Which screw for securing metal shed down onto wooden base?

[Croolis]

I have built wooden floor and dwarf 200mm high stud wall (stud wall to raise roof a bit, described in a different thread) that I am going to sit a cheap metal shed on top of.

I am going to wrap the dwarf stud wall in breathable membrane, stapled on, and screw feather board cladding over it, and then put plastic angled trim along the top plate (2x4) beam of the stud wall (which will be laid flat on its 95mm side) , so that it covers and protects the top edge of the feather board cladding.

Then the metal shed will sit on top of this. The bottom plate of the shed wall is thin galvanised metal. There is enough flat surface that it will sit flush on the plastic trim.

So, my question is, what type of screw shall I use? It's going to be going through galvanised steel, plastic trim, breathable membrane and into treated 2x4 laid flat so it's 47mm deep. That's quite a combination of material, and I'm not sure I've ever drilled or screwed into sheet metal before.

Any thoughts?

 

[flying haggis]

So in actual fact your fixing screws are not actually going through a lot, possibly only 10mm max so 50mm screws will do nicely, spax (i think)do ones with a large pan head. Does the shed have a lip inside and how wide is it? If it is narrow you might struggle to get screws in as the sdrewdriver/cordless drill will not allow you to screw down straight.

 

[Bingy man]

Tech fast roofing screws- self drilling available in most sizes. As above depending on your sheds design you may have to send them in at an angle. Impact drill is ideal for this . Had to do this to fix my greenhouse to sleepers .


Forgefix TechFast Hex/Washer Self Drilling Roof Screw 5.5 x 32mm (100 Pack) in Silver | Rubber
£8.57

 

[Spectric]

Wafer heads give a nice clean finish.

 

[flying haggis]

Tech fast roofing screws- self drilling available in most sizes. As above depending on your sheds design you may have to send them in at an angle. Impact drill is ideal for this . Had to do this to fix my greenhouse to sleepers .
Forgefix TechFast Hex/Washer Self Drilling Roof Screw 5.5 x 32mm (100 Pack) in Silver | Rubber
£8.57

trouble is that some of those metal sheds have a very small lip and sending a screw in at an angle might actually mean that it comes out the side of the base. I would almost be tempted to dun some tile batten around the base of the shed and fix from the outside into that then screw the batten down to the base

 

[Jameshow]

Id use penny washers if I were you. Spread the load and resist pulling out!

 

[TheUnicorn]

trouble is that some of those metal sheds have a very small lip and sending a screw in at an angle might actually mean that it comes out the side of the base. I would almost be tempted to dun some tile batten around the base of the shed and fix from the outside into that then screw the batten down to the base

using a screw bit extension, say 300mm, would help get that angle a bit straighter

https://www.screwfix.com/p/wera-1-4-hex-magnetic-bit-holder-300mm/854fp

 

[Croolis]

Thanks for replies. I won't be sure until Saturday when I do this, but I think I might be OK getting the screw straight down into the wood. As I say, I shall be placing the shed on 2x4 turned sideways so the 95mm face is up and the metal base plates are quite wide with a flattened flange.

Here's another question - if I find that my outer rim joist square is not sitting level on my 9x concrete blocks and one corner is a bit up in the air, should I try and shim it or something? The wood I got isn't perfectly straight for the most part and I simply don't have the time to go messing about at the timber yard. The concrete blocks are pretty level I think. But this is strictly amateur night here and I'm not convinced it's all just going to come up lovely once I've screwed it together, even if the blocks are level.

If I end up needing to shim it below the outer rim joist, any thoughts on what to use? I have wooden boards that could go in (all wood will have DPM between it and concrete block no matter what). Or is there a better thing? I have some ready mix mortar handy, could just stick a layer of that on top of a concrete block, though I have no idea if that would last.

 

[Bingy man]

trouble is that some of those metal sheds have a very small lip and sending a screw in at an angle might actually mean that it comes out the side of the base. I would almost be tempted to dun some tile batten around the base of the shed and fix from the outside into that then screw the batten down to the base

I was thinking of a few degrees- in my case I didn’t want the drill chuck to make contact with the glass . I only used 30 mm screws so nothing emerged from the sides . You can also use metal brackets shaped to fit the profile and fixed to the timber but inside .. lots of ways to achieve this task

 

[Jester129]

I would make sure that there is a seal on the outside of the shed onto the wood or you will get leaks from seepage between the two.

 

[Croolis]

Tech fast roofing screws- self drilling available in most sizes. As above depending on your sheds design you may have to send them in at an angle. Impact drill is ideal for this . Had to do this to fix my greenhouse to sleepers .
Forgefix TechFast Hex/Washer Self Drilling Roof Screw 5.5 x 32mm (100 Pack) in Silver | Rubber
£8.57

I bought these. But now I'm looking at them - are these OK for putting into pressure treated wood?

 

[Bingy man]

I bought these. But now I'm looking at them - are these OK for putting into pressure treated wood?

I’ve sent them into all types of timber and had no issues. My greenhouse is still firmly attached to the reclaimed larch fencing posts that was heavily treated . The trick is not to over tighten them ..