nailing flange to header

Hi,
I am about to replace the existing aluminum frame windows in my home with new construction vinyl windows with a nailing flange. I have read in a couple places that one should not nail the flange along the header, so as to allow for seasonal movement of the header. Some suggested bending a couple nails over the top flange. I have also read alot of manufacturers instructions and other resources that have made no mention of this. What is the consensus opinion of folks here, to nail the flange tight or not? I live in the wet but mild portions of the Pacific Northwest if that matters.
Neil
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nlbauers wrote:

Every original window I have seen has the flange nailed on all four side. Replacement window, however, are usually screwed into the sides only. I suggest you go by what the manufacturer of the windows says about installation.
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nlbauers wrote:

People are confusing not shimming at the header with not nailing at the header. The first makes sense as any movement would cause the window to bind. Not nailing does not make sense. Bending nails does not make sense. Andersen windows instructs to fill all nail holes in the flanges. Nailing the _nailing_ flange kind of makes sense, doesn't it?
R
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Makes great sense to me too. But I wasn't confused- the recommendations clearly stated that nailing the flange did not allow the header to move seasonally and could contribute to window failures.
Hopefully, someone who thinks not nailing the flange is a good idea will speak up and explain some more. Until I hear an experienced argument to the contrary, I plan on nailing the flanges.
Neil
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nlbauers wrote:

We do not nail the top flanges on windows. It is not much of an issue with single windows that have properly sized headers, but on longer headers it very well can be. When you have a double or triple window, a large fixed glass window or any window with a header longer than 3', the probability is that the header may sag over time. When that happens, if the top flange is nailed, pressure will be applied to the top of the window frame.
If it is a fixed glass or single hung window (top glazing is fixed) the pressure can break the window. It can cause seals to fail, frames to flex, etc. If it is a double hung, it can cause the upper sash to not close properly, bind, etc.
When we have larger spans of windows, where we must fasten the top flange due to the longer widths, then we drill a hole in the flange and slot it vertically. The nail in the top flange is nailed loosely to allow movement.
What do you hope to gain by nailing the top flange? Install a window, nail just the sides and bottom, then pull on it to see if it is loose. I think you will find that it is very secure with no nails in the top flange.
HTH
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Robert Allison
Rimshot, Inc.
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Thanks for replying. This is the sort of explanation I was hoping to get. We are removing 40 year old aluminum frame casement windows that were nailed on the top flange. These have had chronic moisture/condensation problems on the window sills that led to their replacement. The house was built in the 1940's so if the header was going to sag with age, I expect it would have already done most of it's sagging. You mentioned this as a remedy for a header sagging over time, but do you think this is important for seasonal movement as is more likely to be an issue with my house?
What I expect to gain from nailing the top flange is a lot of support for the caulk sealing the top of the window to the flashing. It seems that without the nails, any twisting force by the window framing may pop the caulk seal along the top flange of the window. And plus, there is the obvious question, why don't the window manufacturers recommend this?
BTW, I hope I'm not coming across as argumentative. I want to hear the case for not nailing the flange, I've just got a number of questions about it.
Thanks again. Neil
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nlbauers wrote:

Whoa, you should not have to rely on caulk to seal the window unless you had to cut off the nailing flange. If you have enough room to nail the flange, then you have enough room to run flashing up under the siding and down over the flange. That keeps out water without the need for caulk. Caulk should be used as insurance, but it should just be a bonus.
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The obvious question yields the obvious answer. The replacement windo comment has no bearing. It's a replacement window, not a prime window two different animals. The header sagging? If the header sags, then yo have a bigger problem than just windows binding. Seasonal movement o the header.? What would make the header move more than any othe framing member? Nail the flange. If it wasn't needed, it wouldn't be there. If yo don't nail it, it's installed improperly and therefore any warranty i void
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I am installing flashing over the top flange, once the window is in place, not relying on the caulk alone to keep the water. But I would prefer to have a secure seal of caulk underneath the flashing as a second layer of protection.
Neil
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nlbauers wrote:

That is the wrong place for caulk. The caulk should seal the crack between the window frame and the siding.
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Maybe we are misunderstanding each other? All of the instructions I have encountered put a bead of caulk on the nailing flange before placing the window into the rough opening to seal the window onto the rough opening and flashing. That is the bead of caulk I was referring to in my previous messages. I was concerned it would be more likely to lose its seal if the header was not nailed. I will also caulk the crack between the window frame and the siding.
Neil
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nlbauers wrote:

That is ok. I've never seen that done with new construction because there will be caulk between the siding and all around the window frame (the outside) and sealing of some type all between the inside wall and the window frame (inside). I understood you to meant to caulk between the flange and the flashing.
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nlbauers wrote:

The no nail rule is also for allowing expansion and contraction of the window unit itself. Aluminum windows are more forgiving in this regard than vinyl windows. I would still not nail the top flange without slotting and nailing loosely.

You should not be depending upon caulk for a seal. The flashing details should keep the water out. Caulk is more for air penetration and backup against water. The window manufacturers don't recommend nailing the top flange because it costs them so much in field calls and repair and replacement costs.

No problemo. That is what this forum is for. Here is a pdf file of a window installation instruction. It only discourages the use of top flange nails in the vinyl version, but it shows another method of fastening.
http://www.intlwindow.com/New_Constr_inst.pdf
You might think of the top flange of the window as more like a flashing detail than an attachment point.
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Okay, thank you very much for the explanations. The installation instructions I have read from Milgard and Jeld-Wen either explicitly state to nail the header or they fail to clearly state that I should not nail the header. I am thinking it would be best to compromise with the slotted nailing along the header.
Thanks for all of your help.
Neil
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