Best rainscreen (clip) system
Just when you thought you had it down, you realize that you’re completely confused by competing claims, products, etc.
I’ve been looking at the Climate-Shield clip system. It seems like a pretty good answer for the rainscreen we wanted on an addition to our house in Chilmark. We’re planning a simple 2×6 wall with closed cell foam, plywood sheathing with a WRB, and horizontal wood siding. The ClimateShield system provided a 3/4″ deep cavity, vents well at top and bottom along with some ventilation at each horizontal joint and allowed air to distribute horizontally (at windows & doors) as well as vertically.https://www.mataverdedecking.com/climate-shield-rain-screen-system
Then Nova says you need the Exoclip because it has a built in spring to keep your siding tight and aligned when it shrinks and swells. https://www.novausawood.com/rainscreen-siding-clips
Then Viking comes along and suggests that you should use their clip because it goes on furring strips which compartmentalize the wall and creates chimneys that are more effective for venting, and also that a furring strip makes a better thermal break than having an aluminum clip directly mounted to the sheathing (don’t know about that…seems a square inch or so of aluminum transmitting heat out of the building is better than 30 or 4o times as much area of furring strip)
And the details leave a lot of questions with all of them…most of them show solid blocking below and above windows as part of the window trim, solid blocking at corners, lack of flashing at windows other than the underlying flashing at the WRB with the window flange.
In short, its a little bit of the Wild West out there with little independent comparisons on which you can base decisions.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Hugh,
Most builders who have been installing rainscreens for years don't use this type of clip. They use furring strips. For more information on furring strips, see "All About Rainscreens."
Are you using this clip because you have chosen to install tongue-and-groove or shiplap siding?
You may not care to hear my opinion, but I'm not a fan of horizontal siding with tongue-and-groove or shiplap joints. Water ends up settling into the horizontal joints, hastening rot.
It should come as no surprise that competing manufacturers trumpet their own products, asserting that their particular product is the best. This type of promotion happens with all categories of materials.
Yes...T&G or shiplap...silly architect's architectural statement. I designed and built our existing home many years ago clad in white cedar shingles as are most homes on the Vineyard. Our new extension doesn't fit well into the original architectural design so am thinking about making it obviously something apart....using a metal roof, more modern form, and different cladding. I guess it's no surprise that most of these clip makers also sell horizontal siding that are tropical hardwood and much more rot resistant. Clapboard is out...just personal taste. Painting is out...so using one of the tropical woods might be the answer. In speaking to one of the clip makers about a detailing issue where the vent seemed to dead end under a window, they said that there is about an 1/8" space at all the joints due to the clip that allows air to move...so that would help. But going back to one of my original questions, is it better to contain the rainscreen venting in a vertical chimney to improve stack effect, or let air disperse in all directions?
I suspect the gap between boards will negate any advantage, if there even is any advantage, to the vertical containment furring strips would provide. With a gap every board width, you’re limiting how much stack effect you can achieve since each gap effectively short circuits things compared to one continuous vertical channel.
I don’t think the gaps would worsen air movement, but they would allow more moisture to enter the rainscreen space so there would potentially be more moisture in there that would need to dry out.
Bill
Hugh,
As clips go the Mateverde looks like a very good one, but I struggle to see what advantage any clip gives over battens - both during installation and over the life of the building.
actually some of the clips mount on battens. The Mateverde clip allows 360 degree circulation..The main advantage I see is there's almost no visible surface fasteners. that's impossible with shiplap, and only possible to a degree with T&G. They also allow some circulation at the joints....But you may well be right.
Hugh,
That's a good point about exposed fasteners, if that is an important part of the look you are going for. The clips are similar to those used with composite decking. Like them I would imagine they represent a large increase in labour over direct attachment. One thing you would need to work out is how to seal the vertical joints between boards. Typically they are backed by a piece of membrane or flashing. That might be difficult where the is no batten behind.
I'm not sure vertical joints need to be sealed given that some rain screens have completely open horizontal joints. That said, as an old school architect, well versed in the "need" to flash anywhere there might be water penetration; window heads for sure, but also sills, and top of trim boards etc., I'm a bit nervous about a lot of Rainscreen details I'm seeing....sure, the WRB should keep water out, and ventilation dries things out, but where I come from the WRB (40# asphalt felt, back in the day) was a secondary line of defense with the siding (and flashing) being primary. Now, in some designs, the WRB is almost primary with no second line of defense, and the siding acting primarily as protection for the WRB and aesthetics.
Hugh,
I agree. A cavity with open cladding doesn't have enough of the attributes we associate with rain-screens to be called one. Our code here in BC agrees with you too. It distinguishes between the primary and secondary layers of protection, and as far as I can see would not allow open cladding where rain screens are required.
Thinking about it again, using clips rather than battens might mitigate the need to backing between the boards. Any wetting will be to the back of the cladding, as opposed to saturating the battens.
Hugh -
You ask a good question about the difference between spacer mesh--that allows planar air movement versus furring strips that allow columnar air movement.
I think the answer is: we don't know. To get air movement you need two holes and a driving force. The driving force with ventilated rainscreens can be either wind or stack effect. To my knowledge, no one has tested in the field or even modeled (I suppose using computational fluid dynamics - CFD) the difference between these two rainscreen configurations.
Has anyone else heard of field testing or modeling of these two rainscreen approaches?
Peter
John Straub looked into this in https://www.buildingscience.com/documents/reports/rr-0907-ventilated-wall-claddings-review-performance-modeling/view
One of his conclusions was:
"Ventilation (top and bottom vents) resulted in marginally faster drying than vented (bottom vents) walls. The width of cavity was also important, and those walls with cavities of 19 mm dried faster than 10 mm."
Hugh,
I don't know if you are still following this thread, but if you are I'm curious as to which clip system (if any) you ended up going with? I'm currently looking into this as well, and if I decide to use a clip, I'm leaning towards Viking's. I like their lower profile design, and there are several places that sell compatible siding. But I would be interested in hearing first hand experience with it. Thanks.
Pat
visited the Climate-Shield showroom in New London, CT and was very impressed with the clip and the system as a whole with Mataverde wood siding. Ultimately, we ended up deciding on a system without a clip, using Nakamoto Forestry Shou Sugi Ban shiplap siding and wood furring strips, partially as a matter of economics and partly because we fell in love with their Gendai finish in a dark grey finish,
Hugh, thanks for the update. A clip system does limit you siding options. So it is a trade-off (as with most things), and I'm still somewhat on the fence which way to go.
Out of curiosity, what are the maintenance requirements with the Shou Sugi Ban finish? I've come across quite a few prefinished wood siding products that look quite stunning. However, most require refinishing every 1 to 3 years to maintain the look, which is more than I want to deal with. The one exception seems to be Accoya (modified wood product). Teknos makes a translucent finish for it that they warrant for 10 years. So I'm looking into it.