Can I cover external vent holes with cement sheet?

[Katetaxicabs]

  

  

Hi I’m in the process of draught proofing my house and I’m filling up my old vents with foam core insulation. I also want to completely cover them to achieve a more streamlined look. You’ll see in pictures that it’s essentially a hole cut out in a single board of timber (a header?), about 50mm in thickness. On the inside I’m planning to cover these bays with plywood sheets painted white to match interior, but on the outside I’m hoping I could cover them up with cement fibre sheets to achieve smooth look. Can anyone see any reason why I shouldn’t? Like if timber needs to breather for example? I am doing a test with one but I didn’t cover it fully cause I didn’t have right size sheet. The plan is to cover these bays and paint them so you can’t see the holes at all

[JacobZ]

Hi @Katetaxicabs,

Thank you for your question about covering vent holes at your property.

I suspect that this vent is there because in the past there was a ceiling cavity created by sheet products being installed directly into the rafters.

Can you see any evidence of screws being used on the underside of the rafters inside your home? If you remove the vent cover, is there anything behind the cover, for example, cables, gas or water lines?

The purpose of a vent like this is usually to allow fresh air to enter an otherwise sealed cavity, such as a ceiling cavity. As there is no longer a ceiling cavity, the need for a vent is likely no longer required. 
 

I'd suggest nothing is stopping you from covering these vents, but allow me to tag @Nailbag, @Dave-1 and @Jewelleryrescue for their opinions.

Let me know if you have any further questions.

Jacob

[Katetaxicabs]

Thanks Jacob, these vents were originally for underfloor gas ducted system as oer old building code. We don’t have gas heating anymore and there’s nothing sitting in these vents. They are literally gaping holes to the outside leaking a lot of warm air. 

[JacobZ]

Hi @Katetaxicabs,

If that is the case, there shouldn't be any issues with covering it up.

While you still have access to them, it is likely worth removing the vent cover and painting the inside of the timber cutout just to seal the timber and give it that little bit of extra protection.

Let me know if you have any further questions.

Jacob

[Dave-1]

Morning @Katetaxicabs 

Generally I dont like covering up air vents, I figure if they are there then there is a reason. I like your reasoning and it makes sense. If you are only covering them up you could check in 6 months time to see if there has been any deterioration in the area. I wonder how big the actual air holes are if the plate is removed?  It may be a mute point.

Dave