When cutting fiber cement siding with circular saw use a blade that has only four or six teeth.
Cutting cement board siding.
For a slow but virtually dustless way to cut siding use power.
These are specialized to reduce the dust caused from cutting these planks.
I recommend the turboshear tsf1a fiber cement pnuematic if you re looking to buy a pneumatic siding shear.
To keep dust to a minimum use a circular saw that s equipped with either a dust collection bag or electric fan that.
The advantage of using the circular saw is that you can cut more than one board at a time.
You have to make the cuts very slowly.
Use a specialized blade used with the saw such as mikita hardiblade or dewalts filber cement blade.
Use your eyeware and ear protection.
One way to eliminate cutting or at least keep it to a minimum would be to remove the entire piece above the window flash the window and then replace the siding.