Dr Roof Inc.                                       Synthetic Underlayments

Synthetic underlayments are being sold as a substitute for #15 felt tar paper as a shingle underlayment. The benefits of synthetics are increased tear strength, easier handling due to its lighter weight and the ability to withstand being exposed to the weather. In the United States, where roofs are routinely left exposed for weeks, the ability to be left exposed is a benefit. In Winnipeg, roofs are not left exposed to the weather so most of the synthetic benefits are not realized in our market. Some synthetics require the use of plastic cap nails under all conditions and some only require regular nails or staples if the underlayment will be covered within two days. Make sure your contractor is following proper procedures to ensure you have a valid warranty.

There are many brands of synthetics such as Alco Shield 15, Grace Syn 15, Rhino Roof U20, Owens Corning Deck Defense, IKO Cool Grey, BP Deck Guard, CertainTeed Diamond Deck and many other brands. What all of these products have in common is they do not breathe and are considered to be vapour barriers.

There is concern in the roofing and construction industry that putting a non-breathable synthetic underlayment or vapour barrier on a roof may cause moisture to be trapped in the attic or in between the synthetic and the roof decking causing moisture problems and wood rot. Nobody is completely sure how these products perform because they do not have a long enough track record in the Winnipeg market.

What we do know is that all synthetic manufactures state that synthetics should only be installed on properly ventilated roofs because they know their products can trap moisture within a structure. Many homes in Winnipeg, due to their construction, are not and cannot be properly ventilated so synthetics, based on the manufacturers’ recommendation, should not be used in these situations.

We also know that polyethylene, a vapour barrier and a commonly used eaves edge underlayment used in the past, was removed from the building code because it was known to trap moisture and contribute to roof deck rot. We are not sure how installing a vapour barrier on the eaves can be detrimental but allowing a vapour barrier to be installed on the entire roof is beneficial?

At Dr Roof we believe that any benefit a synthetic underlayment may provide should be weighed against the potential problems a non-breathable underlayment may cause. Until these products have a proven track record and there is a better understanding of their performance on roofs in our climate Dr Roof will continue to promote #15 felt as the best option as a roof underlayment. Felt is breathable, has been used for decades, has a proven track record and will perform as well as a synthetic without the risk of putting a vapour barrier on your roof. Felts will absorb moisture and allow moisture to evaporate and discourage wood rot. Non-breathable synthetics can trap moisture and cause wood rot.

Many of our competitors promote synthetics. Being in a competitive market Dr Roof must provide our clients with all the options that are available, which includes synthetic underlayments. Under the proper circumstances we will install synthetics if our customer requests it. Our job is to ensure that our customers make an educated decision and understand the pros and cons that go with this decision.

Two synthetic products that are breathable are Breathex and Deck-Armor. If you insist on using a synthetic these are the products you should consider as they are the only breathable synthetic underlayments in our market at this time. As you might expect these products are more expensive than the generic non-breathable synthetics. They also require the use of plastic cap nails. Unfortunately most contractors ignore this requirement and do not follow this procedure which reduces their cost and voids the warranty. If you are choosing Breathex or Deck Armor make sure that your contractor is using plastic cap nails, as required by the manufacturer.

Please call us if you have any questions or would like to discuss synthetic underlayments further.