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What kind of base do you need for your timber garden building?


We’re all thinking about it. It’s time to get organised – get our garden in check and start preparing for Spring. If you’re awaiting the arrival of a Shed of Garden Room to complete your Shedlife dreams then it’s all about the BASE. 

At G&M we’re relentless – everything we talk about comes back to the groundwork. We know that bases are absolutely crucial to the longevity of your timber garden building. And when the base work for it is done right your garden building will thank you. 

The best possible garden building base to construct for a Shed or an Under 12m2 Radiata Garden Room is a slabbed one. 

However, over the past week, I’ve come up against issues caused by a slabbed base not being made correctly. And that’s negatively impacted the garden building – causing problems like rising damp and an out-of-square build.

So, it’s important that we discover together what we mean when we ask for a slabbed base and be very specific about how that is done. 

So I’ve created a 3-step instruction here for you in this article. It will help you understand what we mean by a properly installed slabbed base.

What are the three most important things you need to know about your garden-building base?

There are three main things you need to think about, and these are:

  1. Sub-base
  2. Level
  3. Size

So let’s get into these a little more…

1. Sub-base 

Perhaps the most underestimated requirement of a base.

It’s the Type 1 Hardcore BAYBAY!

Yep, that’s right! We need to dig down at least 4” to firm ground, sometimes deeper, especially in new development sites, and dump in a tonne of Type 1 Hardcore. Level that off and compact before you start your sand layer to level the slabs.

This isn’t a “how to” and we would recommend hiring an actual landscaper to do this for you. However, It is vital that you understand the process so you know what to expect.

Cowboy methods include putting slabs straight onto grass or mud – which is a definite NO. 

sub base garden room
This is what compacted Type 1 Hardcore looks like. This forms the base of your base.

2. Level

Most hardstandings (driveways, patios etc) are constructed with a ‘run’. The intention is to make the hardstanding with a slight slope so that it allows water to drain away to one side/elevation. 

However, when it comes to constructing a base, we absolutely DO NOT want there to be a run. We don’t need it to have one because the building will encase the base (more on this next). 

garden building base with run

We need the slabs to be bang-on level as this sets the building’s level. This impacts the construction of the walls and roof going together but most importantly it dictates the effectiveness of the doors and how they open and close. 

level base

If the base is off-level and therefore the building is off-level, the doors will not be square. This causes them to jam or be off-kilter with the hole they are intended to fill. 

off-kilter doors timber garden building


My favourite explanation – a common misconception – is that a slabbed area should be larger than the building.

NEGATORY! Please do not do this.

I understand that you may want a patio outwith your Shed or Garden Room base, but this is not the way to do it. A patio is a decorative piece and will typically be something like Sandstone slabs, whereas the slabbed base we’re talking about is your basic 2’ x 2’ 50mm thick grey slab. 

basic timber garden building slab

We can see in this picture that there is a lot going on. We have the grey slabbed base for the actual Garden Building, we then have a gravel surround and thereafter the decorative slabs. 

The grey slabbed base for the Garden Building is 12’ x 10’ which is made up of 2’ x 2’ slabs. The external measurements of the building line up with the slabs precisely and the roof eaves overhang into the gravel area.

Why would you want the roof eaves overhanging like this?

Well because, when the water runs off the roof you want it to soak away and not splash back up onto the building. This is exactly why we ask you to create this gravel surround: it acts as a soakaway. It also stops water from pooling under the building. 

Who should build your timber garden building base?

At G&M we are very protective of your foundations and make sure you know exactly what is required. We will guide you throughout the entire process and recommend some amazing G&M-accredited landscapers who know the G&M way and work with us to make your experience the best it can be. 

Talking of which… 

G&M’s Accredited Base Layers

We know what it’s like to deal with trade and worry about whether or not they’re doing the job right. Especially when you yourself don’t know what that job entails. That’s why, when we recommend a trade we have to be 100% sure that they’ll carry the G&M name and reputation.

We can assess their credibility closely as we are the ones dealing with their bases first-hand. We’re able to assist them with base plans and specificity, especially for complicated sites that may not be as straightforward as a full slabbed base i.e. pillars or ground screws.

I guess what I’m trying to get across is the importance of the base but also that you’re not alone in this. We’ve seen it all and there is always a way.

You are our No. 1 priority and we’ll find the right landscaper and the right base for your garden. 

If you need help or want to book a consultation with our team then you can get in touch and we can help you with your garden-building base.

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