Roof and Attic Ventilation | Moisture, Ice Dam and Snow Removal, Leaks, Condensation

One of the most common inquiries we receive on our toll free service line at GRS relates to home owners and business owners that have problems with proRoof, Attic, Ventilation, Moisture,Ice Dam,Insulation,Snow Removal,Leaks, Condensation,Contractorsper roof & attic venting, attic moisture (condensation), annoying and intermittent roof leaks, and ice and snow build up on the roof.

Roofing Contractors Servicing Attic Ventilation, Moisture, Ice Dam and Snow Removal, Leaks, and Condensation in Calgary, Red Deer, Edmonton, Fort McMurray, Lloydminster, Saskatoon, Regina, Medicine Hat, Lethbridge, Canmore, Cranbrook, Kelowna, Vancouver, Whistler, Mississauga, Toronto and points between. Alberta, Saskatchewan, British Columbia, Ontario. 

The following guide will assist you in assessing and bringing forward solutions for roof leaks, attic moisture, roof snow removal and ice damming issues, ventilation problems, etc.


Table of Contents: (click to sub heading)


About Us

About Roof Leaks

Our Roof Repair Technicians

DIY Home Owner – Assessing and Repairing a Roof Leak

Keep Your Attic Dry – Attic Condensation and Roof Ice Damming

Correcting Attic Moisture

You Don’t Want Warm Air from Your House to Enter Your Attic

Inspect for Warm Air Leaks (from your house in to the attic space)

Attic Ventilation – Air Vents Are Not Always the Solution

Roof Venting Rules

Roof Ice Damming Explained

Roof Ice Damming = A Leaky Roof

Proper Roof Underlayment Installed Correctly = No Roof Leak

Ice and Water Underlayment – Building Codes Agree

Why me? Why is there an Ice Dam on My Roof?

Arrgh! - The Cause of the Ice Dam Problem can be Complicated

Temporary Ice Dam Relief - Interim Solutions for Roof Ice Damming

Ice Damming and Snow Removal on Flat Roofs (low slope roofs) – Weight Loads

“Really, the Roof Leak Was There” - Ice Dam, Snow Removal, Leaks on Metal Roofs

Roof Ventilation

Venting has its Advantages

Roof Venting Products

Fresh Air - How Attic Ventilation Works

The Vent Calculator “Net Free Vent Area”

Roof Shingle Material Warranties and Ventilation

Make Sure Your Roofing Company Knows

Hiring a Roofing Company

Contact Us 


 About UsRoofing Calgary, Red Deer, Edmonton, Fort McMurray, Lloydminster, Medicine Hat, Lethbridge,Vancouver

General Roofing Systems Canada (GRS) are Roofing Contractors in Alberta, Saskatchewan, British Columbia. Roofing Contractors in Calgary, Red Deer, Edmonton, Fort McMurray, Lloydminster, Saskatoon, Regina, Medicine Hat, Lethbridge, Canmore, Cranbrook, Kelowna, Vancouver, Whistler, and points between. 


 About Roof Leaks


In many instances, roof leaks are similar to an electrical problem in a car – they are intermittent - they can come and go. Driving rain from wind, ice build, snow pack, moisture in the air, the temperature, and various other variables determine whether your roof will leak.


 Our Roof Repair Technicians


Our roofers do this for a living so they are very well equipped to determine the cause of the leaky roof you may be experiencing. Nonetheless, if you are a DIY kind of person, the following may help you assess the leak and repair it on your own.


 DIY Home Owner - Assessing and Repairing a Roof Leak


Because most home owners won’t go on the roof themselves or would prefer not to or don’t know how to assess a leak from the rooftop, we will give you a step by step process to assess a leak from the inside of your house and attic.


The first step is to assess where the leak is coming in through your ceiling and roof system.


1.     Look up and find where the leak is coming through the ceiling.

2.     Measure from the outside wall to approximately where the water is coming through the ceiling.

3.     Get a flashlight, put on some gloves, bring a tape measure and go in to your attic space and measure from the outside wall as you did below and locate the moisture. Be sure to watch your step in the attic so you don’t damage the ceiling - walk on joists or trusses, and watch for droppings from mice, bats, birds, squirrels, etc. (This may be a good time to get someone else like a friend or family member involved just in case you encounter any problems or to hold your ladder).

4.     From that point, follow the moisture to detect the source of the leak.

5.     You may find that it is not in fact a roof leak and that it is a condensation issue or frost from your attic. Check to see that exhaust vents (at the ridge area) aren't plugged with snow and ice and that the insulation is not covering the intake vents at the eaves (very important).

6.     If the roof sheathing is wet, you could have some ice damming issues (the ice is working back up the roof and under the shingles (see Ice and Water Underlay for ways to avoid this issue in future) or the shingles are damaged or have blown off all together. Roof shingle blow offs are sometimes not detected by homeowners as some roofs can’t be seen from standing at ground level. This (shingle blow offs from wind) is especially common with roofs that at the edge of communities or in the country.

7.     Check any opening in the roof system – anywhere there is something cut in to or through the roof sheathing such as air vents, chimney stacks, fireplace or plumbing stacks, etc. The most common point of entry is at an opening, in a valley (where two roof lines meet), or at flashing (such as along the side of a dormer or at the back of a chimney).

8.     Once you locate the source of the leak, you can either describe that to the roof repair technician prior to having them service your roof, or you can now get up on the roof and fix it yourself. We DO NOT advise you do this yourself however. Two main reasons are that; a. Even our roofers can injure themselves, and b. There is a lot of knowledge required to repair a roof yourself. Nonetheless, as a service, we provide this DIY guide for those that are fearless.


If you are going to do it yourself, the next step is to get up on the roof and fix the leak.

1.     Your ladder has to be tied off to the trough and it should be 3 rungs minimum over the eave.

2.     You have to wear safety harness, rope, etc. (we have to say it)

3.     You have to have a second person present to call for help should something go wrong. (better safe than sorry)

4.     Go to wear the leak is on the roof and repair as required with roof mastic, caulking, shingles, ice and water membrane, etc. (too many possibilities to teach every scenario here)


 Keep Your Attic Dry - Condensation and Ice DammingAlberta, Saskatchewan, British Columbia, Kelowna, Cranbrook ,Saskatoon, Regina, Lloydminster, Snow


Attic Condensation and Ice Damming usually are part of the same problem in your roof system / home insulating design - frost or condensation in your attic space are the primary clue.


An attic space should be cool and dry, free of moist warm air from your home below, and the air flow through and the your roof system needs to be correct.


Improper insulating or air sealing that allows warm moist air from your home to enter your attic space will cause aggravation – one of which is ice dams. Ice damming is very rarely seen on a roof that does not have warm air below as the cause – such as a detached garage with no heater.


 Correcting Moisture


Attic moisture will eventually rot out the attic system. The roof sheathing will rot out and the attic space will have an odour that may enter your living space. Mold may appear on your sheathing and rafters also.


If you experience intermittent roof leaks in the spring, it could be that ice was built up and backed up under shingles on to the sheathing and is now melting or frost in the attic is thawing and now coming through your ceiling.


From a roofing perspective we first check the air ventilation. Venting your roofing system is important, but not always is ventilation the problem. And further yet, if the roofer doesn’t know what proper ventilating procedures are, he or she may actually make your attic moisture issue worse. Before you start adding vents, be sure to start with air flow from your house first.


 You Don’t Want Warm Air from Your House to Enter Your Attic


The first place to start is with air flow from the house to the attic. If there is moist warm air from your house entering your attic, fix the air leaks first. Once fixed, the vents you already have on roof will likely be more than enough to keep your attic space dry and as a bonus, your energy costs will go down.


 Inspect for Warm Air Leaks (from your house in to the attic space)


Hire a contractor to check for leaks or follow this list or any of many available readily on the internet and check for warm air entering your attic space.


Places to check for warm air entering the attic space:

-          Around plumbing stacks and plumbing walls, etc.

-          If you have a chimney that comes through an attic.

-          Partition walls, party walls, perimeter walls.

-          Ducting for heating systems, fans, etc.

-          Light fixtures are a common place.

-          Electrical wiring.

-          Look above pocket door areas.

-          Above sub ceilings or dropped ceilings that are below the attic.

-          Where vaulted, open, or cathedral ceilings meet an open attic area or split level end points

-          Additions are one of the most troublesome areas. Check where the addition meets.

-          Rounded corners, staircases, framing corners, etc.


 Venting – Roof Air Vents Are Not Always the Solution


If you are experiencing problems with your roofing system and you are about to investigate the ventilation in your attic, please BE SURE to read the section above related to warm air flow entering your attic space before commencing work on the roof ventilation. We see this error time and time again from homeowners and roofers alike.


When an attic is sealed well, you will most likely not need to add air vents. There are many articles available from online sources or many other authorities on the topic.


“Your main concern is warm air in to your attic and not roof ventilation.”


We see this error occur primarily because roofers tend to assume that because the manufacturer of the shingles dictates a certain amount of airflow for warranty that this means somehow that ventilation is the answer - this is not correct. Proper ventilation is important, but is the source of the problem perhaps less than 10% of the time. It is easier for a shingle manufacturer to dictate a certain number of vents to qualify for warranty than it-is for them to mandate proper vapor barrier and insulating.


 Roof Venting Rules

Local building codes, shingle manufacturers, etc typically dictate the 1/100 to 1/300 rule (1 square foot of venting or roof opening for every 100 to 300 square feet of roof space – typically closer to 1/300 is the rule). This is a simple calculation that is easy to affect. Wind driven air flow is what drives attic ventilation. Be sure there is intake and outtake appropriate, distribute air vents evenly, and be sure any insulation present isn’t right against the roof sheathing to allow for air ventilation to pass.


That Damn Roof Ice Damming!


 Roof Ice Explained

Ice damming on a roof can be very frustrating for home owners and even more frustrating to a roof repair contractor if he/she doesn’t understand the principles of air flow and ventilation. Our business is built on solving roof problems, without solutions we are out of business. As such, we have had to over the years learn everything we can about this particular problem that so many roofers misunderstand.


Ice dams are created when water runs down a sloped roof and runs in to a blockage of ice. As it begins to freeze, the ice block then grows up slope or up your roof. This is commonly found at the gutter area (hence the reason local building codes are starting to call for Ice and Water Shield Underlayment at the eaves at least).


 Ice Dams = A Leaky Roof

The problem with a mound of ice backing up or moving up your roof slope is that it can then work its way under shingles (shingles are designed as a water-shedding roofing material that moves water off your roof that is moving down and not up a roof slope). When the ice moves up and under a shingle it then will either hit a proper roof membrane (roof underlayment) or the sheathing if your roofing contractor didn’t install underlay or has perhaps installed it incorrectly.


 Proper Roof Underlay - Installed Correctly = No Leak

Roof underlayment needs to be installed as "monolithic" as possible (see our installation procedures “How to Install a Shingle Roof”), have as much elasticity has possible, and be installed so there are no negative laps (negative laps are due to the installer placing membrane connections incorrectly or negative to slope). If your roofing installer has installed Ice and Water Shield (an adhering underlay – preferably a premium product) and has done it properly, your roof can then leak at shingle level and that moisture will never enter your roof system or better put - to the sheathing itself. But sadly, many roofing companies or installers don’t understand what a negative lap is, or what monolithic installation of a roof underlayment / membrane is, so this isn’t always a solution.


 Ice and Water Shield Underlayment – Building Codes Agree

Local building codes are now typically asking for at least ice and water shield to the eave up the slope of the roof to a minimum of 36” and in the roof valleys. Some roofers don’t know or simply ignore the code, but in most areas this is the case.  Further to the code, our installation principles are taken much further to ensure protection to the complete roof and not just to the eave or valley.


 Why me? Why is there Ice on My Roof?


Ice dams show up that are complicated. Roofs that have a lot of valleys, intersecting roof lines and dormers, and on roof overhangs (especially on large overhangs at front porch areas etc).


A cool roof, one that is insulated well and has no warm air entering the attic area will not typically have ice damming – such as the detached garage roof system is cool. A warm roof that is heated from below will not typically have ice damming as it will melt the ice and water on the roof itself.


One method of locating areas where there is not adequate insulation or air leaks are present is by observing a light snow fall or frost on your roof. The area of the roof that melts first is typically where you are having issues with air loss from the house below or poor insulating.


Low slope roofs are notorious for not allowing for adequate space at the edge of the attic floor to insulate correctly. You can attempt to install insulation right at that edge and that may alleviate the ice damming issue. Be very careful however that the intake at the eave is not covered by insulation. A roof needs intake air to vent properly.

Cathedral / open vaulted ceilings are more complicated to address in that there is no space to work with as with an attic area. However, you may want to remove the sheathing and seal all areas below and then re roof but this isn’t always a solution.

The other method is to try is to add ventilation and hope this corrects the issue.


 Arrgh! - The Cause of the Ice Dam Problem can be Complicated


We recently re roofed a beautiful home for a client that had this problem. We took off cedar shake and installed a premium synthetic roof tile.


The issue; a very tough and unusual weather season then kicked in that winter (2010/2011 in Edmonton, AB) and our phones were off the hook with repairing roofs with ice dam and snow issues.

This particular house now was experiencing ice damming that it never typically experienced in past. The first cause was simple... the weather. But further to that a synthetic tile does not hold or have the insulating value a cedar shake wood material would have, so of course the roofing material reacts differently. Also, the roof was vaulted and this poses a host of other challenges. Fortunately for us, and the home-owner, we installed a high grade Ice and Water roof underlay to the complete roof. The point of mentioning this is there are a number of factors potentially at play; weather patterns, the roofing material, the air flow in to the attic space, ventilation, etc and it takes experience and training to assess many situations.


 Temporary Relief - Interim Solutions for Ice Dams


Sometimes the solution won’t be found or will take a few winters to isolate as your roofing contractor attempts to resolve the issue one step at a time.

In the meantime, your roofing contractor can remove snow from the roof and chip away at the ice to create valleys to free up water flow (of course you can damage the shingles though), heat wire can be also used to some extent, and gutters can be taken down but will likely be destroyed and are important for the protection of your homes foundation. 


Usually, if your home is newer and has been built to today’s building code, this will allow us to be able to assess and to correct the problem. Older homes, vaulted roofs, and low slope roofs however can be more difficult and it could be that you will have to affect a number of the solutions each winter that we have suggested.



Ice Damming and Roof Snow Removal on Flat Roofs (low slope roofs) – Weight Loads


We have serious concern with roof load capacities every winter. We get calls daily that are not great to get.


If you have serious amounts of snow on your flat roof, get it off as soon as possible.

The structural weight load capacity of your flat roofing system is definitely being compromised if you have serious amounts of snow and/or ice on your flat roof, not to mention the damage the ice and snow and moisture will cause when the spring thaw occurs.

Which brings us to flat roof drains... – CHECK THE FLAT ROOF DRAINS BEFORE THE SNOW MELTS !

Standing water or "flat roof ponding" should be avoided, and if drains aren't checked before and during the spring melt, your flat roof will most definately leak if the drains are clogged. While your contractor or you are on the roof checking drains, you may as well check scuppers, gutters and downspouts, and metal roof flashing. 


When removing the ice or snow from a flat roof, engage a professional flat roof contractor to do the work or be very sure you know what tools to use so you do not damage your roof membrane. A damaged flat roof membrane in the winter becomes a nightmare in the spring and it costs a lot of money for the flat roof repair.


Proper flat roof maintenance is “key” to flat roof life cycle and the protection of the assets inside the building.



 “Really, the Leak Was There” - Ice Dams, Snow Removal, and Leaks with Metal Roofing


Metal / Steel roofing systems can be the most frustrating of all roof systems in that leaks are intermittent usually, and frustrating for those that experience the leak inside the building. Why? Metal Roofing expands and contracts.


Metal roof coatings are the quickest and most effective solution – they work, and work very well. Technology has solved the problem.


Caulking roof screws and standard roof top vents and the like is helpful, but temporary. Like we mentioned, metal expands and contracts with changes in weather and caulking won’t last.


When we install metal roofing such as standing seam or corrugated panels on a residential property we always apply a premium underlay first to avoid problems.


Metal roofing has a great life cycle and the cost over the long run vs. performance is excellent, but at the point of leakage they can be frustrating at times.


 Roof Ventilation

Roof / attic ventilation is important, not always for solving ice dams (read above please) – but important for effective attic ventilation to protect your home investment.


 Venting has its Advantages


Proper attic ventilation can:

1.     Extend the life span of your roofing material (shingles etc).

2.     Allow your roof system to breath.

3.     Minimize ice damming issues.

4.     Lower energy costs if done correctly.

5.     Reduce condensation.

6.     Minimize roof leaks (condensation can cause a roof leak).

7.     Minimizes “roof rot” sheathing issues.

8.     Minimizes “deck deflection” or “warping of the roof deck”.

9.     Minimize rusting of nails or anything metal in your roofing system.

10.  Minimize frost from accumulating on the underside of the roof deck sheathing.

11.  Minimize the advancement of molds, spores, and fungi.

12.  Increase the life cycle of cooling units.


 Roof Vent Products


Today, we have many options for products to vent roofing systems, all of which are available in many sizes, colors, and styles;

1.     Static Vents

2.     Power Vents

3.     Ridge Vents

4.     Turbine Vents

5.     Gable Vents

6.     Starter or Eave Vents

7.     Cupola Vents

8.     Soffit Vents


 Fresh Air - How  Venting Works


To be effective, fresh air flow or naturally forced air (combined wind pressure and thermal effect known as stack effect) is created by having intake such as at the eave area and exhaust of air through the vents near the ridge.


 The Vent Calculator “Net Free Vent Area”


An air vent’s effectiveness is calculated in terms of net free vent area – in other words, it is the area of the vent that is actually venting that is calculated.


One square foot of net free vent area per 300 square feet of attic floor space is your minimum requirement by most authorities. Check your local building code to be sure. Intake and exhaust ventilation should be installed at approximately a 1:1 ratio. More isn’t better if your ventilation ratio is wrong. Also, do not place vents part way up your roof or between your intake and exhaust on your roof.


 Shingle Material Warranties and Ventilation


Most shingle manufacturers will not warranty shingles with improper attic ventilation.

To be sure the venting is correct when re-roofing, find out what product is being installed, go to the shingle maker’s website and look up the shingle warranty requirements and then hold your roofing contractor to that specification of venting.


 Make Sure Your Roofing Company Knows


Talk to the company you hire and be sure they know the principles contained in this document. This information will equip you with more know-how than most shingle installers care to know about. Be sure to task them with what’s right.


 Hiring a Roofing Company


We’ve addressed many of the concerns home owners should have in selecting their roofing contractor in the document link here “Choosing a Roofing Contractor”. 

 Contact Us


We can be reached at 1.877.497.3528 24 Hours 365 Days a Year. When you call, we’ll put you in touch with our local roofing staff.


We are Certified, Licensed, WCB registered, 5,000,000.00 Commercial Liability Insurance, and carry a Lifetime Warranty on our Workmanship.

General Roofing Systems Canada (GRS) is a Comprehensive Roofing Contractor.

Our Roof and Attic Ventilation, Attic Moisture, Roof Ice Dam and Snow Removal, Roof Leaks, and Condensation services are available in Calgary, Red Deer, Edmonton, Fort McMurray, Lloydminster, AB, Saskatoon, Regina, SK, Medicine Hat, Lethbridge, Canmore, Cranbrook, Kelowna, Vancouver, Whistler, BC, Toronto, Mississauga Ontario and points between. Alberta, Saskatchewan, British Columbia, Ontario.  |  |  1.877.497.3528 Toll Free


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