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What do I need for a Radiata Garden Room base?


A Radiata Garden Room base has a few special requirements. These are all designed to maximise the life and usage of your new Garden Room because you’re going to want to use it for a really long time.

And the great thing is, you absolutely can! With a 30-year guarantee, a Radiata Garden Room (or Rad, as we call them around here) is a solid investment.

Speaking of solid, let’s get on with finding out about the base!

What kind of base will my Garden Room need?

A Radiata Garden Room base surrounded by gravel. There is a green wooden fence in the background.

A Radiata Garden Room base has exactly the same requirements as a Shed base. Unlike our larger Blackstone Garden Rooms which need a concrete plinth, the clever design of the Rads means that a level slabbed base is all you need. Ground screws can be used in some circumstances – more on that in a minute!

How do you build a slabbed base?

A compacted hardcore base for a garden room surrounded by cobblestones.

If you don’t already know the answer to this question, your best bet is hiring a professional. We work with accredited tradesmen to ensure your base is just as solid as your Garden Room.  But the short answer to the question is this:

  1. Dig down to solid ground (at least 4-6 inches).
  2. Fill the hole with well-compacted Type 1 hardcore.
  3. Lay your sand layer and slabs on top of this.
  4. Make sure the base is absolutely level.
  5. Build the base the same size as the building.
  6. Include a gravel border to act as a soakaway.

Why does a Radiata Garden Room base need a hardcore sub-base?

A slabbed base surrounded by grass.

Steps 1 and 2 of our list are often overlooked, but they’re absolutely vital to ensuring that your building stays square. If the ground under your Garden Room is too soft, the building will sink into it, or at least the wooden bearers underneath your building will. 

This may happen uniformly, but most likely the bearers will sink unevenly, resulting in a building that is no longer level and square. To bear the full weight of the building and its contents, the slabs must be on solid ground. 

For step 3 to be successful, the foundations have to be in place first.

Why does a Garden Room need a level base?

Some garden buildings have a run – a deliberate slope that lets water run away from the building. However, our Radiata Garden Rooms don’t fit into this category. They need a base that is absolutely totally exactly level – no exceptions!

Because the building encases the base a run isn’t necessary. And if your base isn’t level, your building isn’t square. This means problems with doors and windows, and in the worst case could even allow water into your building. 

Should a Garden Room base be the same size as the building?

If your building is from Gillies & Mackay then your base should be the same size as the building. Because the building encases the base, this won’t work if the base is larger. So if your building is a 2.4m x 3m Rannoch, the slabbed base should also be 2.4m x 3m. Your Radiata Garden Room base must be the same size as your Radiata Garden Room!

Why do I need a gravel border around my Garden Room?

A Gillies and Mackay Deuchny Radiata Garden Room after a rainstorm. The building has natural ThermoWood cladding and double-glazed doors and windows. The ground around the building is wet, but the gravel border and base of the building are dry.

A gravel border acts as a soakaway, which draws any ground water away from your building, helping to protect the timber. Radiata ThermoWood cladding has been treated to provide exceptional resistance to moisture, rot and insects, but it’s still not a good idea to allow water to build up in one particular area of the building. If the bottom timbers of your Garden Room get wet in the same place over and over again, in time this will cause issues. 

The overhanging eaves keep the base dry. In most cases, this keeps both the gravel and the slabs dry near the building. Adding a soakaway means that even the heaviest rain won’t bother your building, and let’s face it, round these parts heavy rain certainly happens.

Can I use ground screws as a Radiata Garden Room base?

A timber frame base for a garden room on top of ground screws. The ground slopes sharply and the front row of ground screws are around 2m high to accommodate the slope.

Ground screws do exactly what it says on the tin. They’re large metal screws that support your building. They’re a great alternative to a slabbed base in hard-to-reach places.

However, ground screws are not always an option. The ground has to be suitable for placement, and depending on how level your site is, the screws may be visible underneath the building. This either means leaving them exposed, like in the photo, or building an additional surround like fencing or decking to conceal them. Depending on the height of the screws, raising the building up like this may have implications for planning permission.

A site visit from your contractor will determine whether or not ground screws will suit your site.

What do I need for a Radiata Garden Room base?

A Gillies and Mackay Vorlich Radiata Garden Room on a sunny day. The natural timber finish and double-glazed windows and doors reflect the sun.

So there you have it! A Radiata Garden Room base should be level, slabs on a Type 1 hardcore sub-base, with a gravel border soakaway. That’s all there is to it! If you’d like to see our real-life Rads, pop into our Show Area in Errol, right next door to the Cairn O’Mohr winery. You can check out their bases, ask any questions you might have, and have a really good look at these beautiful buildings.

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