The connection between a timber post and its foundation is a critical part of any timber structure. A suitable post base creates a defined connection, keeps the timber away from direct contact with concrete or soil, and helps transfer loads from the structure into the foundation.
There is no single solution for every project. The right post base depends on whether you are creating a new concrete foundation, working with existing concrete, require height adjustment, or want a more discreet connection.
In this guide, we compare four common solutions.
1. Cast-In Post Bases with Welded Rebar
1. Cast-In Post Bases with Welded RebarWhen a new concrete foundation is being constructed, a cast-in post base can be installed directly into the fresh concrete.
These bases typically have a welded section of reinforcing bar that becomes embedded in the concrete. The steel connection remains above the concrete and supports the timber post.
This solution provides a direct connection to a new concrete foundation and is particularly suitable for pergolas, carports and other permanent timber structures.
2. T - Blade Post Bases for a Discreet Connection
2. T - Blade Post Bases for a Discreet ConnectionA T-shaped or blade post base is another cast-in solution, but with a different connection geometry.
The narrow metal blade is positioned in the centre of the timber post. Once the post is installed, most of the metal connection is hidden inside the timber, creating a cleaner and more discreet appearance.
This makes T and blade bases particularly interesting for visible timber structures where the appearance of the connection is important.
They are installed into fresh concrete and should be positioned accurately according to the post dimensions and structural design.
3. Surface-Mounted Post Bases on Existing Concrete
3. Surface-Mounted Post Bases on Existing ConcreteWhen the concrete foundation or slab already exists, there is usually no need to remove it or cast a new foundation simply to install a post base.
A surface-mounted post base is fixed directly on top of the existing concrete using suitable concrete screws or other specified anchors.
Different configurations are available depending on the timber post and connection geometry, including U-shaped, L-shaped and flat-top bases.
This type of base is commonly used for pergolas, decks, carports and renovation projects.
See Surface-Mounted Post Bases
4. Adjustable Post Bases for Easy Levelling
4. Adjustable Post Bases for Easy LevellingWhen accurate levelling is important, an adjustable post base with a flat top provides an additional advantage.
The base is fixed to an existing concrete foundation, while the timber support sits on an adjustable threaded system. The height can be adjusted vertically to compensate for small differences in the foundation level.
This can make installation easier and help achieve accurately aligned timber posts across a structure.
Adjustable bases are particularly useful where several posts need to be aligned to the same finished height.
How Do You Choose the Right Post Base?
The best solution depends on the foundation and the requirements of the structure.
| Project condition | Suitable solution |
|---|---|
| New concrete foundation | Cast-in post base |
| New foundation + discreet connection | T / blade post base |
| Existing concrete | Surface-mounted post base |
| Existing concrete + height adjustment | Adjustable post base |
The timber dimensions, loads, connection geometry and fixing method should also be considered before selecting the base.
The Post Base Is Only Part of the Connection
A post base transfers forces between the timber post and the foundation, but its performance depends on the complete connection.
The post base, timber, fixings and foundation must work together. The concrete itself must also have sufficient strength and dimensions for the loads being transferred.
For surface-mounted bases, use the specified or suitable concrete screws or anchors and follow the manufacturer's installation requirements.
What If There Is No Concrete Foundation?
A timber structure does not always require conventional concrete foundations.
Ground screws can provide foundation points directly in the soil and can be an alternative for suitable structures and ground conditions.
For smaller structures such as decks and pergolas, light construction ground screws may be appropriate. Larger structures with higher loads may require heavy construction ground screws.
See ground screws for light constrution
See Ground screws for heavy construction
The required foundation solution, position and spacing should be determined according to the structure, loads and ground conditions.
Choosing the Right Foundation Connection
From cast-in bases to adjustable surface-mounted supports, different post bases solve different installation problems.
The most important questions are simple:
- Is the concrete new or already existing?
- Does the connection need to be visible or discreet?
- Is height adjustment required?
- What are the dimensions of the timber post?
- What loads must the connection transfer?
Choosing the post base together with the fixing and foundation creates a more reliable connection and makes installation easier.
If you are unsure which post base is suitable for your project, send us the post dimensions, foundation details, drawings or photographs and we can help identify the appropriate solution.
