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Basement ventilation thoughts

Posted by s_carroll (My Page) on
Thu, Aug 25, 11 at 13:58

Hey all

We just had our basement framed and drywall. Prior to the install, we had issues with humidity but a dehumidifier has cleared up the issue. We had moisture vapor coming in through the exterior walls.

Now that the walls are framed, we had/have concerns about humidity building up between the brick foundation and the new walls. That being said, there is a large (about 2'x4') opening to access our electrical panel that we've left open to allow air flow behind the wall. Additionally, the gap behind the wall is almost a foot deep because of working around plumbing. Also, no vapor barrier was installed because of how large the gap is and because I didn't want moisture being bottled up between the plastic sheeting and the brick, which I reasoned would just rot out all the 2x4 framing.

I've been checking the humidity behind the walls, as far as I can reach my arm back there and the humidity has been maintained below 60%.

So here's my questions/thoughts. I plan on leaving the access opening open to allow air flow but will install a set of louvers to 'hide' the ugly brick etc. In addition to that one airflow point, should I consider installing other vents in the ceiling or other walls to suck even more air from behind the drywall? Go crazy with fans to literally suck the air out?

Thoughts are very welcome!

Follow-Up Postings:

RE: Basement ventilation thoughts

It's unfortunate that you didn't read some expert literature on finishing a basement before you undertook your renos. ( See link to Building Science Corp. the principals of whom are several of the leading experts on building science in North America.)

I can't imagine housing in any climate in the US that couldn't benefit from insulation.

The good thing is that you didn't put a vapour barrier the upper section of your basement walls, so no moisture will be trapped there. However, you will still have to use mechanical dehumidification to keep the moisture well below 50% to inhibit mould growth.

Here is a link that might be useful: Building Science Corp on basements

RE: Basement ventilation thoughts

Thanks for the response worthy.

I actually tried to read as much about basement renovations as possible, but most of the information either couldn't apply to our situation or was out of our budget (read: waaaay out of our budget).

I guess mechanical dehumidification is the way we'll go. On that thought, thinking about how air will be moving around/behind the walls, would it make sense to actively ventilate the area? Or do you think simple movement of water vapor from high to low density will be enough?

RE: Basement ventilation thoughts

I rented a house that had a basement finished that way. From what I could tell--no smell of mould--the dehumidification was sufficient.

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