Author Topic: Need advice for roofing underlayment: plywood vs securpan  (Read 726 times)

scottydog

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Need advice for roofing underlayment: plywood vs securpan
« on: March 19, 2018, 06:13:20 AM »
Does anyone have thoughts about whether we should prefer plywood or securpan as a material for membrane roofing underlayment?

I live in a duplex with a flat roof, and this summer my neighbour and I are having the roof replaced. Our place was built in 1924 and has a 29-year-old tar & gravel flat roof. Recent city bylaws require us to get a white roof and we've decided to go with a white elastomere membrane. We're restricting our search to CAA-approved contractors (CAA is the Canadian equivalent of AAA) to ensure the job is done well enough that we won't need to think about it for 2-3 decades. There's a real problem up here with roofing companies filing for bankruptcy and reforming under a new name every couple of years and we want to avoid those guys.

We've narrowed it down to 2 estimates. The cheaper company recommends an underlayment of securpan:
http://www.alcor-inc.com/58-product-securpan.html

The $4000 more expensive estimate has some advantages:
  • The 1/2" plywood underlayment should be much stronger to stand up to heavy snow storms and ice storms
  • The membrane wraps down the inside walls of the roof, like a bathtub or a pool, eliminating silicone joints and promising zero maintenance aside from raking leaves to keep the roof drain clear
  • The company seems more professional. The cheaper company's salesman was too smooth, like a used-car salesman. Both companies are CAA-approved though so they should care about their long-term reputations.

We have no idea what's underneath our current roof. It was last replaced years before either of us moved in. Maybe (hopefully?) there's already a solid layer that they could put the securpan on to.

What do you all think? Is it worth $4000 more to eliminate silicone joints and have a stronger underlayment?