Insulation under a garage floor? -Compression strengths HELP

[angelboy]

Can I use Jablite Jabfloor 70 under a 150mm concrete garage floor?

The plan was to insulate the garage floor down the line and then put in a floating floor but the digger driver has cut too much out of the base so I might as well get the insulation in at floor level rather than first floor (double storey with habitable rood space)

When I contacted Jablite to see if this was OK they said they didn't know - ask an SE!!!

I know we're OK for domestic floors but I don't know for garage floors.

 

[limerockconstruction]

I'm not sure about Jablite, but certainly with the PIR boards there are different grades of it - some suitable for garages others not.

 

[angelboy]

I'm just trying to find the cheapest way to achieve the U values whilst maintaining some structural stability.

I've searched all afternoon and found no answers which makes me wonder why?!?!

Some manufacturers state products with 150 kpa as being for 'high traffic' or 'commercial' applications whilst others have ratings in excess of 200 kpa. I don't want to over specify if it's not needed.

When Jablite tell me to 'ask an SE' then the money that I'll pay for an answer I might as well go for a more expensive product with double the kpa.

 

[angelboy]

Maybe I've made some headway.....


1 kPa (kilopascal) is equal to 1 kN/m2 (kilonewton per square meter)

A normal house floor would have a kN/m2 of 1.5

I've found a garage for vehicles under 2500kg should be 2.5 kN.m2 (with a concentrated load of 9 kN).

So, does this mean an insulation board with a kPa of 70 (compression strength at 10% compression) and 20 (compression strength at 1% compression) is plenty for a garage floor?


If that's right, then why bother with 150 kPa pr even up to 500 kPa. The highest kN/m2 I have is 7.5 for boiler rooms, plant rooms including weight of machinery.


Am I totally wrong or missing something here?

 

[angelboy]

....another thought....


I've just read that I must first work out the area in meters (49sqm) and multiply by the pressure in kPa (which is 2.5 as 1 kPa = 1 kN/m2) which then works out at 122.5 kN

Does this mean I need an insulation board in excess of 122.5 kN? (which may explain the reason insulation boards come with kPas of 150 - 500)


Confused?!?!?

 

[limerockconstruction]

The spec on the garage we just did was 150 - I'm afraid I don't know much more than that!

 

[^woody^]

Kilo pascal is a measure of air pressure. OK for diving bells, not for garage floors

 

[tony1851]

The vehicle won't be standing on the insulation; it will be standing on 6" of concrete on the insulation. A good-grade concrete will spread the load sufficiently to avoid cracking by the insulation compressing.

Put some light mesh in it for additional load-spreading. The worst case loading is when you jack the vehicle up. Just put a short length of 9x2 timber under the jack.

Why bother with garage insulation anyway?

 

[angelboy]

Kilo pascal is a measure of air pressure. OK for diving bells, not for garage floors

It's what all the insulation manufacturers use so I just have to go with it I suppose.

 

[RonnyRaygun]

Kilo pascal is a measure of air pressure. OK for diving bells, not for garage floors

The Pascal is the SI unit for any pressure, equal to 1 Newton per square metre, so a Kilo Pascal is 1kN/m2.

 

[angelboy]

Put some light mesh in it for additional load-spreading. The worst case loading is when you jack the vehicle up. Just put a short length of 9x2 timber under the jack.

Why bother with garage insulation anyway?

I've specced A142 mesh 50mm from the top.

I wasn't going to insulate the slab but the digger driver has been a little over zealous when he's dug out. I've got to make up 560mm instead of the proposed 350mm so as the first floor needed to be insulated anyway (it's a habitable space) then I might as well do away with that insulation and put it in the slab instead. The walls for the garage are 300mm with 100mm xtraterm so it's specced like a 1 3/4 house - which is what we'll get change of use for a few years down the line. The main house can get away with the Jablite 70 insulation (even though I might use Hansons Jetfloor) which would have been fine, but as I never intended to insulated the slab (the slab level is at GL, 150mm below DPC and when change of use was required I'd have put down a floating floor with 100+ insulation to make it up) you can see why I'm confused.

 

[jeds]

Average PIR insulation will easily support normal garage loads under a 150mm slab. 140kPa is the same as 140kN/m² - which is a considerable load. Really you can forget the imposed vehicle load and just work out the concentrated load - which should be minimum 9kN for vehicles up to 2500kg. The worst case will be jacking up. Lets say the concentrated area at the surface is 4mm². That equates to 0.09m² at the insulation for a 150mm slab. Call it a tenth of a metre. Lets say you jack up half the maximum load of 1250kg - or 12.5kN. So that is 12.5kN concentrated load at the insulation surface. The maximum allowable is 14kN so you are well inside. And anyway; the surface area is likely to be more than 4mm², most people would put a plank under the jack (as tony said) and your car is unlikely to be 2500kg and you won't actually be jacking up half of it. So really you are well, well, well inside.

 

[RonnyRaygun]

I've found a garage for vehicles under 2500kg should be 2.5 kN.m2 (with a concentrated load of 9 kN).

So, does this mean an insulation board with a kPa of 70 (compression strength at 10% compression) and 20 (compression strength at 1% compression) is plenty for a garage floor?

You would probably want to limit your compression to closer to 1% than 10% else you will be expecting your concrete to cope with some significant tensile stresses.
However, realistically it's unlikely that if using a 150mm slab you will ever exceed 20kN/m2 pressure on the insulation as the load spread will almost certainly be more than 45 degrees once the slab's stiffness has been taken into account.

 

[angelboy]

So would you think that EPS boards perform the same as PIR boards?

I'm waiting to hear back from the BCO to see what I can get away with regarding the thickness but I'm at about £28.50/board (Celotex GA4000 100mm) so if I can use 75mm then cheaper still. The Jabfloor 70 (50mm) was coming out at £12.50/board to doubled up to £25 to get 100mm. For the £3.50 difference and double compression strength I think the Celotex might beat it. (£65 for piece of mind - and cheaper than an SE!)

 

[SimonH2]

The walls for the garage are 300mm with 100mm xtraterm so it's specced like a 1 3/4 house - which is what we'll get change of use for a few years down the line.

Considered sticking some UFH pipe underneath while you're at it - just hide the pipe ends behind a pile of rubbish when the BCO is about You don't have to use it, but if you decided you wanted it later then it's in.

Hmm, garage with insulated and (potentially) heated floor - I'm jealous !