# Flashing for New Construction Replacement Windows in Stucco House



## BigJimmy (Jun 30, 2006)

I plan on replacing several windows in my house next spring (I'm planning well in advance obviously!). My house has a very old stucco finish which is still in very good condition. The front of the house features a panel of 5 old single-pane windows flanked on all sides with a simple wood surround that looks simply like a picture frame (I'll attach a picture later). These boards are nailed to the window frames and then onto the wood lath. The stucco was basically just applied right up to the edges of the wood without any type of flashing (there is a wooden drip cap along the top).

My new design involves removing the entire panel and outer framing. Then, I intend on installing 3 new-construction casement windows in the RO, arranged so that the two at the ends butt against the existing studs and the middle is centered, leaving about 10-12" between the center window and each of the two L/R units (I will add the appropriate framing and sheathing between each).

My biggest question is how do I flash these new windows. Most of what I've read suggests the installation of membrane flashing at the sill, then the sides followed finally at the head. However, all the details that I see assume new construction where the home wrap is laid over the entire unfinished wall and tucked underneath the window flashing. Except for the 3-4" of bare framing that will be exposed around the opening once I remove all of the old windows/trim, I'm not planning on removing and reapplying the stucco. This being said, does anyone have any recommendations for flashing?

Also, I'm thinking about surrounding each window with some form of architectural stone, like Owens Corning's Monticello series (http://www.culturedstone.com/products/productdetail.asp?id=28).

Finally, if anyone knows of a good reference on the subject of flashing, feel free to suggest. I'd like to pick up something to expand my knowledge.

Thanx!

Jimmy


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## DeeTee (Aug 29, 2007)

*Close inspection is needed*

It might be tough to do much advanced planning in this instance. "Very old stucco" and the "3-4 inches of bare framing" might have conspired over time to create not such a good place for attaching new casement windows. Ideally the membrane flashing would cover the window nail fins (I'm assuming yours will have them), and extend beneath the exterior house finish. If you aren't removing any stucco the membrane flashing won't end up beneath it, unless you add some from where it currently ends until it stops at the edge of the window. But then it sounds like you'll only have 3-4 inches of flashing beneath the stucco. This requires some close inspection once you have removed the windows and surrounding debris. You might need to remove and replace some stucco in order to get a good flashing job. In that case, if it won't interfere too much with your architectural sensibilities, one option would be to reframe the windows with pressure treated wood perhaps of a width wider than what is coming off using L channel between it and the stucco. That's just one approach I can think of but I'm sure there are others that would be just as good if not better.


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## bkhosken (Oct 30, 2007)

*Along the same lines...*

I am building my own geodesic dome house from a kit. I was reading up on the flashing for the windows here, as the entryway will be stucco, and I have a question. The manual for constructing the dome says put the vapor barrier on the INSIDE of the entryway wall, just under the sheetrock...so if I flash the window, what keeps the rain from seeping under the stucco and going into the wall at the end of the flashing? The wall is 2x4PT, with 2" Styrofoam panel on the outside, and stucco outside of that. It will be painted, but that's the only rain barrier on the outside. Am I right in thinking I should put the vapor barrier (Tyvek, etc.) on the OUTside? Maybe outside AND inside? The manual says if I put the vapor barrier on the outside it will cause condensation when it's cold out. In FL, how much could that matter?


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## BigJimmy (Jun 30, 2006)

DeeTee said:


> It might be tough to do much advanced planning in this instance. "Very old stucco" and the "3-4 inches of bare framing" might have conspired over time to create not such a good place for attaching new casement windows.


Thanks for the input. I just wanted to point out that the framing is not/has not been bare; I simply did some investigative work. At one location, I gently pried the window casing back so I could see what I will be working with. Actuall, the original sheathing/lath is in excellent shape. And I carefully restored everything when I was done and added a bead of clear silicone just for GP and to get me through to the spring.



DeeTee said:


> In that case, if it won't interfere too much with your architectural sensibilities, one option would be to reframe the windows with pressure treated wood perhaps of a width wider than what is coming off using L channel between it and the stucco.


If I'm understanding, your concern is that the 3-4 inches of framing to be removed (and the 3-4 inches of bare sheathing underneath) will not provide enough distance from the RO to flash properly. I was concerned too. Regarding the L-channel, would the intent be to place it beneath the PT framing (but above the flashing) so that it creates a water proof surface between the framing wood and stucco? Also, I intend on applying an architectural stone surround once the windows are in which will cover up some of the bare sheathing.

To clear something up for me, is the purpose of the flashing simply to keep water from getting into the house behind the window? If so, (and please excuse my lack of understanding!) some window manufacturers (and perhaps all, but I don't know) recommend a liberal application of sealant to the wall sheathing around the RO before the window is placed in the opening. Since this is beneath the nailing fins, why does this not in itself do the trick (with the exception of possibly the corners)?

Thanks!
Jimmy


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## DeeTee (Aug 29, 2007)

*The L and the Membrane*

Maybe it's more a personal preference but I like the cleaner look that you get when the stucco dies into the L channel, (or you might use Z channel and others). I just think it helps to prevent the stucco from beginning to chip along where it meets wood.

I know the use of sealant _and_ membrane might seem like overkill but to me it's cheap insurance and there's no better time to do it then when you're installing the windows.


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## DeeTee (Aug 29, 2007)

*Caution Advised*



bkhosken said:


> I am building my own geodesic dome house from a kit. I was reading up on the flashing for the windows here, as the entryway will be stucco, and I have a question. The manual for constructing the dome says put the vapor barrier on the INSIDE of the entryway wall, just under the sheetrock...so if I flash the window, what keeps the rain from seeping under the stucco and going into the wall at the end of the flashing? The wall is 2x4PT, with 2" Styrofoam panel on the outside, and stucco outside of that. It will be painted, but that's the only rain barrier on the outside. Am I right in thinking I should put the vapor barrier (Tyvek, etc.) on the OUTside? Maybe outside AND inside? The manual says if I put the vapor barrier on the outside it will cause condensation when it's cold out. In FL, how much could that matter?


I have seen the condensation from inside a stuccoed dome cause bubbles beneath the elastomeric paint on the outside of the structure. This was in a dry climate in the southwest. The paint was used as recommended by the manufacturer at that time. I understand some of these recommendations have been modified but I'm not up-to-speed on it. Sorry I can't be of more help other than to caution you to do some thorough research before you do the flashing. Maybe someone here who has had recent experience in this area might chime in.


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## BigJimmy (Jun 30, 2006)

DeeTee said:


> Maybe it's more a personal preference but I like the cleaner look that you get when the stucco dies into the L channel, (or you might use Z channel and others). I just think it helps to prevent the stucco from beginning to chip along where it meets wood.
> 
> I know the use of sealant _and_ membrane might seem like overkill but to me it's cheap insurance and there's no better time to do it then when you're installing the windows.


Thanks for the follow up. I was definitely planning on doing both (they are recommended by the window manufacturer anyway). I'm just one of those nerdy folk that likes to know the "why" behind everything (I'm an engineer after all)!

Also, was my general thought about _why_ flashings are needed correct, i.e. to prevent the infiltration of moisture through fenestrations?


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## Tscarborough (Mar 31, 2006)

Flashing is not waterproofing. The purpose of flashing is to direct water while waterproofing prevents it's passage. Assuming no air cavity on your wall system, then your goal in flashing the replacement windows will be to cap the top of the window with an L shaped flashing that is tucked under the existing stucco as far as possible, and extends beyond the lip of the window framing. On the sides, it is the same, keeping all laps from top to bottom. On the sill, the flashing should extend under the window frame and provide weeps for the moisture collected from the top, sides, and sill of the window.


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## ncgrogan (Dec 3, 2006)

It sounds like you can install your windows and will have enough room to flash your windows properly but you probably wont be able to integrate your waterproofing with the flashing. It depends on whats behind your stucco. We've recently used STO gold coat over window flashings. Flashings aren't waterproofing but they have to be waterproof. In most cases they are secondary waterproofing measures.


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## Amber (Apr 20, 2007)

Most window companies will include flashing instructions with their windows and also on their websites. I suggest you check these sources out for the brand of window that you have chosen to use. In the event that you run into leak issues in the future your first obstacle in dealing with the warranties will be if you installed per their spec or not.


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## BigJimmy (Jun 30, 2006)

Amber said:


> Most window companies will include flashing instructions with their windows and also on their websites. I suggest you check these sources out for the brand of window that you have chosen to use.


Yes, I had consulted Weather shield, the manufacturer. Their details for new construction windows (which is what I will be using) assume new construction conditions, i.e. no existing exterior wall finishes. In my case, I have the stucco to deal with and I'm not planning on re-doing that any time soon. From others that I have consulted since my original post, it appears that the best approach will be to remove whatever additional stucco around the RO as necessary to obtain the minimum flashing coverage specified by the manufacturer, in this case 9." I'm going to be surrounding the new windows with architectural trim stone which will cover some of area. The rest I'll probably hire a professional stucco guy to complete unless I figure out how to do that myself over the winter.:laughing: 

Thanks,
Jimmy


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