Traditional Flashing Techniques Still Rule


Tom Silva from This Old House at CertainTeed's IBS booth

At the International Builders’ Show in Orlando, January 12 – 15, Tom Silva, general contractor for This Old House answered questions in the CertainTeed booth. One of the recurring issues that Tom discussed was flashing and the importance of proper flashing as a water barrier.  He really believes that barriers need to be constructed and maintained. 

At one point, he was talking about Fiber Cement siding and was asked what he does with the butt joints.  He said that you have to flash with physical materials and use traditional flashing techniques at all times.  He said that he flashes behind the butt joints and back caulks the boards to the flashing to prevent water from running laterally at the butt joints.

He obvious believes in traditional methods and good solid construction practices and flashing is one that is critical.  It occurs to me that we are at a low point in our cyclical knowledge process with regard to flashing. We are seeing more moisture issues because of incorrect flashing that has enabled water to penetrate. Often, we depend on newer materials to get the job done rather than using the time tested practices.  It’s funny because at one point during our discussions with Tom I mentioned SMACNA (Sheet Metal and Air Conditioning Contractors’ Association) and you could immediately tell who the seasoned builders were in the audience.  The SMACNA Manual is the sheet metal workers bible. It illustrates how to fold any piece of metal into any shape so that you don’t have to cut it. It is like origami for sheet metal. It seams that buildings constructed using the types of flashing shown in that manual have fewer moisture issues than their newer neighbors.

There are many traditional building practices that we forget and flashing is one of them. When all the failures to keep moisture out of the wall assembly point back to that simple interface between two dissimilar systems and how they should have been closed with a piece of good flashing, it becomes obvious that the basics will still work. You can’t ignore them! For example, why continuous nailing fins on a window is considered self flashing is beyond me.  You haven’t flashed anything. You have just sealed the eventual window leak into the wall.  You have not flashed and redirected to the outside. After all, it’s not the window that needs to be flashed, it’s the rough opening!


Lucas Hamilton

Lucas Hamilton is Manager, Building Science Applications for CertainTeed Corporation


  1. Dr. Paul Gualtieri on

    Finally the simple truth is that many builders don’t have the skills or knowledge to proper basic construction techniques. Do you homework and do not skip basic construction steps to save money. Most people who hire a contractor have no idea how important flashing is until it is too late. In my opinion metal flashing with materials proper for the job is critical to success. Copper flashing seems to be a lost art. New materials which save money are great but many times are not used as intended. Education of this industry is the key to its long term success by the companies which supply the materials. Wake up America! Stay on top! Do it right or don’t do it at all.

  2. Pingback: Tools for Flashing Rough Openings – Not Windows and Doors | Building Knowledge | CertainTeed Corporation's Official Blog

  3. In Vancouver, we have had 100rds of leaky condo because they try new methods of building. They skip flashing and air spaces in wall. We been fixing leaking building for 10 year because they don’t do the basic of building. Building did not leak for 100 year until they try to build faster and cheaper.

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