Foundations (of a metal roof system)

What are you talking about?  Roofs don’t have foundations.  Things stuck in the ground do.  Building do.  But roofs?  They’re up there, talking to the sky.  What need do they have for foundations?

And yet, they do.

Because roofs are structures, and structures need a base, a foundation.

For metal roof systems, the foundation is the system of flashings.  Flashings are purpose-built pieces of folded metal that perform specialized functions. These functions include:

  • anchorage/support
  • drainage
  • shielding
  • locking/security
  • appearance
House schema Trouble spots

Schema of house, showing the various places where flashings should be used or considered.

A well-designed system pays particular attention to the flashings, as the flashings are used in the places where there are the greatest weaknesses or risks.  The flashing provides a specific way to diminish the risk, to provide additional protection at the point of danger, and to work cooperatively with the other elements of the roof system.

For example, in the above schema, the various elements are described as follows:

A.  Chimney flashing (resist water, snow, ice, uneven chimney surface)

B.  Ridge (usually overlap, flashing and/or cap)

C.  Hip (similar to ridge, but with own issues)

D.   Gable or rake (water flow, wind pressure, exposure)

E.  Valley (concentration of water, snow, ice)

F.  End-wall or Sidewall (interface to siding, water flow)

G.  Eave (water flow, ice & snow movement, wind forces, connect to fascia, gutters)

H.  Base-of-Dormer (transition from roof to vertical surface, interface to siding)

Despite the many types of systems on the market, the flashings generally group themselves into specific families.  For instance, the front edge of the roof, the eave, is usually covered with a starter flashing, which takes a variety of forms, but has common elements:  the fascia portion, the drip edge, the edge lip (or attachment point), and a nailing or attachment flange.  The gable/rake detail is usually built from one or more flashings.

When it comes to flashings, having the right design and installation are the difference between “kinda works when the sun is shining” and “performs well under all conditions”.  Paying attention to how the flashings are attached, joined to each other, and how they interface to the other roof components is the basis of a good installation.

The roof covering is the pretty skin, the flashings are the bone and sinew that allow the roof covering to work.  Good installers know this, and spend the necessary amount of time preparing the roof base, identifying the potential weaknesses, and choosing and installing the right combination of flashings that will minimize or eliminate the weaknesses.  Once this foundation is in place, the installation of the roof covering is almost as straightforward as the filling in of the space between the flashings.

House all flashings

Weak areas of roof protected by flashings and membranes

When things go wrong, they are often connected with one or more of the roof joints, and the way the roof covering was interfaced to the flashing system.

If you want to know how well the roofing rep or salesman/woman knows their products, ask them to describe how they handle the runout of a valley on top of a dormer, and what should be the sequence of layering the various protections that ensure the safety, reliability, waterproofness, and durability of that area.  Or ask them how they will interface to pre-existing siding in terms of the flashings they will use.  If they know what they are talking about, they should be able to draw you a picture or two showing the detail and their specific layering of the underlayments, membranes, flashings, and coverings to give the desired performance.  If they can’t explain, do you really trust them to understand what has to be done on your roof?

Depending on the feedback to this post (there’s a comment button to the right of the post headline), I could go into more detail about the considerations to take into account when choosing both product and associated flashing system.  So if you want to know more, please comment and either ask the questions, or add your commentary to the above.  I look forward to the discussion.



5 thoughts on “Foundations (of a metal roof system)

    • Thank you for stopping by! I have a lot of respect for the work that Jon Eakes has done over the years advising homeowners, and was very pleased to share with him our approach to roofing issues. Unfortunately the approach we take is not universally used. Which is why there is a need for this kind of blog.


  1. You were very thorough in your examination of our roofing requirements. In fact, you were the only company of those that quoted on the job, that inspected our roof from both the inside and out. You presented us with a detailed work plan that addressed the job properly as a total roofing solution “done right”. Decking was replaced, and new fascias were installed to give the eve troughs something substantial to be attached to. Ventilation baffles and soffits were added to give maximum air movement to prevent ice dams. A good layer of insulation was added to the attic to keep the heat in the house. The final touch was a beautiful stone coated steel roof that will last our lifetime. We look forward to saving on our energy costs.
    Our roof is beautiful to behold and the neighbours and passers-by comment on it. We highly recommend your company to others because of our satisfaction with your service.


      • I watch my neighbours change their shingles every few years, and they don’t seem to appreciate that the cause of deterioration is that their attic is not properly ventilated. Many of the houses were built without proper soffits and roof ventilation. The heat build up inside is melting the shingles. In the winter, they have icycles hanging from their eves, which causes water to backup under the shingles and damage their decking. It is important to fix the problem before you just cover it over. A job well-done only has to be done once, saving a lot of money in the long run.


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