Am working on my first project (located in the Houston area) where the Architect wants to use mineral wool board roof insulation. Architect wants to use it because it is non-combustible, but it is not a fire-rated roof. Roof deck is concrete over composite steel deck.
Aside from the fact that we will nee 50% more material to achieve the same R-value (we are looking for R-30 insulation on the roof), are there any drawbacks to using mineral wool board insulation? Any advantabes?
I like the stuff fine. the roofing version will of course be denser than the wall stuff. but it’s good …only R4 per inch but NOT a plastic
Advantage: No reduction in thermal resistance over time.
Disadvantage: Open to air movement and vapor migration, which makes it critical to have a very robust air barrier / vapor retarder at roof deck for heating climates (maybe not as much an issue in Houston).
I’ve not used it on a roof assembly, but I can’t think of a reason why you couldn’t. As you point out, you need more material to achieve the R-value. What about tapered areas? Tapered perlite, perhaps?
It’s intended for wall applications, but Owens corning has come out with a higher compressive strength Thermafiber product
Peter,
Please contact Rockwool for their hybrid system using both mineral wool and polyiso (I believe).
The primary insulation is mineral wool. The tapered is polyiso.
Rockwool TOPROCK DD Plus is their insulation for torch and hot-mop installations.
Please go to https://www.rockwool.com/products/toprock-dd-plus/?selectedCat=toprock%20dd%20plus%20downloads
I thought CRTKL had specified this system. Still looking.
I have been told that the rock wool will compress over time under load from foot traffic. This can create problems for mechanically fastened systems.
I believe that the mineral wool manufacturers can do tapered shapes. I’m not sure about Thermafiber but I know that Rockwool has a high density product to use as a top course either over polyiso or over mineral wool that works great. I’ve specified it on several projects and never heard a negative word about it.
I’ve put in requests with golden reps from both Thermafiber and Rockwool to reply to the questions being raised.
Hope everyone has a good weekend.
Shana Tova to my fellow tribal members.
Peter,
A coverboard such as GP DensDeck Prime (with Evonic) is used over the insulation. It has a compressive strength of 900 psi for all thicknesses. 1/4 inch is all that is required.
Wayne and Peter, Rockwool Multifix - https://cdn01.rockwool.com/siteassets/o2-rockwool/documentation/technical-data-sheets/commercial-roofing/MULTIFIX-flat-roof-insulation-Techdata?f=20181219114310 can be used as a coverboard over polyiso or mineral wool (or, I presume, other foam insulations).
Please let me know if you need a contact person to talk with.