Tools for Flashing Rough Openings – Not Windows and Doors

 

Lucas Hamilton

Lucas Hamilton is Manager, Building Science Applications for CertainTeed Corporation

I am struggling with an issue that keeps coming up with regard to the practice of flashing in building construction.  This is one of the most critical issues for ensuring that moisture will not permeate the building envelope. Earlier this year I wrote about the need to return to the construction techniques that our fathers and grandfathers adopted, especially, with regard to flashing

When I am conducting trainings and webinars on moisture management, which I do on a monthly basis, I am continually asked about flashing windows and doors.  I need to set the record straight – we do not flash windows and we do not flash doors –  we flash rough opens.  This is an important distinction.

Windows and doors are stuck onto a building so how can they be flashed?  They are accessories. The flashing is part of the rough opening in the wall assembly in addition to whatever features the window itself may have.

There are significant documents which clarify window installation practices such as ASTM E2112 which shows how to execute proper installation along with the proper flashing.  One of my favorite resources regarding flashing techniques in general is through SMACNA (Sheet Metal and Air Conditioning Contractors’ National Association). Their manuals give clear step by step instructions for folding materials to make various flashing shapes with minimal cutting.

Do not depend on glues and adhesives to prevent water intrusion.  Chances are they will not be permanently maintained by a building owner.

Stick to solid pieces of material that are installed in a shingle-like manner to continuously shed the water to the exterior and allow gravity an surface tension to drain the water from the building.

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