# Water damage behind house siding



## twd000 (Sep 4, 2017)

The inspector noticed this when I bought the house, but I haven't addressed it yet. The lower roof over my kitchen butts up as against the siding from the main part of the house. Water is running down that edge and damaging the siding. Is there supposed to be a piece of flashing along that corner, or some other way to divert water onto the shingles and away from the siding ?


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## saewoody (Sep 4, 2017)

I'm not an expert, but in my opinion there should be flashing under the siding and caulk along the outside of the siding against the shingles


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## semipro (Sep 4, 2017)

It should look more like the photo below with the flashing exposed and a space between the siding and shingles.  This photo is actually meant to illustrate a "kick-out" at the bottom that prevents damage to siding below.


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## twd000 (Sep 4, 2017)

Well, chit. I think the prior owner had the place re-roofed about ten years ago. Hard to believe the roofers skipped this step. 

This isn't something I can retrofit without pulling off shingles, is it?


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## cd36 (Sep 4, 2017)

The metal flashing is supposed to go under the siding as well unfortunately. And the siding should have an inch space at least to the roof. 

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## Hogwildz (Sep 5, 2017)

There should be step flashing along the wall, under each shingle and behind the siding. The siding should be cut about 1/2" or so from the bottom along where the shingles meet the corner. At the bottom where the last step flashing protrudes out, should have been cut on an angle and bend over some to direct any water back into the gutter. I avoid bending on a 90, as that tends to buck water causing back up in heavy rain. You want to water to flow as easy a path as possible into the gutter  or off onto the ground in situations without gutters.

Your other issue is, it appears to be a none- sunny part of the house, hence the green growing on the shingles and siding. That is typical, and has to be cleaned periodically if you don't like the way it looks.

Lastly, when wood siding is painted, it rots out under the paint, due to moisture in the wood, being trapped from escaping by the paint. Painting exterior wood was the worst idea ever thought of.

The roofers most likely re-used the existing step flashings. They knew better than to disturb that siding, or they would have been eating replacing some of it. Not part of the contract, not getting done.


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## twd000 (Sep 5, 2017)

Is it possible that my roof NEVER had any step flashing installed?  And that it has been slowly leaking and rotting since 1974?  I'm fairly certain that the cedar siding is original.  Was this type of flashing and diverter not required for code compliance back then?  I think I need to climb up there and take a closer look at what is behind the siding.  I haven't seen any damage inside the house to indicate that water is getting past the underlayment/house wrap.


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## Hogwildz (Sep 5, 2017)

It is possible. I have seen where instead of step flashings, some hacks used on long pc of "L" bent flashing, which does not get stepped in with each shingle, and not water tight. Some even leave the flashing out, and expect caulking to keep the corner sealed, that always fails.
Is it leaking into the house, or just the rotted wood you're worried about?
Even in 74, step flashing was a standard. The cedar is rotted, and will have to be replaced, or sectioned in and painted to match. Wood needs to breathe, paint does not allow that. I bet that wood is rotted worse then it looks from the outside.


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## twd000 (Sep 5, 2017)

Like I said, I haven't seen any water damage inside the house.  Which makes me think this joint hasn't been un-flashed for 40+ years . Yes several of the cedar siding boards are rotted and will need to be replaced, which is fine and doesn't require a premature re-roof job. There is no 1/2" gap between the board ends and shingles, which may be due to shingling on top of shingles.  I think I'll poke around in there with an awl and see if there is any flashing underneath the siding.  

The other damage spot is a lower section of siding where the water flow strikes the side of the house, due to lack of kickout.  I wonder if I can lift the bottom corner shingle and retrofit one of these in place to stop that problem?  http://www.dryflekt.com/


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## Hogwildz (Sep 5, 2017)

If it hasn't leaked inside, I agree, there is probably flashing there. Be careful poking back there, if the flashing is the newer aluminum flashing (may have been slid in place when the roof was replaced), it is thin, and an awl can poke through it. Best way to check is at the bottom where the wood is rotted bad, just remove a little of the wood and you should be able to see if there is flashing behind there or not.  Cut at least a 1/2" to 1" gap at the bottom the the siding where it meets the roof. even on the good siding, (all the way up). Installing a small diverter at the bottom is the easy part. Just preform prior to installation, and slide up under the last step flashing. If the last step flashing there has a nail holding it in place under the shingles, you have two options. Removed the nail, insert diverter, renail. Or cut the roof flange side of the diverter down to fit inside the nail area, and slide it up in place. Friction will most likely hold the diverter in place, or you can try and lift the shingle and nail it in place. A small dab of urethane caulk or silicone worked over the top of the nail head with your finger tip to finish it off. Lay shingle back down, done.

Any pc of aluminum metal laying around can be made into a diverter. I shy away from plastic products, as they tend to crack & break in the winter, especially with an ice load pressing against them.


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## Hogwildz (Sep 5, 2017)

Do not caulk where the roof meets the siding! The seal does not last, and all it does is create a damn keeping the water from flowing freely downward.


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## twd000 (Sep 5, 2017)

I agree.  There is currently no caulking in that joint, and I don't plan to add any.


Hogwildz said:


> Do not caulk where the roof meets the siding! The seal does not last, and all it does is create a damn keeping the water from flowing freely downward.


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## sportbikerider78 (Sep 5, 2017)

Plenty of good points and sadly I have too much experience with this issue.  In my house, the flashing was done all wrong.  All of the OSB under that transition from one roofline to an outside wall, was completely wet and rotten to the ground.  In many places, the 2x4 framing was totally gone.  I cut it all out.  Fixed it.  Replaced the OSB with pressure treated plywood, covered it with snow/ice and then flashed over that.  I wasn't taking chances. 

If you run your hand around the first shingle from the ground (where your foundation meets the wall covering) you will find rot.  I'd put money on it.  There may not be any signs inside.  I didn't have any.

I HIGHLY suspect that water is getting behind the siding and rotting the wall.


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## DickRussell (Sep 5, 2017)

All of the above comments on step flashing, keeping the wood up off the roof surface, and the need for the siding to dry are good. To that I would add that all the observations above as to water damaging the wood siding and underlying sheathing are testimony to the usefulness of installing siding over a ventilated rainscreen gap. A gap lets any water that gets behind the siding drain down to daylight, and the ventilation air path behind the siding lets the wood dry after wetting events. There is an interesting old article to be found on the buildingscience.com site (https://buildingscience.com/documents/insights/bsi-038-mind-the-gap-eh) that talks about this. How to implement the gap is discussed in plenty of other places.


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## Hogwildz (Sep 5, 2017)

Rainscreen is fairly new, and a good idea. My thoughts are that if the building is properly built, there should be no need for rainscreen. Water should not be getting behind the siding in the first place, if proper construction methods are initially used. It is almost an acceptance of poor work, and a bandaid for when that work fails. Human nature, and shifty contractors are apt to cut corners knowing they have a back up behind the siding.


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## DickRussell (Sep 6, 2017)

Hogwildz said:


> Rainscreen is fairly new, and a good idea. My thoughts are that if the building is properly built, there should be no need for rainscreen. Water should not be getting behind the siding in the first place, if proper construction methods are initially used. It is almost an acceptance of poor work, and a bandaid for when that work fails. Human nature, and shifty contractors are apt to cut corners knowing they have a back up behind the siding.



It's been known for some time that wind-driven rain can and will get up behind almost any siding, no matter how carefully applied. Information on this is readily available. Here is a good read: http://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-rainscreens


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## sportbikerider78 (Sep 20, 2017)

DickRussell said:


> It's been known for some time that wind-driven rain can and will get up behind almost any siding, no matter how carefully applied. Information on this is readily available. Here is a good read: http://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-rainscreens


Interesting. So, basically, you will have 50 million spiders living inside your wall directly under the siding in a 1/4 gap.


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## cd36 (Sep 20, 2017)

sportbikerider78 said:


> Interesting. So, basically, you will have 50 million spiders living inside your wall directly under the siding in a 1/4 gap.


Supposed to be sealed at the top, and have a screen at the bottom to prevent that.


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## DickRussell (Sep 20, 2017)

cd36 said:


> Supposed to be sealed at the top, and have a screen at the bottom to prevent that.



A "rainscreen" gap certainly needs a screened opening at the bottom to allow free draining of any water to the outside. A vented gap also has a screened opening at the top; this allows slow movement of air up behind the siding, promoting drying. Siding that dries quickly after a wetting event is less likely to curl and will hold paint far longer. Other sources discuss how much gap is needed to allow such air flow, but one says that newer housewraps having tiny bumps to keep the siding from being tight against the wrap, while they allow free draining of most of any bulk water, don't provide enough gap to promote significant air flow.

The method used for for my house involved separating layers of Coravent to get a 1/4" plastic strip full of holes, applying that over a 6" strip of insect mesh, and stapling the screen up and over the plastic strip. These strips were fit between 1/4" wood strips ripped from 2x stock and nailed vertically over where the studs lay under the wrapped sheathing. At the top, the same screened strips were applied, and over that went a frieze board dadoed to let vent air to flow out.

There is an interesting blog currently running on GBA discussing venting at the top: http://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/how-vent-rainscreen


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## semipro (Sep 21, 2017)

sportbikerider78 said:


> Interesting. So, basically, you will have 50 million spiders living inside your wall directly under the siding in a 1/4 gap.


This is a concern to me also.  I'm in the process of doing a deep energy retrofit on our house that includes a ventilated "rain screen" behind our western red cedar siding.  We have lots of brown marmorated stink bugs and I'm doing my best to prevent them from getting behind the siding.


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## Hogwildz (Sep 21, 2017)

The other issue is, any screening you install small enough to keep spiders out, may become clogged with dirt, dust, insect nests, bee nests etc. I stand by the fact that properly installed siding, no matter what kind, will not have any issues. This has been done for longer than any of us have been alive and then some.
I have yet to hear of blowing rain getting behind siding that was properly installed. Not to mention siding should have a moisture or vapor barrier behind it, for just that reason.

If the wind is blowing water sideways enough to get behind siding and damage it, you're in a hurricane, and have other worry's.
I get the idea, but also get that someone came up with an idea, that they're making a decent amount of coin on, and sponsors take over to push the product. For being around for "quite some time". not sure just how long that is, it is not very mainstream for how hard it is being touted. I wonder why that is?


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## cd36 (Sep 21, 2017)

I think it really depends on the area. Here in Manitoba it isn't common unless you're installing foam on the outside, then it's really only done to strap the walls to have something to attach the siding too.

Wind blown rain isn't that big of an issue here and we are very sunny in general. It may rain one day for a few hours, and then be sunny for a week. We don't have many times where it rains all day, let alone a week. 

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## Hogwildz (Sep 21, 2017)

semipro said:


> This is a concern to me also.  I'm in the process of doing a deep energy retrofit on our house that includes a ventilated "rain screen" behind our western red cedar siding.  We have lots of brown marmorated stink bugs and I'm doing my best to prevent them from getting behind the siding.



Your cedar should be installed over laths. If done so, there is no need for screen, as the cedar breathes very well,. and it will ventilate very well over laths. As a matter of fact, cedar is(or at least used to be) typically spec's to be installed over lath(with barrier underneath the lath), and not directly over a flat underlayment. With cedar & slat, you are gong to get insects, spiders, bees etc behind it, that is typical, but they wont hurt the cedar. If you paint the cedar, that would do more damage than anything getting behind it. If one really wants to paint wood siding etc., all sides should be painted to reduce moisture absorption which there is always a degree of with wood, that could become trapped behind the paint. If you ever seen wood siding that was rotted behind the paint, sometimes the paint looks fine, till you touch it, that is a prime example.
Ever see many painted cedar shake roofs? There is a reason there is not many as such.


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## semipro (Sep 22, 2017)

Hogwildz said:


> Your cedar should be installed over laths. If done so, there is no need for screen, as the cedar breathes very well,. and it will ventilate very well over laths. As a matter of fact, cedar is(or at least used to be) typically spec's to be installed over lath(with barrier underneath the lath), and not directly over a flat underlayment. With cedar & slat, you are gong to get insects, spiders, bees etc behind it, that is typical, but they wont hurt the cedar. If you paint the cedar, that would do more damage than anything getting behind it. If one really wants to paint wood siding etc., all sides should be painted to reduce moisture absorption which there is always a degree of with wood, that could become trapped behind the paint. If you ever seen wood siding that was rotted behind the paint, sometimes the paint looks fine, till you touch it, that is a prime example.
> Ever see many painted cedar shake roofs? There is a reason there is not many as such.


Agreed on most counts.  
The type of rain screen I'm installing under the cedar is shown below. Some of my details will differ. I also stain both sides of the cedar board before installation.  Our original cedar siding was installed directly on top of the house wrap and it cupped badly.  My concerns about the bugs are more about providing them a place to live and breed rather than any damage they do.


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## semipro (Sep 22, 2017)

Hogwildz said:


> I have yet to hear of blowing rain getting behind siding that was properly installed.


I can't see how the joint where clapboards meet vertical trim could possibly be sealed to prevent water getting past the siding. From what I've observed sealing this joint with caulk (as shown below) is only a temporary solution due to the linear shrinkage of the clapboards.

I have adopted the view that water tightness (and sometimes air tightness) is provided by whatever is under the siding.  The siding is there for aesthetics and to protect whatever's underneath from sunlight and other physical damage, and to act as the initial weather resistant barrier.  A primary difference between the two is that the siding relies upon gravity for preventing water penetration rather than the adhesive bonding that is used to seal what's behind it.


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## Hogwildz (Sep 22, 2017)

Vertical joints at trim areas should be sealed behind, not on top., and not with latex caulk, which is what appears to be used in your example. Simply installing a pc of metal flashing behind the trim & siding joint will keep any water from infiltrating, for a second measure, a bead of good sealant in place and installing the board over it will also assure no water issues.  The side trim, depending on the thickness, can also be rabbeted to allow the siding to recess behind the trim, which also helps keep the trim in place and uniform. It will also eliminate any end nailing which is where cracks usually begin from nailing at the edge of the board.

Not many folks these days want to take the time to do it right, especially if getting paid by the sf.
I'm not saying what you plan to do will not work. I am merely saying that there are other options just as effective without all the additional steps, materials, labor & costs, to achieve the same results.
The only thing I have issue with in your photo, is it appears the gap is not covered by the screen. Maybe they have the gap line and arrow pointing to the wrong area, as the gap will be between the lath, not behind it.

As far as stain, realize the more translucent the stain, the deeper it penetrates the wood, and less likely it is that it will peel. Solid stains do not penetrate as well, and will peel as it fails, much faster than semi, and flakes/ peels, rather than wears. At least with semi, it will merely wear, and can be recoated every few years or as needed with minimal prep work. Solid will need scraping and feathering.

Good luck with your project, and enjoy. I love working on my place.


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## semipro (Sep 22, 2017)

Hogwildz said:


> The side trim, depending on the thickness, can also be rabbeted to allow the siding to recess behind the trim, which also helps keep the trim in place and uniform. It will also eliminate any end nailing which is where cracks usually begin from nailing at the edge of the board.


Thanks Hog. 
I really like the idea of the rabbet. 
Silicone caulk was used on our original siding to seal to the vertical trim.  Though it stuck amazingly well to one board or the other it couldn't handle the shrinkage and broke loose from either the siding or the trip, letting water in.


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## sportbikerider78 (Sep 26, 2017)

My vinyl siding finds under a 1/2 overhang on the corners.  I guess it is possible in a blowing rain that water could get behind that and wet the OSB.  There is plenty of air movement under that corner and it is pretty much open at the bottom.  If it got wet, it would get dry.  Maybe over 200 years that would be an issue, but I would have much greater concerns at that time...like being dead.


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