# How to properly seal window?



## HomeSealed (Jan 3, 2008)

The siding does not extend to the edge of the window. Once you remove the trim boards you should be able to completely remove the old window and install a new one without any cutting. Be sure to follow the illustrations you've seen online or in the instructions including caulking and taping of the flange, and drip cap on top the trim.


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## bcbud3 (Jan 22, 2010)

The siding does go to the window edge. That is why i would need to cut about 2" all around. To access the flange. I am wanting to know how i would cover up the now exposed flange of the new window, while ensuring no water penetrating.


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## kncshn48 (Apr 29, 2010)

*builder/window replacement co. owner*

As a home builder I tried to avoid ever having windows/doors not protected by an overhang. Of course some are inevitable, so I used galvanized window flashing that was installed up behind the siding (and behind the felt paper/tyvec/whatever's behind the siding) and came out ABOVE the top window trim (1x4) board. Extend the flashing all the way to each end of the top trim board and caulk it so water can't enter at the ends. This keeps the water totally on the face boards and all you have to do is caulk where the new window frame touches the trim. This galvanized flashing is available at home depot here (OK/USA). Look for a 10 foot long and 1.5" x 1.25" x .25" - the 1.5 runs behind the siding, the 1.25 extends out to the edge of the 1x4, and the .25" turns down for the water to run off. (Dimensions are approx.) You might also research the DuPont/Tyvec web site, as they have peel/stick tape to seal around windows and other advice. Good luck, I recommend you build a roof over it!


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## bcbud3 (Jan 22, 2010)

There is a roof with a 18" overhang about 4ft above this window. I guess i am asking the wrong question here. Lets assume i cut the siding, took out old window and flange, and put new window in. The wood siding now only comes up to the edge of the flange. What would be a proper way to trim out the window? Nail a piece of pressure treated to the top of the flange, have it butt up against the siding. And then put my new trim boards over top of the old siding/new pressure treated strip?


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## kwikfishron (Mar 11, 2010)

Trim over the top of siding (as you have) is the worst possible way to do it. 

You need new window trim (2x4). Remove old trim and hold new trim against the window, scribe a line on the siding around the window. Cut the siding without cutting the house wrap behind it (the tricky part) Install the new trim with a piece of Z metal flashing over the top of the trim and with the top flange of the flashing going behind the siding and house wrap and caulk the siding to the trim and the window to trim. Do not caulk the top of the trim between the flashing and siding.


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## bcbud3 (Jan 22, 2010)

So my new trim would be flush with the existing siding... are you saying something like this? Looking at new window from side view. The red is the z channel and the blue is the new trim and the yellow is the old siding.


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## kwikfishron (Mar 11, 2010)

Pretty close but you want put the flashing above the trim and you want your trim to be thicker than the siding. At least 5/4 or preferably 2x so the trim stands proud of the siding and window so you will have a place to caulk.


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## Jim F (Mar 4, 2010)

The things I learn on this site. I don't think I have flashing above my windows either. This would not surprise me as my house was mostly built by the original homeowner who was no carpenter. You can see where the top trim on the window has suffered water damage. And from Bud's description, it sounds like someone butted the wood siding right up against the current window and then put the trim up over that. Careful is the name of the game for cutting the siding over that. I think I would go manual with that. Maybe one of those curved floor board saws?


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## bcbud3 (Jan 22, 2010)

I should be fine with a skillsaw, just won't set the depth of blade too deep.


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## kwikfishron (Mar 11, 2010)

bcbud3 said:


> I should be fine with a skillsaw, just won't set the depth of blade too deep.


Yes, if anything set the blade slightly short. You can get the last of the “sliver pieces” by hand.

I’d pre-paint the new trim too, so after you install just touch up and done.


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## kncshn48 (Apr 29, 2010)

*kwikfishron's answer is ok, maybe...*

I like his answer and have done that in certain cases. His answer is the same as mine in that the flashing is above the top trim and behind the siding. As a matter of fact, you will have to cut the siding above the window 3.5-4" in order to install the top flashing as we agree. However, there is a potential problem with doing this same thing all around the window. If you cut your siding 3.5-4" away from the window you're ok above the window assuming there's a header, but doing this on the sides and bottom the siding may no longer reach the framing beneath. If you have solid wood sheathing underneath your siding, there's no problem of course. But around here most builders quit using solid sheathing about 50 years ago and use only felt or tyvec. So, I guess it depends on what's underneath your siding. There's nothing wrong with 1x4 trim over siding- it's done everywhere. Your proposal to use treated strips to fill in over the new window tabs and then put on 1x4's is fine.


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## Tom Struble (Dec 29, 2008)

many times around this area that ''shiplap'' type siding is also the sheathing


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## bcbud3 (Jan 22, 2010)

should i also caulk the edge of the trim board that butts up against the siding? i guess caulking the bottom piece of trim is not necessary?


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## bcbud3 (Jan 22, 2010)

I think i finally found a good article with pics...other than the crappy drip cap i think this will be the way for me...

http://www.hammerzone.com/archives/window/new/remodel1/vinyl.htm


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