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Metal Roof Gone Bad – impossible to make a Flat Roof Repair

This “metal roof gone bad” was treated with a silicone sealant approximately three years ago. From the evidence, it is clear that the company applying the sealant didn’t know what they were doing.

After investigating and making tests:

  1. The silicone sealant was cracked where the two metal plates joined.
  2. Water got trapped and caused the metal to rust. In some areas, it has rusted and corroded to where the insulation underneath was visible
  3. Most fasteners had water trapped around it and was rusting the metal
  4. The silicone is peeling around the vent units. No sealant or coating will stick properly on a petroleum product.

What we take from this is, that the surface was not prepared properly before the coating was applied. From our experience, no matter how well the surface preparation, silicone sealants do not last more than two years at best.

Why do metal roofs start leaking?

A metal roof should last a long time. Most leaks on a metal roof start with the fasteners. With metal roof installation, screws are used to fasten the roof sheets to the trusses. Thes screws have a rubber or neoprene washer that would make the seal between the screw head and the metal plate.

Over time these rubber or neoprene washers hardens, becomes brittle and crack, compromising the seal and is the beginning of a small drip leak. At first, no one might be aware of it. But over time the water that accumulates around the screw under the washer will cause the metal to rust or corrode making the fastener hole, larger.

Also, with the constant expansion and contraction of the metal, the washers are worn down. For this reason, it is wise to have a metal roof inspected every five years to make sure that the screws are still at the proper torque strength and to ensure the washers are still holding up.

 

Metal Roof Screws and rubber or neoprene washers are the cause for leaks

Watch this video to see how water gets trapped under the silicone causing the metal roof to rust.

Why we decided that a repair is not wise

  1. We could repair it, but because of the silicone coating, we might miss many areas, and this would mean we will have to make numerous trips after the repairs. That could frustrate the client and us
  2. After the repairs, the silicone could loosen up in other areas, trap water and cause new leaks
  3. The cost of repairing will be more than a 1/3 of the cost of replacing it with a new roof
  4. A proper warranty is not possible
  5. Money and time spent on any repairs will be a waste
  6. Our name and reputation is on the line – one bad job and unhappy client can cause more damage for us to potential customers in the future
No Thanks – it’s not worth it
Before considering a metal roof repair, a careful examination of what’s on it and what others have done to it must be taken into account.

Our solution to this metal roof:

Step 1- Preparing the roof for a plywood installation

Remove all debris and screws on top of the risers. Remove and clean silicone sealant from the air conditioner and vent flashing. After preparation, to install 19/32 CDX plywood fastening it to the risers with metal screws.

We use a thicker plywood than a 1/2″ because of the metal roof flexibility.  Install support 2 x 4’s in areas where needed.

Plywood installation over metal roof

Smooth surface ready to install a Rubber Roof Membrane

This image shows what it looks like once the plywood is installed over a metal roof.  The plywood creates a flat surface for a rubber roof installation. The space under the plywood is left open so that air can move freely through. The air movement keeps the roof much cooler.

Plywood installed over a metal roof

Step 2 – Installation of a Self-Adhering Base

Install a self-adhering Modified Bitumen Base sheet over the entire surface of the plywood.

Install aluminum drip edge. We use a heavy gauge aluminum drip edge.

Modified Bitumen self-adhering base sheet is installed

Step 3 – Modified Bitumen Cap sheet installed

After the installation of the metal edging, it’s time to install the cap layer. To Install a white granular Modified Bitumen Cap sheet. The ceramic granules protect the rubber membrane from ultraviolets and also reduces heat absorption.

A special primer is used to secure the cap sheet to the metal drip edge.

Modified Bitumen Rubber Membrane installed over the base sheet

Step 4 – Flashing

After the installation of the cap sheet, installation of flashing follows on all the air conditioners and vent units. Removal of silicone coating that covers all the metal for proper flashing.

Flashing around all the vents and drains are made

Metal Roof Gone Bad

Metal roof gone bad – The image shows what it looks like when you peel back the silicone from the seams on a metal roof. It is wet and rusted. We have seen this over and over where an attempt was made to seal a metal roof with disastrous results.

The reason why silicone coatings or other types of coatings will not work are:

  1. The metal can never be 100% clear from all debris, dust, oils, and rust. Especially around fasteners and seam overlapping.
  2. Where two metal plates overlap is constant movement from the expansion and contraction of the metal. The constant movement will cause the sealant to either crack or peel off.
Metal Roof Gone Bad - peeling back silicone reveals the problems

Silicone Coating over a metal roof seam

Notice the small crack that has developed on the silicone surface. This layer is the 3rd attempt repairing the seams. You can see that by the different colors of sealant applied on top of each other. The constant movement of the metal under the silicone will always cause it to crack.

Silicone coating developing crack over metal roof seam

Metal Roof Gone Bad around Fasteners

When peeling back the silicone coating that was covering the screws on the metal roof, we found them all wet and rusted. By just looking at the surface it wasn’t apparent that there were any problems, but a closer investigation revealed the truth. The screws or fasteners is where most “metal roof gone bad” issues are.

Metal Roof Gone Bad - fasteners are rusted and all wet

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