Shed extension foundations?

[pike]

Hi all,

I still haven't got a workshop since I moved into a new house (now 2 years ago) and got lots of great advice here.

What I did end up with is a waltons 10x10' just for timber/tool storage. I'm used to working in a small space and I think I'll do ok with something just a bit bigger, say 16-20 x 10'. My half baked plan is to build an extension to the existing shed. It's only been up a year and is in an area of the garden I have to use again for the new workshed.

It's only on gravel and large concrete blocks. That seems to be ok for the machines I have (kity combi thicknesser/planer and a triton workcentre) but I will probably want to add a bandsaw. Even so I'm thinking I can get away without a concrete foundation provided I am not planning on buying any big old wadkin heavy machinery or similar.

So initially I thought I'll just add more of the same gravel and blocks but use much stronger joists and framing for the new half. Then I thought, this might be an opportunity to have a stronger foundation atleast for the new half of the shed and put the heaviest machinery on that side.

My question is, would it be a mistake to have one half of a shed with one foundation and the other more substantial to take the heavier things? It seems to me that I might be better of sticking with the on grade concrete blocks and not getting any really huge machines. I'm concerned that using a better foundation for the extension would create a shed which would "break" or shift in the middle.

I'm not wanting a workshop for life, just somewhere to use the above tools occasionally.

Thanks!
Carl

 

[Pond]

Hi,

There is no reason why you can't do this if it's a timber structure.

It sounds like you are talking of a re-inforced floor rather than foundations?

Foundations are really only to support the weight of the structure on the ground, to a depth that will not be affected by movement in the sub-soil from shrinkage and expansion.

A well compacted oversite (type 1 hardcore ideally or anything you can get your hands on realistically), with a 150mm concrete slab, re-inforced with welded steel mesh will take more weight than you should ever need. The sole plates for your structure can then also be bolted to this. If doing this just make sure you put a damp proof membrane under the concrete and 50mm of Jabolite (polystyrene) is a good idea, as it insulates the floor!

If you can mix the concrete by hand it isn't expensive, also weldmesh is dirt cheap!

 

[OldWood]

Hi Carl

I see no reason why you shouldn't have a half wooden floor, half concrete shed. Our living room is such as it had a significant extension added on with a concrete floor.

I think Pond is building you a floor to take some serious machinery - even my self-built garage doesn't have steel mesh in its 150mm concrete. Can I suggest a more user friendly shed floor in terms of work and your pocket is the hardcore as he says with what is called 'blinding' on top (sand or something equivalent) to protect your dpm from the hardcore, then 100mm of concrete. I've two sheds with floors this way and they both carry machinery in the 0.5 ton range.

Making concrete for this size of floor will require a cement mixer and the bringing in of gravel, sand and cement; several friends are also required as will a reasonable part of a whole day with the associated beverage, etc. Take all of this into account and you may well find that delivered concrete is preferable !! If you are not in good muscle trim, you may also have to add in a visit or two to your physiotherapist.

Rob

 

[pike]

Thanks Pond and Rob,

Pond, yeah I see what you mean. I was thinking about the foundations mostly but I would also use much stronger joists than the present waltons shed.

The shed site is 200' or more from the front with no access other than a narrow door. If I go for concrete I think it'd have to be pads/peers.

Currently I don't have any heavy machinery. The heaviest being a kity 439 planer. I think a mid range bandsaw is the largest thing I plan to buy. In a shed which is 20x10 at most, I doubt I'm going to ever have anything large in there.

Thanks for the advice re: to different types of foundation. I see now more clearly what foundation and then floor strength are doing.

I think I might have one part of the extension stronger than the rest and remember to put the bandsaw there.

Carl

 

[Pond]

I only say 150mm as this is the minimum to pass building regs approval, if you ever needed it. it is also a good 'rule of thumb' as anything less could be prone to cracking.

Concrete is funny old stuff! It has no real inherent strength without being re-inforced.

What about a suspended chipboard floor? Moisture resistant T&G chipboard, on small battens, laid on your concrete blocks? As long as you have a solid base, ie compacted oversite, it won't move and will take plenty of weight!

Andy

 

[OldWood]

OK Andy
I suspect you have technical knowledge - I just have empirical knowledge and take the attitude from experience that for the average amateur's shed, 4", unreinforced concrete for the floor works - and saves adding another 50% of the concrete and the hassle of laying reinforcing that seems unnecessary in this application if the hardcore and blinding is done properly.

I will also add in that I'm not of the opinion, again from the economic and effort sense, that insulation is necessary under the concrete - there is just never enough continuous heating to justify it. What is very good are the interlocking 'rubber' flooring tiles you get from the likes of Costco.

Rob

 

[Pond]

Rob,

I'm not saying you are wrong and I'm right! The chap asked for advice, you gave him yours, I gave him mine.

He can heed or ignore either or both, it's his choice. That's the beauty of interweb forums, different opinions, agree or disagree, it's all part of the experience IMO!