Have 4 inch hole was made by builder for no reason and went unnoticed for long time as the hole was in the side wall of the House. the hole is through a basement wall.

How can I permanently block the whole. I am ok to keep vent mounting block as is. so can I just block the hole from inside by a plywood ?

I don't have any requirement to reuse the hole unless I am aware of.

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  • 6
    This is an air vent for the basement designed to avoid high humidity that causing mold to develop. My advice is to leave it alone and make sure the flippers function properly (stays closed normally).
    – r13
    Aug 15, 2021 at 20:30
  • 4
    The space was insulated against freezing that is required to prevent the cold air to get into the living space. The air vent inevitably will allow an insignificant amount of cold air to get in, but most of the cold is blocked by the air vent flippers, which should be automatically closed by the heavier cold air. If there is no/inadequate airflow, the insulation can absorb moisture in the humid air and become damp. With no fresh air to dry the wet insulation, the insulation will not serve its purpose and develop mold.
    – r13
    Aug 15, 2021 at 21:35
  • 1
    If the house has gas or oil heat , it is for combustion air. Modern houses are fairly well sealed and a source of air is needed for any combustion. I have put these into a couple houses ; I usually run a duct to near the furnace . Aug 15, 2021 at 23:16
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    "was made by builder for no reason" This is certainly wrong. Holes take work to make, builders don't do work for no reason. You don't know what that reason was, but before you decide what to do with this hole, you need to find out what that reason was. Looks like ventilation to me.
    – kaya3
    Aug 16, 2021 at 9:54
  • 5
    @kaya3 Exactly. And even if a hole were made accidentally, there would have been cheaper, easier, and cleaner ways to have dealt with it than to put that adorable vent cover on it.
    – Sneftel
    Aug 16, 2021 at 11:01

3 Answers 3


Yes, you can cover it up with plywood. However:

was made by builder for no reason

No, it was for a reason. If it was for no reason, they would have likely just covered it with regular siding. When they went to the extra effort of a proper cover, that's an indication they really intended to make the hole. You just don't know what that reason is. Typically, this would be a vent for a dryer, cooktop or bathroom exhaust. Either there is something typically included in the house that wasn't included here, something that was removed or something that was never installed (that should have been installed).

A plywood cover with a few screws is easy enough to remove if you later figure it out. But consider all of the following:

  • Do you have a clothes dryer? Is it vented? Is it possible that some owners put it in one location and some put it in a different location?
  • Kitchen cooktop - Does it currently have a fan? If not, is this close enough that it could be used for an exhaust fan?
  • Bathrooms - Bathrooms generally require a fan except if they have an operable window of a certain minimum size (specified in the building code). Is there a bathroom near this location that doesn't have a fan but should? Or that doesn't have a fan because it has a window but could have a fan connected here?
  • 2
    Strange, I've never seen just a hole properly covered and no duct work.
    – JACK
    Aug 15, 2021 at 19:09
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    @JACK That's exactly my point. If they goofed and drilled a hole but then realized they didn't need it because "no ductwork nearby" then they would not have also cut the siding and put on a cover. Which makes me think they built 25 of these houses and 24 needed the ductwork but the buyer didn't buy whatever option so they didn't connect any ductwork here. Or something like that. Aug 15, 2021 at 19:13
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    I (and I think Jack) mean "properly covered" in the sense that they put a real "exhaust duct cover" on it, as opposed to just leaving the hole on the inside and simply not cutting the siding. Aug 15, 2021 at 19:28
  • 1
    @LeeSam Properly covered for an exhaust vent but then lacking the duct work. Definitely cover and seal it if it's not needed for a dryer, etc.
    – JACK
    Aug 15, 2021 at 20:27
  • 1
    The dryer, kitchen cooktop and bathroom are vented out. I'll still investigate until I found the purpose.
    – PowerTech
    Aug 15, 2021 at 21:28

Have 4 inch hole was made by builder for no reason

There is a reason; even if that reason is simply "by accident".

went unnoticed for long time as the hole was in the side wall of the house

How long is a "long time" exactly? Can you ask the builder?

My theories:

  • After the siding was installed someone noticed that the hole is in the wrong location so a new one was drilled but there is no incentive to fix the old one
  • Homeowner changed their mind about dryer location. New hole was made but old hole was finished just in case homeowner changes their mind again

My guess here is that there was a basement bathroom going in and this was going to be the exhaust out for the fan. This would fit the location and size.

You don't have to do anything right now except put a screen over it. Without it being a properly ducted orifice there is a requirement for a screen on basement air vents.


  1. Put a screen on it.
  2. Cover it... I would use plywood and small screws so that you could reuse it if you want in the future. Then just throw some insulation over the plywood.

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