Shed base slightly short in middle

[fezster]

I've just paid quite a hefty sum for what I believe is a fairly professional contractor to lay a 20 x 12 shed base. This is for a 20 x 12 wood shed with apex roof. I'd done plenty of homework on this one and their work all looked professional and prices were on the higher side of average.

It looks like the shuttering on one side has slightly buckled inwards which means that the base when measured towards the middle, tapers inwards to fall short of the 12 foot required, by up to a maximum 5cm (!)

I'm annoyed to say the least, esp as I even made the point of saying they should make it slightly bigger, than required. Their explanation for not doing so (shown below) did make sense, so I accepted that.

I'm pragmatic, though, and would just like to understand if this is even an issue, and if so, how to resolve.

I will be having paving slabs laid either side of the concrete slab. These will be butted up against the base (one of the reasons they did not want to make the base larger than necessary) and the finish level will be that of the base - ie. the base and the slabs will be at the same finish level.

Will the up to 5cm shortfall in width be taken up by the sheds wooden frame resting on the patio slab aligned with the base? If not, what is a pragmatic solution?

 

[conny]

The bottom line is, you paid them to do a professional job based on their claims.
If you told them what your plans were for the base and that you would like it slightly larger then they should have complied with your wishes or given you a reasonable reason why they didn't/couldn't do so.
Supposing you weren't having slabs alongside the base or that the ones you are having were/are lower/higher.
I don't know how you are going to fill in the 5cm shortfall to be honest but I would advise getting the contractors back to sort it or give you some sort of discount for their failings.

 

[fezster]

Fair point. But knocking money off aside, I need a solution to move forwards.

If it was a case of adding some more concrete, that'd be easy. But I don't think that is an option.

I'm hoping the slabs either side will more than suffice - seems logical to me. After all, a lot of people suggest bedded down slabs alone instead of a concrete base.

But I'm hoping someone more knowledgeable and independent can confirm for me.

 

[domdee]

what is the shed built like? is it a timber floor or is the concrete going to be the floor?

 

[fezster]

Shed will have a timber floor - 1 inch thick tanalised.

 

[Lower]

What are the slabs that abut the shed base going to be laid on?

Why have the concrete base for the shed if you're laying slabs?

Is the floor going to be laid on bearers to raise the timber floor off the concrete base?

Do the shed walls rest on the timber floor or on the concrete base?

Just trying to understand what your design is.

 

[domdee]

well other than being pee'd off about the contractors not building the base as you wished, i cant see an issue. other than a bit of aesthetics (big joint). Even then the 50mm overhang will hide most of it. pavers up to the edge with good pointing will be fine providing they are level.

 

[fezster]

Thanks domdee - I was hoping that would be the case.

Lower - The sandstone slabs will be laid on a compacted subbase and then a bed of mortar. The reason the entire shed area was not laid with slabs is because the cost of the sandstone, pointing etc would far exceed the cost of pouring concrete.

The shed should be laid on a timber frame. I have to admit Im not 100% on this, but the company have basically said it'll be a tanalised timber frame made of 3x2 and then the floor will be placed on top of this frame.

 

[fezster]

Just so I am aware of all of my options - I'm yet to pay the contractor for his work - is there any option to expand the base by the additional 50mm? I'm assuming you cant just pour 50mm extra concrete because it wont be bonded to the existing pour. What would be the minimum you could pour - or is it advisable not to do this at all?

 

[Scarlet Pimpernel]

If it were me, I'd make the concrete slab slight smaller than the footprint of the shed, so that any rainwater runs down the walls, but not pooling on the concrete slab.
Although slabbing right up to the edge of the shed will compromise this.

 

[Lower]

Lower - The sandstone slabs will be laid on a compacted subbase and then a bed of mortar. The reason the entire shed area was not laid with slabs is because the cost of the sandstone, pointing etc would far exceed the cost of pouring concrete.

The shed should be laid on a timber frame. I have to admit Im not 100% on this, but the company have basically said it'll be a tanalised timber frame made of 3x2 and then the floor will be placed on top of this frame.

On that basis, you've be fine. The sandstone will be on a solid base and will be flush with the concrete so if the shed base overhangs the concrete slab by a couple of inches in places it'll rest on the sandstone. Doesn't sound like you've got anything to worry about.

 

[fezster]

Thank you guys. Appreciate the advice.

Bobby - you make a good point, but for aesthetic reasons, I wanted a nice patio surrounding the shed.

Is there any point in adding a DPC sheet underneath the timber rails/floor, even though they are tanalised? I've seen this recommended in posts when searching.

 

[big-all]

you sure you need the last say 35mm each edge ??
the floor timbers are very likely to be in from the edge by the facing timber off say 12mm and set back say 25mm to stop the water soaking the timbers ??

 

[fezster]

I have double checked with the shed supplier and they say the base is the same size as the shed. But I don't know if they mean precisely or just roughly. I have asked them the question. Thanks for the tip.