How do you cut rectangular holes in fibre cement eaves for roof ventilation?

[neverlostau]

I am needing to install roof ventilation to keep our roof space drier, so I need to cut 200x400mm holes and install screw in vents.  The eave/soffit material is fibre cement (FC) so what tool/blade should I use?

Also any tips on cutting upwards and not getting covered in FC dust, or breathing it in, would be appreciated.

Thanks, Dave

[Jason]

Hi Dave (@neverlostau)

Welcome to Bunnings Workshop. We're pleased to have you join the community. 

Great to see you are being careful, prioritising your safety and thinking about personal protective equipment. Please also ensure there is not asbestos present. 

Apologies but our resident Bunnings D.I.Y. experts are not on the site today. Let me tag some other helpful members to see if they can share their thoughts in the meantime: @TedBear, @JacobZ95, @Jewelleryrescue.

Jason

[JacobZ95]

Hi @neverlostau,

There are a few different methods you could use depending on whether you have any power tools or what your budget is. 

If you had an angle grinder you could use a Flexovit 115 x 20 x 1.2mm Ultra Thin Turbo Diamond Blade Otherwise, if you don’t have an angle grinder, a jab saw such as the Irwin 9tpi Heavy Duty Jab Saw could be used, just note that it is not 100% designed for this purpose and it will cause some wear on this product. 

Ultimately, there will be some dust created from cutting fibre cement. You could get a helper to hold a vacuum up to the cut to reduce the amount of airborne dust, but ultimately there will be some. The best way to avoid it is to use adequate PPE. My suggestion would be the Craftright Safety Goggles and a good dust mask like Trojan P2 Dust Mask - 3 Pack 

If you need any further advice, I’m happy to help. 

Jacob

[neverlostau]

Thank you @JacobZ95 

I have a jig saw but someone did mention to me that an angle grinder might be best.  I will look into the Ozito PXC cordless range, of which I have a few excellent tools already.

It is definitely not asbestos so that's good but I will use PPE as you recommend.

[Jason]

Let us know how you go and whether you need any assistance @neverlostau. We're here to help.

Jason

[neverlostau]

Thanks @Jason 

A friend lent me his Worx Compact Circular Saw (I think Ozito does one similar) with a diamond blade that he used to use for cutting out old tile grout.  It has a laser guide so it was easy to get a good straight cut.  The hardest part is holding it up above your head to push it onto the soffit.  An angle grinder would work too but maybe less accurate?

I screwed the vent grills straight into the FC sheet with the Zenith 8G white headed needle-point screws.  I'm pleased with the result and have included a photo.

Aluminium vents in FC sheet soffit

Thanks for your help.  Happy DIYing, Dave

[Jason]

Great work @neverlostau. Many thanks for sharing the end result.

Feel free to post whenever you need a hand.

Jason