AWF Blog

Not your Grandpa’s batt insulation. Roxul Stone Wool

Not your Grandpa’s batt insulation. Roxul Stone Wool

Posted by Martin Z on Jan 12th 2017

I’ve been reading a lot about Roxul Stone Wool and mineral wool insulation in general. You’ll actually find a wealth of information with a simple search with your favorite search engine. Some of the benefits of Rock Wool over Fiberglass include higher R value, Water Repellence (limits water absorption and mold growth), better sound absorption, better dimensional stability and increased fire safety.

Couple this with the annoying installation problems you run into with Fiberglass and I think you’ll see why Roxul Stone Wool is a smart choice for your next insulation installation (job).

Today I want to highlight some of the advantages Mineral Wool has over Fiberglass that make it a good idea for both outside walls but especially for interior walls.

Fire Safety

One aspect that Stone Wool’s fire resistance is really superior to Fiberglass. Why is this? 

Fiberglass Melting Point: Less than 1300°F
(Binders and other chemicals mixed in can lower this even further)

Stone Wool Melting Point: 2150°F

This means that in a house fire (or installation near a high heat source) fiberglass breaks down and will pass smoke, gases and flames through insulated walls much sooner than a wall insulated with stone wool.

This video shows the two products side by side.

A big issue in commercial building is passive fire resistance. As time goes on residential building codes are also incorporating many of the same standards and concepts. Active fire resistance are things like sprinkler systems and fire extinguishers which are used to actively fight a fire. Passive fire resistance is changing the design of a building to incorporate “compartmentalization” and fire-resistance rated walls, and floors. Basically using materials that are less likely to burn and protect the structure so that people have enough time to exit the building safely.

Many of these fire rated walls use Stone Wool as part of their construction. Fiberglass, due to its lower melting point is not. When constructed properly Roxul Stone Wool prevents the passage of flames and gases into a living space and gives you the time to get out. That’s why you may not just want to consider Roxul for exterior walls but for interior spaces like bedrooms too. To further protect the space, you may also want to seal passages where wires, pipes and duct work pass through the wall with fire stop sealants, such as Biostop Firestop Products. This prevents the passage of smoke and gases and reduces the chimney effect which feeds oxygen to a fire. When you’ve installed Roxul on bedroom walls and used additional firestop products you compartmentalize your sleeping space. This may be the added advantage you need if a fire were to break out in your home. For a full passive fire plan, talk with your building engineer or architect, who can advise you and specify the materials that will meet your local code.

Sound Proofing

Roxul Stone Wool does an amazing job at preventing sounds from passing through walls and floor spaces. Roxul Safe‘n’Sound is in fact designed specifically for this purpose. The structure of the mineral wool batt attenuates the sound much more than comparable building materials. So much so that it’s often used in professional recording studios to eliminate ambient noise. Again this makes it ideal to use on interior walls where you either have a potential noise problem or want to reduce sound to minimal levels.

Again installation in interior bedroom walls reduces the noise that passes through from the noisier rooms in your house.

Better Installation

There is a world of difference installing fiberglass batts vs. Roxul Stone Wool batts.

Fiberglass batts by their nature are soft pillowy pieces that don’t hold their shape well when installing. Batts tend to sag and must be stapled or fastened to the adjacent joists to fill the space. To cut fiberglass you need to press down on the batt and cut with a utility knife. This doesn’t allow precise cuts around existing construction where you want to fill as close as possible to an existing structure. Over time batts can sag and open up air spaces that allow cold air to pass through reducing thermal efficiency.

Roxul Stone Wool Batts like Comfortbatt® and Safe’n’Sound® are much more resilient than fiberglass batts. They retain their original shape better while allow for some compression to fit between wall studs, floor joists or other structural pieces. Cutting and trimming can be done with a serrated knife which allows you to cutout precise shapes to fit around electrical boxes, pipes, ductwork or special shapes. When you carefully trim on installation you create fewer (and smaller) voids that you’ll have to seal with foam, caulk or firestop later.

Here’s a video Roxul produce with Mike Holmes. You can watch it for all the benefits they mention but what I’d like you to take notice is how easy it is to trim and install the Roxul batts.

The batts install between the wall studs tightly and without staples or other hardware and you can trim easily and precisely.

One last benefit:

If you’ve ever installed fiberglass you know you should dress something like this.

While I’d still wear long sleeves and gloves, Roxul is nowhere near as irritating to install as fiberglass.