Options for Insulating suspended timber ground floor

[AdamSee]

I'm trying to figure out whats the best way of insulating my suspended timber ground floor in the under stairs / under upstairs landing cupboard. (roughly 1.5m wide x 1m deep x 2.5m high)

 

My usual go to method is to lift the floor and fit 75mm celotex with a VCL over the top which is then taped and plastered in to the wall. On this occasion tho im leaning towards using rockwall or similar, held in place with some breather roofing membrane and then VCL as per normal. The reasons for wanting to mix it up are because 1 - I hate cutting celotex, the dust goes every where and it would have to be done outside this time around because the house is not occupied. And 2 - because my UFH manifolds are in this area, I have a habit of making a wet mess every so often with the ongoing plumbing works, and im worried that with the celotex the water may sit between it and the floor and cause some issues. At least if it has mineral wool it would pretty quickly pass through.

 

Also, unlike the other floors, this will be old joist that ill be insulating, so there pretty uneven in comparison.

 

So my question really is - What would you do? 

Edited November 14, 2019 by AdamSee

[SteamyTea]

I was thinking about ground floor insulation as I was driving home earlier.

First thing that pops into my head is, how would you deal with airtightness?

[Ferdinand]

18 minutes ago, AdamSee said:

I'm trying to figure out whats the best way of insulating my suspended timber ground floor in the under stairs / under upstairs landing cupboard. (roughly 1.5m wide x 1m deep x 2.5m high)

 

My usual go to method is to lift the floor and fit 75mm celotex with a VCL over the top which is then taped and plastered in to the wall. On this occasion tho im leaning towards using rockwall or similar, held in place with some breather roofing membrane and then VCL as per normal. The reasons for wanting to mix it up are because 1 - I hate cutting celotex, the dust goes every where and it would have to be done outside this time around because the house is not occupied. And 2 - because my UFH manifolds are in this area, I have a habit of making a wet mess every so often with the ongoing plumbing works, and im worried that with the celotex the water may sit between it and the floor and cause some issues. At least if it has mineral wool it would pretty quickly pass through.

 

Also, unlike the other floors, this will be old joist that ill be insulating, so there pretty uneven in comparison.

 

So my question really is - What would you do? 

 

When I attach rockwool these days I do it with a staple gun, or batts which may self-hold.

 

Surely your wet mess will evaporate into the perfect 50% humidity of your newly insulated and ventilated house. ? 

[daiking]

44 minutes ago, SteamyTea said:

I was thinking about ground floor insulation as I was driving home earlier.

First thing that pops into my head is, how would you deal with airtightness?

Is it wildly important?

[AdamSee]

41 minutes ago, SteamyTea said:

I was thinking about ground floor insulation as I was driving home earlier.

First thing that pops into my head is, how would you deal with airtightness?

 

The VCL over the top acts as the air tightness layer. And taping it to the wall with "pro clima contega Solido SL" so that you can plaster over it seems to do the trick.  

[SteamyTea]

10 minutes ago, daiking said:

Is it wildly important?

If you use mineral wool, and external air can pass though it, or parts of it, then you are loosing its ability to insulate.

As @Ed Daviessays, you end up with a plasterboard (or other material) tent.

I think, but without seeing detail, there may be a condensation risk.

[daiking]

6 minutes ago, SteamyTea said:

If you use mineral wool, and external air can pass though it, or parts of it, then you are loosing its ability to insulate.

As @Ed Daviessays, you end up with a plasterboard (or other material) tent.

I think, but without seeing detail, there may be a condensation risk.

For 1.5m2? As part of presumably a much larger ground floor refitted to a better standard?

[AdamSee]

Yes the rest of the house is insulated with 75mm celotex, not exactly great, but only had 2x4 joists to work with and 100mm dosent actually fit  

 

This space im trying to insulate now is in the middle of the house and is the last bit of suspended timber floor to do as the remaining will be swapped out for block and beam when the extension happens. 

 

Currently im leaning towards the celotex with loads of expanding foam as it just seems a bit simpler but I will just have to careful in the future with filling the UFH loops.

[Onoff]

1 - I hate cutting celotex, the dust goes every where and it would have to be done outside this time around because the house is not occupied.

 

Surely if the house isn't occupied that's better for cutting it inside?

Edited November 14, 2019 by Onoff

[SteamyTea]

1 hour ago, daiking said:

For 1.5m2

Forgot that bit.

Do whatever is easiest.

[AdamSee]

40 minutes ago, Onoff said:

1 - I hate cutting celotex, the dust goes every where and it would have to be done outside this time around because the house is not occupied.

 

Surely if the house isn't occupied that's better for cutting it inside?

woops.......typo, should have said "now occupied"

 

By myself, wife and the dog

[Ferdinand]

Change to an English Sheepdog or a Golden Retriever, and it will insulate itself ... ?

[AdamSee]

6 minutes ago, SteamyTea said:

Forgot that bit.

Do whatever is easiest.

 

In reality there both a pain for the tiny amount of space that needs dealing with, but something needs to be done because theres currently a hole that my toolbox is sat over which lets in a draft. Hoping to get this done over the weekend. I guess pictures will follow once I've made my mind up. 

 

2 minutes ago, Ferdinand said:

Change to an English Sheepdog or a Golden Retriever, and it will insulate itself ... ?

 

Considering the amount of ginger fur I keep finding around my house....yes, if I fit the breather membrane, it would eventually fill up. 

[Mr Punter]

Maybe just some 40mm Celotex onto existing floor topped off with VCL and 18mm chipboard would be OK.  Headroom probably not an issue if this is an understair cupboard.