This is the continuation of “Metal Roofing Performance (Part 1)”. Haven’t read it yet? You can read it from this link here.
Another unfortunate approach to installing a metal roof is to install the new roof over the existing roof, claiming that this approach is green because it avoids the cost and mess of a roof tear-off, adds “additional insulation”, and prevents “more landfill debris” when in fact it’s a lazy approach (Missed the first part? You can catch up on all of it here). Would grocery stores rewrap and relabel expired meat? No, of course not (but if they did, it’s considered fraud), and it’s the same case for roofing. The deficiencies of this approach to the homeowner will become apparent later, and include:
- Additional weight to the roof structure (because there are now at least two roof coverings)
- Any roof deck deterioration continues to be there, but is now hidden under two roof coverings
- Waterproofing membrane cannot be installed over the old roof (since the membrane needs to be adhered directly to the deck), so the “new” roof assembly is less protected against water infiltration,
- The old roof covering becomes a water sponge if a leak does occur, and will make it much harder to determine the true source of the leak without disassembling the new roof
- Roof penetrations are usually sealed only with caulking (which can fail in as little as five years), instead of being properly waterproofed and sealed from the deck up.
- The addition of outlet vents in no way replaces a proper evaluation of the insulation/ventilation behavior of the roof, and may actually reduce the performance of the roof system, if the evaluation was not properly done.
To make a metal roof installation a “green” installation, it will need both longevity and performance. The performance comes from how the product is married to the existing structure, and the repair or amelioration of deficiencies that may exist. To get a “green” roof, the roof system needs to be properly assessed, the deficiencies found and corrected, the preparation of the roof be properly done, and the roof covering be installed with all the additional safeguards in place. Then you will have both the longevity and the performance that you should expect.
To summarize: To get a “green” roof the following should occur:
- The product used should be long-lasting (with a track record of performance and durability),
- At a minimum, the product should be installed following the manufacturer’s instructions AND current best practices (which are location-specific).
- The roof system should be assessed to ensure that deficiencies are fully identified, and that appropriate actions are taken to minimize or eliminate the deficiencies. This means that a full inspection (both interior and exterior) be done, the insulation and ventilation capacities are measured and compared to the required standards, and observed deficiencies are discussed with the homeowners.
- The roof (with very few exceptions) should be stripped to the deck.
- The corrective actions identified in #3 above, be performed.
- The appropriate layering of waterproofing, flashing and sealing be carried out to counter the usual modes of roofing failure.
- If the deficiency correction cannot be done (for budgetary or technical reasons), then appropriate measures be designed to minimize the damage that could be caused by those deficiencies.
- The “green” marketing claims can be verified by incorporation of specific features (of either product or installation) that deliver the performance claimed.