Foundation beams explained: Why they matter for your log cabin or summerhouse and how to install them
When installing your log cabin or summerhouse, having a solid, secure base is essential to ensure installation runs smoothly and that your log cabin continues to look aesthetically pleasing and function correctly throughout its lifetime.
Alongside the base, there is another key element that plays a major role in protecting your garden building: foundation beams. These sit directly between the base and the first layer of wall logs for your log cabin or summerhouse. Foundation beams are essential for protecting your building from long-term moisture damage and its longevity.
In this blog, we'll explain what foundation beams are, why they matter and how to install them.
What are foundation beams and why do they matter?
Before building your log cabin or summerhouse on a concrete, patio slab or timber frame base, you need to think about foundation beams.
Foundation beams are lengths of pressure treated wood or composite that sit between the base and the first logs of your garden building. The main purpose is to protect the bottom of your log cabin from rising damp and premature rot in the bottom layer of the wall logs.
Find out more about foundation beams and why they matter in our video:
Types of foundation beams
When building your log cabin or summerhouse, you can choose between two types of foundation beams: pressure treated timber foundation beams, concrete foundation beams and profiled composite foundation beams. All three serve the same purpose, which is to separate your garden building from the base and protect the bottom of your log cabin. However, they each provide their own benefits.
Pressure treated timber foundation beams: These are the most common type of foundation beams and provide a reliable choice for small and medium log cabins and summerhouses. However, because they are still made from wood, they will still require maintenance over time and can rot if exposed to constant moisture.
Profiled composite foundation beams: Composite foundation beams are made from composite materials so will never rot or decay, providing you with a long-term solution that will protect your log cabin throughout its lifetime. In addition, the profiled design helps to direct water away from the building, providing an added layer of protection.
Concrete foundation beams: These are one of the most durable options available and will never rot or deteriorate over time, making them particularly useful for log cabins and summerhouses installed on bases or in gardens where damp conditions are common.
The type of foundation beams you choose will depend on a range of factors, including how you intend to use your building, the base you choose and your budget. All three options are effective for protecting your garden building.
Laying your foundation beams: Where to start
Before you start laying your foundation beams, it’s important to identify the perimeter of your building. All log cabins and summerhouses start with a combination of half logs and full logs which form the first layer and create the interlocking pattern that the rest of the structure is built on.
You can identify these logs with the installation instructions and elevation drawings included with your garden building. Once you’ve identified them, we recommend laying them loosely around the perimeter of your building, so you know exactly where your foundation beams need to sit.
Watch our video for a step-by-step guide on how to lay your foundation beams:
Laying your foundation beams: How to lay different types
The process for laying your foundation beams will vary slightly depending on the material of the foundation beam. In the next few sections, we’ll cover how to lay both standard and composite foundation beams.
How to lay standard foundation beams
Now you’ve established the perimeter of your garden building, you can add your pressure treated foundation beams underneath. Standard foundation beams are made using pressure treated timber which is designed to withstand outdoor conditions and protect the bottom of your log cabin from moisture. They’re usually supplied in 3m lengths which allows them to run along the full perimeter of your building.
1. Position the beams
Position the foundation beams underneath the first layer of logs you’ve loosely laid down on your base, following the exact perimeter.
2. Cut to size
If the beams are too long, you’ll need to cut them down. If they’re too short, butt joint multiple sections together so they cover the entire perimeter of your building.
3. Ensure correct alignment
The beams must sit flush with the outside edge or the face of the wall logs.
4. Temporarily secure beams
We recommend fixing the first logs to the foundation beams by screwing down through the half logs into the foundation beams beneath.
How to lay profiled composite foundation beams
Laying profiled composite foundation beams is similar to standard foundation beams. These beams are profiled to improve water drainage and a solution that will not rot over time.
When positioning these foundation beams, look for the slight upstand or ridge on the composite beam and place the log on top so it rests on the flat section against the inside face of the ridge.
For a full step-by-step guide to installing composite foundation beams, watch our video:
How to trim your foundation beams
Whether you’re installing standard or composite foundation beams, in most cases, they will need to be trimmed to fit around the corners or to span the entire length or width of your garden building.
Position the beam in place: Lay the foundation beam loosely against the edge of the log.
Mark the cut: Use a full-length log as a guide and mark a rough 45-degree angle at the corner using a pencil.
Cut the beam: Use a chop saw or hand saw to create a clean cut.
Repeat for the opposite corner: With the angle cut, position the foundation beam back under the log and complete the same steps under the opposite corner.
The beams won’t always be long enough for a single length, so you’ll need to butt joint sections together until you reach the other side of the building.
Watch our video for a complete guide on how to trim foundation beams:
Securing the first layer of logs to your foundation beams
Once you have the foundation beams in place, the next step is to secure the first layer of logs. At this stage, you should have already identified all four starting wall logs, including the half logs that start the interlocking pattern of the cabin.
To secure them, position the logs on top of the foundation beams (you may have already loosely screwed them in place), check everything is square and level and screw down through the half logs into the foundation beams.
A properly secured first layer helps to ensure your garden building stays square, the logs interlock properly and will help the rest of your installation to run smoothly.
Watch our full video for more guidance on securing the first logs to your foundation beams:
Why foundation beams are an essential part of your log cabin installation
Foundation beams might seem like a small part of the installation, but they help to protect your building from moisture and improve drainage, which can significantly improve the performance of your garden building over the long term.
Now the foundation beams are installed, and you’ve built the first layer of logs, you can continue with the build.
The next blog in our log cabin and summerhouse installation guide walks you through how to start building the walls of your building.
If you’d like additional help and guidance with installing foundation beams for your log cabin, please contact our expert customer service team.