# 18th Century Prison first floor workshop and heavy machinery



## Quickben (16 Mar 2019)

Reading another thread on floor strength got me thinking. Our workshop is the first floor of a small prison built around 1740. It is slightly above street level with a floor below. So basically, we're upstairs.

The main room, which is the main workshop, is around 7mx16m. I belive the room directly below it is the same dimensions. I'm becoming increasingly worried that we won't be able to put any heavy machinery 200kg+ anywhere near the middle of the floor. 

I have absolutely no idea how big the floor joists are. The only thing that is making me feel any better is that when my dad (around 75kg) and I (around 90kg) carried our new drill press (around 85kg) to different areas of the room to see where it would go best, I detected no deflection or movement under my feet. Highly scientific I'm sure you'll agree ! 

Is anyone of a historical architecture bent able to shed any light on how sturdy they built things like prisons in those days ?

Gary


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## Steve Maskery (16 Mar 2019)

From a purely gut feeling point of view, I wouldn't think you have anything to worry about. 200kg is not that much.
You say you are 90kg. I'm more than that. If you and your triplet brothers stood in the middle of the room, would you go through? I doubt it.
If you want a mathematical answer, I bet MikeG is your man.

I once worked on a building site. The floor was made of 600x600 chipboard panels, clad in aluminium, supported on an array of 6" posts, each post supporting one corner each of 4 boards. One day someone used a pallet truck to try to move a full pallet of plaster. That is 56 bags at 25kg each, or 1400kg. The pallet stayed put and the pallet truck went through the floor.

Those chipboard floor panels were only 50mm thick. Your joists will be several times that, and beam strength varies with the square of the depth, so I would be astonished if 200kg is coming anywhere close to your floor's limit.
S


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## Quickben (16 Mar 2019)

Hi Steve,

Yes, I was thinking along those lines. However, I probably should've said "multiple" heavy machines.

Eventually I aim to have a 12" planer, atleast a 12" thicknesser if not wider, both stand alone, and perhaps a panel saw or large table saw along with a large bandsaw. 

So there's four machines which could way between 150-200kg each depending on which models we get. 

This is the scenario I worry about. I mean, we're on pretty friendly terms with Robin at Tynemouth Achitectural Salvage downstairs, but if I suddenly appeared in his shop along with half his ceiling, 300 year's worth of dust and a thicknesser he's going to be a bit pineappled off.

This is an extreme result of course, but you get what I mean.

Gary


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## flying haggis (17 Mar 2019)

surely prison floors will be thick so that former inmates couldnt get through


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## dizjasta (17 Mar 2019)

If your building has a Listed Status it maybe that a survey has been completed to assess it's fabric and clarified matters which include floor loading. Is it possible to check?


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## sunnybob (17 Mar 2019)

Regardless of original specs, we're talking about beams that are TWO HUNDRED AND SEVENTY YEARS OLD. :shock: :shock: :shock: 
How many death watch beetles and woodworms have been at them in that time.
Dont trust... you have to get them checked. If youre talking about multiple machines, a catastrophic failure could involve loss of life.


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## Quickben (18 Mar 2019)

Bob, you raise a good point. And a scary one.

I'll look into getting it checked out.

About twenty years ago the building was used by a metal etching company, my Dad knew the owner and said that they had huge vats of etching acid and quenching solution, which would obviously weigh a _lot_.

However, they had the whole building not just our floor, and he can't remember if the vats were upstairs or downstairs.

Investigation needed, I think.

Gary.


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## sunnybob (18 Mar 2019)

Thats even more worrying. :shock: 
I've worked in and around acid storage and metal chroming and anodising factories. the guys who work there (including me)usually wear welly boots because of the amount of corrosive spillages.

Dont trust that floor.


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## Quickben (18 Mar 2019)

The floorboards look original and in good condition, to be fair. They must've had some kind of hard covering on top of them at some point because when we first moved in I spent the best part of three days pulling up proud flooring tacks !!


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## RobinBHM (18 Mar 2019)

Id be surprised if the floor joists spanned 7 metres

Its more likely there are intermediate beams dividing up the 16 metres and floor joists in between them.

You would be wise to pay a structural engineer to adivse what load the floor can handle -although he wont be able to tell you if the floor has suffered woodworm or rot. And you will need to take some boards to see the structure, if it isnt visible from below


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## Quickben (18 Mar 2019)

Yeah, I was thinking along those lines. 

It's a year or so off, but I'd feel better knowing for certain. I'll have a word with Robin and see if you can see anything from his place.

Actually I think the joists run along the 16m length, as the floor boards run along the 7m :shock: 

There is a join in the floor boards about halfway across, so there must be something there that runs the full 16m. Maybe there is a supporting wall below, I'm not 100% sure on Robin's layout.

Gary.


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## heimlaga (24 Mar 2019)

The good thing with traditional timber floor joists is that as you increase the load they will sag noticeably long before they fail.
So provided that they aren't significantly damaged by beetles or rot they will be safe with good marigins as long as you don't notice them sagging under load.

I am a certified structural engineer though I have never worked as such. Could never get a job so I went back to carpentry and joinery.


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## Chrispy (25 Mar 2019)

As another point of view have you thought about the noise , a wooden floor would make a great sounding board for a thicknesser.


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## Quickben (25 Mar 2019)

Chrispy":3m69ndl3 said:


> As another point of view have you thought about the noise , a wooden floor would make a great sounding board for a thicknesser.



Not a concern.


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