Open cladded rain screen siding

[cayuse]

I live in the Pacific NW. I have a client who likes an open cladded 1x2 siding detail she saw on a building (bar)in Ballard WA. It has cedar 1x2's (with the 1-1/2" face visible) and 5/16" gaps between them. The cedar 1x2's are nailed on cedar 1x2 spacers. The spacers are nailed on old t1-11 siding, not the right method but OK for a bar owner who doesn't own the building.

I have researched and read extensively on rainscreens and rainscreens with open cladded boards from various manufacturers..Vapro Sheild,Delta, Typar, etc.. IE Water Resistant Barriers or WRB's. (the key word here is RESISTANT not PROOF!) They all say to do a layer or a double layer of their product with flashings, tape and fasteners, yada, yada, yada.....etc. They also say do not have any exposed fasteners ??? Well, how the heck you gonna do that? For me as a carpenter it is counterintuitive to allow water to just drip through or be blown through these rainscreens onto my WRB. Also, I just haven't seen any 15 year old buildings with this detail in our area so I am very cautious of doing this.

We have a new small beach house on the lake with SE exposure, no eaves (parapat), and little sunlight. In this environment I do not feel comfortable putting up this siding over ANY WRB. It is a fairly small building so I am proposing: 1x2 spaced cladding over 1/2 x 2 spacers over Hardie panel or 3/8" t1-11 siding (prepainted or stained, no prime on the backside of the Hardie if we use that due to possible efflorscence)over a typical rainscreen detail. Any wind driven rain or snow would drip onto the Hardie or the t1-11 and would never touch the WRB. In this way I am "double siding" the home but since it is fairly small I would feel better about it. We would have the rainscreen "air-gap" behind the panel siding which would promote drying of any moisture coming from the inside or that gets behind the panel siding somehow.

Am I a worry wart and overreacting here? Any advice would be appreciated.

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[Tom Raymond]

I would be far more concerned about a WRB product handling the UV exposure it's going to get through the gaps in the cedar than being able to handle rain loads. If you really don't want to expose your WRB sheath the building with Zip, then whatever you cover it with is sacrificial.

[smarcus]

You could put a drainage mat in the spaces between the spacers to shield from UV rays. I think your issues will come from not installing the WRB and flashing perfectly and how it's detailed. Without a redundancy in the layers of siding, you are only relying on the WRB. You should probably be discussing this with a manufacturers rep.

[randynavarro]

Talk to the guys at Allied Building Supply in Lynnwood. Talk to Don. He'll tell you what you need.

[cayuse]

I guess what I am trying to state is: If you have an "open cladded" siding detail directly over a WRB and on a "rain screen" shouldn't the WRB be totally resistant to UV, rain, snow, acid rain, a garden hose blast of water cleaning the cladding, etc.? Since it is "open cladded" all of these elements can/will potentially get through the cladding to the WRB. So then the big question is: Should I need a layer of siding at all? If installed correctly, the WRB (building paper, felt,vapro sheild, 60-minute paper, typar, delta, etc) should be perfectly fine in the weather. We all know this not to be true so my dilema with all the literature is in treating a "rainscreen" application for an "open cladded" sided building the same as a "closed cladded" (panels, bevel siding, shingles, etc.) sided building. I was always taught that the first line of defense against the weather is your siding and the WRB is the backup....and then nowdays the rainscreen detail adds the ability to get rid of trapped water (outside the WRB) and water vapor (inside WRB between the sheathing). Therefore, I think with an open cladded siding detail the siding should be treated as "decorative" and not relied upon as the first defense against weather. That is why I am comtemplating a panel siding detail over the rainscreen and the :"decorative" or "sacrificial" open-cladded siding over that.

Has anyone ever done this? How is it performing over the years?

Thanks for your previous responses!

[Jim Katen]

I've seen something like what you describe. It was about 10 years ago and I can't find any pics, so this is from memory:

It was a single family dwelling that was part of a small development of houses around a lake. They were all slightly different in geometrical form but all designed by the same architect and they all used the same siding scheme. It included stud walls sheathed in plywood and covered with a single layer of 30# felt. Then vertical battens were installed on 24" centers and horizontal 1x8 boards were fastened in place with about 1/4" spacing between them. (It's essentially the same system you're describing but with wider boards.)

When I saw it, it was about 20-years old and was working just fine. No signs of water damage anywhere. I remember being concerned about UV damage to the felt so I spent a good deal of time with my eyeballs adn a flashlight pressed up to the gaps. It looked fine. I found several nests from paper wasps & mud daubers, but not as many as I had expected.