How To Prevent Ice Dams



Ice dam inspections, thats a good one. Clear, to the point and timely, and applicable to Montreal now too.

One caution though, there are situations where the venting air flow can be out of balance and too high a velocity at the soffits can suck in falling snow.

In the high open volume spaces of the attic this snow falls out as the air slows down resulting in a patch of snow on top of the insulation deep inside the attic.

This snow will eventually melt and cause problems. As inspectors we have to be aware of this possibility and recognize the residual effects of this damage, even when we see attics zones in the summer months.



Hi Reuben,

It’s not so much a case of too much soffit venting but situations where high speed air movement is induced.

This most often occurs where there is high vertical rise between the intake vents (soffits) and the exhausts (here that’s usually ‘Maxi’ vents). The cause can be too many Maxis on the ridge line.

One place had 4 where one would have been sufficient. Some re-roofers think they are doing a good thing and put in too much without doing the math ratio calculations.

The first place I saw this problem had only one Maxi, but it had been converted from the original ceramic tile to an asphalt shingled roof. (Classic ceramic tile roofs are sieves. They are open to the wind, tiles on furring or purlins, no need to vent them.) When I opened that attic hatch, my hair stood on end, not from fright but from  the blast of air going up to that attic. This was stack effect in a 4 story building.

When the hatch is closed the pull from the Maxi at the peak drew air from 4 vents below dormer windows at floor level of the apartment below. The air was sucked up the rafter bays at high velocity because they were slim spaces filled 80% with insulation. This air carried snow with it and as soon as it hit the open volume of the attic above the ceiling it fell out. in other words it snowed.

The snow accumulated in small 2 or 3 square foot patches by the rafter bays and when it melted the water ran back down the bottom edges of the rafters to soak into the walls. (I had been called in to inspect and consult on the visible mold growing in the wall and ceiling corners.)

Other places where I’ve seen snow in attics are where garage (or one story wing) roofs attach to and are continuous with main higher attic space of the house. Again stack effect and big volume changes between the lower and upper vent positions are the common factors.

I hope that gives you a better picture of the sequence for attic snow.


We’ve received over 34″ of snow in Minnesota in the last 25 days, which makes this the snowiest December on record.  While the snow turns our state in to a beautiful white winter wonderland, it also causes nasty ice dams that wreak havoc on homes like never before.


The heavy amount of snowfall and temperatures in the teens have been the perfect conditions to create ice dams.  Water leakage from ice dams is an epidemic in Minnesota right now.  I have friends, neighbors, and family members with water leaking in to their homes.  It’s everywhere.  I’ve taken all of the photos below within the last two weeks.

Water in wall

Ice Dam

Ice on wall

Wet Insulation

Damaged Ceiling

Water at ceiling

The two things that everyone wants to know is how to get rid of ice dams and how to prevent ice dams.  As I mentioned in a previous blog, the only completely safe and effective way to get rid of ice dams is to hire a professional ice dam removal company; they’ll use steam, which will completely remove the ice dam.  Anything else is a hack method.

The best way to prevent ice dams from forming is to address the three factors in your attic that contribute to ice dams; insulation, ventilation, and attic bypasses.

Attic Bypasses (air leakage)

This is the largest contributor to ice dams.  In almost every house that I inspect to determine the cause of ice dams, I find attic bypasses directly below the beginnings of the ice dams.  Attic bypasses are passageways for warmed air to enter in to the attic space, and traditional insulation won’t fix this.  The photos below show some common attic bypasses that I can find in just about any older house.

This first photo shows one of the largest and most common bypasses – the space around the furnace and / or water heater vent.  Sometimes these are huge. The one shown below is quite small.

Bypass at furnace vent

In the photo below, you can see several holes in the top plate of a wall that were drilled for wires to pass through.  These holes could all be easily filled with spray foam, but finding these holes all over the attic would be a challenge without first removing the insulation.

Bypasses at bore holes

With additions, the transitions between the ‘new’ and ‘old’ construction seem to always be sources of attic bypasses.  I had to dig through a lot of insulation to find this gap, but I wasn’t surprised at what I found.

Bypass at addition

When plumbing vents enter in to the attic, the space around the vents needs to be sealed.  This one obviously wasn’t.

Bypass at plumbing vent

Some older houses have whole-house fans that are designed to run on hot summer nights; these fans are gigantic sources of heat loss, because they’re usually not insulated or sealed up.  I took the photo below from inside the attic without a flash on my camera.  There’s some crazy heat loss occurring there, and as you might imagine, there was a huge ice dam nearby.

Bypass at attic fan
What makes most of these attic bypasses so difficult to locate is that they’re almost always buried in insulation.  Finding these buried air leaks turns in to an educated guessing game.  Lately I’ve been using an infrared camera while doing ice dam inspections, and I’ve found it to be very useful for finding these hidden passageways.

If you plan to have more insulation added to your attic, it’s probably a worthwhile investment to have all of the existing insulation completely removed and the bypasses sealed up before you re-insulate.  There’s just no way to find all the bypasses if you don’t do this.  If your home is over 20 years old, it’s almost a guarantee that you’ll have attic bypasses that need to be sealed.  It’s a shame that so many insulation contractors just add insulation on top of what’s already there without sealing the bypasses.

I also practice what I preach; I’m such a firm believer in removing insulation and sealing bypasses before re-insulating that I did this at my own house, my parents had this done at their house, and my sister had this done at her house.  It makes a big difference.


This is a basic concept that everyone understands; you need insulation in your attic.  If there are voids in the insulation, they need to be fixed.

My first choice would be to have about two inches of closed-cell foam insulation applied to the attic floor, and then have several inches of cellulose installed on top of that.  The closed cell foam would seal up every bypass, and the cellulose would be a cost effective way to get the insulation level up to current requirements.  The drawback with this method is cost; closed cell foam ain’t cheap.

My next choice of insulation would be all cellulose insulation, with all of the bypasses sealed first.  I prefer cellulose to loose-fill fiberglass because it has a higher insulating value per inch, it seems to do a better job of stopping air leakage, and it’s not itchy fiberglass.  I’ve been digging through a lot of fiberglass covered attics lately, and my arms start getting itchy just thinking about it.

My last choice of insulation would be loose-fill fiberglass insulation… not that there’s anything wrong with it.  I personally just don’t like dealing with fiberglass.

What about fiberglass batts?  You know, those big rolls of fiberglass?  No way, Jose.  That stuff is impossible to install properly.  Fiberglass batts leave gaps all over the place that add up to an exponential level of heat loss.  I’m pretty sure that fiberglass batts are installed in attics exclusively by handy homeowners.


Having adequate ventilation for the attic space will help to keep the roof surface cold, which will help to prevent snow from melting, which will help to prevent ice dams.  The best way to ventilate an attic space is with continuous soffit vents and continuous ridge vents, but this isn’t always possible.

Reuben inspecting ice dams

If you don’t have enough soffit vents, add more.  If you don’t have enough roof vents, add more.  You can’t have too much ventilation.  If your soffit vents are dirty, clean ’em or replace the grills if they’re painted shut.  Grills are cheap.  If your soffit vents are blocked with insulation, you need air chutes installed at the eaves to prevent the insulation from blocking the vents.

When all else fails…

If you’ve already done everything you can think of to fix your ice dams but they keep coming back, or you’ve hired a contractor to fix your ice dams but they seem to be scratching their head a lot or coming up with a bunch of different guesses, call a home inspector.  We look at this stuff every day, and some of us even specialize in ice dam inspections.

In some cases, it’s not cost effective to control ice dams from inside.  Next week I’ll be blogging about controlling ice dams from the exterior.


Reuben Saltzman, Structure Tech Home Inspections – EmailMinneapolis Home Inspections

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Original blog post on ActiveRain: Link to Blog Post

Could you live in a house smaller than a large closet?

Most of us would have to get used to it, but it is doable. A student that hasn’t accumulated material things would fit more readily. The rest of us would have to do a lot more that de-clutter. More like divesting of material possessions.

The Tumbleweed homes are well done. There is an elegance in such efficient design and we see parallels in motor homes, boats and vacation homes. Pioneer log and sod homesteading structures are also scale related precedents.

Houses are sheltering structures that fundamentally provide a dry place to sleep and the means to heat (or cool) it. Then a room is added to store, cook and serve food. Then a room for bathing and plumbing… a room for entertaining…a room for granny…a room for baby…   …   …   …   …   …a home office…a home theatre…

It’ll never actually stop. We naturally like the convenience of…everything under one roof. When there is the means (usually finances) the trend is to larger and larger (or multiples and more complexity.)

That inertia like tendency will continue till countervailing trends introduce change. One of those will be the ‘green building ‘ awareness and rising cost of planetary ecological limitations.

In that light Tumbleweed homes are right on trend. Realtors used to describe smaller homes as ‘starter homes’ and while that will always be apt, it would also be wise to market them as ‘retirement / aging in place’ homes.

Any modest, easy to maintain home, especially those adapted or easily adaptable for handicapped access, will always have a solid market resale value no matter what’s happening in the finance markets.


In the past, we’ve looked at the largest house in the world. What about the smallest?  How about eighty-nine square feet? It’s not a rambling ranch for a family of five, but it is the home of Jay Shafer, an artist builder, who since childhood has dreamed of building this small house. And so he built the home he calls, “Tumbleweed” in Sebastol, CA. You can even take a tour of his wee-sized abode on YouTube.

Shafer also owns the Tumbleweed Tiny House Company. Since making his first tiny home he received a lot of interest from others and decided to start the company to design more XS homes and sell the plans. Interested individuals can schedule group or private tours of his home to learn more. The smallest home he offers in his catalog is actually smaller than his home, at just 65 square feet. So to be exact, THAT would be the world’s smallest home. It’s called the XS-House. Shafer, built his own XS-House and lived in it for one year before selling it to John Friedman and Kristin Shepherd.

Now I gotta say, while I love the idea of these homes and their green benefits, I get a little claustrophobic just looking at the tour video–so I’m not sure they are exactly a good fit for me. But they do look really cute and very cozy. Here are pictures of two other tiny homes in the Tumblweed catalog. Do you think you could live in one of these homes?

Loring Tumbleweed Small Home

Whidbey Tumblweed Small House

Posted By: Chrissy Doremus, U.S. Inspect Blog


Original blog post on ActiveRain: Link to Blog Post

Don’t Ruin Your Furnace


In short; cracked heat exchangers kill furnaces. They are too expensive to replace. You just replace the whole furnace. Clogged air filters reduce air flow causing furnace heat exchangers to over heat and crack. So changing air filters maintains the heat exchangers and the whole furnace system. Great article Reuben.



When I think of homeowner maintenance, the first thing I think of is changing the furnace filter. Most homeowners know about this regular chore, and at least one out of five homeowners is diligent about doing this.  As for the rest of you…

Do you really know why you’re supposed to change your furnace filter?  Hopefully your dad, your real estate agent, or your home inspector told you about doing this regularly.  There are a couple obvious reasons to change your furnace filter – your heating or cooling system will run more efficiently and the air in the ducts will hopefully be cleaner, but those aren’t the most important reasons for changing your furnace filter.

The most important reason for changing your furnace filter is to preserve the life of your furnace.

Dirty furnace filter

To make it very simple, your furnace works by passing relatively cool household air over a big hunk of metal, which is called your heat exchanger.  As the cool air passes over the heat exchanger, it gets warmed, which dissipates heat from the heat exchanger.  This warm air gets distributed throughout the entire home, and this is what keeps the indoor air temperature at 70 degrees when it’s -10 degrees outside.  That heat exchanger is responsible for transferring a lot of heat to the rest of the house.

Now think about what would happen to that heat exchanger if it couldn’t transfer it’s heat to the rest of the house:  it would get extremely hot, much hotter than it was ever supposed to get, and it would probably fail (i.e. –crack) prematurely.

When you operate your furnace with a dirty filter, this is what you’re doing to your furnace.  You’re preventing the cool household air from passing over the heat exchanger, heat doesn’t get dissipated the way that it should, and the life of your furnace gets reduced… besides costing you more money in heating bills.

In other words, don’t forget to change your furnace filter.  It’s not just about indoor air quality.

Reuben Saltzman, Structure Tech Home Inspections – EmailMinneapolis Home Inspections

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Original blog post on ActiveRain: Link to Blog Post