Coloured shutters of France, volets de couleur de france

What is the purpose of the brace on a shutter or door?

The brace is the support component of a ledge and brace. The brace prevents a gate, shutter or door from sagging because of gravity.

How does bracing work?

The brace works by transferring the load to a fixed point. The fixed point should be towards the suspended mounting such as a hinge.

So why does it work?

I am going to try and explain this simply. So I have an idea so we can understand the physics behind the brace. Now I have an exercise for you? Bare with me but grab a cardboard box a stick and some parcel tape!

  1. Your box has a top and bottom, just cut them away… go for it
  2. You now have a floppy square cardboard tube
  3. Lay it on the table edge down and grab two opposite sides
  4. You can easily bend change the square to a diamond shape
  5. Let’s get that box stiff again
  6. Grab a stick and place corner to corner
  7. Tape it to the corners
  8. The cardboard tube now maintains its shape
  9. You can stiffen further by adding a second stick (brace)in the opposite direction.

So this is the purpose of the brace

The brace helps maintain the shape of whatever it is fitted to. It will make a non-rigid frame rigid.

brace loading

  • Blue: Gravity
  • Red: Load on the shutter
  • Yellow: Transfer to a fixed point
  • Pink: Fixed point such as the hinge

I hope my image helps explain the purpose of the brace that you will find on the ledge and braced carpentry.

The boards of the shutter are attached to the horizontal ledges. Gravity puts a load onto the whole shutter. Because the shutter is hung onto the wall via hinges this fixed point creates leverage. So now the shutter has a load greater at the edge than the hung side. This load can force the shutter bit by bit to sag a little as the slack is taken up on the mechanical fixings. These fixings traditionally would be nails. If you install the diagonal brace the top ledge transfers the load to the brace. The Brace then transfers the load to a fixed point.

Do we still need a brace when the glues are so good?

I would say yes but if you construct your shutter well you could get away without the brace. For instance it the ledges are mortices into the back of the board the cranking will be stopped so ledges can be omitted. You can also double screw and glue but you will need to allow for expansion.

Is the brace only for the garden gate?

The ethos behind the diagonal brace has been adopted in other construction. You will find the same in stick framing to old timber-framed barns. You will find braces in

  • Roofs
  • Floor Joists
  • Scaffolding
  • Garden structures

My Conclusion of the ledge and brace

For a start but the brace has proved to be an essential construction method for centuries starting with the simple fulcrum. I believe it will be here for centuries more with intuitive repurposing.

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