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.