I live in Minnesota. I have a story and a half house (basically, two
bedrooms exist in the attic.). Every year I get nasty, nasty ice dams
and I am trying to get ahead of it now.
Here's my question:
The previous homeowner had insulated kneewall where the highest part
met the room walls. All the way to the top. There was NO AIR going up
over the insulation to escape out the three or four roof vents.
Completely sealed off.
No wonder my upstairs gets to be 100 degrees in the summer.
I ripped that out. I would like to cut in some soffit vents but I have
a tiny (5" overhang).
Are soffit vents going to do me any good?
What about a "Whole house fan" especially in the summer?
Did I do the right thing taking out the insulation batts at the top of
the kneewall connection so that air can move up to the vents?
Another thing that I thought of is my boiler (located in the center of
my home) puts out a huge amount of heat. It rises right through that
ceiling, right through the floor above, and right to the roof, where it
consequently melts a lot of snow.
Would I be doing the right thing by lining the ceiling in the boiler
room (it's a small room) with R 21 insulation, 1/2 sheetrock, followed
up by some 1" R-Board? My goal is to keep that heat downstairs and not
flying right to the roof every time the boiler runs.
any suggestions would be appreciated..
Insulating the boiler is a good idea. I would put gypsum board between
the insulation and the boiler for fire protection.
It sounds like there is inadequate insluation above the bedrooms, given
they are hot in summer and melt snow in the winter. I'm not sure
venting will solve your problems. The Building Science Corporation web
site has a section "venting on venting" which is useful.
thanks for the reply.
i had planned on R-21 between the joists in the boiler room (its a tiny
Over that with 1/2 sheetrock. (i am assuming you mean this when you say
Over that with 3/4 or 1 inch R board.
The insulation above the bedrooms seems sound. I peeked up there from
behind the kneewall and it looks sound. looks relatively new actually
or within 10-15 years old.
I did make some temporary "baffles" to channel air up to the roof vents
(there are three on one side of the house plus a gable vent at the top
of the attic.
I will check the builder site you recommended.
Your issue is a combination of insulation and venting. The ice dam is
caused by your attic air being warmer than the outside air in winter.
The warmer air melts the snow which runs toward your eaves which of
course are surrounded by outside air. The snow melt hits the colder
eave and freezes. In a short time this builds up and holds water back
behind it. As the typical shingled Minnesota roof is not designed to
hold water - the water leaks into the house.
Now, I don't know if you need more insulation or more venting - but the
goal is to keep the attic air the same temp as the outside air in the
well, i think the previous owner has placed some sort of membrane up
there because we do not get any leaks, thank goodness. but it is hard
on the roof and unsightly. Plus, no gutter system will stay up because
the glacier will take it down.
I have no soffits.
I do have vents in the gable (4 total) which vent the kneewall area
both sides, north and south. I also have 2 vents at the top of the
attic area. But the previous owner had plugged all the cavities which
would allow air to flow through to the top.
I removed each of those little plugs of insulation but the insulation
goes right to the roof deck in most cases.
First, as another poster pointed out, and you seem to have missed, it
is probably a very bad idea to leave 1"R-Board exposed above a boiler.
It is not fire resistant in the least, and as far as I know, is
flamable. Put up whatever insulation you want _first_ (R21 +
1"R-board), and then _cover_ it with the 1/2" sheetrock. Thus, no
exposed insulation above the boiler.
I also wonder in general about your whole idea here. Is your house too
hot in the winter? Then turn down the thermostat. Do you spend a lot on
heating (i.e., suspect too much heat escaping out the top)? Then
insulating the boiler room isn't going to help -- the heat will still
go out the top. That extra heat from the boiler has to go somewhere,
and the only place it can go is into your downlstairs. Or you could
send it directly outside. But then you would have a colder house, and
you'd have to burn even more to keep it the same temperature, at which
point you will be losing just as much out the top as before (in
additoin to burning more fuel).
So -- forget about the boiler. Instead try to keep the heat where you
want it -- inside the house, preferably in the rooms you use most
We have a similar setup in our house. One thing the original owner did
was to put a door on the stairs going to the bedrooms. We close this in
winter, and also adjust the heat vents, and can drop the temperature
upstairs by several degrees (by keeping the heat downstairs). This
saves fuel, and reduces the ice dams. Be careful of lowering the temp
too much (condensation, mold, etc., become a problem at some point).
It seem like adding vent to the attic could only help.l
I live in northern Minnesota. I have also lived down south. I assume
you are talking about an attic fan which exhaust the whole house.
Those are common in the south but I have never seen one in my 22 years
in Minnesota and I do not think they aer suited to a climate where we
heat our home 8 month of the year. It would likely contribute to any
ice dam problem since it creates a large opening in the ceiling for the
Hard to say. Less insulation in a wall could actually contribute to
It couldn't hurt but as others have said, use gypsum drywall for fire
protection. dont' leave insulation exposed to the boiler.
Many, many homes in minnesota have ice dams. They are pretty much the
rule in some older neighborhoods. My take on it is that it is a lot
easier to design and construct proper attic venting in a new
construction. It is quite a lot more difficult to do so in an older
home which may not have been properly designed for ventilation and
where previous remodels and upgrades may prevent you from doing so.
By all means do what you can to prevent the problem but don't be
surprised if you wind up in the same boat as many others, with ice
dams. My place has them. I actually gently remove the snow from my
roof after a storm. then when dams do form, I go up there with ice
melt and sprinkle above the ice. there are also ice melt bags that
folk place above the dam and it releases the chemical gradually. I
also understand that some use electric cable to melt the ice. Some
just ignore them but they can cause your roof to leak, damaging your
roof deck, attic insulation and in the worst case leak into the house.
It you can go into the attic to see if it is leaking, it might save
you some work. Ice dams are undesirable, for sure, but they are not
always easily fixable. Monitoring and Managing the situation on a
season by season basis is what you may be stuck with.
Preventing "ice dams" involves a lot of factors, for example here's
an interesting "case study":
It can be very difficult to prevent ice dams at roofs and soffits when
knee walls separate conditioned living and unconditioned attic spaces,
IMO one alternative to consider in such situations are correctly
installed "industrial" grade variable-resistance heating cables
extending into the gutters and down the downspouts, for example:
Done properly this not only addresses the "roof" related problems,
but also the secondary problems of ice-clogged gutters and downspouts.
These are not an inexpensive solutions - for starters they generally
require at least one dedicated electrical circuit to the roof area -
and they address the "symptoms", not the "causes", but OTOH
you know going into the project that if done properly it *will* solve
the problem, which is almost impossible to guarantee in advance for
(For the record, I have no connections of any kind with any of these
companies making such products).
Paragon Home Inspection, LLC
How old is your house? Are the attic rooms the result of remodeling or were
they part of the original plan? Typically, the easiest way to vent finished
attics is by running proper vents from soffit vents to a ridge vent. It's
surprising that this wasn't accounted for when the house was built
(depending, of course).
My Dad's house is over 100 years old. It has a partially finished attic,
with kneewalls containing bookshelves running the length of both sides.
Both sides also have an access door. Here's what I suggest for you, based
on what I did at my Dad's house.
Make sure the tops of the first-floor walls are covered by the attic
insulation. The tops of walls are a source of heat loss, even though the
contain insulation. Trust me on that. If you have no soffit vents, there
is no air from the soffits to worry about. Tuck that insulation back in
there, without crushing it too much, of course. Insulation works by way of
its thickness. Cover the floor area (or the area between joists) behind the
kneewalls with insulation. A second layer probably would help.
You'll want a way for cold air to get in, say gable vents or soffit vents.
My Dad's house has soffit vents, unlike yours, but it also has gable vents
(leading to the area behind the kneewalls) on both ends of the house, behind
both kneewalls. If you don't have those, you should fix that. Without some
form of gable or soffit vent, the heat from your house will pool behind
those kneewalls, with no source of cold air to replace it, and nowhere to go
but through the roof, which makes ice. Make sure that the vents are not
blocked by insulation. While it is important that the hot air has someplace
to go, it won't go very fast if there is no incoming air to replace it.
The heated air needs someplace to go, so there should be proper vents
running up over the kneewalls to a ridge vent. Make sure the tops of the
kneewalls are covered with insulation, and also insulate the kneewalls
themselves. If you have access doors or panels, glue pieces of rigid foam
insulation to them.
Since your attic is finished, those standard solutions may not be
financially viable options at this point. You won't get those proper vents
in place without serious surgery. You may want to look into a solution
involving those zigzagging heater cables or roof flashing. The roof
flashing has a bit of a dated look, but you'll hardly notice the heater
cables after a while.
The following link may help you as well.
The house was built in 1950.
The current rooms were always there I believe.
I do have gable vents at the end of each "kneewall" area, and one at
the very top of the attic.
This is what it looks like
x ------ x
x ____ x
xxxxxxxxxxxxxx x x
The area inside the triangle on the one side of the house is used for
Up the straight portion is insulated up to where the wall meets the
I pulled out the very top part so that air can rise to the roof vents
(there are three box vents on the very top.
What do you mean by "proper vents" running up over the kneewalls?
It seems cooler upstairs today after removing that insulation..
Here are some links with pictures that will make everything much more clear.
(Amazon.com product link shortened)
There's been a lot of research into ventilation in the last decade, the
upshot of which is that it appears that a lot of what "we all knew was
true" probably isn't.
For instance, take a look here:
If it's in fact that case that most attic ventilation in the above
scenario is cross-soffit, then the standard approach for venting past
knee-walls - allowing a space in the rafter cavities for airflow above
the insulation and assuming that convection is going to move the air
up from the soffit to the ridge - is probably a lot less effective than
we been taught to expect.
Paragon Home Inspection, LLC
"MDT at Paragon Home Inspections, LLC"
vents from soffit vents to a ridge vent.
That article is from 1993 - not that that means anything, necessarily. I've
personally seen proper insulation and ventilation make dramatic differences
in houses with ice problems.
Due to the design of his house, the OP doesn't have much choice in the
matter unless money is no object. Either he does what little he can, and
recoups some of the energy costs that will be increasing upon the placement
of the new heater cables, or he's on a ladder with a heat gun, an extension
cord, and a hammer come January 31.
To be clear, I'm certainly not trying to suggest that attic ventilation
does not make a difference, especially as regards moisture control.
Every home inspector sees numerous examples of veneration and moisture
control problems in attics, and there is no question that improved
ventilation can often help correct such problems.
Rather, my point was that you can't just assume that actual houses are
acting like the examples commonly depicted in of diagrams "attic
ventilation" under simple gable roofs, or that seemingly
"similar" systems act in "similar" ways.
For example, if you are depending on convection in rafter cavities to
move air from lower in the attic and up past knee walls to a ridge vent
in order to lower the temperature at the roof sheeting near the eaves
- a situation where you can't get the sort of cross-soffit
ventilation depicted the link in the post above - it's probably
especially important to pay attention to providing sufficient soffit
vent area, making sure every rafter cavity is vented, that you are
using one of the "engineered" ridge vents specifically designed to
assist in exhausting air when wind moves across it, and so on.
And, for example, to be aware that in some cases (ex: rafter cavities
obstructed by cripple jacks or below dormers):
you just can't ventilate the eaves via flow up to a ridge vent.
Homeowners not aware of such issuers are more likely to be frustrated
in their attempts to deal with problems such as ice dams.
Paragon Home Inspection, LLC
The OP doesn't have ridge vent or soffit vents. He just has a few He may or
may not find it beneficial to install a ridge vent, depending on the airflow
up through the rafter cavities. If there is no air getting to the ridge,
the ridge vent is worthless. The impression that I get, based on his
description, is that there is also a cavity above the attic rooms which is
vented by a gable vent and some roof pots. The question becomes one of
ventilating the lower cavities.
If there is no good way of getting the warm air to the vents up above, then
perhaps installing a couple of roof vents above the lower cavities would be
the best solution.
I have a solution for the ice dam problem. My solution does not remove
the ice dams, but it eliminates water accumulation above the dams, and
it prevents leaking due to the ice dams.
I am a Ph.D. in chemistry. I lived in Montreal, Canada for more than
10 years. I invented/found the solution when my house had ice dams.
The solution is simple and inexpensive. It does not use any
For a fee (~$100 USD ?), I can provide a kit and instructions on its
installation. You would need to install it on your roof.
Thanks and best regards.
<This is not a hoax. I am trying to solve people's problems and making
a living at the same time. Only truth stands the test of time.>
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