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Adding new window to existing wall w/aluminum siding

Adding new window to existing wall w/aluminum siding


  #1  
Old 04-13-12, 12:33 PM
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Adding new window to existing wall w/aluminum siding

Wife and I are looking into adding an average-sized (maybe 34" x 52" or thereabouts) aluminum-clad double-hung wood window (or two side-by-side mullioned together) to get some more light into our living area. I'm not afraid of trying to DIY it myself, and I'm well-read and confident with framing the rough opening, re-routing any electrical, etc. from the inside. My concern is with cutting the hole in the exterior sheathing/aluminum siding, and with flashing/sealing/trimming the new window on the exterior. I did some searching and found several other threads (here and elsewhere) asking similar questions, but none of them dealt with aluminum siding and aluminum trim (always stucco or wooden clapboard or shakes with brickmould or 1x4 trim stock)

I guess the first question I have is, should I be looking for a replacement window with no nailing fin, or a new-construction window with a fin? The word "replacement" as a general term doesn't really make sense since I'm not replacing an existing window, but this isn't 'new construction' either as the wall is already sided and I presume I would have to cut back the siding to expose the sheathing so I could nail the fin to it... but then I would have to cover the gap between rough opening and cut-back siding with trim somehow, and I'm afraid it wouldn't match the trim on the rest of the windows on the house.

Assuming I have the window (whichever the correct type I should get is), I've torn down the sheetrock inside and framed the rough opening (minus cutting the hole in the exterior sheathing)... can I just use a reciprocating saw to cut the hole in the sheathing from the inside, flush with the inside edge of my framed rough opening? Or does the exterior opening need to be smaller or larger than the framed opening? Will I need to remove and/or cut the siding back from the edges of the hole I cut in the sheathing, or should I leave it flush? Finally, what type of products do I need to properly seal/flash the window, and then to trim it? I presume caulk, window and door expanding foam (not Great Stuff), some type of flashing tape or wrap, and some white aluminum window trim and screws?

I suppose it would probably help if I posted a couple of pictures of how the existing windows are trimmed on the exterior to assist in figuring out how to make the new window(s) match. I'll try to do that this evening.
 
  #2  
Old 04-13-12, 02:11 PM
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To answer your first question, the answer is that you want a "new construction" window that has a nailing fin. Whether or not they "call it" a replacement window or not (that term is thrown around quite loosely) the bottom line is whether or not it has the nail fin.

Since you mentioned you can handle the framing, I'll omit the advice about needing headers over windows in load bearing walls, since you probably already know that!

then I would have to cover the gap between rough opening and cut-back siding with trim somehow, and I'm afraid it wouldn't match the trim on the rest of the windows on the house.
That is something you will just have to figure out the best you can, since this is your only option, unless you want to take all the siding off that side of the house.

can I just use a reciprocating saw to cut the hole in the sheathing from the inside, flush with the inside edge of my framed rough opening?
Yes, but if you do that, you will likely want someone on the outside who will hold his hands on the aluminum siding to hold it back tight to the sheathing so that it doesn't shake on the blade as you cut it. Use a blade made for cutting wood w/nails.

As to your other questions, once the rough opening is cut, you will need to cut the aluminum siding back farther on all 4 sides so that you can have a spot for the nailing fin to lay and also so that you can install a weather resistive barrier around the opening. How far you cut it back really depends on the size trim you will be using to cover the nailing fin... and as you mentioned you want it to match the size and style of the rest of the window trim on your house. Let's say you have 2" trim (brickmould) around all your windows. Take the width of the window itself (not the rough opening) and add about 4 3/8" to that, and that is how wide you'd cut the siding, keeping it centered on the rough opening. An angle grinder and a 1/16" metal abrasive blade will work best. Tin snips will work for the flat parts of the lap siding, but not for the interlocks. Make sure your cut is perfectly plumb, and try not to cut the building paper behind the siding. (shim the siding out with a scrap of 1/4" plywood or something so that you cut into the shim, not into the paper).

Once it's cut back, you could either apply a flashing tape to the bottom and sides, or some strips of housewrap. Keep in mind that the opening in the siding will allow water to get in behind the siding. Your housewrap or building paper which is behind the siding is what is protecting it from harm. You could then either slip j-channel behind the siding, or if you plan to bend something to cover the cut edge of the siding, you would probably do that now.

When you install the window, follow the mfg's directions on whether or not you caulk the nail fin to the house or not. Some are finicky about not caulking the bottom especially. Be sure you install the window level, plumb and square, and keep it centered on your siding cutout, which also should be level, plumb and square. Then you would install flashing tape over the nail fin on bottom, sides and top. It's always nice when you can seal the tape to the sheathing on top, and then have a flap of housewrap that is tucked UNDER the existing the top edge, and then laps OVER your taped nailing flange on top. You'd probably want to install a drip cap under the siding on top, then slip your trim underneath that as you trim the exterior of the window.

The j-channel which will be hanging loose and unattached can now be screwed up tight to the brickmould with a minimal amount of zip screws. (like what they use on gutter downspouts). If you think it would look better with some caulking around the perimeter, go ahead, but keep in mind that if you do a messy job of caulking it will look worse after you caulk than it did before.

The interior of the window should be shimmed according to the mfg's specs- usually at each corner and every 16" on center. Great Stuff door and window foam can be used to air seal and insulate, but just don't use their regular variety of foam. DAP latex foam also works well but IMO it's best for cracks 1/2" or smaller.

Your "brickmould" doesn't have to be anything special if you are just going to wrap it with aluminum trim coil. Standard SPF or SYP 2x lumber can be ripped to any size you need on a table saw, and you can screw it on as trim. Then rent a metal brake, bend some capping and install.

Some windows have a very flexible nailing fin that will not hold the window perfectly flat on the wall. So you would be wise to check how the window is laying on the INSIDE of the house (in relation to the wall surface) so that it is even all the way around. What can happen is that the window might be sticking in 1/8" beyond the wall on one corner... and be 1/4" behind the wall on the opposite corner. With these kind of windows you really need to have someone outside pushing on the window (before you foam it!!!) while you are inside, and then when the window is flush, pop a trim nail or a trim screw through the jambs and shims to hold it to the rough opening. Do each corner this way, and it will save you a lot of headaches when you go to install your interior trim.

This sure got long. I need to cut down on the Mountain Dew!
 
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Old 04-27-12, 12:12 PM
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pictures

As promised (albeit quite a bit later than "later this evening"...), here are some pictures of how the existing windows are trimmed out. So, this is what I'd like to match:











The wide shot of the entire window is a different window than the close-up shots; the window with the close-up shots was easier to get to to take pictures, but has black shutters on either side, whereas the window(s) I would be adding would be on the same wall as the wide-angle window, without shutters.

Without actually taking the trim off to look underneath, it looks like the existing windows are probably trimmed out with 2" or 2-1/2" brickmould which is wrapped in aluminum trim coil. I notice there's a flange along the top that tucks under the piece of siding that runs across the top, presumably to function as a drip cap. I also notice that there is no J-channel capping the cut edges of the siding where it butts up against the sides of the window trim. Instead, the aluminum trim coil just runs back into the sheathing perpendicular, and the cut siding edge butts right against it.

In the close-up shots it looks like the caulking between the siding and trim does not run the entire length of the sides of the window, but that particular window is under a soffit. I would imagine there has to be caulk down the sides of the window in the wide-angle shot since it's much more exposed to rain?

So, I guess two questions from this: 1) do the existing windows look like they're done satisfactorily, and 2) will this be fairly straightforward to duplicate so the new window(s) match?
 
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Old 04-29-12, 08:38 PM
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Sorry I didn't reply sooner, I must have missed your reply somehow.

To answer the 2 questions... the windows look okay, (the way they bent the metal in lieu of the j-channel is fine) but appearances can be deceptive. The one thing the pictures can't show is whether or not you have an adequate weather resistive barrier (WRB) behind the siding. The way aluminum (steel and vinyl) siding works is that water can get in behind the siding at numerous places (such as between the j-channel and siding around your windows) but its the job of the WRB to protect the wood components of the house from repeated wetting. If you have a WRB behind the nailing flanges of those windows (they kind of look like Pella windows to me), then the installation looks good. Caulking around the windows is quite pointless, but is often done just for appearance' sake. You would never caulk inside a j-channel to try and seal up the cut edge of the siding... that's not the way it's done, although I have seen a few people try.

As to the 2nd question, I think "straightforward" would be dependant on your skill and the tools you have available. For someone who has used a metal brake to bend trim coil, yes it would be straightforward. Problem is, I'm not sure that what you have is just your common run of the mill trim coil. Pella windows often come with an optional exterior Enduraclad trim coil that can be custom bent (with a heavy duty metal break, such as the Tapco Pro19). It is pressed into a groove around the window (it's actually carefully tapped into that groove with the help of a block of wood and a hammer) and that's what your pictures seem to indicate you have. Enduraclad doesn't come with a hem bent on the outside edge, they are only hemmed on one side (the side that fits into the groove) so that would have to be custom bent on site. If that metal seems very stiff ( roughly .032 mills) it is probably Pella's Enduraclad, but if it's thin and bends easily, (roughly .019 mills) then it's probably just aluminum trim coil. Trim coil is easier to work with... the Enduraclad is a little harder to work with and it takes a special metal brake that can bend and hem the thicker material. Most metal breaks will only bend up to .028 if I recall.

It looks to me like they capped the brickmould first (maybe with trim coil) ... then tapped the Enduraclad trim into the window groove last to make a sort of j-channel for the siding.

It's not impossible, but I don't think I would say that it's "straightforward".

I suppose its also possible that the original installer tried to make a cap out of trim coil, and then tried to snap his custom made trim into the window groove in the same manner as the Enduraclad would tap in, but that sometimes results in a loose fitting cladding that might need to be caulked into the groove in hopes that the caulk glues the cladding into the groove. You could try to do that with trim coil too, I suppose. But it would take a bit of skill to get the hem just right.
 

Last edited by XSleeper; 04-29-12 at 09:11 PM.
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Old 04-30-12, 09:12 AM
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No worries! I really appreciate your taking the time to answer my questions!

They are indeed Pella windows, and I had been planning to use Pella ProLine windows for the new ones as well (Lowe's down the street carries them).

As for my skill level, I think the only time I ever used a metal brake was in shop class in 8th grade, so it's been a while. I certainly don't have easy access to one either, I would have to rent one I presume, and it sounds like even a rented one may not be sufficient to work with Pella's special Enduraclad trim?

Despite my enthusiasm, I'm thinking it might be a better idea to hire someone, at least for the exterior/finishing part of the job. As I said, I'm fully comfortable doing the rough framing from the inside, re-routing any electrical, repairing drywall, even installing the window itself. But not having any experience with a metal brake and wanting to make sure the exterior work is done correctly so it looks good and doesn't leak and cause problems later on, hiring someone is probably the better bet.

I understand you're not familiar with my area, but would it be reasonable to hire someone for only the exterior finishing portion of the job, or would it be an all-or-nothing type situation? I would have to imagine that on most home construction projects there are several different crews doing the rough framing, installing the windows, and installing siding/trim... but I also wouldn't be surprised if most contractors wouldn't find it worth their time to come out for such a small job as trimming out a single window. On the other hand, am I likely to save much money by doing most of the work myself, or would the difference in cost to hire out just the exterior trim work vs. the entire job be fairly insignificant?
 
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Old 04-30-12, 12:28 PM
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You would definitely be ahead if you did most of the work yourself, provided you can find someone to come and wrap your trim. Perhaps Lowes can recommend someone to do just the wrapping for you. They have many contractors that partner with them, and some that they will just kind of feed work on the side.

If you buy the Enduraclad through Lowes (tell them what you need bent, your pieces will need to be at least 3" to 3 1/2" wide from the sounds of it) have it ready to go and it will make things go a lot smoother. Be sure you ask for a contractor who KNOWS how to work with the Enduraclad because if you get a doofus, he will not know that he needs the heavy break, or how to cut and hem it, and he would probably put dents in the cladding as he tries to tap it into place. It's not the sort of thing you would want a rookie to be doing for you. So I'm kind of glad you see the wisdom of getting a pro to do this. You might be able to DIY if you found a place that rents the Tapco Pro 19 but there would be a learning curve and you'd probably not be happy with your first few windows you did. And ur welcome, glad to help!

 
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Old 10-01-12, 09:48 AM
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I hate to revive this old thread, but it's better than re-posting the whole story...

Still haven't done this project, but I'm getting ready to pull the trigger before the weather gets too cold, and I'm wondering if someone can tell me whether Pella's Frame Expander and Receptor system would work to trim out the window to the siding and cover the nailing fin? FWIW, I took apart the custom bent trim around one of my existing windows, and it looks like they essentially built a custom version of the Frame Expander with regular trim coil, wrapping it around some 1x blocking strips nailed overtop of the nailing fin. Curiously, though, there's no flashing tape or anything overtop of the nailing fin, and only a bead of silicone along the top of the window where the trim coil meets the siding.

From what I can find online, the Frame Expander and Receptor system is what is recommended for my application: http://www.pella.com/Documents/pdf/I...tions/808M.pdf

However, my question is what to do where the siding butts into the edge of the frame expander? Won't water leak in there? The installation instructions for the Frame Expander that I can find don't make any mention of caulking or otherwise sealing the joint between the siding and the Frame Expander. As I said above, my existing windows don't have anything sealing the siding to the trim either.

Also, will I need to install a drip cap or something similar along the top of the window, or will the Frame Expander serve that purpose, with a bead of silicone between the siding and trim, as in my existing windows?

Thanks!
 
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Old 10-01-12, 04:28 PM
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The person who bent the trim coil did it in such a way that it serves as the j-channel for your siding. If you look closely at the 2nd picture you posted, you will see that there is nothing that keeps water from running in behind the siding (this is normal, because that type of siding relies on the weather resistive barrier- your housewrap- to protect the sheathing and framing. Water that gets behind the siding runs out at the bottom of the housewrap).

You cannot use the Pella expander in the exact same way that your window is currently trimmed, because it will not lay flat. Your thin trim coil has a hem on it and additional bends that help it lay flat. You could get Pella's receptor, which is an L-shaped piece that accepts the end of the expander, and holds it straight and flat. But you would need to install j-channel behind the siding, and some wood trim for the receptor to nail to.

A drip cap is always a good idea, and in your case it would be installed where the siding (or j-channel) meets the trim, so as to shed water out over the trim.
 
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Old 10-01-12, 06:29 PM
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Thanks for the reply!

I figured that I would need both the expander and the receptor from Pella. I was thinking that I would cut the rough opening through the siding and sheathing, cut the siding back from the rough opening to accommodate the nailing fin, and then install some wood trim/blocking overtop of the nailing fin of the proper thickness so that face of the trim/blocking would be flush with the face of the window frame, and so that the outside edges of the trim/blocking would butt against the cut edges of the siding. Then I would install the Frame Receptor to the blocking, with the 'leg' of the frame receptor going between the edge of the blocking and the siding, effectively 'wrapping' the blocking. Then install the frame expander to cover the gap between the window accessory groove and the frame receptor.

In that scenario, of course, there's no "j-channel" which covers the cut edge of the siding; it would just be a butt joint where the siding runs into the frame receptor (similar to how the trim is done here about 3/4 down the page, but in my case instead of Azek trim I would have blocking 'wrapped' by the frame expander/receptor). So, my questions are A) will it look OK or will the cut edge of the siding be unsightly, and B) would I need to caulk the joint between the cut edge of the siding and the frame receptor to keep water out, and/or to make it look clean and finished? It sounds like the answer to B) is "no" for the purposes of water, given that the existing windows do not have caulk where the siding runs into the trim coil... but perhaps "yes" for aesthetic purposes?

Put another way... what is the purpose of the way J-channel 'wraps' the cut edge of the siding, as opposed to the siding just butting right into the window frame or trim? Is it strictly for aesthetics, to hide the cut edge of the siding? Or is it functional, in that it significantly decreases the amount of water that can get behind the siding? If it's aesthetic only, then could I hide the cut edge with caulk, rather than J-channel?

If I were to do J-channel, how would I attach it behind the siding, given that the slots for nailing will be covered by the siding?
 
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Old 10-02-12, 12:54 PM
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J-channel is purely for looks. Siding needs to be able to expand and contract slightly, so the gap is left on the siding perimeter to allow for that. You "could" hide the cut edge with caulk but I doubt that you'd be able to get your cut that exact. If the siding was cut back just enough for the window nailing flange... and your receptor and expander was, say, 3"... you could conceivably lay a 3" wide board against the window and use it to make a line on the siding and then cut the siding back with an angle grinder and 1/16" abrasive wheel. Maybe then the cut would be close enough to caulk. You could also simply slip the j-channel behind the siding before you install any wood trim. Once your wood trim, receptor and expander have been installed on the window, a couple screws through the j-channel and into the side of the receptor and wood trim would pull the j-channel tight to the trim and would hold it in place.

You might also make your life easier by just removing all the siding, starting from the top of the house down to the bottom of the window. Cutting your RO out would certainly be a lot easier this way, and you could ensure that the window flashing tape is stuck to the housewrap all around the opening. This would ensure that nothing will leak around the perimeter of the window / rough opening.
 
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Old 10-02-12, 01:37 PM
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Got it. Using an angle grinder with abrasive wheel to cut back the siding was exactly my plan, but you're probably right about not being able to get it precise enough to have the gap be small enough to caulk.

Right now I'm thinking frame expander and receptor with blocking underneath, and then white J-channel around to capture the cut siding edges -- much easier than trying to get a precise enough cutback on the siding and caulking the joint. A possible alternative would be to use Pella's factory-installed Enduraclad 3-1/2" flat casing exterior trim rather than the frame expander/receptor to cover the nailing fin, although 3-1/2" might be *too* wide and it doesn't come any narrower in a flat profile to match the other windows, which is why the frame expander at 2" or 2-3/4" is more appealing.

As for tearing off all the siding, my understanding is that since it's metal siding instead of vinyl it's very difficult to take it off without bending/damaging and be able to put it back on. Not to mention I'm installing the window on the first floor of a two-story gable-end wall, so that would be a lot of siding to remove...
 
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Old 10-08-12, 12:21 AM
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Do you have any type of sheeting under your t1-11? you might not have anything to flash. t1-11 is not like vynyl siding where water is allowed to get under it and the flashing would stop water from getting in the window. you need to stop water from getting behind it period you dont need a back up flashing.

If it was my house would frame out the window then create a window casing with 1x6's ripped down to fit. put some trim on the ouside and use a replacement window. chaulk every where with best silicone chaulk. if you want extra protection you can add a piece of flashing to the top of the window trim by cutting a line above the window trim in the t1-11 with a circular saw using a plywood blade. then side a piece of flashing in the slot and cover the top of the window trim and chaulk some more.
 
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Old 11-26-12, 07:20 AM
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I finally got this project started, and have the rough opening framed from the interior. Just getting this far was somewhat of a chore -- we found some unexpected electrical running from the basement up to the second floor that we had to reroute, and the wall ended up not being framed the way we thought it was which posed some unique challenges.

Another surprise, and the basis of my question now, is that there is no plywood/OSB sheathing on the outside of the stud wall. Instead, there are sheets of 1"-thick rigid foam board insulation, and then the siding is installed directly overtop of that. This poses a few problems, the first being that I ordered the window for standard 4-9/16" wall thickness (1/2" drywall, 3-1/2" stud, 1/2" sheathing), not realizing that there was 1" thick insulation instead of sheathing on the outside. My planned workaround is to cut the rigid foam out as far back as I cut the siding (beyond the RO), and install narrow strips of ripped 1/2" plywood or OSB to build out the wall to the correct thickness. I'll nail the window's nailing fin to that.

My question is, I should probably caulk between the ripped 1/2" material that I install and the rigid foam surrounding it, right? Will regular door/window sealant (same stuff I'm going to use behind the window's nailing fin) work? Also, I know that in new construction the nailing fin would be taped with a rubberized/butyl-backed flashing tape like Grace Vycor or similar; should I attempt to do the same? If so, I'll have to carefully slip the flashing tape underneath the siding since I'm only cutting the siding back about 1/4" further than the nailing fin, correct? How sticky is the backside of flashing tape? Would I be able to fold it in half lengthwise, attach it to the nailing fin itself first, and then gently pull the siding away from the house while I "unfold" the tape underneath the siding?
 
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Old 11-26-12, 06:57 PM
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Pella windows measure 3 11/16 from the nailing fin to the start of any factory applied extension jamb. So if your windows have a factory applied extension jamb, I'd probably rip it off and make my own. (but that's just me.) You could also leave it on, and just extend it with another extension jamb that will bring it out to the correct width.

I'd recommend that you not caulk the joint between the foam and the osb. instead, just tape it with the flashing tape. in your case, while the window is OUT, I'd probably try and get that flashing tape as far behind the siding as you could, and let it cover the seam between the foam and osb. It is pretty sticky stuff (in the summer... but not as sticky in the winter) Use a heat gun or hair dryer to heat it up as needed.

Install the window on top of that flashing tape, then once it's in, apply another layer of flashing tape on top of that. You will have better success if you do it this way.

One tip I might share is that its sometimes helpful to carefully score the paper on the back side of the flashing tape, and remove only half of the paper from the flashing tape. It enables you to wiggle it back behind the siding without it sticking to absolutely everything. Once you have it in position and press it down you can then peel the rest of the paper off, and press it down too. Not sure if you will want to try that but you can file it away for future use.
 
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Old 11-27-12, 07:45 AM
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The window does have a factory extension jamb installed, since I ordered it for 4-9/16" wall thickness. I thought about removing it and installing my own, but I don't have a table saw so getting precise, straight cuts on whatever stock I used would be difficult, to say the least. Besides, I can't exactly install the nailing fin on top of the foam, so I'm going to have to cut back the foam to clear the nailing fin anyway -- installing some 1/2" osb won't be that much extra work, and then the wall thickness will be correct for the window as-is.

Great advice on using a double layer of flashing tape, and skipping the caulk. That should be easier and less messy. I've got two options for flashing tape: Pella's instructions say to use Pella SmartFlash, which is available at Lowe's in a 3 in. x 50 ft. roll. The other option is Protecto Wrap BT25XL, which is twice as wide (6 in.), also 50 ft., and the same price as the Pella tape. Any experience or preference for either of those? My initial thought would be that since the nailing fin is only 1-1/2 in. wide (or thereabouts), a 6 in. flashing tape is going to stick under the siding 4-5 in. which could make it more difficult to apply, whereas the 3 in. Pella tape would only extend 1-2 in. under the siding.

On more quick question: I presume that I should be installing flashing tape along the sill and up the sides of the rough opening prior to installing the window. Pella's instructions say to just apply SmartFlash directly to the rough opening, but I've seen others site-build or install a pre-built sloped sill to direct any water that happens to get between the window and RO towards the outside of the wall. Worth the cost/effort?
 
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Old 11-27-12, 09:35 PM
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Pella tape is stickier in cold weather than ProtectoWrap is, so I would vote for that. I also like the 3" size for most window installations.

There are all sorts of fanatical ways to use window flashing tape... and without writing yet another long reply, suffice to say that no, I don't think it's worth the time and effort to go crazy with sloped sills, pan flashings, etc. under windows. Bottom line, if you have water getting in your RO's you have other problems that need to be addressed.

To answer your final question, no, the flashing tape is not installed around the RO prior to installing the window. The only thing that is often recommended is to install some flashing around the BOTTOM of the rough opening prior to installing the window. Even this is pretty pointless unless you provide sloped drainage, so...... (see the paragraph above) Your flashing tape is supposed to air seal the nailing fin, and incorporate the window into the WRB. How you do that is pretty straight forward. I generally will put the window in, then apply the flashing tape last, over the nailing fin. I feel this does the best job of sealing the corners of the windows, and with Pella windows, the corners are one of the most susceptible places where leakage can occur.

I don't usually follow Pella's flashing instructions to a "T", to be frank.
 
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Old 11-30-12, 07:36 AM
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Alright, sloped drainage not worth the time/effort; got it.

When I mentioned installing flashing tape in the RO prior to installing the window, I was referring to the method described in Pella's instructions, where tape is installed along the bottom of the RO and about 6" up either side (on the inner surfaces of the RO, *not* on the exterior surface of the wall) -- this sounds like what you're referring to. But your point about it being fairly pointless without providing sloped drainage is well received.

I'm feeling pretty good about doing the actual window install at this point -- my biggest anxiety is just that once I fire up the angle grinder and start cutting siding, there's no turning back. If we run into something unexpected, I'm stuck with a 4'x5' hole in my siding/insulation/sheathing that can't be repaired to match. But I've measured the window and RO over and over again to make sure I've sized the RO correctly, and your advice on how best to use the flashing tape makes me feel good about getting a nice weatherproof seal so there are no leaks. Installing blocking, frame expander trim, and J-channel should be pretty straightforward.

I can't thank you enough for answering all of my questions! Hopefully I can remember to snap a couple photos as we work, and definitely of the finished product.
 
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Old 11-30-12, 05:03 PM
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Sounds good. A piece of plywood is a good backup plan in case you need to board the window back up for some unknown reason.

After you put the window in, be sure to apply the tape nice and straight, and as tight to the window as you can. The corners of a Pella window are the biggest leak potential because the factory foam corners they put on there are garbage.
 
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Old 11-30-12, 09:20 PM
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Should the flashing tape that goes on over the nailing fin have a lengthwise fold in it, so that it is affixed to both the outer face of the window frame and the nailing fin (like drywall taping an inside corner)? Or should it be flat, only on the top of the nailing fin, with the very inside edge of the tape butted tightly into the corner between the fin and window frame?

Also, drip cap. I think from your previous posts it sounds like I should install one between the frame expander/receptor/trim and the J-channel along the top of the window, correct? Should I expect to find building paper or some other barrier between the siding and foam sheathing? If I do, does the top edge of the drip cap go between the siding and paper, or between paper and foam sheathing? If between paper and sheathing, I suppose that means that the bottom layer of flashing tape I apply before the window goes in should also go between any building paper and the sheathing, rather than on top of the building paper? Finally, it's OK if I don't apply flashing tape overtop of the top edge of the drip cap, correct? It would be pretty difficult to do so, given that it will be completely underneath the siding above the window.
 
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Old 11-30-12, 10:34 PM
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Flashing tape flat on the nail fin. No need to fold onto the window. Not sure if you will find housewrap or not. If you do, it's usually easiest (but not best) for the drip cap (z-flashing) to go on top of the paper. You can also slit the paper and insert the top edge of the drip cap behind the paper.
 
 

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