# Preventing board and batten siding failure



## OhioJoe (Jan 1, 2014)

Hi all, this is my first posting, and it is a question on the treatment of board and batten siding. I live in south eastern Ohio by Marietta in a barn. It's a 170 yr old barn that was converted to a house (we didn't do the change over). They kept the original siding and insulated from the outside in, so there is not a continuous sub-surface skin. Much of the siding looks original to the structure. Needless to say its time to replace. When ever a popular tree goes down on the property I have it cut up and stick it to save for siding. I have rods in my back from a tractor accident so I will not be doing the work but you can be sure I will be watching closely. I have been working with wood since I was about 10, I'm 45 now, I have done many cedar siding jobs, so I'm pretty familiar with wood, but not so much with popular B&B. I've been looking it up and one of my questions is once the house is stripped and sheeted, there is a tyvec now that comes with a matrix on it so that there is a air space behind the siding for moisture control. Do you really need that or what is best for behind popular B&B? And the second question is for the bottom of the boards. I have a buddy that had B&B on a carriage house, had Z flashing along the skirt boards and where the boards came down on that flashing they started to rot within seven years. Did the wood react to the galv flashing, or were the boards not sealed good enough on the ends or do the boards need to be cut with more of a gap between the flashing for drainage. I don't want a large gap for looks but does it need one for water control. A barn is built to breath more than a house so when I tighten everything up I don't want to create cracks where water will cause damage. I'll stop here for now. I tried to give as much info as I could so you could get an idea of the answers I'm looking for. Thanks in advanced for any help. Joe


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## Smitty_Cabinetshop (Mar 26, 2011)

I've got B&B siding on a shed that's been in place for the better part of a century, it's all pine. There is decay along the bottom edges to varying degrees so I know what you're referring to. The absolute best way to mitigate the rot is by installing gutters on the structure; it's roof run-off that splashes up along the siding that gets it too wet from comfort. Unfortunately, modern wood isn't tight-grained enough to last as well as the vintage stuff for outdoor use. Can't speak for poplar in this application, but something like cypress would be a better material choice.

Did the Z flashing actually cut under the edges of the siding? If so, that's probably not a good design choice; the end grain needs air to dry. If replacing, I'd prime / treat the ends especially well and even prime the inside of the boards maybe a foot or so up from the ends for some additional protection.

All this is not based on a ton of first-hand experience, but rather on the fact that I've cared for a building like yours for 20 years now and have seen what you're referring to; I've pondered solutions myself. Good luck!


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## WibblyPig (Jun 8, 2009)

The end grain sucking up water is what lead to the failure. I would put a water table molding at the bottom to cover the end grain and caulk everything with high quality caulk.


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## OhioJoe (Jan 1, 2014)

Thanks for your reply, Smitty. The siding on my buddy's place was actually on the second story so gutter splash was not a problem. And to your question -yes the Z flashing went under the edge of the B&B. He wanted a rim or skirt board below the B&B. The skirt board being horizontal and the B&B being vertical, he put the Z flashing behind the B&B so that it came out under the B&B and over the edge of the skirt, so any water would shed forward. I know this may not be real common for B&B but I have seen it before. It did look good. I've seen a similar style with cedar and I know cedar in more rot resistant, but I never thought it would fail in 7 yrs.

I would love to use cypress, but in southern Ohio and especially my property, popular will have to be the wood of choice.

And to Wibbly, I described the Z flashing with the skirt bord, wouldn't the flashing have acted similar to the molding you mentioned?


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## Smitty_Cabinetshop (Mar 26, 2011)




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## Grandpa (Jan 28, 2011)

I believe you are soaking the end grain in water if you use metal flashing under the lower ends of the siding. This would cause rot I believe. The trim shown by Smitty is what we call bull nose around here. It drains the water away from the siding. and also keeps it from drain directly onto the siding below in many cases. The saw kerf prevents the water from travel back to the siding. Surface tension will cause the water to cling to the under side of the bull nose and travel back to the wall but the kerf stops it there. I would be cautious using caulks. This is the last line of defense and usually temporary. Look for what most people call caulk and you should find some tubes that say sealant. This is the key word for sealing anything - Sealant. I think polyurethane is the better sealant. The life expectancy of this product is about 15 to 18 years in SW Oklahoma where I live. I have observed some of this first hand and have been impressed with it. The 50 year caulks are a hoax. They all crack and begin to turn loose in just a few years. I recently read a good article on caulks and sealants. In my younger years I would have known where I found that. I will look for it again. Water splashing on the siding is not good. Even a second story situation will allow water to get on the siding more than we would ever believe. In my country lawn sprinkler systems are often the culprit. In your original question/statement, you asked about Tyvek. I think it is great and should be used. 75% of the homes heat is lost through wind infiltration. Tyvek actually breathes. We use it on all new construction and in any repairs where we can get back into the wall. I used it on my storage building when I changed the siding. It will keep the water out and water does get back into the wall. I am wondering if this could be the problem. Is the siding caulked and it is still holding in places. This would trap water in the wall causing a problem. Often we look at a 200 year old building (not here since we have only been a state for 100 years) and think we can even improve on that siding or structure with these new products. When we are disappointed we don't know where to turn. We have sealed up parts of the wall to the point the water can't drain or empty to preserve the siding.


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## OhioJoe (Jan 1, 2014)

Thanks for your input Grandpa. I am leaning towards tyvec, some guys say tar paper under wood siding, but I was really wondering about the tyvec that has a matrix on it. It is supposed to hold the siding so that there is an air space behind the siding to allow moisture to escape in case some got behind the siding (tyvec brand is called drainwrap) or is this over kill and a waste of money. Now the other thing is about this "bullnose". I threw a drawing together so that I make sure I'm on the same page with you. I know about rain grooves like what the bullnose has, but the joint I'm concerned with is where the B&B meets the top of the bullnose or the Z flashing. We are just replacing the flashing with the bullnose so if the water wicks with the flashing why won't it wick with the bullnose. I left spaces between things in the drawing so you could tell where I was putting things. On the house I want as small of a gap as possible.










I see why the bullnose may keep the water off the skirt board better, but where the siding meets the top side of the bullnose is where I am concerned about. I don't see much of a difference whether the siding sits on a bullnose or on a piece of flashing. I was planning on staining the ends of the siding, but I don't see where that one step will keep all the water out of the wood. Maybe it will keep the wood from rotting a few more years, but I still see that as a problem the I will have to fix again and that's what I'm trying to avoid. I see that the top of the bullnose has a slope on it and I was planning the Z flashing to be sloped on top also. I hope I haven't confused things I just still don't have a clear picture what I need to do yet. Thanks again for everyone's input


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## jdh122 (Sep 8, 2010)

I think that an air gap behind siding is a very good idea and personally I'd be very reluctant to install siding directly to the wall (although builders did it for a long time and it often worked). Don't know the tyvec product you mention, but I have installed a version of cor-a-vent on a friend's house. A simpler idea is to use plastic sign material as furring strips (stuff that is made like cardboard, except out of plastic, two sides with a layer between - just make sure that you orient the channels so the water drains down, obviously). Since you would need to install furring strips horizontally instead of vertically, this would allow for better drying than would wood furring strips (which are probably fine on clapboard). a search for "rainscreen" on the Fine Home Building website will get you started - you could even ask the question on greenbuildingadvisor.come (affiliated to fine home building).


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## Grandpa (Jan 28, 2011)

The bullnose will drain quickly. The Z flashing will get bent and hold water most of the time. both are good but I believe the bullnose will be easier to replace when the time comes and it will come. I would close that gap and seal it with polyurethane sealant. Put your saw kerf as far out as practical so it doesn't empty and closer to the wall than necessary. We usually pus some metal flashing behind the siding and also behind the wrap whether it be felt paper or Tyvek. This flashing should extend up behind the paper and then come out the lower edge. It would turn 90 deg. outward and go over your bullnose but never be seen. Yes all this can cause rot if water gets behind siding and it will some day. stop it as it clears the siding. There are dozens of ways to do this. This is the way I have done it and the way I was taught. Always use flashings and sealants and plan on water getting behind the siding.


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