T
hi,
I am getting a flat roof in an extension replaced and upgrading the insulation which is probably non-existent. I've had 2 builders look at it. They are both suggesting a PVC roof but their insulation methods are different.
One proposes using 2 layers of 60mm Kingspan foil faced insulation boards - the 2 layers laid in opposite directions to minimise gaps. The boards go above the joists (I think) and then there is a sheet of plywood followed by PVC.
The other proposes laying 200mm of rockwool on the existing ceiling and then plywood/PVC layers similar to above. He says the rockwool is better than the rigid boards as it can be pushed into every area.
How would these 2 options compare in terms of effectiveness of insulation and cost - I don't have prices from them yet. The man proposing Kingspan says the combination of the 2 60mm layers would have a U value of 0.18.
Stuffing anything in will not work. Any insulation has to be 'fitted'. That means installed according to the makers wishes. I insulated my entire house after I gutted it (back to bare walls, top to bottom). Where ever possible I used foil faced Kingspan or Xtratherm. And I used as much as the situation would allow. Foil faced has way higher values for the thickness used and does not sag. It is also moisture resistant, which any wool product is not.
Hi guys,
Allow me to join in: Rockwool vs Kinspan.
1. The properties of these materials are different. Rockwool is flexible and allows for slight movements in the building. Kingspan is rigid and doesn't allow any shifts (due to seasonal changes, temperature day/night shifts). Kingspan is fitted with insulation foam, which will flake (due to these movements) and even 1mm gap may increase U value by 500% (not a good thing).
2. Breathable/Non-breathable. Rockwool would allow air movements and escape of moisure, whereas with Kingspan will trap condensation, which will rot the joists.
3. U value = lambda/m.
Golden standard of U value in residential buildings is 0.16. (even thought SEAI recommends U value = 0.23 for atticks with Rockwool). That's what we were taught in FETAC Thermal Insulation course.
a) 3 layers of Rockwool (300mm), thickness 0.30m. U=0.044/0.30=0.146. Rockwool will go above the joists.
b) 2 layers of Kingspan (60mm), thickness 0.012m U=0.022/0.012=1.83. Mmm... Really bad U-value!!!
4. My favourite. Rockwool consists of fibres, so just be careful. Kingspan is board with phenolic resins - really bad for the health. Rockwool meant for inside, Kingspan for outside (and mainly industrial buildings)
5. Finally, Kingspan lost NSAI Agrement certification and only Weber is approved to be fitted inside the residentials. Ring NSAI, if in doubt.
Hope this helps to fire builder #1 (cowboy) and get the job done with the most appropriate material, as recommended by builder #2 (good reliable guy).
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?