Durability issues with wooden rainscreen furring
GBA上最近的帖子都是关于水分保温的湿度问题。但没有人似乎担心毛茸茸条带的长期结构完整性。我在护套之前看到了木制的1x4s。
我同意所有“现代”建筑技术，提高能源效率和耐用性。但是我无法克服的一个细节，是使用1×4捆扎刚性泡沫。作为一个Rainscreen，它预计会弄湿。暴露于极端温度，最重要的是，它最常是壁板的结构连接。
我的情况比平常更困难：
- 165英里/小时设计风速（131英里/小时曝光C）
– Corten “western reveal” vertical panels, consealed fasteners (with 1.5″ air gap to the building due to its profile)
-The usual 2×6 16OC studs with tapped 7/16″ zip sheathing.
-Zone 5, class A/ignition resistant exterior
-Tall (30’+), difficult to access exterior, above 40+ degree slope. Top of building down to road 70’+ (see attached picture)
使用所需的R5连续绝缘和垂直面板壁板，我将不得不做水平捆扎。幸运的是，金属面板型材已经是一个巨大的Rainscren。但我忍不住觉得在50多年以上，捆绑将失败，并将金属飞越落入日落的生锈条带。授予，我不在乎居住50年，但我认为别人做了。
So I started looking into commercial techniques, and learned that they have been doing exterior insulation forever and use metal Z-girts as standard. And now with these lumber prices, Z girts might not be more expensive than 1×4 strips of plywood. Problem solved. Except then its not really continuous insulation anymore due to the metal z girt thermal bridging. So I look into thermal isolation clips that hold girts and rails like Knight wall systems, Smartci, etc.
Another good solution is furring master’s FM3 hat channels, other than having to buy 10000′ minimum. But I’d still have a problem. The corten manufacturer recommends any metal in contact with the corten to be stainless steel, not just galvanized. So apparently I cant use metal girts/rails/hats, clips or not.
就在我即将分解并返回1x4s并让后代处理我的职责责任，我了解到有一个复合Z Girt，即热隔离和结构。
https://www.armatherm.com/products/z-girt-structural-thermal-break-cladding-attachment/
This has the advantage of allowing me to use “semi-rigid” rock wool batts – which is lower in cost compared to “rigid” insulation like comfortboard or even EPS. So my next challenge is to find this composite girt, hope that its not crazy expensive, and continue to complain about how that’s not industry standard, how 1x4s are acceptable, why I didn’t choose to use metal faced SIPs like a warehouse would, etc. etc. And then just to find out the composite Z girts are out of stock, or they won’t sell to builders directly, and need my lumber yard to order 10000′ minimum.
不管怎样,有什么更好的建议吗?其他的如果milar products that’s easily obtained? Is it a good idea to do rockwool BATTS on top of taped zip? Whatever I install, I never ever want to have to go up and access the siding again, that’s why I chose weathered steel. I expect it to last 100 years without intervention.
But maybe my concern about flying siding is moot when the roof avalanche off the solar roof will kill cyclists below on an annual basis anyway.
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Replies
Bernard,
Nice house! I hope you post pictures when it is finished.
There are a couple of assumptions in your case against using wood as strapping I'm not sure I agree with.
The strapping in a rain-screen cavity is not expected to get wet. The cladding should be detailed so that no bulk water gets past it. For a rain-screen to have to drain moisture something has gone wrong. That's a back-up function. The primary ones are facilitating drying, and avoiding water getting behind the siding by capillary action..
我们担心湿防潮的原因是它is located in the wall assembly where it is the First Condensing Surface. That's why we try and keep it warm. We don't worry about the studs, or the rain-screen strapping because they aren't in a position to accumulate problematic amounts of moisture as it moves through the wall.
I don't know enough about the composite alternatives to comment on them. Perhaps the answer is a simple as using PT 1"x4" or PT plywood strips to assuage your concerns?
ok you have convinced me. I guess my feeling that wood of insufficient thickness deteriorates over time in unconditioned spaces is unfounded. I guess you do need at minimum bacteria which needs moisture. And if we are confident that the rainscreen sees no water then the wood, however thin, should stay put forever. Hard concept to accept given the average person's experiences with wood. I guess nothing lasts forever. Ironically repeated heating cycles might actually cause composites/fiberglass to become brittle and fail over time. So wood might actually be better. But the metal clips and rail system is still the most durable.
Having said that, I do really like the idea of the ability to use mineral wool batts which are more cost effective per R. This can be achieved using the clips/rails. I'll have to do more cost analysis to see if its worth it. If there's a time to spend more on metal/composites to substitute for wood, this is the time with 400% rise in lumber prices. Its $5 a piece of 1x4x8' for me, and $80 per sheet of 3/4" ply.
最后，保持罗克沃尔前面的一切金属在狂野的火灾中真的很好。邮政局县让我做了2层Typex Drywall，以便在拱门处获得1小时的额定值。Class-A消防额定壁板（金属）和屋顶（钢化玻璃），甚至窗户不能是乙烯基（熔化太快），甲板必须是金属，混凝土或复合材料。虽然如果我们对自己真的诚实，我怀疑房子值得挽救，如果森林火灾真的足够接近，以点燃金属壁板后面的木材毛皮。只是烟雾污染会谴责建筑物。也许我已经思考了它。
Its going to be EPS+1x4s vs CavityRock batts + clips and rails. I'll try to price this out on monday and make a decision.
您还可以撕开一些复合甲板板或修剪并使用它作为板块。
I have thought of that. But I wonder if composite decking can be used as a structural component. If I can't find data for approved tests done for pullout resistance etc. my engineer can't spec for fastening schedule. In a high wind zone I'm not allowed to just wing it.
One option is to strap out your walls with horizontal 2x3s on edge (PT or SPF) 17.5" OC. You can install 2.5" AFB or Ultrabatt which is meant for metal studs between them. Your panels can now attach to the 2x3 directly. The 2x3 can be spaced off your WRB using larger washers or running a couple of saw kerfs to allow for drainage.
The horizontal strapping gets you close to 95% of the benefit of continuous insulation without any of the hassle or cost of dealing with clips and semi rigid mineral wool. Way lower material cost, much quicker install. I have done this for roofs before and it works great.
P.S. The way most commercial installs around me are done is with the furring channel held off the walls with metal L clips through the exterior rigid. This avoid most of the thermal bridging of Z grits, allows for easy shimming to get the wall dead flat and uses standard off the shelf pieces.
> horizontal strapping gets you close to 95% of the benefit of continuous insulation
A good idea in terms of lower priced exterior insulation. But do the thermal bridging and resulting sheathing cold spots cause moisture problems, canceling all but the R value advantage of continuous exterior insulation? UScodeis clear about the need for *continuous* insulation to protect sheathing from moisture entering the wall via a Class II or III vapor retarder.
Similarly, fasteners are thermal bridges too - do they ever cause very localized sheathing rot (or excessive fastener corrosion)?
建筑物组件中的凝结与窗户或金属表面上看到的冷凝不同，没有液体水建设和滴水。水分通过吸附到木结构中缓慢增加其水分含量。即使是我们认为有“冷凝控制”的大会也将有一些水分进入一年中的组装部分。
从木头捆扎或金属紧固件的小型热桥的局部冷/暖点会在本地造成一些额外的吸附，量化的数量远远良好，但我的猜测它落入蹲下类别。
The only time I've seen corrosion and rust is around window water leaks and on roof fasteners where there was lot of interior air leaks and heavy condensation on the roof deck. If you are near salt spray, might be a different story.
I've take out a small section of siding installed with rain screen over rigid at my own home that is about 7 years old now. Everything underneath was pristine, just like the day I installed it.
> near salt spray
In February, I was replacing roofing panels where the screws were completely rusted through to the point where the panels were falling off. Yes, this involved salt dust and radiant cooling causing condensation (not sorption),
我看到你所得到的 - 基本上有2层的非连续绝缘层，一个在WRB前面，一个落后，并且通过两个层的唯一“全部深度”热桥都是GIRTS的地方和铆钉相交。这实际上与水平使用复合Z Girt的实际完全相同，但木材更容易来源。建筑物部门可能对象，因为它们要求外部绝缘是连续的。我认为2x3s的导热率在实践中的玻璃纤维裙子的热导电是多于玻璃纤维裙子。
But yes, your way would allow me to use batts instead of boards. which does have a cost difference. The commercial way with clips and rails would also achieve the same thing, but possibly more durable. A year ago I'd believe the 2x3's would be much cheaper. Today, I think I'm going to get some quotes on the clips and rail system.......if they let a residential owner builder buy it....
> no one seem to be concerned with the long term structural integrity of the furring strips
Rainscreen：“压力处理的捆扎只需要在高雨中
areas, though it is recommended in all jurisdictions. " Also says 1x3 ??
https://cdn01.rockwool.com/siteassets/o2-rockwool/documentation/technical-guides/residential/comfortboard80-installationguide.pdf
只要木材可以比它弄湿更快地干燥，它就不会腐烂。你的包层将阻止大部分散装水分进入，并在它后面的3/4英寸通风空间，你会得到充足的干燥。只需确保您的全部顶部/底部有一个条目和退出点。
外部毛皮在加拿大东部很长一段时间内已经代码。没有人正在使用压力处理的木材，但你从未听过冒险的东西。
亚历克斯，
"Exterior furring has been code for a very long time here in eastern Canada."
I'm pretty sure Coastal BC has the only code requirement for exterior furring in Canada.
I could be wrong but I think it's code as well in Quebec :
9.27.2.2. Minimum Protection from Precipitation Ingress
Except as provided in Sentence (6), exterior walls exposed to precipitation shall
be protected against precipitation ingress by an exterior cladding assembly consisting
of a first plane of protection and a second plane of protection incorporating a capillary
break, where
a）度数的数量小于3400，水分指数是
greater than 0.90, or
b）学位的数量为3400或更大，水分指数是
greater than 1.00.
I have never seen a house built without a rain screen here.
亚历克斯，
这非常有趣。语言类似于我们的代码中的语言。我知道在安大略省和魁北克省的外部绝缘层都在普遍存在，但我不知道雨屏被授权。我想知道玛丽亚是否会效仿？
A bit late to this party, but I do have one comment on the above: The OP should do some more research before using PT furring with Corten steel. The chemicals used in PT are very corrosive to steel in general. Even though Corten is designed to have a rugged corrosion layer that protects the rest of the steel, the galvanic couple could be too much for it. I have no direct data on this, but raise it as a potential concern. I'd be very comfortable with the composite systems, if they are available and reasonably economical.
It's true. I can't use ACQ. Even those commercial clips and rails has galvanized rails which should touch corten. So pretty much wood or the fiberglass z girts is the only way to go.
I'd say "ACQ can't touch the corten". So a thin plastic separator (eg, tape) might work.
你有很好的悬垂，我猜不过过雨 - 我怀疑未经处理的木材毛皮会很好。
You could pre-paint untreated wood to make it considerably more durable.
Is ACQ still the most common pressure-treated lumber in the States? Around here it has largely been replaced by MPS, which doesn't have the same corrosion issues.
没有读取线程。有没有人提到热改进的木材（例如，Americana）？