Concrete roof for outhouse

[Groovejet]

The outhouse is block built with I beams supported across roof span.
Between beams are blocks again .
Just like a house foundation ..
Then dpm sheet over the blocks & 8mm mesh supported on 40mm stand off blocks.
So we’d like to know about the weight of concrete and load acceptable to finish the roof off?
We wanted 4inch with a slight run off down to 3.5”.
The concrete guys said it’s about 5 tonnes of concrete that we need .
This sounds a lot, but we know our works solid.
We’ve even fitted a strengthening steel under the beams , inside the outhouses ceiling . It’s running diagonal on ceiling & supported on 2 walls.
So any thoughts if we need to reduce the depth of concrete?

 

[Notch7]

Are you worried about a nuclear attack?

 

[Groovejet]

@Notch7 Yes .does it show. ? We were trying to keep it under wraps, but you’ve blown our cover.
So anyway , do you know owt about concrete roofs

 

[mikeey84]

I think you would need to share the beam dimensions before anyone could hazard a guess

 

[Groovejet]

There’s beams spanning 215mm centers approx.
There’s 7 beams.
With approx 60-70 , 7.3n blocks between beams.
Between each T beam is a row of 7.3N blocks
T beam is 10mm thick steel.
The T beam is 100mm high, from where blocks sit on , upto top of block.
So the T beam is inverted T , with T upside down & the blocks between each beam, sit on the T by 50mm either side.
Also under the roof . Up at ceiling height is a box section 3” x 3” that spans all T beams , for extra support. And it’s resting on both ends, being inserted into block and darbo’d up & slate packed.
Finally-
The lengths of the t beams gradually decrease ,due to the outhouse shape .
One supporting side wall of the build is following the natural run of the road ,so 3 walls are standard 90’ square bulid, but 1 wall is diaganol. Creating a odd shaped room. Basicly imagine a box room that’s disected in 2, making a diaganol wall.
The beams start at 4.5m long and decrease in length until the last beam rests on the wall to wall at 2.8m long
I know it’s a lot of info . Any questions can be asked at the end of presentation. And there’s a quiz after the results.

 

[Mr Chibs]

That's heavy. You need it worked out properly.

An old uncle was always fashioning this and that in his garage... he had a moan a few times of water leak in his garage roof, fibre asbestos corrugated job. Went to see him one week, said he'd been busy, he'd covered the whole roof with sand & cement. I was concerned about the weight, but he was a step ahead and had got some 'old' joists to reinforce the underside.

He never had any issues, and it was then dry.

Do you need 100mm?
At 16m², 50mm depth using an online concrete calculator I get .8m³, seems to be 1800kg, could you not screed it instead 3:1 mix and as dry as possible?

Is it single skin or on their backs?

Won't condensation be an issue?, perhaps kingspan on top of blocks and then concrete/screed with the mesh in.

When's the quiz

 

[freddiemercurystwin]

Concrete roof, whatever next. Bizarre.

 

[Groovejet]

@Mr Chibs what you mean not to screed it and use 3-1 mix dry as possible ?
Obviously you mean a strong 3-1 dry mix , which will lower weight, from less water.
But what you mean about don’t screed it

 

[Mr Chibs]

Think you may have misunderstood, I was saying ‘could you not’ screed it… as a question and point of discussion.
Lower water, less shrinkage/cracks.

What’s the deal with the concrete roof anyway?

 

[cdbe]

If the steel beam is up to reducing the span and assuming the reinforced slab is at least partially self supporting then I would be happy with that arrangement, provided the lateral stability of the building is suitable (not a single leaf etc). My only concern would be that wet concrete is heavy and has no strength and I would be using some serious temporary props untill it all goes off. Obviously you really need an engineer to confirm (you might get a bit of help from the beam manufacturer).

As already intimated a bit pointless anyway - ott for normal use and inadequate protection against nuclear attack.

 

[Tigercubrider]

At work we had a covered pathway that was in fact the lid of a massive duct.
when they made some DDA modifications, they added concrete to the existing pathway with a slope to bring the path up to the floor level of the buildings. The original had a probable 4” step.

I remember being interested as they had to install a foam core, the wet concrete was apparently too heavy for the ductwork.
However with the foam it was ok . The dry concrete was strong enough.

I guess it depends on your intended use but why 4” solid? Concrete is bloody solid and a foam core adds strength.
you can also use chopped strand to concrete to make very thin but strong slabs