A heavy load (for a shed)

[Chris Puttick]

Very interested in getting a planer-thicknesser into my workshop (née shed) which already is home to a lot of tools, a compound mitre saw, bench sander, bench pillar and most recently a floor standing bandsaw. The weight of the latter, particularly as it is wheeled, gave me pause before installation, but I went with a long sheet of 18mm hardwood ply to spread the load over the t&g floor and joists.

The planer-thicknesser on the short list is nearly double the weight of the bandsaw, more than double once you add in the required extractor - at which point I start to worry about the entire floor construction. So...

Is the shed going to collapse under the weight? The shed is approx 4.9m x 3m, and the floor looks to have been prefabbed in 3 sections over the 4.7m length with joists of 45x70 at 380 centres attached (I assume) to a timber base of 100x50 joists at 530 centres. Those joists are supported in their centres (so approx 1.4m unsupported spans. It seems sturdy enough, but then there's quite a load building up in area (the bandsaw and planer-thicknesser/extractor will all be in one section, though the bench with drill and sander etc. runs along the opposite wall.

I have enough access to allow adding additional supports to the base around the heavy load areas (using Castlewood's neat deck supports - slide them into place and then adjust the height) and will add more (screwed down to joists) 18mm ply for the planer-thicknesser and extractor to sit on. Should that do it or do I need to do something more?

 

[Jameshow]

I think you'll find the joists will be fine but any point loads might too much for 18mm osb or pine? A Sher if 18mm hardwood plywood might help spread the load.

 

[Fitzroy]

What is the machine weight? PTs vary from 250 -> 1000+kg

 

[Chris Puttick]

What is the machine weight? PTs vary from 250 -> 1000+kg

Axminster AW2260S lists at 170kg, the extractor I've specced to support it is 48kg when installed. I'm limited to 13A, so there's not a lot to shortlist from. The bandsaw is a bit over 100kg, I guess a bit more with the extras bolted on.

 

[Chris Puttick]

I think you'll find the joists will be fine but any point loads might too much for 18mm osb or pine? A Sher if 18mm hardwood plywood might help spread the load.

Yeah the plan is to screw 18mm hardwood ply over the existing floor to deal with point loads and add some rigidity.

 

[--Tom--]

170kg is roughly 2 people stood in the shed- should be absolutely fine

 

[TRITON]

Why 18mm ? wouldnt 25mm or even 32mm be a better choice.

With lots of screws. lots and lots of screws.

 

[Molynoox]

C16 will do 1.46m at 600mm centres and 1.82m at 450mm centres in a floor joist situation.

Like has been said 170kg is just two people stood close together and I would expect it to be fine, especially with that plywood you are going to add.

 

[Lard]

170kg is roughly 2 people stood in the shed- should be absolutely fine

I use this 'rule' all the time.....in your head convert the weight into human terms and it'll make more sense

 

[Chris Puttick]

My civil engineering skills are rusty, but I seemed to recall there's a difference between a mobile load and one that's more or less permanently located.

 

[Croolis]

Came across this thread.

When I made my metal shed floor I used this span table, but now, after looking at it again after reading the above, I think I didn't really understand it.

https://www.timberbeamcalculator.co.uk/en-gb/span-table/floor-joists?load=1.5&class=C16

I used C16 47*95mm at 400mm on centre spacing with a span joist underneath at 1.25m (shed's 2.5m wide). So that's plenty of tolerance to give "Dead load per square metre (in kN/m²) supported by joists" of "More than 0.5 but not more than 1.25".

Now I'm thinking about it again I'm wondering what that means.

 

[Chris Puttick]

As I read it the second row is the dead load, and 200kg that's on a convenient 1m2 base is 200kg/m2 = 1.96kN/m2. The base of a planer is rather less than 1m2 (the one on my shortlist, pending electrician sign-off on a 16A socket, is 470*435mm=0.24m2, so its weight of 176kg makes it rather more than 200kg/m2. Which is why I'm nervous and the use of a full sheet of screwed down 18mm ply over the floor where the planer/extractor are going.

Slightly OT but I ran into a version of this problem back when I was involved in IT fit-outs for new builds. We sat in this meeting on site, IT people being late in the cycle as always, and the architect explained the server room was going on the 1st floor. We asked "are you sure that's a good idea?" to which the response from the construction team was "no problem, you could park a Sherman tank on these floorplates" so we let it slide and carried on with finalising the spec. A little later we had both a list of tech and the spec for the floorplates - which had a point load rating of something like 1000kg/m2. Only a server rack is rather less than a m2, there were 4 of them and 2 of them were over ~700kg fully loaded, so at the last minute we had to get a 20mm thick steel plate fitted into the server room to sit the racks on - and I'm told that a few years later the ceiling below started have issues as the floorplates slowly bent under the load anyway.

The thing about a Sherman tank is that it might be heavy but it's long and wide, and doesn't stand in exactly the same place for years at a time.