What is a good, affordable construction detail (in terms of long-term UV and water protection and overall durability) for the popular contemporary horizontal, spaced cedar cladding look?
(Examples of what I am referring to can be seen at:http://vastern.co.uk/wp-content/uploads/2013/03/Splayed-cladding-detail.jpgANDhttp://www.bartonqualitytimber.co.uk/images/categories/chestnut%20cladding.jpg)
I am not terribly conceded about the cedar: if it is stained all 6 sides with two coats and placed on black painted strapping, then it should handle the elements reasonably well. My main concern is what the substrate behind it should be. I have done this before with flat black painted hardie board panels over rain screen strapping, but I am wondering if there is a more cost effective method? Delta has a product that is apparently designed specifically for this situation (http://www.cosella-dorken.com/bvf-ca-en/products/wall_ext/wrb_open-joint/index.php). I am wondering if anyone has experience with this product, of they think it would still be wise to place it over a layer of Typar, etc. Links to construction assembly details would be great!
Replies
Burke,
I thought that a GBA reader would step forward to answer your question, but after several days, I see that no one has done so yet.
That's probably because this type of gapped siding (or open-joint cladding) is rarely used in the U.S. -- even though it seems to be all the rage in some European countries.
The only relevant GBA article on the topic is one I wrote in September 2010, when I reviewed a durable WRB intended for use behind gapped siding. The WRB is called Delta Fassade S. Here is a link to my review:New Green Building Products — September 2010.
Below is a photo that accompanied my review.
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Thanks very much for your feedback Martin. The link to your past article was helpful. I'm glad to know that someone as reliable as John Straube can vouch for the durability of the Delta product, especially for its price! I will have to evaluate the affordability of the Fassade S versus doing a layer of house wrap, rain screen, black-painted hardi-panel, another layer of rain screen and then the spaced cedar cladding. Material costs may be higher with the Delta Fassade S, but the substantial labour savings and the reduced thickness of the assembly may make it come out ahead in the end. Thanks again!
Gapped cedar siding is the only building envelope element I can think of which is used entirely for stylistic reasons while having none of the properties or virtues and many of the shortcomings we associate with various claddings. So right off the hop it's a little hard to understand why someone would want to spend a lot of time detailing something so unsuitable for its purpose. I see from architectural periodicals it is also often used in the UK as a permanent screen for windows and that a similar detail is used on roofs. I just can't understand it.
We have a few rolls of the Delta Fassade in stock but as yet no user reports. I brought it in because I've seen builders use membranes that I don't trust for this application such as Vaprosheild or Pro Clima in black. SIGA does not recommend their membranes in this application even though they have a black tape that they do recommend for open joint cladding.
Between the Tannins from the cedar and the UV, the membrane has to be much stouter than even the "good" membranes. The Delta Fassade is obviously a differant grade of membrane. You can tell when you pick it up.
马尔科姆-我很欣赏你的评论关于这个班dding style, which is precisely why I am looking hard into the details of how it can be done properly. Living on the northwest coast, rain is an element that I am forced to have respect for! However, I think that the drying potential of an assembly is just as important as its ability to resist wetting in the first place. I think that having ½" gaps between horizontal cladding would realistically have not too much effect on how wet the substrate behind said cladding would actually get. I would guess that in a typical rainfall event, over 90% of the rainwater would stay on the face of the cladding, and the remainder would run down the backside of the cladding. The rain screen furring would keep all but a tiny wind-blown amount off the waterproof breathable membrane on the actual house. Only during occasional major storms (or pressure washing of the house) would that membrane actually get substantial wetting, and then the incredible drying potential of the assembly would deal with that in a day or two. It actually gives me not too much concern overall, especially in a house with large overhangs and meticulous flashing details behind the vented cladding. And it provides an aesthetic that is appealing to contemporary designs- after all what's the point of having a home that lasts forever if you don't particularly enjoy looking at it? ; )
Albert- your shop is the Small Planet Workshop down in Washington, is it not? I live and work on Vancouver Island, so would be interested in getting in touch with you about pricing for this and a few other products for some other houses we're working on up here. I'll likely try to give you a call in the next couple of weeks!
Burke, I don't want to downplay your point about liking the look. Houses are human artifacts and as you say we do want develop a happy relationship to them which sure is helped if we like how they look.
However gapped siding just has so many downsides. The 1/2" spacing is too large to exclude insects and even small rodents, so there is a good chance that the drainage plane will be blocked and who knows what mischief they will get up to behind there. While it does have unmatched drying potential I think you are underestimating the amount of bulk water that will get behind the siding - and the exclusion of bulk water is what cladding on a rain screen assembly is for. A wall like this which relies on a membrane behind the strapping to exclude bulk water means the assembly will be unable to dry to the exterior, which is the preferred and most common approach in our PNW climate.
Practical considerations aside, you should know that it runs afoul of the BC Building Code rain screen provisions. You might want to run this by your building inspector and warranty provider before going too far along this route.
Malcolm- those are great points about the insects, which I hadn't considered. I'm wondering which part of the BC Building code regarding rain screens this contravenes?
We had done this for an architect's renovation of his own offices at one point, and perhaps this is why we did a typical hardi-panel over rain screen installation, painted it matte black (which satisfied all the code requirements for cladding, and then did this horizontal rain screen assembly over top of all of that. This certainly was fine in the eyes of both the architect and the building inspector, but I will have to consult him to see if he's had any issues with pests. Good points to consider for sure, Malcolm.
Burke,
The concerns about insects are a practical one not one addressed by the code. The main problem with your proposed assembly is that the BC Code, in both rain screen and conventional construction separates walls into two parts mandating that they have "First and second Planes of Protection" (9.27.2.3.).
The first plane (the cladding) must be "designed and constructed to minimize the passage of rain and snow into the wall by minimizing holes and managing precipitation ingress caused by kinetic energy of raindrops, surface tension, capillarity, gravity and air pressure differences"
Off the top of my head I guess there are two ways around this. One is a variation on the assembly you built for the architect's office. The other would be to treat the cladding as a screen and build a full, separate rain screen wall behind the furred out cladding.
雨屏幕和最近的地震修正to our code sure have changed the way you have to built here. I'm still working my way through the implications of the latter. I guess they are both for the good but add a layer of complication to things that takes a while to integrate into the designs.
Good luck with your build!