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Last modified: 2023-02-06 | Approximate reading time 5 mins
Roofing underlayment isn’t a luxury. It’s the one element that guarantees a decent and weather-protected structural design.
Its many benefits are far from being limited to this role; roofing underlayment strengthens the structure against leaks, protects the roof from mould, and acts as a protective barrier between the wood’s resin and the covering.
A roofing underlayment is a protective layer of roofing felt; in other words, a pressed material made of:
This material is available as a self-adhesive membrane made from modified bitumen or SBS polymer. When made as such, the material can be used as a protective roofing layer and as a protective screed shield.
However, underlayments aren’t made for long-term exposure to nature’s elements. The more durable materials can withstand being in the open air for a maximum of 90 days, while most other models can withstand 60 days, tops. Bitumen-coated roofing underlayments are more prone to drying out and becoming increasingly permeable; the complete opposite of what’s actually desired. So, that’s why the covering must be laid within a reasonable time period.
The material used is extremely important. There are other material components available in lieu of synthetic ones, but using these can damage the roof’s framework.
The elements to avoid using for your roofing underlayment are:
The above-mentioned materials won’t prevent humidity caused by freeze-thaw weathering between the underlayment and the covering.
When building your house, it’s imperative that you protect your structure’s interior from adverse weather as soon as possible. Laying the roofing underlayment, which occurs after the framework is finished and the wooden covering is set, allows the structure to be weatherproofed in between the completion of the work.
The earlier the roof is rendered watertight by the underlayment, the quicker the house’s interior will dry, meaning the work can officially begin. Laying a roofing underlayment will thus also allow one to move in at an earlier stage.
The first owners of an asphalt shingled house quickly detected leaks as a direct result of insufficient waterproofing layers. The roofing underlayment counteracts the effects of this eventual problem. It also acts as a protective barrier between the structure, water leaks, and mould.
There’s a chemical incompatibility between asphalt shingles and wood resin. The roofing underlayment will act as the divider between these two layers and prevent them from coming into contact.
To really understand the answer to this question, we have to discern the two main types of underlayments: synthetic and bitumen.
Weighing in at 25 pounds, this polypropylene underlayment is lightweight and perfect to temporarily cover a roof, as well as protect the interior of the structure from adverse weather. This underlayment resists traction, tears, and temperatures ranging from -55°C to 110°C.
This underlayment, which only weighs 21 pounds, has the added benefit of being non-slip, unlike the former. Therefore, its installation is made rather simple. However, beware of using this underlayment in Quebec. It can only withstand temperatures dipping just below -40C°, but nothing lower. In other words, it can barely ride out some of the cold fronts experienced in the province.
Designed to provide greater waterproofing qualities, this membrane has several advantages:
Of all the synthetic underlayments, this one appears to be the most advantageous.
Anti-slip and relatively lightweight, this underlayment has somewhat of a drawback: its minimal service temperature is only -43°C, versus 116°C during summertime. Therefore, it isn’t made for harsh winters.
However, it has a few advantages that render its installation rather easy:
These usually have the benefit of being resistant to high temperatures.
However, it weighs 49 pounds and its uncovered lifespan is two months tops.
This one’s the best underlayment for sheet metal roofing. This underlayment was designed to be self-adhesive, anti-slip, and resistant to harmful UV rays. Its sole drawback might be its maximum service temperature, which doesn’t exceed 90°C, which can oftentimes be quite plentiful for Quebec’s infrastructures. Another version of this model was designed with the same components, and it can resist maximum temperatures of 126°C.
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Once you’ve landed on the perfect roofing underlayment based on its temperature, weight, and resistance, you can install it yourself!
For a synthetic roofing underlayment, expect to pay between $65 and $140. Keep in mind that, if you need to cover a low-sloped roof, you’ll then need to double the underlayment layer, thus doubling your budget. Also, if you opt for the waterproof, self-adhesive strip, it’ll cost you roughly an additional $20, per unit.
Cover photo source: Matt Thompson – Flickr
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