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Mineral wool revisited

I have been following the discussions about mineral wool insulation below grade (Roxul Drainboard) and have the following questions/information to share.

1) Cost and availability
From one of the posts I got the impression that Roxul would be around the same ball park as rigid foam regarding cost (per Jonathan Ram, Roxul) and that they are serious about improving availability (per John Straube). Well, so far I have only found one supplier in my area (Minneapolis/St. Paul) that could get it, with a minimum order of a pallet (432 sq ft) at a cost that seems way out of the foam ballpark.

Here are the costs per R-foot (R1 per square foot) I got as of 2/20/14:
$0.31 Roxul Drainboard in 2 3/8" 4x6 or 3x4 sheets
$0.13 Dow Thermax polyisocyanate in 1 1/2" 4x8 sheet
$0.08 Owens Corning 150 Foamular xps in 2" 4x8 sheet
$0.08 Owens Corning 250 Foamular xps in 2" 4x8 sheet
$0.05 Cello Foam eps in 1 1/2" 4x8 sheet

2) Durability
Has there been any more input other than Albert Rooks response to Sherrie VandePutte's question about insects and Roxul? John Straube may have no concerns because "insects don't eat rocks", but in another(?) post I see that birds love to build nests in it. If birds love it, perhaps mice, rats, chipmunks or even the occasional insect will find it to be a nice home.

3) Attachment to concrete below grade
If Drainboard is held in place by earth below grade (as was mentioned in another post) is there any concern about it being moved by frost heave of the adjacent soil? I know the backfill should be free draining, but what about the soil cap on top?

Attachment to concrete above grade (walk-out basement).
Martin mentioned using Plasti-Grip PMF fasteners. These would work to attach 4 inch insulation without furring strips, but is there anything similar but longer that would work with 2 layers of Drainboard plus furring strips (5 1/2")?

Asked by Stephen Martinson
Posted Thu, 02/20/2014 - 18:18
Edited Fri, 02/21/2014 - 09:24

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2 Answers

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Stephen,
Good questions. I can't answer all of them, but I'll respond to some of them.

I think that you are correct that mineral wool has limited availability, and is hard to purchase in many locations unless a builder orders a large quantity. Moreover, because it is a special-order item in many locations, it's likely to cost significantly more than rigid foam. That may change, but right now it is a fact.

If you are attaching furring strips on mineral wool, you don't need washers or plastic fasteners. All you need is long screws. The furring strips act like washers. Of course, if you are attaching to concrete, you'll need to use concrete screws (like Tapcons) that require predrilling and are expensive.

Answered by Martin Holladay, GBA Advisor
Posted Fri, 02/21/2014 - 09:36

2.
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I live in southwest Missouri near Joplin and ordered (294) 1"x4'x6' sheets of Roxul Drainboard on December 30th from a local Lumber Yard and received it February 20th. My cost was $10.41 per sheet or $0.10 per R-foot. The Lumber Yard was listed as a stocking distributor for Roxul.

Answered by Jonathan Kreissler
Posted Fri, 02/21/2014 - 15:05

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