Fiberglass versus rockwool for top-up insulation

MrThrifty

I know this topic has been raised before and based on what I read, I actually decided to go with rockwool which people were saying has similar thermal properties but does not settle with time.

I had to first lay some fiberglass insulation on a new section of attic and then topped up the whole attic area with 200mm rockwool (€10 a roll from B&Q).

But here's the thing. I actually found the rockwool a pain in the ass to use compared to fibreglass. Came up with the following list of disadvantages compared to fibreglass:
1) Rockwool much more dense than fiberglass -> packs much heavier, notice when lifting into attic!
2) Rockwool didn’t come pre-cut or perforated - you definitely need a saw or knife to cut it to size unlike fiberglass which you can easily tear even if wasn’t perforated
3) Rockwool was a pain to position/drag because of its weight. Almost needed a second person to manouver a 600mm wide length of it.
4) Rockwool doesn't really stretch like fiberglass and so neighbouring layers don't tend to blend together at the joining
5) Rockwool breaks apart and tears really easily
6) Rockwool compresses really easily when holding the edges to position but seems to stay compressed after unlike fibreglass
7) Less rockwool in a pack than fiberglass equivalent -> need more packs
8) Rockwool looks crap - like a rotting bed mattress from 30 years ago

So, am I missing something?! Also, point 6 really concerns me. If you step on fibreglass, it bounces back into shape whereas the rockwool seems to stay compressed. Should I be worried about this?

ShaunC

I don't mean to be critical but points 2) and 5) seem to contradict each other.

MrThrifty

ShaunC wrote: »

I don't mean to be critical but points 2) and 5) seem to contradict each other.

True... Let me explain better...

To cut it along it's length, you really need to either use a saw or knife when it is rolled up, or a knife if it is rolled out in order to get a good edge to join up to another roll. You don't need a good edge if ever tearing or cutting fiberglass coz of point 4.

As for breaking apart easily, if you fold a length of rockwool over itself or even try to roll it up again, it tends to split apart. Or if you're repositioning a length of it, it will tend to break apart. Granted fiberglass can tend to lose strands and this type of thing, but it sticks mainly together at the end of the day. Even if you brush against the laid rockwool, you'll find bits crumbling off all over the place.

Finally I've since confirmed that the rockwool is not 200mm in thickness when carefully laid, but actually typically closer to 150mm, even after leaving for a few days to fill out. Fiberglass always fills itself out after a few days.