No Concrete floor slab

[Croccy]

Can I put a floor slab (30m sq) down without a 100mm concrete slab? 

Using more MOT, 250mm? Insulation & Screed on top?

I know it can be done this way on refurbs!

[jayc89]

Unless spec'd by an Engineer BCO wouldn't sign that off. 

[Iceverge]

4 hours ago, Croccy said:

Can I put a floor slab (30m sq) down without a 100mm concrete slab? 

Using more MOT, 250mm? Insulation & Screed on top?

I know it can be done this way on refurbs!

 

It can be done with OSB in lieu of screed.

 

Compact the stone base well and get it dead level. It may need to be laid in several layers to achieve this. 

 

Install a layer of EPS. 

Install your DPM.

Another layer of EPS with all joints crossed. 

 

Install 18mm OSB with a suitable expansion gaps. 

 

Glue and screw another layer of 18mm OSB on top. With all joints well staggered. 

 

Tape the edges of the OSB to the walls to prevent any air or water leaks into the floor. 

 

 

 

 

[Roger440]

37 minutes ago, Iceverge said:

 

It can be done with OSB in lieu of screed.

 

Compact the stone base well and get it dead level. It may need to be laid in several layers to achieve this. 

 

Install a layer of EPS. 

Install your DPM.

Another layer of EPS with all joints crossed. 

 

Install 18mm OSB with a suitable expansion gaps. 

 

Glue and screw another layer of 18mm OSB on top. With all joints well staggered. 

 

Tape the edges of the OSB to the walls to prevent any air or water leaks into the floor. 

 

 

 

 

 

Very interesting. Thanks for posting.

[G and J]

1 hour ago, Iceverge said:

 

It can be done with OSB in lieu of screed.

 

Compact the stone base well and get it dead level. It may need to be laid in several layers to achieve this. 

 

Install a layer of EPS. 

Install your DPM.

Another layer of EPS with all joints crossed. 

 

Install 18mm OSB with a suitable expansion gaps. 

 

Glue and screw another layer of 18mm OSB on top. With all joints well staggered. 

 

Tape the edges of the OSB to the walls to prevent any air or water leaks into the floor. 

 

 

 

 

I think you’ve just solved a dilemma I have with my pigpen (man cave, thing).  Brilliant.

[Mike]

6 hours ago, Croccy said:

Using more MOT, 250mm? Insulation & Screed on top?

To do it in accordance with the Regs, you'd want MOT (or other suitable crushed stone), sand blinding, DPM, insulation as needed, 100mm concrete on top. Not forgetting the perimeter insulation.

[G and J]

34 minutes ago, Mike said:

To do it in accordance with the Regs, you'd want MOT (or other suitable crushed stone), sand blinding, DPM, insulation as needed, 100mm concrete on top. Not forgetting the perimeter insulation.

My 25m2 garden building doesn’t have to comply with regs and we won’t be throwing money at it as it is just a man cave, but I still want it nice and useable.  
 

This idea would solve my ‘getting concrete down the bottom of the garden after we’ve built the house’ problem.  I’m keen. 

[G and J]

9 hours ago, G and J said:

My 25m2 garden building doesn’t have to comply with regs and we won’t be throwing money at it as it is just a man cave, but I still want it nice and useable.  
 

This idea would solve my ‘getting concrete down the bottom of the garden after we’ve built the house’ problem.  I’m keen. 

But in all things I lay awake thinking……

 

So if the no concrete slab/screed idea works with well enough compacted hardcore stuff then that means (I think) that I could do a hand mixed concrete layer on top of the compacted stuff to then put insulation then floated wooden floor on.   I’ve been thinking I needed proper poured concrete which will be sill expensive to pump the circa 75m from the road.   I guess I’m thinking more like a string oversite than a slab.   
 

I wonder…..

[Iceverge]

2 hours ago, G and J said:

that I could do a hand mixed concrete layer on top of the compacted stuff

 

What exactly is the concrete doing other than making a surface than is less lightly to be disturbed during floor laying. 

 

Another no concrete idea is to opt for an Adobe floor. 

 

Stones. 

Insulation. 

DPM.

Compacted earth. 

Linseed varnish. 

 

Take off your stilettos before entering and you're done. 

[mjc55]

On 07/11/2024 at 12:23, Iceverge said:

 

What exactly is the concrete doing other than making a surface than is less lightly to be disturbed during floor laying. 

 

Another no concrete idea is to opt for an Adobe floor. 

 

Stones. 

Insulation. 

DPM.

Compacted earth. 

Linseed varnish. 

 

Take off your stilettos before entering and you're done. 

Which reminds me....

 

Many years ago in our second house I laid a parquet floor.  Forward a few weeks after finishing it and we had a 1st birthday party for our eldest ( who is now 39!) and my sister in law arrived in stilettos.  The next day we couldn't work out at first why there was lots and lots of small indentations in the floor. 😮

Edited November 11 by mjc55

[saveasteading]

On 06/11/2024 at 17:02, Croccy said:

floor slab (30m sq) down without a 100mm concrete slab? 

Yes but I wouldn't.

Ground moves. If yours is clay it may shrink seasonally.

You'll need high quality stone and rather thick.

A floating floor of eps  will be tricky to get level.

 

[Russell griffiths]

On 06/11/2024 at 23:08, G and J said:

My 25m2 garden building doesn’t have to comply with regs and we won’t be throwing money at it as it is just a man cave, but I still want it nice and useable.  
 

This idea would solve my ‘getting concrete down the bottom of the garden after we’ve built the house’ problem.  I’m keen. 

Isn’t the Solution to pour the garden room at the same time you put the house foundation in. 

[G and J]

51 minutes ago, Russell griffiths said:

Isn’t the Solution to pour the garden room at the same time you put the house foundation in. 

Good thought though because of the length of our garden that would necessitate a pump and access issues and cost would encourage me to do otherwise.  
 

I’m looking at beam and block floors for the house at the mo and I’m surprised how cheap it would be for the garden room, so that’s probably the other practical option.

[G and J]

1 hour ago, saveasteading said:

Yes but I wouldn't.

Ground moves. If yours is clay it may shrink seasonally.

You'll need high quality stone and rather thick.

A floating floor of eps  will be tricky to get level.

 

Noted.   Our garden is really sandy once you get below the soil.

 

Hadn’t factored in the difficulty of getting the insulation level, I’d assumed a sand blinding would do that job without too much difficulty. 

[JohnMo]

7 minutes ago, G and J said:

Noted.   Our garden is really sandy once you get below the soil.

 

Hadn’t factored in the difficulty of getting the insulation level, I’d assumed a sand blinding would do that job without too much difficulty. 

Our garden room is on sand base - slabs first (cement bedding), wooden perimeter frame 90mm thick (2x 8x2 timber) and 200mm deep. Filled with 50mm EPS, DPM, 150mm EPS, Log building above fully insulated. Floor OSB in 2 layers glued and screwed together floating.

[saveasteading]

An isolated garden room can be made of anything.  Slabs on the floor is easiest.

 

I don't think I would insulate the floor as any  heating is to warm the air for a short time.

 

Ditto a lightweight temporary add-on ( greenhouse/ orangery).

 

25m2 at 75mm thick concrete is about 2m3. 20 mixes and / or barrowloads. 

 

A proper extension is very different. 

 

[Iceverge]

41 minutes ago, saveasteading said:

 

I don't think I would insulate the floor as any  heating is to warm the air for a short time.

 

[saveasteading]

But seriously.  Is this outbuilding  for a potting shed, or sitting with the newspaper for an hour occasionally , or an office.

[G and J]

13 hours ago, saveasteading said:

But seriously.  Is this outbuilding  for a potting shed, or sitting with the newspaper for an hour occasionally , or an office.

In our case the initial purpose will be a gym and workshop, with a corner hived off for a shed (with that section having its own door).

 

However, I would like to build it to last and it to feel good and solid (yes, over engineered).  
 

So that gets us a basic sort of spec/plan.  Then I scratch my chin and think, “with just a little extra effort and cost I could make it…..”.

 

Repeat that exercise enough times and I have a plan for an expensive building with the potential for easy conversion to a guest suite (I am not sociable and billeting guests at the far end of the garden appeals) or carers accommodation (we plan ahead).

 

Not so much requirements ‘creep’ as ‘gallop’!

 

So, day one it needs a floor as steady as a normal indoor floor.  A bit of insulation would be nice but it isn’t really essential, but fitting it later would be a lot harder.  A potty would be handy, but difficult as evidenced in other threads due to the fall of our site and the fact that inexplicably, none of the neighbours have offered to let me dig up their gardens and connect to their sewers.  
 

It needs lecky, as large TVs (essential for rowing, naturally) don’t run themselves and I’ve an 18v Makita obsession to constantly recharge.  
 

 

Now, all this seems a bit over the top.   Until you factor in the presence, literally 250m away, of a leisure centre with gym, pool, steam room and sauna that I almost certainly will be a member of anyway.  Then it becomes downright silly.

 

But I still wants it, precious.

[saveasteading]

It's not over the top at all.

Build it properly with a concrete floor, fully insulated.

 

But I'd advise against fudging this to avoid planning and building regs. We have a system gor a reason, and shouldn't avoid it.

 

If the propriety doesn't concern you, then think of the risks in being forced to remove it, of not being able to sell.

 

Yes it will cost a lot more.

40 minutes ago, G and J said:

 I have a plan for an expensive building with the potential for easy conversion to a guest suite

Exactly. Do it properly.

[G and J]

3 minutes ago, saveasteading said:

If the propriety doesn't concern you, then think of the risks in being forced to remove it, of not being able to sell.

 

We’ve got full planning permission to build it, though we’ll do it after we’ve finished the house when we know what money we haven’t got left.  
 

We’re planning it at this stage partly because it may be a good idea to do some of the bits like the foundations at the same time as those on the house.

 

The danger isn’t that it’s not built properly.  The danger is massive over specification. 

[sgt_woulds]

You could try the Geocell system (from Mike Wye) - although it would mean wheelbarrowing a ton of expanded glass rubble to your back garden which might be just as hard as pumping concrete there.  Is very DIY-doable though:

 

 

 

 

 

 

Back to Earth also do something similar:  Solid floor insulation – How to create a solid, insulated floor - Back to Earth

 

 

 

 

 

 

 

 

 

[sgt_woulds]

4 hours ago, G and J said:

A potty would be handy, but difficult as evidenced in other threads due to the fall of our site and the fact that inexplicably, none of the neighbours have offered to let me dig up their gardens and connect to their sewers.  

 

 

A toilet doesn't need to be connected to a sewer for occasional use:

 

Online Shop - WooWoo Waterless and Composting Toilets

 

 

[Roger440]

22 minutes ago, sgt_woulds said:

You could try the Geocell system (from Mike Wye) - although it would mean wheelbarrowing a ton of expanded glass rubble to your back garden which might be just as hard as pumping concrete there.  Is very DIY-doable though:

 

 

 

 

 

 

Back to Earth also do something similar:  Solid floor insulation – How to create a solid, insulated floor - Back to Earth

 

 

 

 

 

 

 

 

 

Foamed glass is easy to move as it weighs next to nothing.

 

[sgt_woulds]

Says a man who has never done it ! 🙂

 

Try shovelling 2 1/2 tons of it into wheelbarrows and making what feels like the equivalent of a round trip to the sun backwards and forwards!

 

Geocell binds together making it incredibly hard to get a shovel in, (had to use a shallow frying pan in the end) - moving it was the hardest physical thing I've ever done.  I'm saying this as an ex-roofer used to shifting tons of slates up onto a scaffold 'cos the boss was a tight old so-and-so who wouldn't pay for a Bumpa.

 

Other than that, yes it's lovely and light...