Post anchored into concrete: suitable U-post support or concrete-mounted support.
Pergola, canopy or heavier timber structure: usually an H-post support or another suitable structural post support.
Need to adjust the height: adjustable post support.

Important: never select a post support solely by the dimensions of the timber. The weight and height of the structure, wind load, ground conditions, foundation and intended use all matter.

What is a post support?

A post support is a metal fitting used to secure and stabilise a timber post to the ground, concrete or another suitable base.

Depending on the type, a post support can:

anchor a timber post to the ground;
connect a post to concrete;
keep timber clear of damp ground;
provide lateral stability;
allow adjustment during installation;
make future replacement of the post easier.

Keeping timber away from permanently damp soil can be particularly useful because prolonged exposure to moisture can accelerate deterioration.

There are several different types of fence post supports, so the best choice depends on the application.

What types of post supports are available?

Common types of post supports for garden and timber structures include:

post spikes;
U-post supports;
bolt-down post supports;
H-post supports;
adjustable post supports;
post support bases.

There is no single post support that is best for every timber structure.

The correct solution depends on what you are building and how the post needs to be anchored.

When should I use a post spike?

A post support spike is driven directly into suitable ground. It allows a timber post to be installed without creating a conventional concrete foundation.

Post spikes can be a practical solution for relatively lightweight structures such as:

lightweight garden fences;
small garden dividers;
certain fence panels;
other lightweight garden structures.

One of their main advantages is relatively quick installation.

However, a post spike is not automatically suitable for every fence. Very soft, loose or unstable soil can provide less support, while tall, heavy or wind-exposed structures may require a more substantial foundation.

When should I use a bolt-down post support?

If you already have a suitable concrete base, a post support that can be mechanically fixed to the surface may be a practical solution.

A U-post support base can be used to secure a timber post to a suitable solid base, depending on the specific product and construction.

This type of installation can be useful for:

posts installed on concrete;
certain garden fences;
small timber structures;
applications where the post cannot be driven directly into the ground.

The existing concrete must itself be strong enough for the loads involved. A heavy-duty metal post support cannot compensate for an inadequate foundation.

Which post support should I use in concrete?

When a timber post needs to be connected to a new concrete foundation, use a post support designed for that method of installation.

Depending on the structure, an H-post support or a suitable U-post support may be considered.

Anchoring the support into concrete can:

provide a stable connection to the foundation;
keep the timber post above the soil;
transfer loads from the post to the foundation;
provide a robust connection for timber structures.

The foundation itself must always be appropriate for the structure and the loads it will carry.

When should I use an H-post support?

H-post supports are commonly used for heavier timber structures that require a strong connection to a concrete foundation.

Typical applications can include:

pergolas;
canopies;
larger timber structures;
heavy-duty garden structures;
applications where posts require a substantial concrete anchorage.

The post is positioned between the two vertical sides of the H-support and secured using suitable fixings.

The lower section of the support is anchored into concrete, allowing loads from the timber post to be transferred into the foundation.

Important: using an H-post support does not automatically make every structure safe. The posts, beams, connections, support and foundation must all be appropriate for the loads involved.

When should I use a U-post support?

A U-post support holds the timber post between two metal sides.

U-post supports are available in different designs and can therefore be used for a range of applications.

Depending on the model, they may be suitable for:

fences;
garden posts;
lightweight timber structures;
posts installed on concrete;
posts connected to concrete foundations.

When choosing a U-post support, check both the internal dimensions of the support and the intended fixing method.

What is the difference between an H-post support and a U-post support?

An H-post support is commonly used for heavier timber structures requiring a substantial connection to concrete. U-post supports are available in several designs and can be suitable for both fences and other timber structures.

Feature	H-post support	U-post support
Typical application	Heavier timber structures	Fences and various timber structures
Concrete	Commonly anchored into concrete	Depends on the model
Pergola	Frequently used	Possible depending on design and loads
Lightweight fence	Often more substantial than required	Can be suitable

When do I need an adjustable post support?

An adjustable post support is particularly useful when the position or height of the timber post needs to be fine-tuned during installation.

This can be useful when:

the base is not perfectly level;
several posts must finish at exactly the same height;
adjustment is needed during assembly;
the structure requires accurate alignment.

An adjustable support can make installation easier, but it does not replace the need for a sufficiently strong foundation.

Which post support do I need for a fence?

For a lightweight fence in suitable ground, a post spike can be one of the simplest solutions. If the fence is being installed on an existing concrete base, a bolt-down post support may be more appropriate.

The correct choice depends on:

fence height;
weight of the fence panels;
distance between posts;
ground conditions;
wind exposure;
type of fence posts;
method of installation.

A tall, solid fence can be subjected to much greater wind loads than a low, open fence. The support therefore needs to be selected as part of the complete fence construction.

Which post support do I need for a pergola?

A pergola will normally require a more substantial post support than a lightweight garden fence.

H-post supports are commonly considered because they allow the timber posts to be connected to concrete foundations while keeping the wood away from direct ground contact.

However, do not choose an H-post support simply because the structure is called a pergola.

Also consider:

overall dimensions of the pergola;
height;
weight of the structure;
post dimensions;
wind loads;
foundation dimensions;
connections between posts and beams;
any additional loads.

For larger or heavily loaded structures, the complete construction must be appropriately designed.

Which post support do I need for a canopy or heavy timber structure?

A canopy or other substantial timber structure can transfer considerable loads to the posts and foundations.

For this reason, robust structural post supports such as suitable H- or heavy-duty U-post supports are often required in combination with an appropriate foundation.

Factors to consider include:

structure size;
roof or canopy weight;
wind loading;
height;
post dimensions;
foundation design;
connections between structural components.

The dimensions of the timber post alone are not enough to determine the correct support.

Which post support should I use on existing concrete?

When a suitable concrete base already exists, a bolt-down support can often be used.

A U-post support base is one option for securing a post to a suitable existing base.

Before installation, check:

condition of the concrete;
thickness and strength of the base;
position of the anchors;
loads from the structure;
required edge distances;
suitability of the chosen fixings.

A thin or damaged concrete slab does not become a suitable foundation simply because a heavy metal post support is bolted to it.

Which post support do I need for a 70x70, 90x90, 100x100 or 120x120 mm post?

The support must be compatible with the actual dimensions of the timber post, but post size alone does not determine which type of support you need.

For example, two 90x90 mm posts may require completely different supports:

a 90x90 mm post for a lightweight fence may be installed using a suitable post spike;
a 90x90 mm post on concrete may require a bolt-down support;
a 90x90 mm post forming part of a heavier structure may require an H-post support or another structural solution.

First determine what the post is supporting. Then select the correct type and size of post support.

Does the post support need to match the timber post exactly?

The post support must be compatible with the actual dimensions of the post and allow it to be fixed correctly.

Do not force an oversized timber post into a support or improvise a solution for excessive clearance.

Check:

actual timber dimensions;
internal dimensions of the post support;
product tolerances;
hole positions;
required bolts or screws;
intended application.

Intergard supplies a range of wooden posts for garden and fencing applications.

Is it better to use a post spike or concrete?

Neither method is automatically better. The correct choice depends on the construction.

A post spike offers relatively quick installation and can be suitable for lightweight fences and garden structures in appropriate soil.

A concrete foundation is generally more relevant when:

the structure is heavy;
the construction is relatively tall;
wind loads are significant;
a structural foundation is required;
the soil does not provide sufficient support;
the structure requires a more substantial anchorage.

Not every garden post needs to be concreted. Equally, a post spike should not be used simply because it is easier to install.

Can I put a wooden post directly into the ground?

Timber posts can be installed directly in the ground in certain applications, depending on the timber species, treatment, ground conditions and construction.

Using a post support can, however, help keep the bottom of the timber away from permanently damp soil.

This can reduce direct moisture exposure and may also make future replacement of the post easier.

The most suitable method depends on the timber, structure, soil and required service life.

Which post support is best for soft ground?

Soft or unstable ground requires particular attention because the soil itself forms part of the support system.

A post spike that performs well in compact ground may provide considerably less stability in loose soil.

Consider:

soil type;
depth of stable ground;
height of the structure;
wind exposure;
weight of the construction;
whether a concrete foundation is required.

For heavier structures, creating a suitable foundation can be more important than simply choosing a longer post spike.

Which post support is best in a windy location?

Wind loading is particularly important for tall or relatively solid structures.

A closed fence panel can act like a large surface for the wind to push against.

Therefore, consider the complete system:

fence or structure height;
surface area exposed to the wind;
post spacing;
post dimensions;
post support;
foundation;
all structural connections.

Simply choosing a heavier post support will not compensate for an inadequately designed structure.

What mistakes should I avoid when choosing a post support?

Common mistakes include:

choosing the support solely by post dimensions;
using a post spike for a structure that is too heavy;
bolting a strong support to inadequate concrete;
ignoring wind loads;
not checking the internal dimensions of the support;
using unsuitable fixings;
failing to align the posts correctly;
assuming all H- or U-post supports have the same capacity.

The correct choice should always start with the complete structure rather than the metal support alone.

Post support selection table

Application	Post support to consider	Important consideration
Lightweight fence in suitable ground	Post spike	Check soil and wind exposure
Post on existing concrete	Bolt-down/U-post support base	Concrete must be suitable
Post anchored into concrete	Suitable H- or U-post support	Foundation must be correctly sized
Pergola	H-post support / suitable structural support	Consider the complete structure
Canopy or heavier timber structure	Heavy-duty H- or U-post support as appropriate	Loads and foundation are critical
Height adjustment required	Adjustable post support	Does not replace a suitable foundation

How do I choose the right post support in 5 steps?

1. Decide what you are building

A garden fence, pergola and canopy place very different loads on their posts.

2. Check the ground or base

Determine whether the post will be installed in soil, on existing concrete or into a new concrete foundation.

3. Measure the timber post

Check the actual dimensions of the post and select a support with compatible dimensions.

4. Consider the loads

Take account of the weight, height, wind exposure and purpose of the complete structure.

5. Select the support type

Choose a post spike, bolt-down support, U-post support, H-post support or adjustable support according to the application.

Frequently asked questions about post supports

Which post support do I need?

It depends on the structure and the base. A post spike can be suitable for a lightweight fence in appropriate ground. A bolt-down support can be used on suitable concrete, while pergolas and heavier timber structures often require substantial H- or U-post supports combined with appropriate foundations.

Which post support do I need for a 90x90 mm post?

First determine how the post will be used. A 90x90 mm fence post may require a completely different support from a 90x90 mm pergola post. Once the application is known, choose a support that is compatible with the post dimensions.

Is an H-post support better than a U-post support?

Not necessarily. H-post supports are commonly used for heavier structures anchored into concrete. U-post supports are available in several versions and can be suitable for a wider range of applications.

Do fence posts need concrete?

Not always. A post spike may be suitable for certain lightweight fences in appropriate ground. Taller, heavier or more wind-exposed fences may require a more substantial foundation.

Which post support should I use on a concrete slab?

A bolt-down post support may be suitable if the concrete slab itself has sufficient thickness and strength for the expected loads.

Which post support should I use for a pergola?

H-post supports are commonly used for pergolas because they can provide a robust connection between timber posts and concrete foundations. The final choice should always be based on the complete structure and its loads.

What is an adjustable post support used for?

An adjustable post support allows the position or height of the post to be fine-tuned during installation. This can be particularly useful when several posts need to be aligned accurately.

Are post spikes strong enough?

They can be suitable for lightweight structures in appropriate ground. Heavy, tall or highly wind-exposed structures may require a more substantial foundation.

Does a post support prevent timber from rotting?

A post support can help keep the end of a timber post away from damp soil, reducing direct moisture exposure. Timber durability also depends on the species, treatment, drainage, construction and environmental conditions.

Where can I buy post supports?

Intergard supplies a range of post supports for fencing, pergolas and other timber structures.

Options include:

Combine the appropriate support with suitable wooden posts and always adapt the fixing method to the structure, foundation and ground conditions.

Find the right post support for your project

Building a fence, pergola or other timber structure? Choose your post support according to the timber post, ground or base and the loads the structure needs to withstand.

View post supports » View H-post supports » View post spikes »

Conclusion: which post support do I need?

The right post support depends on the structure, the ground or base, the dimensions of the timber post and the loads it needs to withstand.

As a practical guide:

lightweight fence in suitable ground: post spike;
post on existing concrete: bolt-down post support;
post anchored into a new concrete foundation: suitable H- or U-post support;
pergola or heavier timber structure: H-post support or another suitable structural post support;
height adjustment required: adjustable post support.

Never choose a post support based solely on the dimensions of the timber post. A support that physically fits the post can still be unsuitable for the loads, foundation or intended use.

The best choice therefore starts with the complete structure: timber post, post support, fixings, foundation, ground conditions and loads.