Garden Room Base - on top of existing paving or new concrete base?

[tommad1]

I am planing on constructing a garden room (2.5 x 4m) at the back of my garden in an existing paved area. The room is a timber kit from Garden Buildings Direct. I am going back and forth on what to do about the base - the proposed area has existing paving which is not completely level as probably has been there for 20+ years. I'm thinking to take up the slabs and re-lay to make level and I will need to extend the front by 500mm or so to cater for the building. I will also need to raise the area slightly by 100mm so it's slightly above the existing ground level for drainage.

My question is, if I'm re-laying the paving and raising the level slightly is it worth doing this or if I need to mix cement anyway, should I just pour a slab instead. Given I already have the paving I'm thinking re-laying might be a more cost effective option given I have most of the material already. I'm also assuming the sub-base is sound.

I've attached a few pictures for reference.

Thanks

 

[Ivor Windybottom]

A building will put a much higher load per slab than a person standing on it. So you could get movement that it's currently resisting.

We had a wood garden shed built on slabs, it was bent and buckled all over the place.

It would be a risk to build on it. You should look at whether the building could be taken away and reinstated if you did have issues after a few years, but it's often not possible without wrecking it.

Personally I wouldn't take the risk. Get the lot up, dig out, crushed rock compacted down then concrete. You could hire a mini crusher to turn the slabs into crushed rock, which may make sense vs the work and cost of disposal, probably depending on your proximity to a road.

 

[VDubDan]

I'm with @Ivor Windybottom - Do it once, do it right. Assuming you're already investing a few quid into the garden room, a DIY concrete base will run you into the hundreds, not thousands and will last the lifetime of the building.

I wouldn't trust what's there

 

[tommad1]

Thanks for the advice @Ivor Windybottom @VDubDan. Appreciated