Hello, I live in Philadelphia and had some problems with ice dams in
the back (north) side of my house after a big storm last winter. I
have a split-level home with a pretty simple "A" roof (no valleys or
dormer windows).

I had a new roof installed in the spring and had the entire roof
surface covered with ice and water shield (I know that ice/water shield
won't prevent dams from forming, but hope that it will minimize or
prevent any leaking to occur inside the house in the event dams do
form).

I also had the roofer extend the eaves in the back of my house out to
about 1 foot, allowing for a continuous soffit vent to be installed
underneath the eave. A gable vent and two cap vents were previously
installed in the roof as well.

Finally, I am having my existing attic insulation upgraded (not much
there right now at all).

Should these measures be sufficient in order to prevent damage from ice
dams in the future, or are there other things that I should be doing as
well?

Make sure that there is a path for the air to follow between the ridge
and soffit vents. The soffit vents don't do any good if they're
blocked by insulation. As you add insulation, staple some of the
styrofoam vents along the roof near the edge of your attic to keep the
insulation from closing off the space entirely.

Thanks...the insulation contractor said he will use baffles to make
sure the soffit vents stay clear.

Interestingly enough, another contractor said that soffit vents were
not necessary in this area and would have covered them with insulation.

wrote:
Thanks...the insulation contractor said he will use baffles to make
sure the soffit vents stay clear.

Interestingly enough, another contractor said that soffit vents were
not necessary in this area and would have covered them with
insulation.

I'm glad you did not choose the other contractor. :-)

You should be free of the problem except for some very unusual
situations.

--
Joseph Meehan

Dia duit

irman wrote:
On 5 Dec 2005 12:41:48 -0800, wrote:

Hello, I live in Philadelphia and had some problems with ice dams in
the back (north) side of my house after a big storm last winter. I
have a split-level home with a pretty simple "A" roof (no valleys or
dormer windows).

I had a new roof installed in the spring and had the entire roof
surface covered with ice and water shield (I know that ice/water shield
won't prevent dams from forming, but hope that it will minimize or
prevent any leaking to occur inside the house in the event dams do
form).

I also had the roofer extend the eaves in the back of my house out to
about 1 foot, allowing for a continuous soffit vent to be installed
underneath the eave. A gable vent and two cap vents were previously
installed in the roof as well.

Finally, I am having my existing attic insulation upgraded (not much
there right now at all).

Should these measures be sufficient in order to prevent damage from ice
dams in the future, or are there other things that I should be doing as
well?

You can always fill an old tube sock or two with ice melt and throw them up on
the roof just above the ice dam.
This will punch holes through the dam and help prevent it moving up the roof.

You got that right. Tried it last year in a pinch and it saved me some
major damage.

writes:

Should these measures be sufficient in order to prevent damage from ice
dams in the future, or are there other things that I should be doing as
well?

Ice dams are like floods. Eventually a year will come along when the snow
is so thick, you will have them; better construction just raises that
thickness.

According to Richard J Kinch :
writes:

Should these measures be sufficient in order to prevent damage from ice
dams in the future, or are there other things that I should be doing as
well?

Ice dams are like floods. Eventually a year will come along when the snow
is so thick, you will have them; better construction just raises that
thickness.

On the contrary. Ice dams have _nothing_ to do with snow thickness, and
indeed, most ice dams occur with less snow rather than more.

If the eaves/attic is cold like it's supposed to be, you don't get ice dams.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

Chris Lewis writes:

On the contrary. Ice dams have _nothing_ to do with snow thickness,
and indeed, most ice dams occur with less snow rather than more.

If the eaves/attic is cold like it's supposed to be, you don't get ice
dams.

Nonsense.

The interior of the structure is above freezing, and assuming the
outside is below freezing, then somewhere in or around the structure, is
a boundary line between the two regions. Call this the freeze-thaw
boundary.

Whenever the freeze-thaw boundary moves out to the snow on the roof, you
get melting on the roof. Anywhere the melt runoff crosses the boundary
again, such as at an eave, refreezing will occur, and a dam will form.

Snow thickness definitely affects ice dam formation, because it affects
the motion of the freeze-thaw boundary, by virtue of its action as a
very effective insulator.

Do not confuse temperature with heat. Sub-freezing snow can very
effectively insulate heat that results in above-freezing temperatures.

No passive construction can avoid ice dams. Certain conditions will
always cause them. People are confused about this, because (1) they
don't know thermodynamics, (2) it depends on the weather pattern and
this varies, and (3) it depends on the type of construction which also
varies. Bad construction makes for bad ice dams, but that doesn't mean
the best construction can always avoid them.

Your error is in assuming the attic is always "cold like it's supposed
to be". Attics may be prematurely warm from poor insulation, but
eventually they all get warm from exterior heat. Eventually the weather
turns warm, and the freeze-thaw boundary moves out of the house and up
to the roof. When and how often this happens depends on the weather and
the quality of construction, but it does inevitably happen.

The only guarantee against ice dams is active removal, by heating or
mechanically or even chemically, which are all expensive and/or
impractical.

If you think ice dam control is simply a matter of proper construction,
then consider the Space Shuttle. $Billions and lives lost to a similar
type of ice formation, despite the concerted effort of the best minds to
avoid it.

According to Richard J Kinch :
Chris Lewis writes:

On the contrary. Ice dams have _nothing_ to do with snow thickness,
and indeed, most ice dams occur with less snow rather than more.

If the eaves/attic is cold like it's supposed to be, you don't get ice
dams.

Nonsense.

The interior of the structure is above freezing, and assuming the
outside is below freezing, then somewhere in or around the structure, is
a boundary line between the two regions. Call this the freeze-thaw
boundary.

Whenever the freeze-thaw boundary moves out to the snow on the roof, you
get melting on the roof. Anywhere the melt runoff crosses the boundary
again, such as at an eave, refreezing will occur, and a dam will form.

Right. But, that's only if the freeze-thaw boundary _ever_ gets on the
roof.

On a properly ventilated roof, it never does (except during overall thaw) -
the attic is just as cold as the outside.

When it gets warm outside, if the roof has a uniform coverage and has
relatively uniform temperature across the whole thing (which is what
proper venting _does_), the eaves warm up slightly before the rest,
and the snow cover erodes from the perimeter in. More to the point,
proper venting ensures that the eaves are never colder than the outside
or the attic proper. Which means you don't get ice dams.

Certainly, there can be very unusual weather conditions that might trigger
some ice dam formation (rapid temperature excursions). But, with our house,
for example, we get uniform coverage up to 3 feet of snow by winter's end,
without a hint of ice damming or icicles throughout the whole time, including
throughout spring thaw.

Properly constructed/ventilated, the only time people around here consider
snow removal is if the overall weight gets too high (our codes specify 70 PSF
snow load).

If you think ice dam control is simply a matter of proper construction,
then consider the Space Shuttle. $Billions and lives lost to a similar
type of ice formation, despite the concerted effort of the best minds to
avoid it.

That's a rather different situation - we're not dealing with liquified
gases venting at absurdly low temperatures into very humid climate.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

Chris Lewis writes:

On a properly ventilated roof, it never does (except during overall
thaw) - the attic is just as cold as the outside.

A perfectly vented and insulated attic would still make ice dams under
certain conditions. The roof can thaw while the eaves freeze, for reasons
other than heat loss from the house.

According to Richard J Kinch :
Chris Lewis writes:

On a properly ventilated roof, it never does (except during overall
thaw) - the attic is just as cold as the outside.

A perfectly vented and insulated attic would still make ice dams under
certain conditions. The roof can thaw while the eaves freeze, for reasons
other than heat loss from the house.

During a rapid temperature drop (above to below freezing), there can be
a short period where water that's already melted off the main roof and
slowly flowing out will get caught by a quickly freezing bare eave. But
that's pretty short duration.

Remember, (assuming proper ventilation) while the roof & eaves are
snow-covered they can't go above freezing until the snow cover comes
off.

On a properly ventilated roof, the melting starts at the roof edges
and progresses inwards, hence, the eaves clear first.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

Chris Lewis writes:

Remember, (assuming proper ventilation) while the roof & eaves are
snow-covered they can't go above freezing until the snow cover comes
off.

It melts wherever there is enough heat, whatever the temperature. Snow can
melt in a below-freezing ambient from heat from solar radiation. That's
one way you get ice dams on a perfectly insulated structure.

It all has to do with that 32 deg F isotherm envelope I mentioned. You can
never guarantee it will enter and exit the house uniformly, and then you
will have a potential melt/refreeze situation.

According to Richard J Kinch :
Chris Lewis writes:

Remember, (assuming proper ventilation) while the roof & eaves are
snow-covered they can't go above freezing until the snow cover comes
off.

It melts wherever there is enough heat, whatever the temperature. Snow can
melt in a below-freezing ambient from heat from solar radiation. That's
one way you get ice dams on a perfectly insulated structure.

That tends to sublimate (solid - vapor) rather than melt, and with an even
snow cover, the melt water tends to stay where it is (ie: uniform ice buildup).

It all has to do with that 32 deg F isotherm envelope I mentioned. You can
never guarantee it will enter and exit the house uniformly, and then you
will have a potential melt/refreeze situation.

In practise, however, a properly ventilated roof will almost never build
up enough of ice on the perimeter to do anything bad. Even in the worst
conditions, our roof has never build up anything noticable, meanwhile,
buildings with poor ventilation build absolutely amazing ice dams
and icicle formations.

[The only time we've ever had icicles is when the ceiling vapor barrier got
badly damaged in two places in the detached garage. Major ice
buildup in the adjacent eaves. Went away when I fixed the plastic.]
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

In article , Chris Lewis says...

According to Richard J Kinch :
Chris Lewis writes:

On a properly ventilated roof, it never does (except during overall
thaw) - the attic is just as cold as the outside.

A perfectly vented and insulated attic would still make ice dams under
certain conditions. The roof can thaw while the eaves freeze, for reasons
other than heat loss from the house.

During a rapid temperature drop (above to below freezing), there can be
a short period where water that's already melted off the main roof and
slowly flowing out will get caught by a quickly freezing bare eave. But
that's pretty short duration.


In the latter part of the winter here in the northeast that can happen every 24
hours, though. Which is when we (not me so far in 11 years, thank all dieties)
get ice dams.

Banty

wrote:
irman wrote:
On 5 Dec 2005 12:41:48 -0800, wrote:

Hello, I live in Philadelphia and had some problems with ice dams in
the back (north) side of my house after a big storm last winter. I
have a split-level home with a pretty simple "A" roof (no valleys or
dormer windows).

I had a new roof installed in the spring and had the entire roof
surface covered with ice and water shield (I know that ice/water shield
won't prevent dams from forming, but hope that it will minimize or
prevent any leaking to occur inside the house in the event dams do
form).

I also had the roofer extend the eaves in the back of my house out to
about 1 foot, allowing for a continuous soffit vent to be installed
underneath the eave. A gable vent and two cap vents were previously
installed in the roof as well.

Finally, I am having my existing attic insulation upgraded (not much
there right now at all).

Should these measures be sufficient in order to prevent damage from ice
dams in the future, or are there other things that I should be doing as
well?

You can always fill an old tube sock or two with ice melt and throw them up on
the roof just above the ice dam.
This will punch holes through the dam and help prevent it moving up the roof.

You got that right. Tried it last year in a pinch and it saved me some
major damage.


Thanks for the helpful responses. Here's another question...if I
remove most of the snow from the eaves (as far up as I can reach) with
a roof rake or other similar device, will that help alleviate the
potential for ice dams to form?

wrote:
irman wrote:
On 5 Dec 2005 12:41:48 -0800, wrote:

Hello, I live in Philadelphia and had some problems with ice dams in
the back (north) side of my house after a big storm last winter. I
have a split-level home with a pretty simple "A" roof (no valleys or
dormer windows).

I had a new roof installed in the spring and had the entire roof
surface covered with ice and water shield (I know that ice/water shield
won't prevent dams from forming, but hope that it will minimize or
prevent any leaking to occur inside the house in the event dams do
form).

I also had the roofer extend the eaves in the back of my house out to
about 1 foot, allowing for a continuous soffit vent to be installed
underneath the eave. A gable vent and two cap vents were previously
installed in the roof as well.

Finally, I am having my existing attic insulation upgraded (not much
there right now at all).

Should these measures be sufficient in order to prevent damage from ice
dams in the future, or are there other things that I should be doing as
well?

You can always fill an old tube sock or two with ice melt and throw them up on
the roof just above the ice dam.
This will punch holes through the dam and help prevent it moving up the roof.

You got that right. Tried it last year in a pinch and it saved me some
major damage.


Thanks for the helpful responses. Here's another question...if I
remove most of the snow from the eaves (as far up as I can reach) with
a roof rake or other similar device, will that help alleviate the
potential for ice dams to form?

Rescate wrote:
wrote in
oups.com:


wrote:
irman wrote:
On 5 Dec 2005 12:41:48 -0800, wrote:

Hello, I live in Philadelphia and had some problems with ice dams
in the back (north) side of my house after a big storm last
winter. I have a split-level home with a pretty simple "A" roof
(no valleys or dormer windows).

I had a new roof installed in the spring and had the entire roof
surface covered with ice and water shield (I know that ice/water
shield won't prevent dams from forming, but hope that it will
minimize or prevent any leaking to occur inside the house in the
event dams do form).

I also had the roofer extend the eaves in the back of my house out
to about 1 foot, allowing for a continuous soffit vent to be
installed underneath the eave. A gable vent and two cap vents
were previously installed in the roof as well.

Finally, I am having my existing attic insulation upgraded (not
much there right now at all).

Should these measures be sufficient in order to prevent damage
from ice dams in the future, or are there other things that I
should be doing as well?

You can always fill an old tube sock or two with ice melt and throw
them up on the roof just above the ice dam.
This will punch holes through the dam and help prevent it moving up
the roof.

You got that right. Tried it last year in a pinch and it saved me
some major damage.


Thanks for the helpful responses. Here's another question...if I
remove most of the snow from the eaves (as far up as I can reach) with
a roof rake or other similar device, will that help alleviate the
potential for ice dams to form?



Yes, that's what I use.

Rescate wrote:
wrote in
oups.com:


wrote:
irman wrote:
On 5 Dec 2005 12:41:48 -0800, wrote:

Hello, I live in Philadelphia and had some problems with ice dams
in the back (north) side of my house after a big storm last
winter. I have a split-level home with a pretty simple "A" roof
(no valleys or dormer windows).

I had a new roof installed in the spring and had the entire roof
surface covered with ice and water shield (I know that ice/water
shield won't prevent dams from forming, but hope that it will
minimize or prevent any leaking to occur inside the house in the
event dams do form).

I also had the roofer extend the eaves in the back of my house out
to about 1 foot, allowing for a continuous soffit vent to be
installed underneath the eave. A gable vent and two cap vents
were previously installed in the roof as well.

Finally, I am having my existing attic insulation upgraded (not
much there right now at all).

Should these measures be sufficient in order to prevent damage
from ice dams in the future, or are there other things that I
should be doing as well?

You can always fill an old tube sock or two with ice melt and throw
them up on the roof just above the ice dam.
This will punch holes through the dam and help prevent it moving up
the roof.

You got that right. Tried it last year in a pinch and it saved me
some major damage.


Thanks for the helpful responses. Here's another question...if I
remove most of the snow from the eaves (as far up as I can reach) with
a roof rake or other similar device, will that help alleviate the
potential for ice dams to form?



Yes, that's what I use.

Chris Lewis wrote:
According to Richard J Kinch :
Chris Lewis writes:

Remember, (assuming proper ventilation) while the roof & eaves are
snow-covered they can't go above freezing until the snow cover comes
off.

It melts wherever there is enough heat, whatever the temperature. Snow can
melt in a below-freezing ambient from heat from solar radiation. That's
one way you get ice dams on a perfectly insulated structure.

That tends to sublimate (solid - vapor) rather than melt, and with an even
snow cover, the melt water tends to stay where it is (ie: uniform ice buildup).

It all has to do with that 32 deg F isotherm envelope I mentioned. You can
never guarantee it will enter and exit the house uniformly, and then you
will have a potential melt/refreeze situation.

In practise, however, a properly ventilated roof will almost never build
up enough of ice on the perimeter to do anything bad. Even in the worst
conditions, our roof has never build up anything noticable, meanwhile,
buildings with poor ventilation build absolutely amazing ice dams
and icicle formations.

[The only time we've ever had icicles is when the ceiling vapor barrier got
badly damaged in two places in the detached garage. Major ice
buildup in the adjacent eaves. Went away when I fixed the plastic.]
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.


Interesting discussion temperatures. If it snows a decent amount
(6" or so) and then the high tempartures over the next couple of days
are around 40 degrees, with lows in the mid 20s, are you more prone or
less prone to having ice dams forming? I'm wondering if it's a good or
bad thing to have some thawing during the day, when runoff is just
going to re-freeze overnight.