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SMRcalidiv 06-27-2013 10:14 PM

New windows and old siding?
I have searched and watched and searched again and I feel like I'm almost ready to install new windows, but I want to double check a few things.

I will be replacing my old ('89) aluminum windows with some vinyl single hung windows from a big box store. I have T-111 siding with no sheathing and the old windows are nailed directly to the studs. My plan is to:
1. remove trim
2. cut back siding enough to get to old nail flange
3. remove window
4. put flashing on sill extending onto the siding, and 6" up sides
5. put a z channel up behind siding at window head
6. run a bead of caulk around opening
7. install window, level and plumb
8. run flashing down sides of window on top of nail fin and extending onto siding at the sides
9. run flashing at the head of the window but behind the z channel
10. replace trim
11. caulk the living hell out of all gaps or seams...except for the bottom of the sill trim piece to let water escape

This is more or less what I am thinking...http://robjundt.hubpages dot com/hub/How-To-Install-New-Construction-Windows-In-an-existing-home#

(cut and paste the above but place .com instead of "dot com")

My main concern here is the flashing of the window. Is it ok to put the flashing on top of siding on the sides? Does my plan for the z-channel at the head of the window with the flashing up and behind it makes sense? The old windows have none of this and aren't even caulked in place and I haven't had any issues so I don't want to get myself all worked up for no reason, but I want to do it right. I would also like to avoid having to remove the siding if at all possible.

If you're still reading this...thank you for your time:thumbsup:

Westbrook 06-28-2013 11:03 AM

here goes...

If you want to avoid removing the siding then you will want replacement windows. But like you said you have aluminum windows, so i wouldn't put replacements on top of an aluminum window frame. even if you support it with a whittled piece of wood. Besides you can scrap that aluminum for some extra cash.

1. ok
2. ok
3. ok
4. good idea, now thinking way ahead, what's going to cover the flashing on the siding? Think aesthetics.
5. not sure what z channel is, probably what we call drip cap. nail that above window head. i didn't install it on mine as new construction windows have nail fins and that was flashed to the wall. caulk the top corners of the window head, where the flashing tape intersect. any rain will ride along the head and down the sides, drip cap can help deflect.
6. ok
7. right on, try the dry fit before caulking though
8. you want the flashing to adhere to the wall not the siding, pointless if there is a gap. whos to say water isn't traveling behind the siding? all that flashing is wasted then.
9. correct, adhere to wall
10. ok
11. you shouldn't need much caulking if you flash it properly, flash the bottom of the window too. water will escape via weep holes in the new window, don't cover them or seal them.

SMRcalidiv 06-28-2013 11:29 AM

Thank you for the response, now I see I need to clarify:

I am buying new construction windows with a nail fin, the old windows also had a nail fin and I will be completely removing them, not just cutting the fin off.

The flashing would be covered by the trim pieces as only about an inch of the flashing would actually extend onto the siding. I guess I could trim the flashing down to just fit between the window and the siding (yet still covering where the nail fin meets the stud).

Here is the z channel I was talking about

http://www.lowes dot com/pd_209653-52595-SZB716G_0__?productId=3284202&Ntt=z+flashing&pl=1& currentURL=%3FNtt%3Dz%2Bflashing&facetInfo=

I would slide the long side up under the siding at the window head and have the flashing tape up and under the small lip so water would run off of the channel and have no way to get up and behind the flashing.

The weep holes are in the bottom of the window frame so it will be easy to avoid getting caulk in there.

Thanks for your help!

Westbrook 06-28-2013 01:29 PM

You got it. flash the bottom first, then sides (trim or squeeze under the siding), then flash header last.

that's drip cap/z channel, you got it.

sounds like you have a plan and are ready to install windows.


SMRcalidiv 06-28-2013 06:43 PM

Thank you sir:thumbsup:

So to be sure you would not let the flashing running down the sides extend onto the siding as shown in the link I provided? Rather you would trim it to fit the gap between the window and the siding, even if it's only 2-3 inches. I'm assuming as long as it covers the nail fin and extends onto the stud I would be good.

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