PIR v EPS/XPS

[Steveb21]

I am planning on insulating a basement.

Would XPS be a suitable product for this as it has a low moisture absorption and tolerance of wet environments (v PIR).

Basement walls are uneven so would rigid board be a hassle to fix? Planning to use adhesive to stick the boards as I do not want to compromise the tanking on the walls.

Once i get the boards on I will be installing a metal stud in front (so will help keep the rigid boards pressed back) with 50mm of rockwool or glasswool insulation in between the studs.

 

[freddiemercurystwin]

If the walls are tanked then why is a tolerance of a wet environment important?

 

[Steveb21]

Basements are generally known to have a higher humidity/moisture level. In addition, XPS comes in at a lower cost that PIR, hence the question.

 

[freddiemercurystwin]

Not if they're properly tanked/ventilated. XPS is just a fancy name for polystyrene and has a higher thermal conductivity than PIR so you typically need about 60% more thickness to achieve the same as PIR.

 

[Steveb21]

Understood.

My plan is to add an extractor to help with the ventilation.
The basement is 2/3 in ground, 1/3 out, it has 3 windows with trickle vents to again help with ventilation.
If needs be I can install a dehumidifier.

Option1
50mm rigid board against the internal walls.
50mm metal stud framework (floor to ceiling)
Metal stud to be infilled with 50mm rockwool or fiber glass insulation
12.5mm plasterboard fixed to metal stud
Skim over the top.


Option2
50mm metal stud frame work (floor to ceiling) slightly away from internal walls
Metal stud to be infilled with 50mm rockwool or fiber glass insulation
37.5mm insulated plasterboard on top fixed to metal stud (25mm insulation and 12.5mm plasterboard)
Skim over the top.


Rockwool v Mineral Fiber Glass
Any preference on which one to use?

As the walls are uneven I am thinking it might be a bit of a pain to install the PIR boards. Therefore option2 may be better as the stud frame can be positioned to square off the walls.

Thoughts please?

 

[robinbanks]

has a lower thermal conductivity

(He means higher conductivity)

 

[freddiemercurystwin]

Yes my bad, the lower the better.

 

[robinbanks]

Curious why you think PIR/PUR is worse than XPS regards the environmental moisture aspect, Steve

 

[Steveb21]

Was purely from googling ..... feels like my head is about to explode .

Any suggestions on my previous post?

 

[robinbanks]

Mmm, I dislike them both equally. If it were my money i'd probably form the inner leaf of a timber frame wall (from outer to inner: breather membrane, 6mm osb, studs with insulation infill between studs, insulation over studs, vapour membrane, battens for service void, plasterboard) and have it be spaced off the uneven cellar walls, with vents into the cavity front and back for a through draft