"Russian doll" shed foundation question

[Pallet Fancier]

I have a 10x6' pent roof shed, and an old 8x6' used for storage, that needs replacing. I need a bigger working shed, so want to build a custom 12x10' shed on the footprint of the existing 10x6'. The 10x6' will relocate to the storage shed, with the old storage shed being scrapped.

So, the new working shed will be longer and wider than the old, in the same location.

Problem 1: I can't stop using the current working shed long enough to tear it down and build a new one from the ground up.

So, I plan to build the new one around it, only dismantling the old one at the last minute to minimise the time that the contents are exposed, and that I can't use it. I've seen an entire house built this way, the new one "eating" the old one. The owner then knocked down the old one and passed the bricks out of the new windows!

Problem 2: how to lay the foundations for the new shed when I can't see/measure from one side to the other. I'm planning a perimeter foundation, partly to help keep the rats out and partly to keep dry in case the nearby stream overflows in winter. The ground isn't level. It's not too bad, but it was hard enough levelling for the working shed and that's when I could see and measure across the whole space.

If I'm pouring a perimeter, do I just dig deep enough trenches that the concrete will self-level? Is this a thing?

 

[Jameshow]

Could you move the 10x6' shed on scaffold tube rollers and ratchet straps?

 

[artie]

Prob 1
Make the new one in sections. Then you can pop it up in a very short time after you take the old one down.

Prob 2.

Not a problem, you can measure the four corners and get the rest from that.

Concrete won't self level you need pegs to screed from.

 

[MARK.B.]

If i have read and understand correctly your new shed is longer and wider so you won't need to see round the old shed,just put two pegs and a string line on one side then two more pegs measured of them to give you your width and length for the other side.

 

[MARK.B.]

was typing when artie posted his reply ,looks like we both are thinking along the same lines

 

[Terry - Somerset]

Building the new in sections is sensible. I had a 12x8 shed delivered in sections - floor, sides, roof etc - erected by the two who delivered it in about 2 hours.

Foundations need to be done ahead of time and take longer. The normal way to ensure it is square is to measure diagonals - not possible with the old shed in the way. The length of each side can be measured. Pegs can be inserted and checked for level anyway.

Ensuring the corners are 90 degrees - a simple "T" square would suffice with a long (top) side of (say) 6ft and a short side (leg) of (say 3ft fixed at 90 degrees in the centre of the top. Accuracy can be validated simply by ensuring both angles are equal - turn it upside down.

 

[Pallet Fancier]

Prob 1
Make the new one in sections. Then you can pop it up in a very short time after you take the old one down.

Prob 2.

Not a problem, you can measure the four corners and get the rest from that.

Concrete won't self level you need pegs to screed from.

So, as you and Mark.B have said, I can measure the corners rather than measuring diagonally. That gets me square. But how do I get the pegs level?

 

[Pallet Fancier]

Building the new in sections is sensible. I had a 12x8 shed delivered in sections - floor, sides, roof etc - erected by the two who delivered it in about 2 hours.

Foundations need to be done ahead of time and take longer. The normal way to ensure it is square is to measure diagonals - not possible with the old shed in the way. The length of each side can be measured. Pegs can be inserted and checked for level anyway.

Ensuring the corners are 90 degrees - a simple "T" square would suffice with a long (top) side of (say) 6ft and a short side (leg) of (say 3ft fixed at 90 degrees in the centre of the top. Accuracy can be validated simply by ensuring both angles are equal - turn it upside down.

The difficulty with building it in sections is that I'm using a recycled pile of beams and joists, not the usual skinny bits of CLS in the stick-on-frame approach. I'm doing this primarily because I've got the wood in hand - can't afford to buy a shed-worth of building materials from scratch. Each of these timbers is a minimum 5 or 6" around (they came out of an old Victorian building that was being demolished) so a frame that used these things for studs would take ten men and a mini-digger to lift!

Unless I had lots of very short sections, but when you start doing that, surely you lose the advantage of building in sections, and may as well assemble from the component timbers?

 

[MARK.B.]

Try using a lump hammer
The pegs don't really need to be level as at this point you are only marking out the size and where to dig,when you have done the digging you can use some more pegs and a level to give the depth of your concrete.

 

[Normancb]

You can level over pretty much any distance and round all sorts of obstacles using a length of hose, a couple of bits of transparent tubing, and some water. A search for "levelling with pipe and water" will get you all you need to know.

 

[Pallet Fancier]

Try using a lump hammer
The pegs don't really need to be level as at this point you are only marking out the size and where to dig,when you have done the digging you can use some more pegs and a level to give the depth of your concrete.

Right! Insert forehead slap. I level the concrete by measuring its depth, all round.

Hey... it's Sunday. It's brain's day off.

 

[johna.clements]

So, as you and Mark.B have said, I can measure the corners rather than measuring diagonally. That gets me square. But how do I get the pegs level?

You can level with a laser, automatic / surveyors level or a water level (these are a pain in the ass but cheap).

Regarding squareness. If you have enough room you can set up two parrellel string lines that project beyond the existing shed. Have the string running from nails driven into the top of two pegs. (make sure the string is running from the cebtre of the nails and not from the side). the Then on one of the string lines knock in a peg where you want two corners of the shed and put nails below the string line. Then measure from the corner nail back to the nail in at the end of the string line. You can then calculate the diagonal (using pythagoras) to get the distance from the nail at the end of the string line to the corner of the shed on the other string line. Put a peg in there and put a nail in. Then check the position by measuring back to the nail on the peg on the second string line, so you can calculate and measure the diagonal to the first corner. To get the last peg you just measure along the second string line to the other corner.

When you have all four corners marked with nails you could pull a string through in the other direction and put in pegs with nails in them eyond the excavation. Then you can reestablish the corners. Write on the pegs the distance to the corners, it will be useful.

 

[MARK.B.]

My week consists of 7 Sundays but every once in a while the ole brain cells line up for a brief period of time

 

[artie]

So, as you and Mark.B have said, I can measure the corners rather than measuring diagonally. That gets me square. But how do I get the pegs level?

Well. square enough for a shed.

You can get three corners perfect with a laser or spirit level then move it for the last one.

That will get you near enough exact.

A twelve ft straight edge might be hard to come by so I'd prefer a laser.

 

[Mcdemon]

You can use intermediate pegs to level with a straight edge and a good old fashioned spirit level.

 

[Jones]

Use Pythagoras 3-4-5 to get the corners at 90 degrees and put pegs in to get the levels, you can measure down to get the correct level for the concrete. Sometimes people put pegs in the trench level those up to finish level and then pour around them, then withdraw the pegs before setting, this works best with steel rather than wooden pegs.

 

[artie]

Use Pythagoras 3-4-5 to get the corners at 90 degrees and put pegs in to get the levels, you can measure down to get the correct level for the concrete. Sometimes people put pegs in the trench level those up to finish level and then pour around them, then withdraw the pegs before setting, this works best with steel rather than wooden pegs.

He won't be able to get assistance from Pythagoras as the old shed is in the way.

 

[profchris]

He won't be able to get assistance from Pythagoras as the old shed is in the way.

He can if there's space next to the shed, put the triangle there! Just extend one line to make one side of the triangle and measure 3 (or 4) along that.

 

[Stevekane]

If you can see the slab or base of the old shed and your happy with its squareness why not just measure off of that, if it ultimatly transpires that your a bit out does it really matter on a shed your building to fit? I know its not ideal but its the situation your in,,
Steve.

 

[bansobaby]

I would use my Total Station, but it's overkill really.....