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Gaps in fiber cement lap siding


Chris Bernhardt
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New construction. End joints gapped and not caulked between fiber cement lap boards.

My understanding is that the manufacturers installation instructions call for either butting in moderate contact or gapping no more the 1/8" and caulking.

I could see no other treatment of the gap, no space behind boards for a rain screen, just black tar paper.

I would ask is it possible that the boards wrinkled and produced the gaps post installation but I have seen one of the big builders here install this siding butted with moderate contact and never see it just gap all over the place. Looks like in this case they purposely installed it this way.

Is there something new out there about installing this stuff that I don't know about that makes it ok for them to gap it and not caulk it?

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Chris, Oregon

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Is there something new out there about installing this stuff that I don't know about that makes it ok for them to gap it and not caulk it?

My preferred method is to leave a slight gap and place a piece of steel flashing or a small rectangle of building paper behind the gap to act as flashing. I prefer not to caulk the butt joint because the caulk always fails.

Could this have been what you saw?

- Jim Katen, Oregon

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I've had very good results by flashing the joint as Jim described and filling the gap with urethane caulk. Tool the caulk with the edge of credit card and the joint is invisible.

Those are really bad details in the photos you posted. The joint that directly below the side edge of the window is certainly funneling water into the wall.

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I looked carefully at several of the wider gaps thinking that maybe that they had a piece of flashing behind the joint but if they did, the flashing did not lap onto the course below so any water would appear to be heading behind the siding.

Why would you put joints above windows or adjacent to them? Seems like you would want to try and avoid this no matter how well the WRB was installed.

Either they made a big mistake or they are doing something new that I don't know about. The adjacent houses were the same.

I can not tell by looking at the photo. Isn't there suppose to be a metal cap flashing on top of the window?

Head flashing is not required here as the siding is acting as counter flashing over the flange of the window. If there was a casing, yes then a head flashing over the top of the casing would be needed.

Chris, Oregon

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Are you sure there wasn't a little square of felt back there?

I think now that there had to be because the installation instructions require an inch and a quarter overlap and the exposure between the bottom of the board and the black was about a half of an inch. I was looking for that but I could not detect the edge of the paper thru the gap.

Chris, Oregon

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Originally posted by Chris Bernhardt

Head flashing is not required here as the siding is acting as counter flashing over the flange of the window. If there was a casing, yes then a head flashing over the top of the casing would be needed.

Chris, Oregon

Lots of contractors here thought that too....until their walls began leaking. Now, some of the larger and more reputable builders are at least using head flashings on the south and west sides of homes where the weather comes from here.

The Northwest Wall & Ceiling Bureau says that they've got documented proof that wind will push water 4 inches up behind claps and copings and into a wall, therefore it's smart to use head flashings and z-flashings over every horizontal detail. Still, there's lots of guys who don't and the only thing keeping water out is caulk and the paper.

Had a couple yesterday that just moved up here from Portland. They'd bought a house in Portland a few years ago. It had no head flashings and the windows were caulked around their perimeter, as so many vinyl windows are nowadays. Their inspector remarked that he had no way to know whether the window was properly flashed behind the siding.

They found out within months. When the rainy season came, they had water coming in at the heads of the windows. They spent a pretty penny on having the issue fixed and were pretty nervous about yesterday's home, which had no head flashings at all - only the ubiquitous caulked perimeters.

The plus side is that whatever's been done behind the siding seems to be working, 'cuz the home is 3-years old, we've just gone through the absolute wettest winter on record, and the walls were dry as a bone.

Still, after more than a decade in this business, and knowing that the number of homes with problems without them is comparatively few, I continue to write up the lack of head flashings. It just seems, to me at least, like using caulk and paper, instead of spending $.80 on a piece of sheetmetal and a dollar on an extra 3ft. of bituthene per window, is a foolish toss of the dice.

ONE TEAM - ONE FIGHT!!!

Mike

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In all of the cases that I am aware of leaking was due to improper or a complete lack of flashing above the window and usually involved siding joints too that were above the window

Is it because the flange of the window is not deep enough and they are getting failures of adhered flashings over the top flange?

So what you are saying for added protection against wind driven rain they install a metal flashing which travels up the wall further then the flange, twice as far or more?

I think that Joe L. said don't count of adhered flashings adhering forever but it seems that a lot a guys have faith in all that tape their using.

Chris, Oregon

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Yeah,

I don't trust the adhesive on the back of bituthene - especially when it's bonded to OSB.

Hell, you've gotta understand that I was brought up learning to spline (flash) windows with 60# felt and a piece of hand-bent sheetmetal for a head flashing. There weren't any self-adhering so-called "flashings" and goop (caulk) wasn't used around the perimeter of windows or at siding or trim because these areas were all splined properly with 60# felt and won't leak. Caulk should never be a substitute for good workmanship. Period.

I want to see splines in drainage plane from top to bottom of the window against the sheathing with the head flashing under/behind the top spline and extending well above the window behind the paper. Done right, ain't no way it'll leak short of picking the home up and immersing it in a lake.

But that's just me, I suppose. Change doesn't come easy to some old farts.

ONE TEAM - ONE FIGHT!!!

Mike

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