There is some debate among both architects, engineers, home builders and roofers in regards to which is better – a breathable or non-breathable shingle underlay or does it even matter? Although there are valid points for both sides of the equation, further study and evidence is leading towards the benefits of using a breathable membrane, which can provide long lasting value to houses of all ages.
The question of breathable membranes is directly related to the importance of proper attic venting – a commonly misunderstood element of your home design. Although we in Canada don’t have to worry as much about long hot summers like homes in the southern United States do – our long cold winters create a unique challenge for proper attic air circulation – and the removal of moisture in your attic during winter months especially when we get a long cold snap followed by a warm spell.
As warm air rises in the winter time and seeps into your attic – so does the moisture contained in the oxygen residing in your attic through a process called vapor diffusion. Even though we may think of our Edmonton winters as having very dry air – every home that is heated and occupied has moisture in the air.
Common Producers of Moisture in the Air of Your Home
- Human Breathing – the process of when we breathe involves the conversion of Oxygen to Carbon Dioxide and produces up to 1 liter of moisture in the air of your home per person and up to .75 litres per pet depending on its size.
- Cooking – The steam that rises from cooking can produce large quantities of moisture in the air.
- Bathing / Showering – Hot showers and baths produce very large amounts of moisture and make the attic space above your bathroom particularly vulnerable to moisture problems caused by diffusion.
- Humidifiers – Many homes in Alberta use humidifiers to keep the air moist in their homes – but adds extra moisture to your attic and can cause problems.
- Dishwashers – Dishwashers produce significant amounts of moisture during both the cleaning an drying process.
These are only a few areas where moisture is created in your home and do not include such activities as plants, washing clothes and other sources of moisture.
How Alberta Winters and Vapor Diffusion Effect Your Attic and Your Roof…
As the warm air rises in your home towards the attic – it will naturally attempt to find its way into your attic through light fixtures and boxes, attic entrances, skylights and any place in your attic where the insulation is weaker than the rest of the area.
As this moisture gathers in your attic – it naturally bonds to anything cold such as your rafters and roof decking (the plywood on your rafters). Depending on the air temperature – this then can result in a condensation drip much like the water beads on a can of pop in the summer. As this water drips down, it can soak insulation and damage the drywall that makes up the ceiling of your home – or seep undetected into your walls where it can start to mold and cause potentially serious health issues.
An equally as common issue is the formation of ice in your attic caused by the condensation of moisture which can freeze on contact during cold months where the temperature of your attic and be very cold. Come spring or warm spells, when you have what are essentially large internal ice damns in your attic starting to melt – the water needs to escape and is drawn downwards by gravity – in which case it will either be absorbed by your insulation or find its way in your ceiling, walls, chandelier or fans thus creating the potential for the formation of mold and damage to the walls and ceiling of your home. In addition, as insulation becomes wet or saturated – it will condense and lose much of its insulating properties which can create cold spots in your home – and the subsequent magnification of the problem in each winter seasonal cycle.
So How Does this Affect the Shingle Underlay and Whether It Should Be Breathable?
In cold weather, not all warm air in your attic will adhere to your rafters in the form of frost or condensation– but instead will seek an outlet, which most commonly is the 1/8 of an inch space between the plywood sheeting on your roof. (This gap is to allow for the sheeting to expand and shift without causing the plywood to buckle). As moisture seeps between these spaces – it will gather underneath the underlay and shingles and potentially cause damage in the form of mold and rot to your homes ceiling if it can’t escape.
Another factor that can have bearing on the importance of your roof being able to breathe is that in newer homes plywood and other building materials continues to release moisture for several years after being installed despite it being kiln dried at the lumber mill. A breathable underlay allows the wood to continue to dry naturally and without the potential of a mildew buildup.
GAF Deck Armor
Although considered a premium product for roof deck protection – a breathable underlay membrane such as GAF’s Deck Armor provides your roof the ability to breath and prevents moisture from building up and potentially causing mold, mildew and structural damage to the rafters and framing of your home. Rated at 600% stronger than normal #30 roofing felt, Deck Armor is part of the 5 steps of GAF’s 50 Year Warranty that is included with your GAF Shingle installation. As a certified installer of GAF products, Rapid Roofing can provide you with maximum protection to your home using this Deck Armor Guard shingle underlay.
Some experts claim proper venting coupled with proper airflow in your attic is all you need for an effective roofing system in order to maximize the life of your roof, your homes rafter structure and decking as well as the maximum R Factor integrity of your insulation. Ultimately you will need to decide, which is best but we can assist in your decision making.
Talk to your Rapid Roofing Service Specialist about using GAF Deck Armor on your roof or contact us directly at 780-221-8411 or through the contact page on our website.