Open joint cladding system Canada
I am building a semi-detached home in Ottawa Canada. I think the look of vertical Open Slats is fairly attractive and it would also save a bit of money, but I worry about cold/water/bugs and general durability. The exterior portion of the wall would go: sheathing, typar (due to prolonged uv exposure), Magvest 700 black uv barrier, vertical furring, horizontal furring, charred wood with 1/4″ gaps.
This wall works in theory, it bothers me to have a direct pathway to the membrane. That being said, the membrane is of better quality than it otherwise would be and the wood will dry out faster. The reps tell me the membrane has been installed in Iceland and cold European countries, though I haven’t seen an example here in Canada. Is this an unnecessary risk and generally a bad idea, or am I worrying for nothing?
If this is not a crazy idea, is there an insulation with a membrane black finish I could put on instead of just the membrane, or simply a better membrane to use? I was also looking at a rothoblast membrane.
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Replies
ARKHOUSE,
I know it have been used successfully, but I just can't warm to open slat siding. The primary function of any cladding is to stop water and pests from getting into the wall. Slat siding transfers those duties to the WRB, and compensates for the extra burden by using a more robust material for it. All the detailing of walls - drainage, sealing, laps, and tapes - is premised on them being located in the second layer of protection, not the primary one. If you want that look I would consider a reverse board and batten where the gaps were backed by another layer of siding.
This!
Paint the batten black and it will disappear in the shadows especially if the gaps are smaller. The bonus is you don't need all those extra strapping layers or fancy UV rated WRB.
Also if you want charred to last, you really have to char the heck out of it, nothing that looks like a dark stain will last.
Malcolm, I only kinda agree with you. The WRB stops water, it is the drainage plane. The siding I view as the sacrificial layer that has the role of mitigating water, not stopping it. It the siding was the "stopping" component, we wouldn't have rot and failure.......
Steve,
And I agree with you - when there is no rain-screen gap. Especially here in the rainy PNW it has been a real game changer. I hate to see the benefits negated by what is a very different wall assembly which forgoes the primary role of the cladding.
All this is of course very climate specific. Things that are hugely important one place may have only incidental effects elsewhere.
ARKHOUSE,
A great resource for all things Shou Sugi Ban: https://nakamotoforestry.com/faq/
Thank you all for the comments. I have a hard time feeling safe with it it as well even though the reps say it's safe... It wou'd also save a bit of money... I am thinking of doing it around the entrance only. It's low to the ground which is unfortunate, but if there's any issue, we can likely see it.
A reverse board and batten is similar but does not achieve the same look unfortunately. There is a house nearby which did paint the batten black, but I think, as Akos notes, they did have a small enough gap. It does look like paint once you get anywhere closer than the street. Nonetheless I do think a reverse batten is a good idea, as it will create a "thicker" crease than their shiplap.
That being said I'm not sure how the front planks of the reverse batten affix themselves to the furring in this situation? Is there a gap between these and the horizonal furring? And how much overlap should there be for the front plank and the batten behind?
ARKHOUSE,
https://www.greenbuildingadvisor.com/question/proper-nailing-pattern-for-reverse-board-and-batten
You also don't need all the layers of strapping underneath. The batten and siding by itself forms the rain screen cavity. If you want better than that, put a strip of cedar breather under the battens.
The cedar breather is just another layer of furring......
ARKHOUSE, consider using Benjamin Obdyke's UV Batten strip, it drains very successfully in the horizontal orientation. It's one layer, 3/8" thick and solves for everything
Typically speaking, the wrb is supposed to handle minor water shedding, where the siding is to manage bulk water.
If you want the open joint cladding, I suggest you treat it more of an aesthetic than a function. So instead of putting it all on your wrb, consider another layer to manage the bulk water before the open joint cladding.
Just spitballing, consider a 2" of rockwool comfortboard between a wrb (preferably roll on) and the black UV sheeting. Comfortboard is pretty bombproof for shedding water because it's hydrophobic and rodents and bugs don't like it.
That would protect the wrb and five you the opportunity for some show siding.
Jamie
I agree it is more of an aesthetic. Narrowing the gap to 3/16" would have the water grabbing the edge and riding the joint down to dripping. I am not seeing the 2" rockwool as anything but complication.......keep it simple, give water a path, and let it dry.......it's how mother nature intended
hello Jberks, the thought crossed my mind, but we are likely too far in the build to do this. It would change the thickness of the wall a little too much. Though perhaps a 1/2"-1" may work. I would have to make sure the UV roll and all exterior siding could be mechanically fastened through the roxul.
On a different note, looking at the reverse batten, I worry about the batten stuck against the wall and it's ability to shed water. Would it rot over time. The other issue is that this revers batten takes the place of 2 pieces of furring, so it would have to be at least 2" thick, which might be an issue as I would want it to be the same charred wood as the rest of the finish.
What are your thickness dimentions for the reverse batten system? I assume ¾" each so your total furring stack is 1½".
So, if you're worried about wall thickness and you want to get crafty:
Roll on wrb.
1" rockwool comfortboard 110
Majvest UV layer
½" hardwood horizontal furring, coated with black tinted epoxy (or also charred as the siding) with the top side cut at a 45 deg angle to shed water out.
Black vertical siding
The 1" rockwool and ½" furring would be the same thickness as your original reverse batten plan, and just as robust. Without having water standing on the horizontal furring, and your wrb double-protected with the majvest and rockwool layers.
Just a thought.
Jamie
Arkhouse - yes I agree on the reverse batten, I would not do that
I tend to agree with the cautions and concerns about open joint cladding, but I am also curious to hear from those who have done it successfully. Are there specific products and details that you prefer given what Malcolm said - that with an open-joint system, the WRB become primary protection against everything?
Brian see my opinions above. I have done a number of these, always successful. The cladding is a water shedding mitigating device. The WRB is the preventative measure, the "buck stops there". Recently we have done 1x Boral boards on a 3/8" Benjamin Obdyke UV batten Strip on Benjamin Obdyke's UV WRB. I have not used the Majvest 700, but we are about to, and I have full confidence in it. I understand people's concerns, but my preference is to trust the science.
ARKHOUSE I have done a number of open joint cladding systems, the oldest being over 15 years ago. I like them. I would do it on my own house without hesitation. All of the fears people cite, bugs, mold, rot...etc, are just that fear (and guesses). In fact we recently finished one of the most expensive cladding systems we ever have done and it is a Vertcally oriented board system, on a rainscreen, with Benjamin Obdyke's UV Barrier. It worked perfectly. Like its predessesors, no rot, no bugs, no mold.......While I have done open joint claddings in a horizontal orientation, my preference is the vertical orientation. Here's why - with 3/4" thick boards and a 3/16" space, the space ends up relatively deep and narrow. While I didn't do it, testing experience on other projects would suggest that if I sprayed water on the joint, it would catch the edge of the board and ride it to the bottom. I do not think alot of water is actually making it back to the UV membrane. If it does, who cares? the wall is "air open" and my rate of drying is likely far longer than my rate of wetting. I know many people want to seal up, tape, and caulk all joints. I have seen those homes - because we were investigating them for rot, bugs, and mold. Water management is always a rate question - and an open joint cladding has a huge drying potential - I am a fan!!!! The only park of your detail I would reconsider is the 1/4" space moving to 3/16", I think it simply looks better aesthetically.