Building shed on 1% sloped concrete slab

Ompl

I want to build a 32ft x 20ft x 12ft to the eaves steel shed.
The existing concrete base has a gradient slope of ~1 degree for water run off.
The poisioning of the shed would mean the slope runs the 32ft lenght of shed.
If I bolt the RSJ uprights to the slab will i run into issues due to the slab not being level or is a 1 degree fall minimal enough to make little to no difference?

Calahonda52

1 degree is approx 1:50 so 1 foot for every fifty

so the last one will be between 7 and 8 inches lower than the first one

typo corrected

https://www.archtoolbox.com/calculating-slope/

lmk123

https://www.boards.ie/discussion/comment/122716713#Comment_122716713

1% is exactly 1:100 so there will be roughly 4 inches of a fall, 97mm to be exact

Calahonda52

https://www.boards.ie/discussion/comment/122716721#Comment_122716721

My typo mistake its 1 degree as per OP post, my post corrected

Peregrinus

Thread header says a 1% slope; first post says a 1 degree slope. Big difference! So that needs to be clarified.

If it's 1%:

1% is 1:100, surely?

By my calculation, for a 32ft shed build on a 1:100 slope, one end of the shed will be 3.84" lower than the other. With a 12' eave height each of the uprights will be out of true by just under 1.5" at the top. I'm no engineer but I would have though that the uprights being out of true would be the bigger issue.

On edit: OK, it's a 1º slope. That's 1:57.

Over a 32ft distance one end of the shed will be abput 6.7" lower than the other. Each of the 12ft uprights will be 2.5"" out of true at the top.

Calahonda52

https://www.boards.ie/discussion/comment/122716729#Comment_122716729

Good point , however I would expect the uprights to be plumb, which make the problem worse

Getting decent bolts that length, ie slab plus 6 inches will also be a problem

Lumen

That's a big shed, I assume you're on agricultural land.

Your options

1. Install parallel to the slab, and live with it looking wonky.
2. Install parallel to the earth by shimming the uprights, and then deal with the big triangular gap down each side.
3. Level the slab.
4. Jack up the slab and shim underneath (only half joking, it might only be 20-25 tonnes. is it reinforced?)

If option 4 fails you can pour a second, level slab properly and put the first one in a skip 😀

rayjdav

What depth is the existing slab where the columns will be bolted into? You sure it is designed to take the holding down bolts.

Unless this is off the shelf columns??, surely the fabricator will allow for the difference in elevation of the slab and the columns on grid will be differing heights. A non plumb frame is going to be very difficult to bolt together, end plates won't match etc. unless you have packers under the base plates??

chooseusername

6in concrete blocks on the flat to level the shed. Columns bolted down trough the blocks with these.

If one column in the middle raise about 3 ins, if two columns raise about 2ins and 4 ins, and so on. (Someone on here will be able to do it accurately for you) Shutter and fill in the voids.

lmk123

OP for the love of god make the 2 middle RSJ’s 50 mm longer and the 2 end ones 100mm longer than the first 2 on the other end and please ignore almost everything that’s posted here

chooseusername

https://www.boards.ie/discussion/comment/122723010#Comment_122723010

OP good advise here, (if you want a sloping shed.)

Whatwicklow

If its a kit garage will have murder cutting and trimming the wall and roof sheeting if it's not put together plumb and level.

lmk123

https://www.boards.ie/discussion/comment/122724043#Comment_122724043

no the shed will be plumb and level if it’s done the way I said, the floor will be sloping as it already is. By the way those bolts you suggested that cost almost €10 each would be utterly useless if used the way you’re saying it. Anyway I’m done, over and out.

Esel

On YouTube I've seen slabs being raised by injecting expanding foam underneath them.

Might be worth investigating anyway.