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Gap suggestions for Cedar 1X4 rain screen applications

Gap suggestions for Cedar 1X4 rain screen applications

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  #1  
Old 09-28-13, 10:27 AM
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Gap suggestions for Cedar 1X4 rain screen applications

Our house is in the PNW and we will be siding it with 2 layers of 30 min felt and 1X4 cedar horizontally connected to vertical 1X1 ripped Trex Decking furring strips. We are adding fiberglass screening to the top and bottom.

Because of the wasp and other creatures and their desire to inhabit warm dark spaces, we were wondering if anyone had a good rule of thumb for gaps between the boards.

Our plan is for a 1/8th inch gap. Should we simply cover the entire surface behind the boards and atop the battens in the screen material, or will that have its own problems?

thank you for any suggestions.
 
  #2  
Old 09-28-13, 01:40 PM
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Welcome back after 5 years' recess!! Trying to figure out your layers. Are you indicating you will be using 30# felt? If so, why? Why not use a standard WRB such as Tyvek, which will breathe? If you rip Trex, it will fail, especially in 1x1 strips. What is the reason for Trex? The fiberglas screening has me stumped, too. are you building a deck or siding a house?
 
  #3  
Old 09-28-13, 02:59 PM
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Larry, Tyvek and cedar don't play well together if there is any wetting. The tanins in the cedar will eventually destroy the quality and performance of the Tyvek. I've seen it a few times. The Tyvek becomes brown, brittle and dry almost like a thin paper grocery bag.

Felt is certainly breathable. Statistics will vary but according to this page, felt reacts differently depending on whether it is wet or dry. (5 perms dry, 60 perms wet) Felt clearly is not water proof, but is only water resistant. That being said, felt does a great job of protecting the sheathing. I've torn off many a roof where the shingles have been practically GONE in some places and the felt paper is the only thing that saved the roof from a major leak.

The "screen" on the rainscreen is to keep bugs from entering the air space either at the bottom (drainage) or top (ventilation).

I have never installed siding using rainscreen techniques, but have read a lot about it. If I did, I'd probably use the cor-a-vent product. 1/8" is the minimum space, according to the Oregon code (2010) but... how wide would a raindrop be if it was running down the wall behind your siding? Any variation in the paper or sheathing and you would have contact. IMO, 1/8" may allow drainage, but more is better if you want the back of the siding to stay dry. That seems to me to be half of the point of the rainscreen. I would probably use rips of 7/16" OSB as the furring, and then use the cor-a-vent product to vent the top and bottom. Some omit the ventilation at the top and the system still works just fine.

What I don't quite understand from your post is where you say you are using 1x1 trex as vertical furring, but then say you are going for a 1/8" space. Which is it?

Or are you using the 1x1 like a batten, to break up the 1x4 cedar into shorter vertical sections?
 
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Old 09-28-13, 05:19 PM
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Didn't know that about Tyvek, Brant. Thanks. I can't figure out the lay of the materials he is proposing. Horizontal 1x4 cedar and vertical 1x1 Trex???
 
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Old 09-28-13, 07:56 PM
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1/8" gap at butting siding boards is recommended by manufacturer; http://www.google.com/url?sa=t&rct=j...L9aWzw&cad=rja

Be sure to add Grace I&W behind joints, 6" wide onto lap coverage one below. OSB will stay wet very much longer than plywood, don't use it. Trex (50/50; resin/wood dough) will mold, don't use it. A vented (bottom only) RS will allow for drainage and stop capillarity, a ventilated (open top/bottom) will also dry any materials there (sheathing) due to air movement rather than just pressure-equalizing (less air movement) from the gap; http://www.google.com/url?sa=t&rct=j...mVSMmbkOSfRsgA

Water or oil based primer; Benefit From Airspace Behind Your Siding

More thoughts; All About Rainscreens | GreenBuildingAdvisor.com

Best-Practice Wall Shingles - Rainscreen, Siding, Exteriors - JLC Online

Flashing; notice pp.8 head flash returns; http://www.mtcc1170.com/images/BCRainScreen.pdf

Gary
 
  #6  
Old 09-29-13, 02:27 PM
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Cedar Siding Example

Here is the look we are going for and should help explain the questions asked. Thank you all for you input.
 
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  #7  
Old 09-29-13, 04:26 PM
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I'm trying to figure out why you would want an open air structure as pictured in a weighted cold 4 season section of the country such as WA. If you are in Kentucky, and you own a tobacco farm, then yes an open design is beneficial. If in a temperate climate such as So. California, then also, no issues. But in a very wet, cold state, I would want my exterior buttoned up pretty tight. Particularly on a house.

You can achieve a very similar look by going with a Cedar Ship lap. It has a flat face and strong horizontal lines that shadow and mimic what you have pictured (ship lap is what I have on my house). It also is sealed and all moisture will sheet to the outside and not get stuck on the inside. You also will not have to work your math so tight around doors and windows that the open air design looks natural. Most likely will look like thin strips of almost right measurements with visible z-flashing around the top of the openings. You also will not have to worry about sealing and maintaining a surface (the back side) that you can not see. Raw Cedar and moisture do not have a fabulous track record with longevity.
 
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Old 09-29-13, 05:03 PM
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My oh my you really want to be different ;-)
IMO with open gaps between every course you don't want gaps behind as well or you will have greater vermin problems than just digging cocoons, spider egg sacs, mud dauber nests, etc, etc out of those cracks. You should use a rainscreen mat behind the wood. It has a filter fabric face over expanded polypropylene webbing. 1/4" thickness is common and may avoid the headaches of adding jamb extensions to every window & door. Rainscreen techniques are not new but the airy matting is a little more familiar to masons than carpenters--but it IS intended for both applications. The matting would go up over house wrap or felt paper as a wind and water barrier.

There are many brands but I chose Keene "DriWall" because its 4' width means less piecing and less waste on walls. They will sell direct with free freight.

 
 

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