roxul, eps, xps?

OaktownNovember 22, 2012

We are considering exterior insulation options and would appreciate any feedback from folks who have used or considered Roxul/Rockwool. I've spent a while looking at other sources and forum discussions which are fairly technical, but it appears that the main drawbacks to the product are cost and availability (or lack thereof)? Any insights would be appreciated! Architect and builder typically use XPS or EPS.

Here is a link that might be useful: General article on insulation types

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How would mineral wool be used on the exterior? Did you mean polyiso?

XPS and EPS have very different R values.

You need to first design the wall system and determine what R value you need then consider the insulation types that are appropriate.

    Bookmark   November 22, 2012 at 6:23AM
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Good morning and happy Thanksgiving!

Renovator8, it is mineral wool, a consultant suggested this as an option but the architect has not used it in this application before. I've linked an article describing the product that would be used on the exterior.

My notes on the wall system are sketchy but generally speaking on the exterior we will have an insulating layer, a housewrap and siding, my understanding is that the placement of the housewrap/barrier would depend on the type of insulation used.

(The consultant is for certification to get a building permit and CO in this location. New construction or major remodels require you to satisfy local green building requirements or get LEED certified.)

Here is a link that might be useful: Mineral wool on exterior

    Bookmark   November 22, 2012 at 10:40AM
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First things first, as noted above.

I like using XPS in our cold climate behind masonry, as in the pic below.

Photo: Heather Joy Investments Ltd.

Why at this point exterior mineral wool doesn't appeal to me:

1) Need for a sheathing inboard of the insulation. By contrast, the XPS can be used for both purposes as long as there is internal bracing (seismic and other local requirements may differ);

2) The attachment, as described in the linked Halliday article, looks awfully fiddly to me. As well, the carpenters attach the XPS to wall sections being completed on the building platform and then raise them. It looks like this may be more difficult with much thicker sections of wool.

3) The walls sheathed in XPS stand up well to the weather as the house awaits the final cladding. I can't imagine leaving mineral wall in the rain and exposed to insects etc. for two months.

4) XPS does not require a separate weather or air wrap.

Behind masonry, though, I let the bricklayers put on their usual felt.

I wouldn't even consider EPS as an exterior above grade insulation. In most climates you'd need a thick layer, creating concerns about attachment. As well, it's so flimsy, there's bound to be mechanical damage, especially at the edges.

Below is a schematic from Roxul on exterior installed mineral wool.

Here is a link that might be useful: Building Science Corp.: Guide to Insulated Sheathing

    Bookmark   November 22, 2012 at 11:32AM
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Rather than using a trade name it is best to use the true name of materials. What you are referring to is rigid rockwool insulation board.

In past decades I have seen rigid rockwool and fiberglass boards used in the cavity of a brick veneer wall system, under membrane roofing and on the face of foundation walls below grade but in general, rigid foam insulations have taken over.

I have never seen rigid rockwool used behind siding but I guess it's possible. There are a lot of issues to consider and the advantages are unclear to me. That's all I know.

    Bookmark   November 22, 2012 at 11:36AM
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Actually I believe "Rockwool" is the tradename of Roxul outside of North America so the best description is mineral wool.

The issue I would be concerned about is rigid mineral wool's ability to absorb water regardless of how fast it dries out in the open air. Wood also dries fast in the open air but it rots when wet in a wall system. There is too much contradictory information about that aspect of the material and I need better information before putting it on the face of a building.

    Bookmark   November 22, 2012 at 12:34PM
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Worthy, thank you for the opinions and the article. What I am taking away is, the rigid mineral wool might be a nice concept but no one has yet devised a clear method to make it work, at least not as a preferable option to XPS? (Exposure to the elements is less of a concern here, the climate is such that we typically have a stretch of 5-6 months with no rain and that should be around the time of the build)

Renovator8, sorry I was not trying to be confusing, all of this terminology is new to me -- I am trying to learn as much as I can and "Roxul" was the name that the consultant and architect used. I saw something about the mineral wool being water repellent but I will certainly ask the consultant about that!

Think I have more reading to do, I very much appreciate the education.

    Bookmark   November 23, 2012 at 11:59PM
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It's typical of designers and builders to use brand names but when you research you need to also use the generic name to avoid being limited to the marketing propaganda of one manufacturer although in the insulation industry a great deal of the available information is from industry paid organizations so it can be difficult to know who is on the level. Question everything you read and ignore Mike Holmes and Bob Villa.

    Bookmark   November 24, 2012 at 9:47AM
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no one has yet devised a clear method to make it work, at least not as a preferable option to XPS?

Mineral wool is a fine insulation. And unlike XPS, for instance, aging doesn't reduce its R value. But for what I build in my climate there are simpler energy efficient alternatives when it comes to insulated sheathing.
Just because someone's shilling doesn't mean they're wrong.

    Bookmark   November 25, 2012 at 12:36AM
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