making trim lay flat over window nailing fin


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Old 09-23-08, 08:12 AM
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making trim lay flat over window nailing fin

Hi Folks:

My wife and I are going to reside our house with fibercement lap siding. While we're at it, we plan to replace the windows with new-construction type vinyl windows. We've already purchased the windows. They have a 1-1/2" wide nailing fin that's about 3/16" thick. After we add some flashing tape to seal the nailing fin to the housewrap, we'll have a nice 1-1/2 inch wide bump all around the windows.

We plan to trim around the windows with 1x4 rough sawn cedar, but how do we make the cedar lay flat against the wall with that bump in the way? Is it better to shim out the far side of the trim boards, or cut a rabbet to go over the nailing fin bump, or something else?

Thanks for your thoughts

WildTurkey999
Bozeman/Lansing
 
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Old 09-23-08, 08:39 AM
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Wow, thats a pretty thick flange. If it really needs it, use the shim method. You could just rip long strips of the right thickness from a 2 x 4 and picture frame around the flange with it. Put it under the flashing tape.

Don't know if thats a pro solution, but its what I'd probably do if it needed it.
 
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Old 09-23-08, 03:49 PM
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I'd suggest you go with the shim option as well, but I'd staple it to the back side of the trim, on that outer edge. And not put it behind the flashing tape.
 
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Old 09-23-08, 05:28 PM
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Well X, that might a better solution. I just figured that the shim would prob be pine, so I'd attach it to the house framing and protect it from the weather?

Diff folks, diff thoughts..
 

Last edited by Gunguy45; 09-23-08 at 05:56 PM.
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Old 09-23-08, 06:23 PM
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Yeah, there's more than one way to skin a cat. (where did that saying come from anyway? gross!) Nothing says my suggestion is better, just different.

I assumed he'd make the shims by ripping thin strips out of the rough cedar 1x4 that he is using for trim, since it's soft and easy to staple through. Putting the shim on the very outside edge of the trim would give him the option to make it a little thicker or thinner, as the need may be. Thinking of it as part of the trim then, it wouldn't need to be protected with the flashing tape.

Just to explain why I wouldn't put the shim behind the flashing tape ... If the shim is behind the flashing tape, a greater percentage of the flashing tape won't be perfectly sealed to the house. It's really better if the flashing tape goes directly from the nailing fin to the sheathing or housewrap since that makes the "best" seal. And the possibility would exist that if the shim happened to get too close to the edge of the 1x4, there might still be a bump beyond the trim where the flashing tape is tapering off of the shim and back down to nothing... then the fiber-cement siding might not lay perfectly flat next to the trim. But that's a hypothetical problem.

Just mentioning this so as to discuss all the options. Beer 4U2
 
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Old 09-23-08, 07:06 PM
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I'm sure you've found out by now that Andersen and Jeld-Wen windows can be purchased with exterior trim in colors that will match the rest of the window....

Can't remember how Jeld-Wens works, but the Andersen has bolts that fasten them together on the top and bottom of each horizontal piece tieing the verticals together.....a real professional look over the fins........I always add trim beside it...but the time it saves and agony over the fitting the things by shimming is well worth the small incremental cost.
 
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Old 09-24-08, 01:22 PM
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Thanks for the replies, folks.

HoPro.... sadly, we have already acquired windows that did not come with the factory-trim feature you mentioned. Next time we'll look at those options more carefully.

XSleeper ang Gunguy45.... Why do you prefer shims to rabbets? Playing devils advocate here.... as the trim gets shimmed out, wouldn't that leave a capillary space between shim and trim for water, if any gets past my caulking, which it eventually will? In addition, I can't see any time savings using shims instead of rabbets. Either way take three steps if you don't backprime:
SHIMS
(1) feed stock thru table saw 1x to rip shims
(2) handle/install the shim pieces,
(3) handle/install the trim.
RABBETS
(1) feed stock through table saw 1x to start rabbet cut,
(2) feed stock again to complete rabbet cut,
(3) same 3 as before.
Actually, if I thoroughly backprime all wood pieces I use, the rabbet approach would be a big time saver (one set of pieces to paint instead of two)

So why would you go with the shims instead of the rabbets? Please pardon my direct question. I appreciate you taking the time to reply and value everyone's input and am concerned that I may be missing something.

Thanks again,
WildTurkey999
Bozeman/Lansing
 
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Old 09-24-08, 02:17 PM
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Well, here's my point of view. And PLEASE remember, I am no expert, just a do everything myself kinda guy.

I don't like modifying anything that I can just buy off the shelf, in case of future replacement. I'd rather modify the substrate so that off the shelf items can be used later.

XSleepers preference does the same thing, yer not modifying the trim, just adding to it.

Maybe you have better tools than me, but ripping a bunch of thin strips off a board is easier than rabbiting,....TO ME.

To expand further on my original reply, pine is cheaper than cedar, so I figured you'd be using that. Tack/staple the shim to the framing (with glue/adhesive underneath, if desired). It doesn't have to be exact. No painting required, since it will be under the tape, just like your untreated framing. Use 6" flashing tape from the flange all the way over to the sheathing. Your surface is now even across to the siding, and you have a 6" barrier for water intrusion.

Good caulk should last years and years if quality products are used.
 
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Old 09-25-08, 04:05 AM
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Sounds like you're leaving a few steps out.
Wrap the opening.
Square the window and only attach at top.
Attach the bottom metal term flashing and extend it 4" or more past each corner.
Install the metal side flashing.
Nail the flanges the rest of the way around.
Now, tape the flanges to to metal.
I like to run the hardie into the window channel and use step flashing on each piece too.
Never caulked one.
 
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Old 09-25-08, 10:40 AM
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Thanks for your post Tinner.... I've been step flashing the butt joints on the courses below the windows... adding more where a piece of lap siding butts against door/window/corner trim is interesting... I'll think about that. Alas, the windows we purchased do not have built in window channels so that option is out. I see some hardie-wrapped houses in Bozeman MT where there is no caulk at the windows or butt joints but the climate here is pretty dry. This job I'm doing is back east, in the rot-prone, severe thunderstorm mosquito infested climes of Michigan swampland. EVERYTHING is getting caulked, except the drainage channels.

Thanks for the followup to you too GunGuy... rabbeting for cabinet joinery is tedious, but just making a crude rabbet for the nail fin is no big deal on my table saw. So far, that still seems easiest to me, and would create less means for water infiltration.

More thoughts anyone?

wildturkey999
Bozeman Montana / Lansing Michigan
 
 

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