insulation for suspended floor

[harrison_633]

hi folks
I need to insulate a suspended floor and Im open to suggestions, some guy reccomended something called cellotex is it any good or a waste of time?if its ok how thick does it have to be and whats it like to install? thanks in advance.

 

[tony1851]

If you can get underneath the floor, use Kingspan or Cellotex boards. Cut to just fit the gaps between the joists (ie tight, friction fit) and push up to the underside of the floor boarding.
Drive a few nails underneath the boarding and into the sides of the joists to preveent any tendency for the boards to drop.
Don't use anything like fibreglass or the multifoil quilts (both a waste of time).
You could use polystyrene board but it is not as good as the above-mentioned boards.

 

[harrison_633]

If you can get underneath the floor, use Kingspan or Cellotex boards. Cut to just fit the gaps between the joists (ie tight, friction fit) and push up to the underside of the floor boarding.
Drive a few nails underneath the boarding and into the sides of the joists to preveent any tendency for the boards to drop.
Don't use anything like fibreglass or the multifoil quilts (both a waste of time).
You could use polystyrene board but it is not as good as the above-mentioned boards.

 

[freddiemercurystwin]

Don't use anything like fibreglass or the multifoil quilts (both a waste of time).
You could use polystyrene board but it is not as good as the above-mentioned boards.

Fibreglass can be used successfully in this way, not quite as good as PIR's but does a reasonable job for much less wonga.

Same applies to polystyrene.

 

[indus]

Don't use anything like fibreglass or the multifoil quilts (both a waste of time).
You could use polystyrene board but it is not as good as the above-mentioned boards.

Fibreglass can be used successfully in this way, not quite as good as PIR's but does a reasonable job for much less wonga.

Same applies to polystyrene.

What is PIR?

Thanks

 

[freddiemercurystwin]

celotex or kingspan, there are others too.

 

[indus]

Thanks.

Just so I never have to ask this question again (as I know you hate this topic coming up again and again ): If you were to put forward a 'gold standard' for insulating a suspended floor would it be celotex/kingspan cut to size and squeezed in between the joists?

Thanks

 

[freddiemercurystwin]

Yes.

What I don't like is when people can't see the wood for the trees.

 

[^woody^]

A "gold standard" would be 50/50 rockwool/pir for both sound and heat insulation

 

[indus]

Thanks Freddy.

Woody

1) Why a 50/50 mix?

2) When you say a mix do you mean half the joist depth to have pir and the remaining depth to be packed with rockwool?

3) Why is sound insulation important if we are talking about the ground floor.


Cheers

 

[TheHandyAndy]

I just did a suspended floor, with the underside being exposed to the outside air.

I used 50mm Cellotex, nice tight fit, then put fibreglass (rockwool) insulation on top.

You can't even tell the floor is exposed to the outside air, even in winter!

 

[indus]

I just did a suspended floor, with the underside being exposed to the outside air.

I used 50mm Cellotex, nice tight fit, then put fibreglass (rockwool) insulation on top.

You can't even tell the floor is exposed to the outside air, even in winter!

Thanks.

Which one is in contact with the undersurface of the floorboards, the celotex or the rock wool.

Cheers

 

[TheHandyAndy]

Indus,

My installation is as follows;

From the top of the floor down to the ceiling below.

Carpet
Underlay
Floor boards
Rockwool
Cellotex
Fireboard platerboard
Skim finish.

Hope this helps.

Just make sure that the Cellotex is cut so it's nice and tight between the joists, you don't want any gaps. I used 50mm thick Cellotex and then filled the rest of the space with rockwool. It's now the warmest room in the house.

Andy.

 

[theoldun]

Indy,
The current U value for suspended ground floors is 0.022Wm2/K.
The thickness of the insulation required is arrived at by the perimeter/area ratio.
In the worst scenario of 1, to achieve above U value you will require 75mm of either, Kingspan TF70,. Celotex FR4000, Eco Therm Eco-Versal, Recticel Ecotherm GP or Xtratherm XTUF.
All the above have a lambda value of 0.022W/mK.
There are other materials that can be used but your thickness will increase from 140 to 200mm.
Forget all about a 50/50 mixture as acoustics do not come into the equation on a ground floor.
Regards oldun

 

[Perry525]

Interesting thing insulation.
When it comes to floors, keep in mind that our body temperature is about 30C.
The average floor is about 17-19C.
This means that heat is moving from your feet into the floor, the whole time you are standing or sitting.
Putting the insulation as close to the heat in the room as possible, means your feet and the room, loose heat at a slower rate, the room costs less to heat, your are more comfortable.
Therefore, carpet, underlay, oriented strand board floating floor, polystyrene or similar closed cell fully floating insulation , original floor.
This is a lot easier to install.