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.
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.
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?
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.
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
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.
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
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
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.
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
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
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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.
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.
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.
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
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
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.
You might think of the top flange of the window as more like a
flashing detail than an attachment point.
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.
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