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Roxul Comfortboard IS rigid board insulation for exterior: many performance and environmental virtues

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 As the landscape around our building site disappears under a blanket of snow, the sheathing on our houses has been disappearing under a thick layer of exterior insulation. Known as Comfortboard IS, this insulation is impressing us with its green virtues, versatility and price.

Made in Canada by Roxul, Comfortboard is one product in a line of “stone wool” products that combine the power of rock with the characteristics of insulation wool. Originally inspired by the way wind spins molten lava into fibrous material during a volcanic eruption, stone wool is fire, mold and insect resistant and water repellent. It also has excellent thermal properties and will add an R-value of 8.4 to our walls (at two inches thick – it also comes in thinner and thicker boards).

 While our staggered stud wall has less thermal bridging than many standard walls, the top and bottom plates, rim joists, and plywood window boxes do have some. This exterior insulation helps reduce heat loss in those places and brings the weakest parts of the wall (aside from windows and doors) up to R 18. This is better than the average for most 2×6 stud wall systems. The rest of the wall will be over R40 with 9.25"  of dense packed cellulose insulation and the R 8.4 Roxul board.


Mounted on the exterior like a rigid foam, Roxul Comfortboard IS has the added benefit of allowing walls to dry out to the exterior (research on this topic is available at It helps prevent condensation on the inside of the sheathing by keeping it warm most of the time. You can use some rules of thumb from to figure out what R-value you should have on the exterior of the sheathing (though the minimum thicknesses listed for foam are not as vital for the permeable Roxul).

 Comfortboard is also made of natural, inorganic materials and has a high recycled content. In addition, the company has invested deeply in emission reductions and other green initiatives. (Mineral wool has a minimum recycled content of 75%, making products in this category a nice alternative to petroleum-based foams and the greenhouse-warming, blowing agents and flame retardants associated with XPS and EPS.)  Melting rock certainly takes energy so the insulation is not as green as straw or cellulose but those products can't be used in this way. The boards are also softer than the foams so care must be taken to maintain an even plane when installing the strapping (we put cap nails under the strapping to help prop it out.) The fuzzy boards can't be taped and air sealed like foam, so we used housewrap for that (sheathing is even better for that purpose.)

For more information and photos and to follow the project on our blog, please visit

Patrick Walshe, R.P. Bio.

Please pull your spam.  I've (post #207302, reply #1 of 4)

Please pull your spam.  I've already complained to Roxul.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

I dunno Dan (post #207302, reply #2 of 4)

I'm not convinced this post falls into the category.

Spreading information and including links to products in an educational format is way different that some of the [JOBSITE WORD] we've seen pulled here.

Could be wrong, but with some discussion we should be able to figure it out.  I'd hate to lose information on a guess.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


this is a genuine owner builder post on Roxul Comfortboard IS (post #207302, reply #3 of 4)

Hi there. This is a genuine post. I own this property and am general contracting my build. I was happy to discover the Roxul product and want to share our project as I know there is much interest in the topic and many questions. I am not affiliated with Roxul and have not been paid by them. This is a genuine post that I feel provides useful information in the text and the links to reputable building science sites including and Yes there is a link to the Roxul website as one would expect so that anyone can easily check out the detailed specs. This is not spam. Spam is generally useless blatant advertising with little value to the readers. I am a biologist and researched my products, but am not a builder, industry rep or otherwise affiliated. So Dan H feel free to send praise to Roxul on a great product and an apology  -  it would be rude and unfair to complain to them.


Patrick Walshe, R.P. Bio.

Well then Patrick............ (post #207302, reply #4 of 4)

Welcome to Breaktime!


Please continue with your background to the build and the continuing story.  Referencing the blog is good, but a serial update here would be great.

If you can.



A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.