There are various options for creating a suitable footing for your planned garden room, which can vary wildly in expense, effort required, and time needed. There are loads of YouTube videos on every method, and to be fair there is seemingly lots of evidence that all of them work well. When deciding what to go for, I’d suggest you consider the following three points:
- The intended use of your garden room
If it’s going to be a timber framed and clad room to sit and chill in, or an art studio or an office, then it’s essentially a glorified shed and will be relatively light in weight. You could probably use any of the methods below (though I wouldn’t suggest the slabs method purely because I think this is too basic and too open for subsidence and water ingress). However, if you are creating something with a steel lintel or metal framing, possibly a workshop with heavy machinery or a gym with significant weights all over the place, you really want something as solid and stable as possible. This bit will be fundamental to the rest of your build and it is unlikely you will be able to change it later (at least without enormous difficulty) if you discover what you put in just wasn’t up to the job. - Level / flatness
Whichever method you use, it cannot be stressed enough that your footings must end up both flat and level. If you try to build on anything other than a level surface you are going to enter a whole world of pain and waste so much money. You can of course build on a sloping on uneven plot, but whatever is holding your building up must be level. I appreciate this sounds obvious but the state of your plot may help determine which method to use. - To DIY or not to DIY?
This really depends on your skill, appetite, tools, and budget. Many garden room builders successfully lay their own foundations. But if you have zero experience of laying concrete and need a 30m2 slab, it may be a steep learning curve. Out of all the garden room building jobs this is the one where many people get someone in to do the work. These are literally the foundations you are going to be building your dream room on, so there is absolutely no shame in paying to make sure you start off on the right foot.
Concrete slab
This has always been a popular choice as it provides a level, strong, solid base and can be created relatively quickly. You can mix the concrete on site by hiring or buying a mixer (mixing by hand and bucket would be unbearable and probably impossible), but for large areas most people tend to get the concrete pumped in from a mixer that turns up outside your house and runs a massive pipe to where it’s needed. Check with some companies in advance, though, if access is a problem and especially if your build is way back from the road as there are limits to how far they can pump it. Many people also add insulation before the concrete slab is poured which is a great way to minimise heat loss as of course this method doesn’t require you to construct a separate base which is where the insulation would otherwise go.
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Ground screws
As well as being entertaining to see (it is literally an enormous screw akin to something you’d see in Land of Giants), ground screws are now being used as foundations in all sorts of builds, including multiple story houses. YouTuber and building mastermind Robin Clevett has used these is a number of seriously impressive projects. For a garden room, though, you’re not likely to need very many (probably only 10-20 depending on size). I understand that there are DIY options but the professional installers do use some pretty heavy duty machinery to get these screws in the ground so I’m not sure it would be that easy to do yourself.
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Threaded rods
As championed by garden room guru and all round lovely fella Liam Griffin (who has done some brilliantly thorough YouTube demos), these are a great DIY alternative to ground screws. Utilising 24mm diameter threaded steel rods, you dig narrow holes around 600mm deep every metre or so and concrete the rods in place, using some flat plates (all levelled up precisely with some appropriately massive nuts), before cutting off the surplus top part of the rod.
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Piers and plinths
There are various products on the market from plastic piers with screw adjustable height to concrete plinths with a metal bolt which can be adjusted to the height required. Or, you can simply use dense concrete blocks as Ali Dymock featured in his excellent YouTube series, though getting everything level on those can be a bit trickier. With any of these it would make sense to ensure you’re putting them on solid foundations, so a decent amount of hardcore and some concrete, to avoid the weight of your room just driving the pier into the ground.
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Paving slabs
The old tried and tested method of preparing the base of a shed, this generally involves simply digging out the turf and levelling an area which you then cover with sand and lay some paving slabs on top of. You could add hardcore as well to make it more robust but, while these may be great for small sheds or greenhouses, you really should be thinking of building your garden room on something better.
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Used any of these methods? Let us know how you got on. This list isn't exhaustive, so please also let me know if you think I'm missing something and we can include it in a further update down the line.
