What is the best way to cut an insulation board?

[nanuuk]

Hi,
I would very much appreciate if there is somebody who has experience in cutting insulation boards and can give advice on what is the best way to cut them.
Even if I take perfect between the rafters measurements for a snug fit I cannot fit the board in. I cut it with a panel hand saw for general use. It's the right angle I struggle to achieve on the side.
Does it make a difference whether I cut down the shorter or longer side of the insulation sheet?
Do I need a circular saw?

Many thanks.

 

[Maxsys]

Sorry to be blunt but you need a bit more practice.

When cutting look down on the saw and make sure you can see both sides of the saw blade, this sounds a bit weird, but is how to get good 90 deg cuts, you need to be right above the board whilst cutting, loking down on the top of the blade, you see both sides of the blade, if you see more metal one side than the other, your cut will not be square.

Practice is what its all about.

 

[fl00rsander]

I simply use a long blade knife to cut celotex, there is less mess.

Practice cutting a straight is also needed by the sounds of it.

 

[ladylola]

I've just done this very job last week on an old barn that had rafters all shapes.
I started by cutting the celotex a bit oversize often with a knife, then holding the sheet in place I ran an old saw down the side of the rafter to in effect scribe it to the rafter. Depending on the shape of the rafter it took a couple of cuts to fit it. Then repeated on the other side to form a snug fit.
Circular saw NO!
The insulation marked with a grid pattern would be helpful to you.

 

[nanuuk]

to get good 90 deg cuts, you need to be right above the board whilst cutting, loking down on the top of the blade, you see both sides of the blade

I see my problem was that I cut the board down its longer side and in a horizontal position. I will try the vertical position and cut down the shorter side which will allow me to see the blade. Cheers.

 

[nanuuk]

I started by cutting the celotex a bit oversize often with a knife, then holding the sheet in place I ran an old saw down the side of the rafter to in effect scribe it to the rafter.

Good idea although I would worry about possibly cutting through the felt. I guess you didn't have that.

Circular saw NO!

Why not?

The insulation marked with a grid pattern would be helpful to you.

Hmm, mine doesn't come with the grid. Maybe next time, thanks for the tip.

 

[ladylola]

I started by cutting the celotex a bit oversize often with a knife, then holding the sheet in place I ran an old saw down the side of the rafter to in effect scribe it to the rafter.

Good idea although I would worry about possibly cutting through the felt. I guess you didn't have that.

No , this time we were fitting it from the outside before fitting ply over the top then tyvec etc although I've done the same from inside with no problems.

Circular saw NO!

Why not?

sledge to crack a nut springs to mind , besides you need to watch the dust.

The insulation marked with a grid pattern would be helpful to you.

Hmm, mine doesn't come with the grid. Maybe next time, thanks for the tip.