Insulation... rockwool vs kingspan

[unclebob1]

Good Morning all,

Im having a 6m extension built, and wanted to know what the difference in wall insulation would be - assuming there will be sufficient rock wool or solid insulation to cover building regs, would it be better to have a full filled cavity of rock wool or half filled of say kingspan?

Cavity will be say 80/100mm, block on both sides, with render on outside and plasterboard/plaster on inside.

I'd rather pay a bit more now in insulating better then spend more over the next 20-30 years in heating costs...

I understand there will need to be holes made for ties in the solid, plus foaming closed the edges. anything else to watch out for?

 

[unclebob1]

or would it be better to use the rockwool now, then externally insulate when the rest of the house is done? (would there be any issues with condensation?)

 

[tony1851]

Rockwool (full-fill) is easier for the builders and less prone to mistakes/poor workmanship.
Rigid-board partial fill takes a little more care to do properly.
Insulation-wise, not much difference.

 

[unclebob1]

I'll let the builder carry on with the rockwool then, and when i get enough £££ i'll externally insulate if its still cold for my linking!

putting 100mm in the solid floor and 125mm in between joists in the roof space for single story rear extension... will try and put more but tight on height.

 

[u587162]

Similarly, we have the same dilemma. 100mm warm deck roof, but if we put 100mm acoustic rockwool in the ceilings, does this have the same insulation properties as normal rockwool and regard it as 100+100=200mm insulation?

 

[chappers]

To the two previous posters, I don't think either of your amounts of insulation will meet regs- Unclebob from memory you need about 200mm of celotex if only insulating between the rafters, due to the thermal bridging of the rafters.
100 mm celotex warm roof just falls short too, the addition of the extra rookwool would probably take you under the required u-value but it's not recommended to insulate on either side of the deck

 

[unclebob1]

Noted - i'll see what the builder says - would it be possible to say put 50 on top of rafters, and then the rest in between?

 

[tony1851]

Noted - i'll see what the builder says -

Don't just 'see what the builder says', ask your architect/plan-drawer.

If you put 50 above the deck 'and the rest' underneath, you are asking for trouble without considering the condensation issue.

 

[unclebob1]

The rest being between rafters, without a gap between , the drawings show 175 rockwool but I don't have the height for on top

 

[tony1851]

Before you or your builder start putting insulation here, there and everywhere, take a look at this 90-second video.

 

[u587162]

Noted - i'll see what the builder says -

Don't just 'see what the builder says', ask your architect/plan-drawer.

If you put 50 above the deck 'and the rest' underneath, you are asking for trouble without considering the condensation issue.

just to clarify but you are not referring to warm deck right, because no condensation should form if you stick more insulation under a warm deck roof.