Black fabric for hiding furring strips and ext insulation on an open rainscreen?
qofmiwok
| Posted in Green Products and Materials on
I’ve already got an air/wrb membrane over my sheathing, which will have 2″ rockwool outboard. We’ve decided to go with an open rainscreen cladding (3/16″ gap) so I need black fabric to cover the rockwool and furring strips. Is there anything less expensive than Invisiwrap since I don’t need it to be a WRB/air barrier?
Thanks
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Regular roofing felt?
Roofing felt can't handle uv exposure for more than a month or so before it starts to fade and become brittle, I don't think that would be a long term choice for this.
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Go to a commercial greenhouse supply store and look for "shade cloth". Shade cloth is a black mesh material make to put over greenhouses when you need to cut down on the amount of light getting in. The material is available in various grades based on the percentage of light it blocks. This stuff can handle UV exposure.
Another option would be geotextile fabric, but you'd need to get one that is rated for UV exposure (which some are).
Bill
qofmiwok,
I think you need to be careful what material you use and where you situate it. When you use an open-cladding you forgo one of the main attributes of a rain-screen, which is the cladding acting as the primary layer of protection against bulk water intrusion. That function gets transferred back to the WRB, and the cavity has to designed to drain the significant volume of water that will get in, rather than just incidental amounts.
- If the new fabric is located directly behind the cladding it will mean that drainage occurs against the back of the siding.
- If the fabric holds moisture (as products like filter fabric does), the back of the siding will stay wet, and also effectively those layers become a reservoir cladding capable of moving moisture back into the wall through solar vapour drive.
I think the place for the proposed second layer is behind the furring strips, and it needs to be something that is permeable, but doesn't hold water. Effectively that's a real WRB.
Alternately paint the furring strips and omit the second layer altogether - alth0ugh that's asking your mineral wool to effectively be the drainage plane for much of the water that gets thr0ugh.
Thanks for the comment. More details are required to explain why I am not concerned about drainage. Having a rainscreen at all is actually overkill in my climate 6B where we get about 5 inches of rain a year, and I have 42" overhangs. There is Blueskin on my sheathing, then 2" Rockwool, then a furring strip rainscreen. The Rockwool drains, the Blueskin protects, and more cladding gaps just means more drying potential. Lastly, my cladding is composite PVC and not a reservoir cladding. The only potential benefit I see of an outboard additional WRB is for solar vapor drive but I think that is minimal given everything else.
I have thought about painting the furring strips but the rockwool still has a color, although it's not too far off from the siding color so could be a possibility.
You said :"I think the place for the proposed second layer is behind the furring strip." Did you actually mean behind? Because then the furring strips still need to be painted.
There's also the issue of how to attach a black WRB to furring strips and rockwool in any "tight" way.
qofmiwok,
It's a funny situation. You live in a climate where you don't really need a rain-screen to exclude bulk-water intrusion, but end up with quite an extensive one with many layers anyway.
My only suggestion would be to reiterate that you should choose a backing fabric that doesn't hold moisture. Your wall may have enough redundant layers that it doesn't matter, but the fabric, which is there to solve the problem caused by choosing an open-cladding, should at least not reduce the resiliency of the wall.
You are right. I wouldn't mind not having a rainscreen, but most of the siding products these days require a rainscreen. And because I have 2" exterior Rockwool, furring strips are the best way to get a good attachment of the siding to the studs.
One of the geotextile fabrics that are woven from polyethylene would probably work here -- such material won't hold water. Some types of shade cloth will. Note that geotextile material made of WOVEN polyethylene fibers is very different from polyethylene sheet.
Bill
I don't think this is an area where you want to cheap out and use an unproven alternative. Shade cloth is pretty durable, but I have a hard time believing that a high-quality product will deliver significant savings over something like InvisiWrap.
https://www.proremodeler.com/how-build-rainscreen-open-joint-cladding
https://www.synapseconstruction.com/blog/synapse-construction-open-joint-siding/
There are a few manufacturers with specific products for open joint rainscreens - here are just a few:
https://foursevenfive.com/blog/fronta-quattro-the-allblack-airtight-wrb-for-modern-openjoint-rainscreens/
https://benjaminobdyke.com/product/invisiwrap-uv/
https://www.dorken.com/en/our-products/products/commercial/delta-fassade-s.php
Thanks. I'd found the Dorken but it was quite a bit more expensive than Invisiwrap. The Fronta isn't much more and is more permeable, which I like.
A much better option is to look for the show line trim. These are aluminum extrusions that give the look of open cladding without any of the issues. They are not cheap, but in your case it will be much simpler than adding in a UV stable housewrap and painting all the battens.
I haven't used these but seen them on commercial construction around me. Unless you are up close to it, can't tell that it is not open cladding.
Search for Lighttrim or Easytrim Reveals. Probably many more out there. A good sheet metal shop can even also bend most of these shapes for you out of black coil stock.
The nice part about these is that they keep the water from getting behind your cladding and also keep critters and bugs out.
Thanks, I'll check that out. I'm not actually "looking" for an open joint look, I just like the Fortress Apex siding and it is installed with hidden clips and needs a 3/16" expansion gap between the boards.
At 3/16" you'll only see the Rockwool within about 5 feet if you know to look for it. I'd paint the furring strips, install siding and be done. For a picky client maybe pull out the paint sprayer and apply a coat to the rockwool as high as can be reached from the ground. Above that you'll never see, it's already UV stable and dries better with nothing over it.