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Recommended concrete slab thickness - garden room


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Hi All


My first post here, hope you're all well


Just after some advice pls. I'm preparing a base for a wooden (cedar cladded) insulated garden room (4.2 m by 3.02 m) 


So far we have cleaned and levelled the area and put down 4 inches of Mot, we plan to put down a 4 inch concrete base 


However I'm getting mixed reports and opinions from tradesman /  friends etc.. that 4 inches is either enough or its not enough and I should go for a 6 inch with re-bar 


The room will contain me, a small sofa, desk, some music equipment, you know typical man cave / office type set up 


Not being an expert in this areas you can imagine I'm a bit undecided and worried I'll make the wrong decision. 


I just wondered if anyone has done a similar project and if a 4 or 6 inch base is best etc..? 


Many thanks in advance :) 

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I have been speaking with my SE recently about a garage / garden room.


If it was never going to have a car in it, he reckoned to do 100mm concrete (he didn't say if it needed rebar or not).

If was going to have a car in it i needed to be 150 with rebar.


Put some sand blinding over the mot it get smooth and put in a dpm prior to the concrete

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Are you insulating the floor? In my shed I put down 100mm EPS, dpm, then 100mm concrete. Worked a treat. The guy that owns the house now has a laser etching machine in it and from memory it was at least 200kg, more like 300, sitting on two feet. No issues that I've heard.

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Your choice it’s a couple of cubic metres if it’s 100 or 150mm thick, all depends on the quality of ground, preparation and workmanship. You get one shot to do it right with minimal grief, after that remedial works are a pain and generally a compromise.


you could have fibres added to the mix to add reinforcement that way?




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