Metac vs Earthwool

papa john

Hi all
I was installing 150mm of Metac insulation today on sloping ceilings and 200mm of Earthwool on the flat ceilings.The conductivity of metac is 0.034w/m2k,while the earthwool is 0.044w/m2k.On both packs it said that they covered 5.6m2. The metac had an R value of 4.4 while the Earthwool had an R value of 4.5 which means the earthwool gives a very slightly better U-value.However the metac seems to be a lot better and stronger insulation and the metac pack is twice the weight of the earthwool pack.I also note that Metac is double the price.What i am wondering is how can it be better when it is so much lighter and a lot less rigid than the metac and is also half the price? Any replies grateful.

Rock12

I am open to correction but as far as I am aware both materials use trapped air within them as part of their insulting value, this is why they should not be compressed or they lose their effectiveness.
Maybe the earth wool uses this trapped air more so to compliment its insulation value meaning less of the actual material itself!?
There is a substantial price difference so if you have the space I would use a thicker application of the earth wool laid in two layers laid perpendicular to each other.
I have used the Metac in areas like the roof-wall junction where space is limited.

Hope this helps.

papa john

Yes i think you are right.Its strange though as there seems to be a world of difference between the 2 materials.Wonder will metac last longer.I have used the metac on the slopes and i will roll out more earthwool on the flat as you said.I have to floor some of it so i may use the insulated loft boards and more wool everywhere else.I already have 0.16 with the 200mm earthwool and the 50mm insulated slab so maybe i dont need anymore.

kieranhr

The metac has a lower thermal conductivity than the rock wool, making it the better insulator per mm thickness, by around 25%. I don't know why the R-values don't correspond. They may be assuming different build-ups.

BarneyMc

papa john wrote: »

I have to floor some of it so i may use the insulated loft boards and more wool everywhere else.I already have 0.16 with the 200mm earthwool and the 50mm insulated slab so maybe i dont need anymore.

Insulated loft boards - anyone know where I can get these?

sydthebeat

http://www.kingspaninsulation.ie/Products/Kooltherm/Kooltherm-K7-Plus-Attic-Storage-Board/Overview.aspx

this is the product

you could always do your own by screwing through the insulation to the joists

BarneyMc

Thanks so much - didn't know this existed! This is exactly what I'm looking for.

My joists are 200mm deep and this filled with mineral wool will not get me my target U value so a layer of this on top of the joists would be great (I want to floor the centre part of my attic for storage space). I'll go with 400mm mineral wool on the other parts that can't be used for storage.

If doing my own version what type of insulation can be used - e.g. floor insulation? So put down the insuation and then the ply, e.g. 18mm on top and screw all down?

sydthebeat

BarneyMc wrote: »

If doing my own version what type of insulation can be used - e.g. floor insulation? So put down the insuation and then the ply, e.g. 18mm on top and screw all down?

yes, it doesnt really matter whether the product is advertised as 'floor' 'wall' or 'roof' insulation, the material is the (pretty much) same... whether its polyurethane (PU) polyisocyranuate (PIR) or phenolic (K)

and yes, install as youve stated....

893bet

Would compressing the wool not reduce its u value?

I am planning on 3-400mm (can't remember what spec says) and plan on building up the floor where storage is required.

sydthebeat

The board insulation is the alternative to the quilt over the joists, So the depth installed should be at least equal as to maintain the same overall u value

PROJECT K

papa john wrote: »

Hi all
I was installing 150mm of Metac insulation today on sloping ceilings and 200mm of Earthwool on the flat ceilings.The conductivity of metac is 0.034w/m2k,while the earthwool is 0.044w/m2k.On both packs it said that they covered 5.6m2. The metac had an R value of 4.4 while the Earthwool had an R value of 4.5 which means the earthwool gives a very slightly better U-value.However the metac seems to be a lot better and stronger insulation and the metac pack is twice the weight of the earthwool pack.I also note that Metac is double the price.What i am wondering is how can it be better when it is so much lighter and a lot less rigid than the metac and is also half the price? Any replies grateful.

R-Value is thickness in metres divided by conductivity:
0.15m / 0.034 = 4.5m2k/W R-Value
0.20 / 0.044 = 4.5m2K/W R-Value

Earthwool gives better R-Value cos its thicker. Earthwool at the same thickness of 150mm would give an R-Value of just 3.4m2k/W.

I would spec Metac any day over Earthwool as its a denser material and much less likely to sag/compress over time and is less affected by air movement. Alternatively use earthwool between joists with a rigid insulation (PIR/Phenolic) over (check condensation risk though) - 200mm earthwool with 100mm PIR over works well and shouldnt present an issue assuming a vapour check is behind the plasterboard...

BarneyMc

PROJECT K wrote: »

Alternatively use earthwool between joists with a rigid insulation (PIR/Phenolic) over (check condensation risk though) - 200mm earthwool with 100mm PIR over works well and shouldnt present an issue assuming a vapour check is behind the plasterboard...

Do you mean the vapour barrier membrane fitted under the joists and above the plasterboard?

BryanF

BarneyMc wrote: »

Do you mean the vapour barrier membrane fitted under the joists and above the plasterboard?

Yes
(Always warm side of insulation)

BarneyMc

BarneyMc wrote: »

My joists are 200mm deep and this filled with mineral wool will not get me my target U value so a layer of this on top of the joists would be great (I want to floor the centre part of my attic for storage space). I'll go with 400mm mineral wool on the other parts that can't be used for storage.

If doing my own version what type of insulation can be used - e.g. floor insulation? So put down the insuation and then the ply, e.g. 18mm on top and screw all down?

Just about to go out and buy this stuff but have the following last minute questions:

1. Do I need to use ply or will OSB 3 do?

2. Will the insulation boards get 'squashed' over time where they cross the joists? If so should I lay some sort of light board over the joists before the insulation boards go down?

3. Does the ply/OSB 3 need to be T&G?

4. Is going the alternate route (lay another layer of mineral wool over the joists and create a raised floor) a better option?

hexosan

Go for osb over the ply.

PROJECT K

osb 3 is fine though T&G would be recommended to minimise localised stress on the PIR insulation (if insulation supported directly on joists). Typically T&G flooring grade chipboard (0.6x2.4m) is used for this and tends to work well. PIR will be ok on 50mm joists at 400mm crs - if thinner joists (35mm or less) or joists at >400mm crs then a thin base board would be a better spec - be carefull while fitting as it will be fairly flimsy until the insulation and chipboard goes on. With this thin board layer in you could get away with non t&g boards on top. Your second option means a higher build up and therefore less headroom - also a little bit extra work

BarneyMc

I've 400mm centres and 45mm thick joists so laying the PIR boards directly on the joist should be fine, then the 18mm OSB 3?

PROJECT K

it really depends on what you are storing up there but for normal domestic storage that would be fine - T&G is normally used for this as it helps spread the loads, it also helps keep a level floor (sometimes, as the PIR is rarely completely flat - especially thicker boards - and other building tolerances, non-T&G boards can have up to 5-10mm lips between boards. Not normally an issue for attic storage but personally i would go with T&G, bit more solid underfoot to...

BarneyMc

I'm getting 8x4 18mm non T&G OSB 3 boards at €12 each so this is sort of putting me down that route! I think I'll also lay a thin board directly on the joists, under the PIR, just to keep things right.

PROJECT K

yeah that helps alright!!! To be honest based on your joist centres and width, the additonal thin board is of very little benefit - i wouldnt bother for the additional cost and time to do it...just make sure that the osb joints are completely staggered over the PIR joints and you should be fine! Do you mind me asking where you are sourcing the OSB 3? Seems a reasonable price...