Fanfold over lap siding at corners

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Old 01-18-12, 05:33 PM
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Fanfold over lap siding at corners

I'm preparing to install vinyl siding over my existing lap siding.

I'm putting fanfold over the lap siding but don't know how to handle the outside corners. The corners have 1 x 6 corner boards the stick out 3/4 to 1 1/4 inches past the lap siding. Do I cover the siding and corner boards with fanfold? This would make the wall smooth but uneven. Or do I cover the lap siding with fanfold but stop at the corner boards? This would leave the corner boards uncovered (with fanfold) but would make the wall more even for the vinyl siding.

Thanks for your help.
 
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Old 01-18-12, 06:04 PM
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I would remove the corner trim and replace it with plywood that has been ripped down to the right width and that is equal in thickness to the thickest point on your lap siding. Can't tell you the thickness (3/4" ply usually works with 1/2" - 5/8" thick cedar clapboards), but you will have to measure that to be sure. Once you do that, your fanfold can run clear to the corner and you can tape the seam, if desired.
 
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Old 01-18-12, 06:31 PM
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That sounds like a good way to handle it. Many of the corner boards are starting to rot at the bottom anyway and would need to be replaced before I put on the fanfold and siding.

Thanks
 
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Old 01-18-12, 06:35 PM
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no problem... if you run into anything else, c'mon back. there's plenty of ppl here willing to help.
 
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Old 01-18-12, 07:16 PM
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Thanks. I do have one more thing. I guess I should start a new thread but...

How do I install the fanfold around the windows? The bottom edges of the existing lap siding is even with the edges of the window. When I put the fanfold over the siding, then the J-channel/vinyl siding, the window will really look sunk into the wall. Also, it seems like you would be able to see the fanfold under the J-channel where it meets the window and it doesn't seem like it would keep out water.

Any ideas? I can ask this question in another thread if no one answers.

Thanks
 
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Old 01-18-12, 08:16 PM
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Yes, it does make the windows appear "sunken in" but there is no way around that with vinyl siding. Unless you are going to retrim all your windows with thicker material, or pad them out and cap (clad) them, that is.

How you proceed depends on the thickness of the window trim and the thickness of the foam. If you are using 1/4" fanfold and the trim sticks out beyond the siding by 1/4", I would probably lay the j-channel on top of the fanfold, and just caulk the perimeter of the trim to the j-channel to hide the edge of the fanfold. When the j-channel is on top of the fanfold, any water that gets behind the siding will stay on top of the fanfold that way.

Alternatively, some guys will put the j-channel on first, and put the fanfold inside the j-channel. Depending on what size j-channel and what thickness of siding you are using, this sometimes makes things fit too tight inside the j. It also creates a leak potential that I'll discuss further down.

A third option is kind of a weird one, since it makes your trim look 1 5/8" narrower than before... assuming your windows have sloped sills, you cut your sills about 1 5/8" shorter on each side and use a chisel to knock off the waste on each side so that the cut portion of the sloped sill will be flush with the face trim. You can then lay your j-channel right on top of the face trim, and down past the ends of the sill. I usually will install j-channel + finish trim or a utility-j under the sill, and on top of the window. You often need to shim behind the fanfold immediately under the sill nose, and sometimes over the top piece of trim so that it will still lay flat when you nail a j-channel over it.

Fanfold shims on clapboard siding: If you cut some 3 1/2" strips of fanfold, then take that 3 1/2" piece, measure down 1 1/4" or so and slice about 1/2 way through, you can fold the whole thing in half, turn it over, and that makes a nice shim that will usually lay pretty flat on the siding, if you butt the fat end of the shim up under the fat end of the clapboard. I'll put those shims anywhere I'm nailing where I want the fanfold to lay perfectly flat... like under a sill nose where there might otherwise be a void behind the fanfold, that would cause a j-channel to suck back too far if it was nailed too snug.

There's really no way around water getting behind your vinyl siding at windows. When water runs down the siding and gets to a window, the top j-channel catches it, the water runs down the sides, and when it gets to the bottom of the side j-channel, it runs behind the siding! If there is a WRB behind the siding (housewrap or your foam w/taped seams) that water will harmlessly find its way out around the bottom edge of the siding. But if there is no WRB, it can sometimes result in problems. Some guys think, well, the old clapboard siding used to get wet, so what's the diff??? But that's also another topic. LOL

There are a few tips to direct that water out more quickly by adding additional flashing under the j-channels, but if the fanfold is put inside the j-channel, it makes even that kind of tough to do.
 
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Old 01-18-12, 08:35 PM
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Thanks for the information. You've been a great help! I'll try all of the options to see what looks best. I'll have to wait until it gets a little warmer here before I start putting on the siding.

Thanks again.
 
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