Can anyone give me a brief list of the pros and cons of extruded polystyrene and rigid mineral wool insulation for interior applications? Why would one be preferable of the other?
Check the following [and related links] for many types of insulation and explanations:
Extruded Polystyrene (XPS):
Pros: Typical R-value of 5/inch; moisture tolerant; low moisture absorption; low water vapor permeance (effective as a vapor retarder at about 1 inch or more thickness); can be adhered or mechanically attached.
Cons: Flamable (some jurisdictions may not allow in non-combustible walls); requires a 15 minute thermal barrier; does not conform to imperfections in substrate walls.
FYI, Mineral wool is considered semi-rigid, not rigid.
Semi-Rigid Mineral Wool:
Pros: Moisture tolerant; low moisture absorption but higher than polystyrent or spray foam; permeable to water vapor, non-flammable (unfaced FS/SD of 0/0); can be left exposed to view; available with Class 1(A) facing; conforms better to irregularities in substrates.
Cons: Requires mechanical attachment; Typical R-value of 4.2 per inch; facing not protected by gypsum board subject to damage.
I won’t compare the two types line by line, but the main difference is flammability and especially toxicity under fire conditions for plastic insulation.
Plastic insulation is also dimensionally unstable.
There are a number of different types of “plastic insulation” products of which the extruded polystyrene is one. These are usually specified according to ASTM C 578. Molded polystyrene also fall under this spec. There are differences in terms of open/closed cell, R-values, and densities. Polyiso (another type of rigid plastic insulation) is specified under ASTM C 1289 and has several different types as well. Pay particular attention to applicable code requirements on “plastic insulation.” This can get kinda hairy if you don’t watch out.
despite the question, why are you thinking of EITHER of those insulations for interior work? typical in an interior condition would be fiberglass, either faced or unfaced.
Mineral wool is typically expensive and is used for flammability reasons (and typically at the exterior, but not always) and I can’t think of a code agency that would allow EPS on the interior of a building in anyform unless fully encapsulated in a concrete floor. (I have used it once in a while where we needed to build up thickness but not weight for a podium – and used the high density version).
Plastic insulation: Toxic smoke potential
Mineral fiber, including glass fiber: Airborne irritant potential.
Considering my personality, I’ll advocate for irritants.
The irritant may irritate you, but it probably won’t kill you. On the other hand, many people have died from smoke inhalation that contained fumes from burning plastic insulation.
Interesting answers. I am a bit confused because there seems to be several expanded polystyrene products that are marketed for interior walls.
So, when you are faced with interior furring, with a small cavity for insulation, (let’s say less than 3 inches), what insulation do you recommend?
There is no prohibition in the building code to using foam plastic insulation on interior walls.
The only requirement beyond the maximum smoke developed and flame spread indeces is the requirement to provide a thermal barrier between the foam insulation and the interior of a building. The prescriptive requirement is applying a layer of 1/2-inch-thick gypsum board or a material that will survive 250 degrees for 15 minutes complying with the ASTM E 119 time-temperature curve.
Robin,
You rec’d a lot of responses and said, “I am a bit confused…” It would help if you noted your application a bit more specific than interior use (comparing extruded polystyrene to rigid mineral wool). If you’re talking about using rigid insulation on an exterior masonry or concrete wall, I’ve specified extruded polystyrene with Z furring in those applications for 1-6 story buildings and never mineral wool.
Is the application against an exterior wall? If so, what is the wall construction and proposed interior finish? Is this a high-rise building?
Robin,
I have a client who often renovates older buildings constructed with single wythe CMU walls. They like to put metal studs and extruded polystyrene insulation on the inside face of the wall, then cover it with GWB. The existing 8-12 inch thick wall is an air barrier (in theory); this doesn’t make it a super high performing wall; but it seems to work well enough; it passes the Massachusetts Energy Code.
Is this what you are thinking about?
Perhaps one of the foamed-in-place insulations would work?
If you need to achieve an R-value within a limited space you might want to look into some of the nanotechnology aerogel insulation products that are coming on line.
Look at Aspen Aerogel “Spaceloft” and Cabot’s “Thermal Wrap” come in thin rolls usually less than 0.5-inch thick.
Robin-
you’re still not saying what you want the insulation for. there are a lot of small cavities that are just left as small cavities. are you insulating for sound, temperature differential; is there moisture; is there air blowing through there? each of them might suggest a completely different answer.
I appreciate all the answers..my thought process switched mid-stream, that’s why my questions sounded all over the place. The first few responses implied that extruded polystyrene is never used on the interior of a building for any purpose, but my confusion came because I know there are several commercial products that are intended for that very use. So, why would they marked products that are prohibited by code.
Ron, you cleared things up, so I think I understand now. Thanks,