Hey guys

Since purchasing my home I have noticed every spring through summer my basement experiences rather extreme condensation... At first I thought the basement must be leaking but after pulling back the builders insulation that runs halfway down the wall... I noticed the concrete was dry and the only water to be found was forming between the vapor barrier and the insulation..

If this were a minor problem I probably wouldn't worry about it but there is usually so much condensation that the bottom of the insulation becomes soaked with water and once walls go up I'm concerned this will be a problem..

A friend of mine who has renovated several of his own basements suggested that I take a knife and slash the existing vapor barrier, then once the studs are in put insulation between the studs and the existing insulation and install a new vapor barrier..

Any suggestions?

1)Run a dehumidifier in the summer.

2) Some of this humidity may be entering the house through the walls and concrete floor. It way help to apply a waterproofing sealer to the walls and the floor. it will reduce migration of moisture. You can use the tin foil test to see if this is the case.

During the months you mention tape a square of tin foil to the floor and a section of wall. wait a couple of days and peal back the tin foil. If it is wet underneath than you know where the humidity is coming from.

stating the obvious here, but any water/moisture issues is your #1 priority right now w/r/t your basement. glad to hear you're at the early stages still.

www.buildingscience.com/documents/reports/rr-0308-renovating-your-basment/

Never put a vapor barrier on the inside of a basement wall where the other side is concrete. The concrete needs to breathe, and the vapor barrier traps the moisture between the concrete wall and the barrier - and then all kinds of funky things start to grow in the wall.....

Apparently, the bigger problem can be warm, moist air in the spring and summer coming in contact with the colder concrete wall and condensing. For that, Building Science recommends XPS foam against the concrete (its semi-permeable), then non-faced insulation, then sheetrock for the fire barrier.

I've outfitted my basement walls per the photos on Building Science (plus some extra waterproofing). I've never had a water problem in my basement, but now I really have peace of mind.

Dehumidfier works too, but now I won't have the noise or the hassle of one.

what's the deal with conditioning in your house? do you have or plan to install central air (if the latter, planning for that comes into play when planning for a new ceiling in the basement)? if the answer is yes, think about adding some extra inlets and an extra return (ie., off the same air handler servicing the first floor, if applicable) in your basement. relatively modest additional cost (extra insulated duct work and time to install). note: this won't fix a significant moisture problem though the additional dehumidification will help....still may need a dehumidifier when really humid out. but but helps mitigate that "basement smell" by circulating air throughout (and also across filters, etc.)

(plus some extra waterproofing). I've never had a water problem in my basement, but now I really have peace of mind.


btw, we went the water proofing route too. expensive, but view it as an insurance policy (first checked into a real homeowners insurance policy or rider but couldn't find one that made any sense in terms of what's actually covered sub-grade.....and we're not in a flood zone). ended up putting about 5x the amount of that system into the basement in terms of carpentry, electrical, furnishings, etc.....so still an expensive "policy" but peace of mind is good...FWIW, those water proofing contractors must be having it tough these days (like everyone else), so prob. good time to look into if appropriate

I just went through all of this as well last summer.. Here's from my experience...

Definitely do what monorailfan says when you do actually start putting up walls.. the rigid foam route is the best current thinking on basement moisture control. The articles at basementscience.com are top-notch.

At the very least, remove the vapor barrier for now and let the insulation dry out before it starts getting moldy.

You should also do your best to make the basement air-tight from the outside. Humid outside summer air entering the basement will cool and raise the relative humidity. If the humidity gets too high, the dew point of the air exceeds the temperature of the basement and causes condensation.

The water collecting behind your vapor barrier could be either from humid basement air getting past any gaps in the vapor barrier (which is never a perfect seal) and condensing on the basement walls, or from moisture wicking through the concrete. Either way the vapor barrier is hurting you.

You should also seal around your rim joist, basement windows, vents, pipes, and anywhere humid summer air can enter the basement. If humidity levels are still high (above 60%) then consider an active drying method (such as exhaust fan or dehumidification) to regulate humidity.

If you DO decide to put up XPS against the concrete first, my experience was that concrete walls are never perfectly flat. The Building Science website says to either use fasteners, or have the wall studs 'sandwich' the XPS against the concrete. Do the first and not the last. At least in my basement, I would not have a flat wall. In other words, to get a plumb wall, there are spots where the studs are right up against the XPS, and some are about an inch away.

The other thing to consider is that rigid foam is like solid gasoline. Under the right conditions, even with a built in fire retardant, it could ignite if there was some fire source inside the wall. So I then was thinking about fireblocking...anyway, what I did was instead of putting up XPS and then building the wall frame in front of it, I put a CCA top plate that was a 2x10 so that is actually sat below the joists but on top of the concrete wall, and then it extended out above the XPS, and the studs were then attached. If that XPS would ever catch fire, it would temporarily be blocked by the top 2x10 CCA plate, rather than burning around a 2x4 plate and then up into the joist cavity.