Roofs: Retrospective 3, Oct. 30, 2015

After showing you the product and the tools necessary to create that product, I am going to attempt to describe the process.

The product was a standing lock roof (see 2 posts ago) that I made with the tools I showed (see 1 post ago). I am not going to try a recreate the entire roof, but will focus on the main event: the locking of the metal sheets together as a mini demonstration.

The first thing to do is create the metal sheets, or “pans” that the carpenter will attach to the roof and to one another to make a waterproof finish.

I created these pans with the use of a sheet metal break – in the old days the carpenter would create them on site with the gigantic pliers I showed in the last post. Using the break, I can manufacture pans that are 10 feet long….back in the late 1800’s, the materials available and the tools at hand would have necessitated making much shorter pans that would have been joined together.  In this post, I will make two short pans and focus on the standing lock seam that makes them one piece of roofing.

Essentially, I make a “U” of the metal (in this case 30 gauge flat galvanized steel), with one side 1-3/4″ high and the other 1″ high.




Our task will be to fold the high side of one pan over the low side of the adjacent pan, not once, but twice.

To make my life easier, I used the break again to make the initial fold:



Before attaching the pans together, we have to attach the first pan to the roof using home-made clips of scrap steel:



These clips will be invisible and strong as they will be under the steel and will be integrated into the seams. More clips, more strength

Next I begin the folding process:


Using the iron with the higher side against the seam, I hammer the tin over the low side of the adjacent pan to make the first fold.  The iron acts like a anvil to let the hammer do its work.


I work my way up and down the seam to make sure the fold is tight and crisp. Once done the fold it is as high as the opposite edge of the pan: it is now 1″ high.


That is phase one. Now I want to fold the entire seam over itself to make it durable and watertight and strong! Turning the iron so that the low side is against the other (right) side of the seam….



I begin to gently bend this edge over onto the iron:


Once again, I can only work where the iron is, so I have to work up and down the seam….


When this step is accomplished, I move the iron over to the left side of the seam to complete the fold.




It starts to look like this:



And finally this:



Almost like a jelly roll!!! (If you have an imagination!!)

You can see that this double fold technique is really strong and watertight….you can also see why it is extremely labour intensive!

And here I am with the first seam of our “roof”:


A tiny demo of a larger process.  I can say that it was fun to do those two roofs, but not something I would want to do all the time.  Fortunately, there are new systems that are currently in use that create essentially the same joint without all the hands on labour.  Keep your eyes open and you will see different roofs all around you and if you are observant, you may see someone in action and you can ask questions and learn from the carpenter on the job site.

Happy Halloween!


About jhcarpentry

I am a teacher in the Construction Carpentry Program at the Chateauguay Valley Career Education Centre (CVCEC) for the New Frontiers School board. This blog is a way for me to connect with my students.
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