PIR insulation underfloor

[Smallfry]

Without getting into it too much, we will have to bring up a floor level in a garage, which will be semi underground. The excavation was overdug years ago, so the raft slab will be too low, unless we pay many thousands for extra concrete to bring the level up about 18 inches.

I could build off the slab though, and would need a few extra courses of blocks. Someone suggested I bring up the level with 300mm of PIR insulation, and put a 150mm concrete slab on top of that.

Bearing in mind this will be a garage floor, with vehicles, a lathe and milling machine, and a couple of tons of stuff on shelves bearing down on it, my concern is that it is going to crush. Maybe not straight away, but over time.

I know that a lot of domestic floors are being done like this now, and obviously it is taken that it will be OK, but as with things that are supposed to be UV resistant, there is no substitute for the passage of time. This stuff hasn't been around long enough to really know.

Or am I worrying too much ?

 

[addjunkie]

You could do hard core blind with sand and new floor…pir insulation is blooming expensive. My house has 100mm but nit cars or lathes in the living room

 

[Agroshield]

Why PIR? Polystyrene would do.

Look up Jabfloor. The standard product, used under domestic floors, is 70, but they do higher grades. The technical data sheet will tell you the allowable load for 1% compression. Convert that to kilograms per square metre and marvel at how strong it is (Jabfloor 70, the lowest grade, is 2000kg per square metre). That means you could cover the entire floor with pallets, each with 80 bags of cement on it.

You need a soft joint at the edges to accommodate the movement.

If you want super strong, Dow floormate 700 is used under lorry loading bays inside buildings so will withstand HGV axle loading.

 

[KaneH]

Run in 300mm of compacted type 1 then add your 150mm slab on top. That is unless you want it insulated. Which if so polystyrene (eps/xps) would be perfect as it’ll be cheaper than PIR. 300kPa compressive capacity (30tonne/m2) is possible with some products so if you throw in some small mesh in your slab you’ll have no issues with the loads you’re looking at.

 

[Smallfry]

You could do hard core blind with sand and new floor…pir insulation is blooming expensive. My house has 100mm but nit cars or lathes in the living room

The problem with hard core is getting it here. Drive is narrow and a difficult turn in. Plus it is a steepish slope, so any vehicle trying to get in cannot be any bigger than a transit sized tipper, and if there is much overhang, the back end hits the drive. I don't want to make the drive bigger, as its a bit of a security feature. There would have to be many trips, and that will end up costing a lot too, and the PIR is a lot easier to move and handle.

We are going to need 27 to 30 cubic metres of concrete pumped from the lane for the main slab, plus whatever goes on top. I can hear people moaning already

 

[Smallfry]

Run in 300mm of compacted type 1 then add your 150mm slab on top. That is unless you want it insulated. Which if so polystyrene (eps/xps) would be perfect as it’ll be cheaper than PIR. 300kPa compressive capacity (30tonne/m2) is possible with some products so if you throw in some small mesh in your slab you’ll have no issues with the loads you’re looking at.

Thanks for that. I will look into it. Its not really about needing insulation, although I guess its not a bad thing, even in an unheated space, but its a whole lot easier than hardcore and type one.

 

[gaz1]

if you want to save on concrete within the floor you can also use 2" carpet rolls as long as the cardboard is protected from the water advantages to tubing the floor you can use it as underfloor heating

and as you are adding a deeper layer it dosnt matter how thick the floor is

the pic shown is hollow core flooring used in high rise buildings and other applications

H

Thread 'Insulated concrete slab for workshop'

Oct 7, 2022

Not sure if this is in the right section, but didn't really feel like "project" or "tools and materials" either...

Anyway, I have a space of about 6.4 (width) and 6'ish length where I want to build a reasonable workshop. The walls will probably be double skinned breeze blocks (maybe with render or fake wood cement cladding), with sound absorbing insulation in between the skins.

I will build it slightly smaller than the available size, because I want to be able to fix issues around the building, so probably leaving 0.4-0.5m per side (left, right, back), so internal floor area will...

• Henrik
• Replies: 40
• forum: The Brew Room

• 

 

[Agroshield]

As above, the logistics of installing a 'heavy' material can be considerable.

There are about 34 number 8' x 4' x 300mm blocks of polystyrene in 30 cubic metres. The weight of each block is about 13kg. That makes use of child labour feasible for moving them from point of delivery to point of installation. April 2024 cost of Jabfloor 70 (equivalent) was £77 per cubic metre.

Motorway embankments are built on polystyrene blocks over poor ground, so the material itself has a track record.

If putting mesh in the slab, on no account cut it with a grinder - until the polystyrene is encapsulated, it is a fire risk.

 

[RBDIVE]

My view would be a self drive transit type tipper and bring in more sub-base MOT1 other options around such as crushed recycled concrete/ brick.
But jabfloor as mentioned would work if you want

 

[sako243]

@Smallfry is there somewhere nearby that's accessible for larger tippers to dump a stockpile?

A digger and 3-4t dumper would quickly shift it. Hell I had 20t of clean stone dumped on our drive as I took pity on the driver trying to reverse up our drive in pouring rain and the dark. Having to ferry it a hundred yards in the 2CX only took a couple of hours with the front bucket which isn't as big as your 3CX one.

 

[Gareth J]

As above, the logistics of installing a 'heavy' material can be considerable.

There are about 34 number 8' x 4' x 300mm blocks of polystyrene in 30 cubic metres. The weight of each block is about 13kg. That makes use of child labour feasible for moving them from point of delivery to point of installation. April 2024 cost of Jabfloor 70 (equivalent) was £77 per cubic metre.

Motorway embankments are built on polystyrene blocks over poor ground, so the material itself has a track record.

If putting mesh in the slab, on no account cut it with a grinder - until the polystyrene is encapsulated, it is a fire risk.

Compared to concrete, looks cheap. Be interesting to see how it would compare to stone + handling, levelling and compacting.

You could also consider pricing a block and beam floor. If they come specced to take the loads you require.

 

[iNf]

If going the PIR route then these are usually much cheaper https://www.secondsandco.co.uk/
If going the hard-core route then look for road planings, much cheaper than scalpings

 

[Blobber]

If going the PIR route then these are usually much cheaper https://www.secondsandco.co.uk/
If going the hard-core route then look for road planings, much cheaper than scalpings

Road planings would be the last thing you'd want to use inside as a base

 

[Mick Annick]

I designed and built a workshop for Ford in Tilbury docks many years ago, we had to raise part of the floor 1.5m to accommodate two conveyor fed car washes - the design engineers used polystyrene under the new slab.

 

[roofman]

Without getting into it too much, we will have to bring up a floor level in a garage, which will be semi underground. The excavation was overdug years ago, so the raft slab will be too low, unless we pay many thousands for extra concrete to bring the level up about 18 inches.

I could build off the slab though, and would need a few extra courses of blocks. Someone suggested I bring up the level with 300mm of PIR insulation, and put a 150mm concrete slab on top of that.

Bearing in mind this will be a garage floor, with vehicles, a lathe and milling machine, and a couple of tons of stuff on shelves bearing down on it, my concern is that it is going to crush. Maybe not straight away, but over time.

I know that a lot of domestic floors are being done like this now, and obviously it is taken that it will be OK, but as with things that are supposed to be UV resistant, there is no substitute for the passage of time. This stuff hasn't been around long enough to really know.

Or am I worrying too much ?

what area are you mate..dumping a load of insulation board currently

 

[iNf]

Road planings would be the last thing you'd want to use inside as a base

Why? They compact down well whenever I've used them.

 

[KaneH]

Why? They compact down well whenever I've used them.

Lack of grading makes them susceptible to movement. Two 150mm layers of compacted type 1 would be best practically speaking.

 

[Blobber]

Fumes, the tar soon reactivates with warmth, I should think it would attack any membrane or insulation, perfect out side

 

[tom2207]

glass bottles was the old fashioned way ,,, depends on what you have to hand

 

[Smallfry]

what area are you mate..dumping a load of insulation board currently

Sadly the other end of the country, in Kent, but thanks for the thought !