Reuben's Home Inspection Blog

Ice Dams

February 11th, 2014 | 26 comments

I’ve been seeing ice dams all over the Twin Cities, and I’ve heard from a number of homeowners who are having problems with ice dams right now.  I’ve written about ice dams extensively on this blog, so I’m putting together links to my three main blog posts on ice dams in one place.  The topics are how to prevent ice dams the right way, how to prevent ice dams from the outside if you can’t prevent them the right way, and how to get rid of ice dams.  I also have few more ice dam observations; file these under “advanced ice dam prevention”.

How To Prevent Ice Dams (the right way)

Ice dams form when snow is melted on the roof, then freezes again at the eaves.  The main reason the snow melts is because heat is getting to the roof decking from the house.  Stop the heat transfer, and you’ll probably stop the ice dams.  The main way to stop the heat transfer is to have air sealing performed in the attic.  The next step is to have insufficient insulation addressed.  Finally, if venting is improper, consider fixing it… but venting only plays a small role.  Ice dams are mostly about air leaks and insufficient insulation.  Click this link for more information about preventing ice dams the right way.

Anatomy of an ice dam

How To Prevent Ice Dams from the Exterior

Roof RakeIf you live in a 1-1/2 story home in Minnesota, you probably get ice dams.  There’s not much that can be done to prevent ice dams the right way at this style of house, short of gutting the upper level and framing down, or tearing the roof off and framing up.   Homes with vaulted ceilings and other inaccessible attic spaces can also be a real challenge.  In these cases, ice dams may need to be controlled from the exterior.  The standard way to do this is to get a roof rake and pull snow off the roof.  When this is not practical, roof de-icing cables can be used, but should be considered a last resort.  Click this link for more information about preventing ice dams from the exterior.

How To Remove Ice Dams (hire a pro)

There are plenty of hack methods for removing ice dams, so I tried ‘em all out.  The methods I discuss involve an axe, ice pick, pantyhose, salt tablets, heat cables, a pressure washer, and even a blowtorch… just for fun.  I don’t recommend any of these though.  If ice dams need to be removed, hire a pro to steam them off.  Don’t let anyone near your roof with a pressure washer, or the shingles might end up like the ones shown below.

Hack Ice Dam Removal from pressure washer

Click this link for more information about how to remove ice dams.

A Few More Tips

Here are a few more tips on preventing ice dams.  These deal more with the design of a house than anything else.

Valleys Can’t Be Vented

Ventilation plays a small role when it comes to preventing ice dams, because vents can help to cool the roof temperature.  The problem with roof valleys is that they can’t be vented.  If I were to design my own house, it would certainly be a big boring box with a plain hip roof; no valleys.

Plain hip roof

Plain hip roof

Valleys Should Never Meet

Valleys can’t be vented, they have a lower slope than pitched roofs, and ice from two roof surfaces gets concentrated.  Ice dams are always the worst at valleys.  What happens when two valleys meet each other?  The potential for ice dams goes way up.  In my humble opinion, this is just plain stupid design when it comes to performance.

Valleys Meeting

Oh, and don’t get me started on what this means for water management during the summer… never mind, I already blogged about that: Have Your Builder Plan for Water Management.

Don’t vent fans through the roof

What happens when bath fans and kitchen fans terminate at the roof?  Snow melts when the fans run, of course.  This leads to water running down underneath the snow, then freezing again at the eave, or in some cases, right in the middle of the roof.

Bath fans at roof with ice dam

This can be a major contributor to ice dams, or in the case of the photo above, can be the sole cause of ice dams.  The way to avoid this is to have bath fans and kitchen fans terminate at walls, not roofs.  This also applies to clothes dryers; while it has become standard practice to put laundry rooms on the second floor in new construction homes and terminate the vent at the roof, I think this is a bad place to terminate the dryer duct.  It will melt a lot of snow, and there is usually no easy way to clean off the terminal.

Oh, and whatever you do, don’t place vent terminals for bath fans, kitchen fans, or clothes dryers in a place where the melted snow will pile up in a valley.  That’s almost a sure way to get ice dams, even if everything else is done properly.

Author: Reuben Saltzman, Structure Tech Home Inspections



Roof Vents: Problems and Solutions

December 24th, 2013 | 17 comments

Back when I first started doing home inspections, I was under the impression that roof ventilation was the cure-all for everything.  I would look at a lot of problems and quickly point to insufficient roof ventilation as the cause, and recommend more roof ventilation as the cure.

Blistered shingles?  Not enough roof ventilation.

Ice dams?  Not enough roof ventilation.

Frost in the attic?  Not enough roof ventilation.

Today I’m much more ho-hum on roof ventilation.  Take it or leave it.  Asphalt shingle manufacturers require roof ventilation to help preserve the life of the shingles, despite the fact that the color of shingles will have a greater effect on their life expectancy than roof ventilation will.  An attic with insufficient ventilation will get warmer than a well ventilated attic, which may increase the temperature of the shingles, which may decrease the life of the shingles… just a little.  Proper ventilation will also help to keep the attic space cooler during the winter, which may help to prevent ice dams.  Let me say that again; proper ventilation may help prevent ice dams.  I’m not saying it will, but it might.  The same thing goes for frost in the attic; as I mentioned last week in my post about frost in the attic, proper ventilation may reduce frost accumulation in attics, but it won’t prevent it.

In other words, roof ventilation certainly isn’t a cure for any condition, but it’s still required.  Roof vent manufacturers publish installation instructions that are easy to read and should be easy to follow, and roof ventilation is required in section R806 of the building code, but a lot of folks either don’t read the instructions or they don’t care.  Today I’m going to go over a few of the most common roof vent installation errors and issues.

Mixed Exhaust Vents

For proper ventilation, both high and low vents should be installed.  On paper, the high vents are supposed to act like exhaust vents while the low vents should act like intake vents.  Convection is supposed to help make this happen.  In reality, it all depends on how the wind blows, convection has little to no effect, and it’s never perfect.  The intake vents will typically be soffit vents, while the exhaust vents may consist of ridge vents, turbine vents, box vents, or powered vents… but only one of those.  The photo below shows an example of these different types of vents, all installed on the same roof, which is a no-no.

Four roof vents

When different types of roof vents are installed, there is an increased potential for air in the attic to basically short-circuit.  In the photo above, the power vent would probably end up sucking in air from all of the other high vents in the photo, while pulling in just a small amount of air from the lower soffit vents.  The solution here is to install only one type of exhaust vent.

Power Vents

Power vents shouldn’t be used because they create more problems than they fix.  I blogged about this earlier this year: Attic Fans Won’t Fix Ice Dams (or anything else).  I use the terms ‘attic fan’ and ‘powered roof vent’ interchangeably.  I also use the terms ‘roof vent’ and ‘attic vent’ interchangeably.

Crooked Turbine Vents

I’ve never been a huge fan of turbine vents because I have it in my head that they may end up causing some of the same problems that powered roof vents do, but the fine folks at Complete Building Solutions swear by ‘em, and I trust those guys, so I won’t complain about turbine vents.  The one thing I’ll mention is that turbine vents need to be installed perfectly level; when they’re not installed level, they don’t turn.  In the photo below, the vent on the left wasn’t level.  Do you see anything else that’s wrong in the photo?

Crooked Turbine Vent Small

The other thing about turbine vents is that they really do pull air out of the attic; if air sealing hasn’t been performed in the attic, they’ll pull air into the attic from inside the house, and shouldn’t be used.  That bears repeating: do not install turbine vents if the attic has not been professionally air-sealed.  

Insufficient intake vents

Current standards specify a 50/50 split between high vents and low vents, but how are low vents supposed to be installed in a house with no soffits?

No soffits

Without any low vents, the high vents will tend to pull conditioned house air into the attic through attic air leaks.  One solution would be to install fascia vents, and another less desirable option would be to install a bunch of box vents low down on the roof.  I could go on and on with these roof vent installation errors or shortcomings, but I never make a huge deal about any of this stuff because I don’t think it makes a ton of a difference.  As I mentioned at the end of last week’s blog post about frost in the attic, focus on sealing attic bypasses before addressing ventilation.  Ventilation mostly helps to hide other problems.

For more reading material on roof ventilation, check out the links below:

  • Green Building Advisor: All About Attic Ventilation – this article looks at all of the reasons that attic venting is required, and goes on to say they’re all ho-hum reasons.  I completely agree.
  • Building Science Corporation: Understanding Attic Ventilation – a discussion of vented vs. unvented attics.
  • Building Research Council-School of Architecture: Early History of Attic Ventilation – A long explanation of why our current rules for attic ventilation are arbitrary.  This is a fascinating read.

Author: Reuben Saltzman, Structure Tech Home Inspections


How to prevent ice dams from the exterior

March 4th, 2013 | 1 comment

I’ve written about how to prevent ice dams by fixing attic air leaks and insulation, as well as several hack methods showing how to remove ice dams, but I still get a lot of questions about ice dam prevention.  For homeowners with a one-and-one-half story house or a house with a vaulted ceiling and no true attic space, correcting attic air leaks and insulation can be an extremely expensive project.

In these cases, it’s not always cost effective to fix the problems that are causing the ice dams – the ‘repairs’ might outweigh the costs of controlling the ice dams, and even if the repairs make economic sense, it’s not always in the homeowner’s budget.  In those cases, I recommend ice dam control from the exterior.

Remove The Snow

Roof RakePulling snow off the roof with a roof rake will keep ice dams to a minimum. This becomes a constant chore, but it’s better than dealing with water leaking in to the house.  Just raking the first several feet of snow from the eaves is typically enough to prevent the formation of ice dams, but in some cases, this will cause ice dams to form higher up on the roof.  The trick is to get the shingles exposed to the sun; once that happens, the sun will warm the shingles enough to prevent ice from accumulating.

Raking snow off the roof with a roof rake is a safe way of removing snow, as long as you don’t get too close to your overhead power lines.  In theory, a roof rake could cause some premature wearing of shingles by removing the aggregate, but I’ve never seen any real life evidence of this.  Some roof rakes have little wheels at the bottom that prevent the rake head from actually rubbing on the shingles.

Roof Rake

While the roof rake pictured above is the most common type, there are many other variations of this designed to make the work easier – one such version is the MinnSnowta Roof Razor®.

Removing snow from the eaves is an effective way to prevent ice dams, but it won’t work 100% of the time.  Two years ago, I inspected several houses with ice dams forming right where the snow stopped being removed.  This is not typical, but it can happen during especially cold, snowy winters. When this happens, people start to get depressed and wonder why they live in Minnesota.

Second Ice Dam

The fix for this is to have all of the snow removed.

For two-story homes where using a roof rake from the ground isn’t practical or possible, the options are to risk your life getting up on an icy roof to shovel the snow off, hire someone else to risk their life, or install roof de-icing cables as a preventative measure.

Shoveling snow off roof

De-Icing Cables

Roof de-icing cables, also known as heat cables or heat tape, should be considered a last resort when it comes to preventing roof leaks from ice dams.  De-icing cables themselves aren’t cheap, it costs money to have them professionally installed, and they’ll cost money to operate – between five and eight watts per foot.  I’ve also heard that they can damage shingles, but I’ve never seen any evidence of this.

Roof De-Icing Cables

On the flip side, de-icing cables are very effective.  When de-icing cables are properly installed and operational, ice dams won’t cause leakage.   De-icing cables won’t prevent the formation of ice at the eaves, but they’ll keep enough ice melted to create drainage channels for water.

If you choose to install roof de-icing cables yourself, here are a few tips:

  • Measure the areas where you need to install your de-icing cables first, and buy appropriately sized cables.  For a simple 15′ section of roof with no overhang, a gutter, and one downspout with an extension, you will need a 60′ heating cable.
  • The cables should extend 6″ up the roof past the exterior wall line, through the gutters and downspouts, and 2/3 of the way up the valleys.
  • Don’t bother removing the snow from your roof; you could damage your cables, and you could potentially create another ice dam higher up on the roof, defeating the purpose of the heating cables.
  • Don’t expect the snow and ice to melt the way it does in the promotional photo above.  It’s like comparing a photo of a fast-food burger to the burger that actually comes in the fast-food bag.

If fixing the causes of ice dams isn’t a possibility and safe removal of snow isn’t possible, de-icing cables or de-icing panels may be a good choice.  Sometimes this is the most cost-effective way to prevent roof leakage from ice dams.

Author: Reuben Saltzman, Structure Tech Home Inspections  Google Profile


How To Remove Ice Dams

February 12th, 2013 | 18 comments

With the recent snow storm we received in Minnesota and the crazy snow storm that dumped several feet of snow on the east coast, there will be plenty of people dealing with leaking roofs from ice dams.  I have already blogged about how to prevent ice dams from happening, but I get far more inquiries about how to remove ice dams.   There are plenty of ‘hack’ methods of removing ice dams, so I decided to discuss them.  The methods I’m going to discuss involve an axe, ice pick, pantyhose, salt, heat cables, a pressure washer, and even a blowtorch… just for fun.

Let me repeat – these are all hack methods.  I don’t advise any of these methods, but when people have water leaking in to their home, these DIY methods are what people turn to.  Hopefully I can talk people out of doing most of these.  The most effective and safe way to remove an ice dam is to hire a professional ice dam removal company that will use steam.


The most obvious way to get rid of ice dams is to take a blunt instrument and hack away at the ice dams.  I tried an axe.


Pros: Fast results.  I hacked through several feet of six-inch thick ice dams in a matter of minutes.

Cons: Unsafe, cumbersome, and you’ll wreak your roof.   I had to set up a ladder on the icy ground and swing an axe while standing on a ladder.  The ice also really flew in my face – I should have been wearing goggles.  I was only able to remove the ice down to the gutter, and only able to get close to the surface of the roof without risking damage to the shingles.  I’ve inspected dozens of roofs where someone got crazy with an axe at the eaves.  It’s a great way to ruin your roof.

Verdict: This is a high risk, yet fast and effective way of getting rid of a lot of ice, but leaves the job incomplete.  You’ll probably damage your roof doing this, and you might hurt yourself too.

Ice Pick

This sounds like a natural choice, doesn’t it?  I actually used my awl, but close enough.  I gave it my all.  <insert crickets chirping>

Reuben's Awl

Pros: Very fast results, very little effort.  It’s as though this tool was made for picking at ice.  Oh, wait…  Still, I was genuinely surprised at how fast and accurate this method was.

Cons: Unsafe.  Again, I was jabbing at ice dams while standing on a ladder, which was sitting on the icy ground.  I also had to be very careful to not damage the roof.

Verdict:  This worked quite well… but again, you’ll probably poke a bunch of holes in your roof doing this.

Roof Tablets

Yes, this is a product designed specifically for preventing damage from ice dams.  Contrary to the name on the container, the product doesn’t actually melt your roof (whew).  The instructions say to toss the tablets on to your roof and they’ll melt through the ice dams, allowing for “water to drain safely”.

Roof Melt Tablet Container

Roof Melt Tablet Instructions

Roof Melt Tablets

I tried tossing the tablets on the roof like the instructions said to do, but it didn’t work out very well.  I consider my tablet tossing skills to be well above average, but I still couldn’t get the tablets to end up in a good location – they all just slid together in one place.  If I didn’t get a ladder out to take pictures, I never would have known that the tablets didn’t end up in a good spot.

Roof Melt Tablets Tossed

Just to give the roof melt tablets the best possible chance for success, I hand-placed them on the ice dam and I used about four times as much as the directions called for.  The instructions said to put them higher up on the roof, but I wanted to make some holes in this ice dam.

Roof Melt Tablets Placed Day 1

By day two, I had some pretty dramatic results – the tablets had melted all the way through the ice dam.  By the way, for anyone in a southern climate that might be reading this blog, that white stuff on the ice is snow, from a very light snowfall the night before.

Roof Melt Tablets Day 2

By the third day, not much change.  There were definite holes in the ice dam, and some channels had formed for water to drain through, but the majority of the ice was still there.

Roof Melt Tablets Day 3 #2 Roof Melt Tablets Day 3 #1

Pros: If you had perfect aim and tablets didn’t move after you tossed them on to the roof, this would be very safe.  Some channels were created for water to drain through, which might be enough to prevent leakage at your roof.

Cons: The tablets don’t stay where they land, which negates the whole safety thing.  I still had to set up a ladder on the icy ground and move the tablets around myself.  This method was also pretty ineffective – it created a bunch of holes in the ice dam, but so what?  Most of the ice dam was still there in the end.

Verdict: This might be a nice way to get down to the roof surface, and it might prevent leakage from ice dams if enough channels are created for water to drain through, but you’re still left with a huge ice dam.

Salt Filled Pantyhose 

Take off your pantyhose, fill ‘em up with calcium chloride or something similar, and toss ‘em on your roof perpendicular to the ice dams.  The idea is that the salt will leak through the pantyhose and create channels for the water to drain through, preventing water from leaking in to your house.

I filled one pantyhose leg with “Ice Melt”, which contained a blend of calcium chloride and rock salt.  I filled another with an ice melting salt that didn’t have the contents labeled – I suspect it was just rock salt.  I also poured the Ice Melt in a perpendicular line along the ice dam, using far less salt than I used in either of the pantyhose.  I did this just to compare the results.

10:00 AM (Start Time)

Salt Filled Pantyhose 10am Salt On Roof 10am

2:00 PM

Salt Filled Pantyhose 2pm Salt On Roof 2pm

4:00 PM

Salt Filled Pantyhose 4pm Salt On Roof 4pm

The pantyhose were a bit of a bust for me.  With salt alone being so effective, why bother with the pantyhose?  I’ve heard several opinions on this:

  • The pantyhose will contain the salt and prevent runoff.  The idea is apparently to leave the pantyhose there all winter.
  • The pantyhose can be ‘flung’ on to the roof with a rope – no need for a ladder.  After the work is done, you pull the pantyhose back down.
  • The pantyhose will gradually release the salt.
  • The pantyhose method works much faster if you start by pouring water on the pantyhose.  I didn’t try this myself.
  • When salt alone is used, it will wash out within a week and the ice channel will freeze over again.

Pros: If you fling the stockings on to your roof from the ground, it’s pretty safe.

Cons: This takes a long time.  After a week of near-zero temps, the pantyhose looked just the same.  They hadn’t even made a dent. I don’t think I would have the patience to do this if I had water leaking in to my house.  Also, this could lead to damaged gutters.

Verdict: Better than nothing.

Heat Cables

For the record, heat cables aren’t supposed to be placed directly on ice dams, but some people might try it anyway.  My friend did this at a house he owned in Saint Louis Park… so I took pictures.  These photos all show the heat cables after about one day.

Heat Cables #2

Heat Cables #3

Heat Cables #4

Heat Cables #6

Pros: Gets the job done eventually, I suppose.

Cons: Heat cables aren’t made for this, and I’m sure the manufacturer would tell you that this poses some type of safety hazard.  Stringing up the cable was also very unsafe.

Verdict: Don’t do this.  Seriously.


I received a request to use a blowtorch on an ice dam, so I tried it.  This video was taken about four years ago. Sorry for the poor audio.

Pros: You can tell your wife you tried everything, even a blowtorch.

Cons: Cold fingers, waste of propane, waste of time, dangerous, etc.

Verdict: I think you get the picture.

High-Temperature Pressure Washer

A pressure washer will certainly remove ice dams, but it will create a ridiculous ice mess below, and will surely damage the shingles.   This was one method that I didn’t even test.  The photo below shows what can happen to a roof after a pressure washer or high-temp pressure washer is used on a roof.

Pressure washer ice dam removal

There is a big difference between a steamer and high-temperature pressure washer.  In the video below, Steve Kuhl discusses the difference with me.


Ice dams are no fun. As I mentioned at the beginning of this blog, hiring a pro to steam the ice dams off is the only thing I recommend.

Oh, and one more piece of advice: if you know someone who has water leaking in to their house from ice dams, don’t tell them to “stop focusing on how to get rid of the ice dam, and spend your time fixing what caused it.”  It’s like telling someone with a gash in their finger to be more careful around knives.  “Great, thanks, now please pass the Band-Aids.”

Reuben Saltzman, Structure Tech Home Inspections


Poorly Insulated Eaves at Old Houses

January 22nd, 2013 | 6 comments

When we inspect houses, we frequently make recommendations for more insulation in the attic, but one challenging place to properly insulate on old houses is the eaves.

The edges of attics, referred to as the ‘eaves’, rarely have enough insulation on old houses.  The problem is that houses never used to be constructed in a way that allowed for enough room for proper insulation at this location.  The photo below could be any old rambler in Minnesota – almost all of them look like this.

Minimal insulation at eave

Today, homes are built with raised-heel trusses, or ‘energy trusses’.  This creates a bunch of extra room at the eaves just so the proper amount of insulation can be added.  I pulled the insulation away at the eave in the photo below to show this.

Energy Truss

A minimal amount of insulation at the eaves results in energy loss, which is unfortunate, but not a major concern.   Usually.  The time that this lack of insulation at the eaves starts to become a bigger concern is when the home has ice dams.  Insufficient insulation at the eaves is a common contributor to ice dams, and there’s no simple solution for this.

The best approach in these situations is to use an insulation with a higher R-value per inch – specifically, closed-cell spray foam insulation.  It’s not necessary to have the entire attic lid insulated with spray foam, but having spray-foam insulation installed at the eaves is a great way to help compensate for the lack of space at these locations.  The illustration below, provided by the Minnesota Department of Commerce, Division of Energy Resources, shows what this method looks like.

Foam insulation at eave


The only downside to having this type of insulation installed is that it’s more expensive than other types of insulation, and the work should be performed by an experienced spray-foam insulation installer.  It’s not a DIY project.

Reuben Saltzman, Structure Tech Home Inspections