For this week’s Question of the Week: an architect/designer is looking for an effective solution for his wall design:
I am developing a rain screen wall design consisting of a rain screen held in place by a knight wall system, mineral wool insulation, then an air & water barrier adhered to exterior sheathing. We are concerned about rain/ice getting into the mineral wool and are looking for a water resistive barrier to install between the mineral wool and rain screen such as this product: http://www.cosella-dorken.com/bvf-ca-en/products/wall_ext/wrb_open-joint/products/fassade-s.php . Do you have any additional product recommendations? We would not expect to have any noticeable gaps in the rain screen.”
We recommend using SOLITEX FRONTA QUATTRO for this application – it can be taped with Pro Clima’s TESCON INVIS – an all-black airsealing tape with very similar properties to our all-around TESCON VANA waterproof airsealing tape. We recommend TESCON INVIS in conjunction with SOLITEX FRONTA QUATTRO because of the extra UV stability added to both the membrane and tape, as well as the ability of the all-black system to hide behind an open-joint rainscreen.
When comparing to DELTA’s Fassade-S, FRONTA QUATTRO is easier to put up, not super thick like the CORSELLA product, and it’s more waterproof, while being actively vapor open. We can additionally recommend special techniques to put it over mineral wool boards – secure the membrane in place with 1″ roofing nails under the overlaps, and be sure to not leave any penetrations exposed. It’s also important to note that Fassade-S is not an airbarrier – it is rated at .9L/s*m2 – it needs to be below .02L/s*m2 for ICC-AC38 compliance. SOLITEX has been tested to be 100x tighter than that.”
Why are these differences important?
Certainly, both products have extra UV stability and are vapor open, which are important components of an open-joint rainscreen assembly. But avoiding windwashing of the insulation is an important reason to have airtightness on the exterior of the assembly, even if there is an additional inboard airbarrier such as INTELLO. At 32lbs, FRONTA QUATTRO is lighter than Fassade-S, so getting it up on the wall is noticeably easier. At $0.49/sq ft., you get better quality at a better price, along with a tape whose acrylic adhesive sticks better than anything else out there.
This week we launched our monthly newsletter, and as with all of our newsletters, we tried to feature some topics and projects that would not only be of interest to you, but would also stimulate debate. We had some great activity on our blog this week specifically from our post about unvented foam-free roof retrofits, but since you already have access to the conversation that ensued, we’ll simply give our first commenter’s question – “What’s the track record of this approach?” – an honorable mention this week. Thanks to the inspector, architects, and builders who contributed to the discussion.
Have a great weekend!
**Please note that in republishing our question of the week, we sometimes edit the text of the original question and response in order to provide additional clarity to the issue.**