Hi-
For the past week or so, and as I speak, we have been reroofing our
25-year old Colonial. Much of the house is brick, however, some parts
do have cedar siding. In these areas there is a lot of
roof-meeting-the-siding going on, and they had been originally flashed
with galvanized steel. However, it is impossible to remove the
flashing without severely damaging the cedar siding. We had choosen
to use copper flashing on all parts of the house, and the roofer
thought he probably could just put new copper flashing, for the new
fiberglass roof, over the existing galvanized steel flashing, which
was for the existing shake roof and is incompatable with the new roof.

So my question is, is it safe to flash a different metal on top of an
existing one? We are worried about creating current or some unforseen
problem with what should be a fairly mundane thing.

I'd appreciate a really quick reply from anyone who has an experience
at all in this, as the roofing is being done as I write this.

Thank you.

Jay Spenchian wrote:

Hi-
For the past week or so, and as I speak, we have been reroofing our
25-year old Colonial. Much of the house is brick, however, some parts
do have cedar siding. In these areas there is a lot of
roof-meeting-the-siding going on, and they had been originally flashed
with galvanized steel. However, it is impossible to remove the
flashing without severely damaging the cedar siding. We had choosen
to use copper flashing on all parts of the house, and the roofer
thought he probably could just put new copper flashing, for the new
fiberglass roof, over the existing galvanized steel flashing, which
was for the existing shake roof and is incompatable with the new roof.

So my question is, is it safe to flash a different metal on top of an
existing one? We are worried about creating current or some unforseen
problem with what should be a fairly mundane thing.

I'd appreciate a really quick reply from anyone who has an experience
at all in this, as the roofing is being done as I write this.

Thank you.

Don't know the answer but your question strikes as being very apt
and to add my two cents;
With the prevalence of acid rain and/or a salty maritime climate
the possibility of corrosion between the zinc galvanizing and
copper; I believe the two metals are somewhat apart on the 'table
of elements' the possibility of electrolytic corrosion may be
high?
However it may come down to practical experience and whether you
can find unbiased advice that exactly fits your situation. Maybe
we are talking 50 years before any corrosion would, in practical
terms (i.e. your grandson will have to fix it?) have any effect.
Whereas, if 5 years from now you have discoloured water leaking
down the cedar siding due to holes in the 'new' flashing you will
be most disappointed?
Terry.

Jay Spenchian wrote:

Hi-
For the past week or so, and as I speak, we have been reroofing our
25-year old Colonial. Much of the house is brick, however, some parts
do have cedar siding. In these areas there is a lot of
roof-meeting-the-siding going on, and they had been originally flashed
with galvanized steel. However, it is impossible to remove the
flashing without severely damaging the cedar siding. We had choosen
to use copper flashing on all parts of the house, and the roofer
thought he probably could just put new copper flashing, for the new
fiberglass roof, over the existing galvanized steel flashing, which
was for the existing shake roof and is incompatable with the new roof.

So my question is, is it safe to flash a different metal on top of an
existing one? We are worried about creating current or some unforseen
problem with what should be a fairly mundane thing.

I'd appreciate a really quick reply from anyone who has an experience
at all in this, as the roofing is being done as I write this.

Thank you.

Don't know the answer but your question strikes as being very apt
and to add my two cents;
With the prevalence of acid rain and/or a salty maritime climate
the possibility of corrosion between the zinc galvanizing and
copper; I believe the two metals are somewhat apart on the 'table
of elements' the possibility of electrolytic corrosion may be
high?
However it may come down to practical experience and whether you
can find unbiased advice that exactly fits your situation. Maybe
we are talking 50 years before any corrosion would, in practical
terms (i.e. your grandson will have to fix it?) have any effect.
Whereas, if 5 years from now you have discoloured water leaking
down the cedar siding due to holes in the 'new' flashing you will
be most disappointed?
Terry.

"Jay Spenchian" wrote in message
om...
Hi-
For the past week or so, and as I speak, we have been reroofing our
25-year old Colonial. Much of the house is brick, however, some parts
do have cedar siding. In these areas there is a lot of
roof-meeting-the-siding going on, and they had been originally flashed
with galvanized steel. However, it is impossible to remove the
flashing without severely damaging the cedar siding. We had choosen
to use copper flashing on all parts of the house, and the roofer
thought he probably could just put new copper flashing, for the new
fiberglass roof, over the existing galvanized steel flashing, which
was for the existing shake roof and is incompatable with the new roof.

So my question is, is it safe to flash a different metal on top of an
existing one? We are worried about creating current or some unforseen
problem with what should be a fairly mundane thing.

Is it safe from the stand point of the new flashing being prematurely corroded?

Nothing will happen until the galvanized coating is gone, which probably will be
pretty quick once it is in contact with the copper. After that the underlying
steel will be next. Since the copper acts as a cathode it will not be consumed
during this galvanic process (copper only supplies electrons the zine and iron
supply the chemical energy during the oxidation process which causes the loss of
material, also known as rusting).

Painting both the new and old flashing surfaces that will be in contact will
help slow the corrosion process. Any nails which pierce both materials should
be copper nails--otherwise the nails will quickly be destroyed by the
concentrated galvanic currents present at the point of contact between the two
materials created by the nails.

Regards,

John

"Jay Spenchian" wrote in message
om...
Hi-
For the past week or so, and as I speak, we have been reroofing our
25-year old Colonial. Much of the house is brick, however, some parts
do have cedar siding. In these areas there is a lot of
roof-meeting-the-siding going on, and they had been originally flashed
with galvanized steel. However, it is impossible to remove the
flashing without severely damaging the cedar siding. We had choosen
to use copper flashing on all parts of the house, and the roofer
thought he probably could just put new copper flashing, for the new
fiberglass roof, over the existing galvanized steel flashing, which
was for the existing shake roof and is incompatable with the new roof.

So my question is, is it safe to flash a different metal on top of an
existing one? We are worried about creating current or some unforseen
problem with what should be a fairly mundane thing.

Is it safe from the stand point of the new flashing being prematurely corroded?

Nothing will happen until the galvanized coating is gone, which probably will be
pretty quick once it is in contact with the copper. After that the underlying
steel will be next. Since the copper acts as a cathode it will not be consumed
during this galvanic process (copper only supplies electrons the zine and iron
supply the chemical energy during the oxidation process which causes the loss of
material, also known as rusting).

Painting both the new and old flashing surfaces that will be in contact will
help slow the corrosion process. Any nails which pierce both materials should
be copper nails--otherwise the nails will quickly be destroyed by the
concentrated galvanic currents present at the point of contact between the two
materials created by the nails.

Regards,

John

Thanks guys for your help. I've yet to relay this to the roofer, but
the question remains "what to do?". He claims that he has combined
the two before and has not had an incident in twenty years since he
originally did it. That case was a galvanized drip edge meeting
copper gutters. It's somewhat of a conundrum, because we'd really
love to have the more aesthically pleasing look of copper, but don't
want to risk roof discolration or having to replace the flashing
again. Option A might be to just get rid of the galvanized all
together, but that would open the door to a lot of carpentry and
painting work for new siding (not to mention cost!).

I don't want to put anyone on the spot, but would you recommend to
just flash new galvanized steel over the old galvanized product?

Thanks guys for your help. I've yet to relay this to the roofer, but
the question remains "what to do?". He claims that he has combined
the two before and has not had an incident in twenty years since he
originally did it. That case was a galvanized drip edge meeting
copper gutters. It's somewhat of a conundrum, because we'd really
love to have the more aesthically pleasing look of copper, but don't
want to risk roof discolration or having to replace the flashing
again. Option A might be to just get rid of the galvanized all
together, but that would open the door to a lot of carpentry and
painting work for new siding (not to mention cost!).

I don't want to put anyone on the spot, but would you recommend to
just flash new galvanized steel over the old galvanized product?

"Jay Spenchian" wrote in message
om...
Thanks guys for your help. I've yet to relay this to the roofer, but
the question remains "what to do?". He claims that he has combined
the two before and has not had an incident in twenty years since he
originally did it. That case was a galvanized drip edge meeting
copper gutters.

His experience is probably valid for that particular arrangement. If yours is
similar and he looks like he will still be around in twenty years, then go for
it.

Galvanized over galvanized would be a no brainer. But, if you have your heart
set on the look of copper then he ought to be willing to humor you and do it up
with all the bells and whistles the way you want.

Regards,

John

"Jay Spenchian" wrote in message
om...
Thanks guys for your help. I've yet to relay this to the roofer, but
the question remains "what to do?". He claims that he has combined
the two before and has not had an incident in twenty years since he
originally did it. That case was a galvanized drip edge meeting
copper gutters.

His experience is probably valid for that particular arrangement. If yours is
similar and he looks like he will still be around in twenty years, then go for
it.

Galvanized over galvanized would be a no brainer. But, if you have your heart
set on the look of copper then he ought to be willing to humor you and do it up
with all the bells and whistles the way you want.

Regards,

John

(Jay Spenchian) wrote in message . com...
Hi-
For the past week or so, and as I speak, we have been reroofing our
25-year old Colonial. Much of the house is brick, however, some parts
do have cedar siding. In these areas there is a lot of
roof-meeting-the-siding going on, and they had been originally flashed
with galvanized steel. However, it is impossible to remove the
flashing without severely damaging the cedar siding. We had choosen
to use copper flashing on all parts of the house, and the roofer
thought he probably could just put new copper flashing, for the new
fiberglass roof, over the existing galvanized steel flashing, which
was for the existing shake roof and is incompatable with the new roof.

So my question is, is it safe to flash a different metal on top of an
existing one? We are worried about creating current or some unforseen
problem with what should be a fairly mundane thing.

I'd appreciate a really quick reply from anyone who has an experience
at all in this, as the roofing is being done as I write this.

Thank you.


Why not cover all the bases? Roofing felt is a more significant
barrier than painting. While it's true that the copper will not be
eroded by the galvanic action with the galvanize flashing; I would
recomend placing a layer of 15# roofing felt between the galvanized
flashing and the new copper. This will keep them separated and retard
any galvanic action.

Use copper nails or 304 stainless steel, galvanic action with the new
copper flashing will eat galvanized nails in a very short time.

Good Luck!

(Jay Spenchian) wrote in message . com...
Hi-
For the past week or so, and as I speak, we have been reroofing our
25-year old Colonial. Much of the house is brick, however, some parts
do have cedar siding. In these areas there is a lot of
roof-meeting-the-siding going on, and they had been originally flashed
with galvanized steel. However, it is impossible to remove the
flashing without severely damaging the cedar siding. We had choosen
to use copper flashing on all parts of the house, and the roofer
thought he probably could just put new copper flashing, for the new
fiberglass roof, over the existing galvanized steel flashing, which
was for the existing shake roof and is incompatable with the new roof.

So my question is, is it safe to flash a different metal on top of an
existing one? We are worried about creating current or some unforseen
problem with what should be a fairly mundane thing.

I'd appreciate a really quick reply from anyone who has an experience
at all in this, as the roofing is being done as I write this.

Thank you.


Why not cover all the bases? Roofing felt is a more significant
barrier than painting. While it's true that the copper will not be
eroded by the galvanic action with the galvanize flashing; I would
recomend placing a layer of 15# roofing felt between the galvanized
flashing and the new copper. This will keep them separated and retard
any galvanic action.

Use copper nails or 304 stainless steel, galvanic action with the new
copper flashing will eat galvanized nails in a very short time.

Good Luck!