Sign post foundations: 

best practices and guide

As a supplier of aluminium and steel sign posts to the trade we often get asked; What foundations do I need for my sign post? How deep should the post be buried? How big should I dig the hole?

So we have compiled the information below to help guide you through the main points to consider when installing sign posts into the ground. Of course, all installations should be checked by a qualified structural engineer and this guide should only be considered a rule of thumb to help with quotation purposes.

1. What depth foundation for sign post?

A point of confusion when installing sign posts is how deep should the foundations be dug. As a general rule the height above ground directly correlates with the depth needed below ground. 

Advice surrounding this does vary but we have seen a popular rule that runs through:

For every 1000mm out of the ground you will need 200mm below ground e.g:

1000mm height = 200mm foundation depth

2000mm height = 400mm foundation depth

3000mm height = 600mm foundation depth

4000mm height = 800mm foundation depth 

(This does not take into account soil type and wind loading location)

aluminium post foundation planting guide

2. What height should my sign be mounted?

Determining the height of a sign is all about the viewing distance, placement and use of the sign. However sign height is often a key point that is left unspecified.

For road and traffic signage a minimum mounting height to the lowest edge of the sign is 2.15m or 2.4m in cycle areas. This is for the obvious risk of injury caused when walking or riding into signs. However the 2.15m can be a good rule to work from for a multitude of sign installations.

3. How to install a sign post onto solid concrete foundation

In some instances you may be required to install a sign in a location that has a solid concrete foundation. In this scenario we would advise using a welded baseplate post. These have a 10mm solid aluminium plate welded to the bottom of the post with 4 fixing holes. You can then drill into your concrete foundation and use 12mm through bolts to secure the post in position.  

 Although these are not suitable for installations above 3000mm without further structural reinforcements they are a fantastic way to rapidly install signs in hard to dig areas.

4. What concrete mix should be used for sign post installation?

Sign posts often require a fast setting concrete mix. Time and efficiency is paramount when onsite and installing signs. 

A popular option is to use a fast setting pre-mix specifically designed for post installation. This takes away the need for aggregate and mixing machinery on site and also speeds up the curing time to as low as 5 minutes.

When looking for a premix for your post installations it is important to note if it is suitable for low temperature curing, As this can have a dramatic effect on cure times throughout winter periods

5. What are post baseplates used for?

Bolt on baseplates are designed to provide a stable and more secure post installation when using concrete post installations.

The base plate is tightly secured to the post with M8 bolts and this provides a sturdy anchor to stop posts twisting and being lifted out of the ground.

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