a better insulated roof/attic is less prone to ice damn formation,



"Bob K 207" wrote in message
...
I think I understand the mechanics of ice dams. Up until recentely they
were
just an academic topic for me. I now own a home that is suglect to
occasional
ice dams. Two occurances in the last 5 winters.

The roof is metal (standing seam?), dams (so far) have only occured in two
places on the ~south facing roof slopes.


Question............is this a design problem, construction problem or so
they
just happen?

Is the solution something like Raychem heating cable?

Bob

I think I understand the mechanics of ice dams. Up until recentely they were
just an academic topic for me. I now own a home that is suglect to occasional
ice dams. Two occurances in the last 5 winters.

The roof is metal (standing seam?), dams (so far) have only occured in two
places on the ~south facing roof slopes.


Question............is this a design problem, construction problem or so they
just happen?

Is the solution something like Raychem heating cable?

Bob

On 06 Jan 2005 04:09:23 GMT, (Bob K 207) wrote:

I think I understand the mechanics of ice dams. Up until recentely they were
just an academic topic for me. I now own a home that is suglect to occasional
ice dams. Two occurances in the last 5 winters.

The roof is metal (standing seam?), dams (so far) have only occured in two
places on the ~south facing roof slopes.

Only being the south side implies you have good insulation, it might
be the sun over warming the upper parts of the roof sending down
melted snow.



Question............is this a design problem, construction problem or so they
just happen?

Not an expert here, but I wonder why it's blocking up at the bottom,
do you have a blocked up(dirty) gutter?


Is the solution something like Raychem heating cable?


I think that is something you should think about over the summer since
gettin up on a wet/icy building could be unsafe.

Try this. Get some of the safest ice melt out there( I think it's
magnesium cloride), fill a sock with it, and tie it to a rope. Toss
it up to the roof. pull it down so it's right above the ice dam. The
ice will melt around the sock giving a path for the water and other
melting ice a path to the gutter. Might even unblock your potentially
frozen gutters.

Bob


Now that's what I would do...

Tom @ www.ChopURL.com

On 06 Jan 2005 04:09:23 GMT, (Bob K 207) wrote:

I think I understand the mechanics of ice dams. Up until recentely they were
just an academic topic for me. I now own a home that is suglect to occasional
ice dams. Two occurances in the last 5 winters.

The roof is metal (standing seam?), dams (so far) have only occured in two
places on the ~south facing roof slopes.


Question............is this a design problem, construction problem or so they
just happen?

Is the solution something like Raychem heating cable?

Bob

Ice dams are caused when snow on the roof melts and then refreezes
several times over.

There are many things that can cause them.

I refer to the roof over an attic, but same factors apply to cathedral
ceiling and other areas where there no attic, although the cures may
be different.

Inadequate attic insulation allows heat from the house to warm the
roof, melting the bottom layer of snow, which then refreezes when it
gets colder (usually overnight).

Inadequate attic ventilation can cause or contribute to the problem by
not removing any warm air that does make it to the attic. Ideal is to
have both soffit vents and ridge vents so a steady flow of cool air
flows under the roof deck, keeping it very cold so snow doesn't melt.
Sometimes otherwise adequate ventilation is blocked in some areas by
skylights, poor framing, misplaced insulation, etc.

Local heat sources, such as light fixtures, especially older ceiling
can lights that were not well sealed, can generate local warm zones
that cause ice dams.

Air leaks from heated space into the attic or roof area can also cause
local heating and melting. Again, light fixtures, wiring and plumbing
penetrations, and bath fans are common areas for air leaks. Likewise
bath fans that are vented into the attic rather than through to the
outside dump both warm air and moisture right where you don't want it.

Finally, under some weather conditions it is almost impossible to
prevent ice dams. If the roof warms up above freezing during the day
(maybe in sunny areas) and then drops below freezing at night, you are
going to get some ice formation. Periods of sleet or freezing rain
also can lead to dams. That's why current best practice (and most
codes) require ice and water membrane near the edges of the roof under
the shingles (metal roof in your case) so that even when dams occur,
the water doesn't work through the roof and cause damage.

Heat cables can prevent the problem by preventing any buildup of snow
in the first place, but they are really a poor substitute for fixing
the actual problem. And they can be quite expensive to operate. They
are really only effective if you have them turned on before it starts
snowing...they don't generate enough heat to melt big loads of ice and
snow after the fact.

HTH,

Paul Franklin

Ice dams occur when heat rises th rough the roof. This melts the bottom of
the snow. The water runs off the roof, and then refreezes when it reaches th
e (unheated) eave.

The solution is more insulaltion under the roof, and also ventilation
between the roof and the insullation.

Icicles mean that you are losing heat through the roof. My parents house had
this problem for many years. I remember my Dad up on a ladder with an ice
pick many years. Blown cellulose, and a couple of eaves vents solved the
problem.

--

Christopher A. Young
This space intentionally left blank
www.lds.org
www.mormons.com


"Bob K 207" wrote in message
...
I think I understand the mechanics of ice dams. Up until recentely they
were
just an academic topic for me. I now own a home that is suglect to
occasional
ice dams. Two occurances in the last 5 winters.

The roof is metal (standing seam?), dams (so far) have only occured in two
places on the ~south facing roof slopes.


Question............is this a design problem, construction problem or so
they
just happen?

Is the solution something like Raychem heating cable?

Bob

There's been several good notes on ice damming causes and solutions so far.
I'll just relate my experience which will probably just reiterate points
already made.

My roof problems occured in three places:

In cathedral cieling above recessed light fixtures

At junction between two sections of my house - one being the cathedral
cieling section, the other being an attic type roof (truss).

Near same junction where furnace chimney comes out.

Solutions:

Placed roof vents directly over recessed lights. Surprisingly cheap and
easy, totally effective in eliminating melting at those spots.

Add ridge vent to attic-roof portion of house. Made this a truely "cold
roof" without any melting except around chimney.

This has solved my problems completely, for over 5 years now. I still get
melting around the chimney, but it doesn't cause damming problems, yet. If
it does.... The roofing guy told me (as others have said) that there are
certain places and/or times that melting is just impossible to prevent.
Nowadays, well designed houses of course try to eliminate these areas, but
they can also use a material to provide a waterproof layer between the
roofing and the sub-roofing. Can't remember what it's called. Of course,
retrofitting would be a "project" on my house (asphalt shingles), but I'll
do it if needed and/or when I need to re-roof. We did a small section this
way at our previous house and it was not a huge deal with a metal roof
(which you can remove without destroying it).

Good luck

Paul Franklin wrote:

.... al lot of good stuff other than...
Heat cables can prevent the problem by preventing any buildup of snow
in the first place, but they are really a poor substitute for fixing
the actual problem. And they can be quite expensive to operate. They
are really only effective if you have them turned on before it starts
snowing...they don't generate enough heat to melt big loads of ice and
snow after the fact.

I beg to differ with where that last statement is going. Heat cables are NOT
intended to melt your roof clean, even if they are up before the storm. What
they do is prevent a total dam build up by keeping open drainage channels.

I had some success with putting heat cables up "after the fact over the past
fiew years.. It was a truely miserable experience, (well I did it several
times, and got it down to an art) but once they were up, they melted channels in
the ice, and drained out any subsequent backup.

Once installed, you should only power them when you need them. You can get
temperature sensitive controllers too.

Dave.

"Marina" wrote Thanks for the info,Dave. I'll put up
the cables in the spring for next
winter.
Last winter the south side of the house had thick ice dam across the whole
length of the roof. The ice was even over the edge of the gutters.
I went to the hardware store and bought a hose attachment for the kitchen
faucet. I hooked up garden hose and spent the day spraying water on the
ice to create channels & dragging the hose back inside and back out again.

It was a pain, but I had success with the project. I don't think this
will
work if anyone has a 2 story house cuz the water cooled off really fast.
I must have gone thru 20 tanks of hot water doing it.
Marina

marina and others: next time go to your local rental store and rent a
steamer. This is a device that you hook a hose into and it pumps out hot
water. Looks kind of like a pressure washer, but puts out hot water instead
of pressurized water. This is the tool for dealing with ice dams.

Cam