Basement Humidity Mitigation

[pghmyn]

I haven't really been posting much on here because my hands have been just full working on my house.

 

I have a fair amount of humidity in my basement, and I have a 45pint dehumidifier running down there. The humidity is still around 70% - on average. Is there anything I can do in addition to the dehumidifier running?

[Trip]

How big a basement?

What type of construction?

Open plan or partitioned into separate spaces?

Central A/C?

Any existing sumps, slab drains, etc?

[pghmyn]

How big a basement?

What type of construction?

Open plan or partitioned into separate spaces?

Central A/C?

Any existing sumps, slab drains, etc?

500-600sq ft

 

Cinderblock. All walls painted, all cracks sealed, french drain installed around perimeter diverting to sump pump.

 

Open plan.

 

No central A/C.

[Tpt life]

You'll have a couple of issues. Any air transfer at all hurts. With no AC this means your upstairs windows are open? New humidity is constantly invading. Also, humidity equalizes almost universally. This is why a humidifier in a single spot in your house does not generally create a large spike in one region but more a specifically local spike that evens out fairly close to the unit. What this means is that you'll not just be drawing moisture out of the air but also the framing and sheathing. Keep in mind that dehumidifiers are rated by the amount of air they cycle and range from tiny machines to machines that'll pull five gallons of water out of the air per hour. 45 pint is a capacity of the reservoir so also check fan ratings etc. My 30 pint per 24 hour will take my basement from 80% to 65% in two or three days and discharges directly to my sump. I also am not running AC and have windows wide open through thunderstorms at times. If I recall they just recently mitigated foundation seepage? It may just take time or you may want a different/additional dehumidification system.

[Trip]

Part of your solution may involve a larger dehumidifier, but part of any long-term solution is going to involve retarding moisture infiltration…

 

Your long-term solution is going to involve several components… One part will be to understand the source of the moisture (air infiltration, through the walls, through the slab, etc or a combo of sources) and identify methods of retarding infiltration. Do you know the source of the moisture? There are several DIY sites with simple test-methods for you… Some sources of moisture infiltration are easier to mitigate than others...

 

Part of the answer is going to understand your ground water situation – i.e. why the French drain? Does the sump usually have water in it? How often does it run? Do you know the source of the ground water (hydrostatic pressure, site drainage, storm run-off, etc)? Some sources are easier to mitigate then others… If you don’t know, you should get a site survey by a reputable contractor…

 

Obviously, it’s going to be hard to help via forum posts… Might as well give the final advice first, you will be best served by a site visit by a qualified contractor…

 

But a couple of questions may help...

 

How often do you need to drain the dehumidifier?

Does it run ‘constantly’?

What’s your target humidity?

 

If your dehumidifier runs constantly, emptying it daily and you’re still at 70%, then you certainly need a bigger unit in the short-term until a longer-term moisture mitigation solution is installed…

 

==>No central A/C.

But do you have forced-hot-air heating? Can you circulate air without the furnace running (i.e. fan-run-on mode)?

[wdwerker]

Triple H has lots of valid questions ! There is no magic fix. You have to isolate the source of the moisture then execute a plan to remove it.

[pghmyn]

Why was the french drain installed? I am really not sure to be honest. I thought of it as an added bonus when they did the foundation work. I thought only it was only going to be fixed structurally, but when I heard about the french drain I was even happier.

 

The dehumidifier runs 24/7. However, we have been having a really rainy season as of late. More so than I would say is normal for my area. Couple this with the hot days after the rain, the humidity is constant. 

 

I do have forced air, but I do not have an option to run a fan only - old thermostat. I will have that replaced eventually.

 

I will contact the contractor who did the work, and ask them why the french drain was installed, and about any other information they know. I will also do self tests for moisture.

 

I guess my real question, what should be target humidity for my basement if I want to put up some drywall and maybe carpet or laminate wood with throw rug.

[rodger.]

I just sold my home, and the unfinished basement is huge (rural property) - somewhere near 2300 square feet. The basement was very damp when I moved in. I found three small cracks in the foundation and had them sealed by a pro with epoxy/urethane injection. Solved those problems in a matter of hours.

This helped, but I still had lots of humidity. I created a custom cover for my sump, with a 4" abs access to get at the pump for repair, etc. I also put a poly window in it. I'll post a pic later. For this house, the sump pump was just a back up plan, there is a gravity drain that exits at daylight at the end of the driveway.

Next, I resealed all basement windows, and a bunch of above gear windows as well. I run my furnace fan 24/7, wether the heat or AC is on or off.

Finally, I bought a Powerful dehumidifier - and it was a but pricey (about 500). This thing pulls a lot of water from the basement. My next step was to be to seal the concrete floor, but I have since sold the house so I guess I'm not gonna do that.

I know for a fact that my area has a very high water table, so there is almost always water in the sump pit. I feel like a lot of the moisture in this house migrates through the floor, and because it is so large, a lot of water vapour can find it's way in.

Humidity can be a very difficult thing to pinpoint, even for a seasoned pro. Each of the steps I took above helped in their own way, and reduced the overall humidity in the basement.

I had some help from the guys in ridgidforum.com. There are some waterproofing contractors on there, so you may want to do a forum search there.

[rodger.]

1/2" plywood, sealed to the floor with outdoor caulking. One hose is for my dehumidifier, one for my softener, the abs is for the sump ejection.

[wdwerker]

I would be thinking about paperless drywall, metal studs and a tile floor if the humidity can get high even if it's just seasonal .

[pghmyn]

I am in process of having radon mitigation installed. Once they get their equipment finished with, I will see what I can do to cap the sump pump. There is always water in it.

How affordable are tiles? Is prefer not to get the bottom of the barrel brand, but I don't want the absolute finest on my basement floor. For a 200-250 sq ft area, how much would tiling run? I've never tiled, I have no clue what to look for in terms of supplies.

[wdwerker]

Take a straightedge and see how flat the floor is. Really large tiles can be tricky to set if the floor isn't pretty flat. I haven't set tiles in years but you can either buy or rent the tools. Look for a few videos on tiling a floor. Just look at the tiles you like and avoid the cheapest ones.

[rodger.]

I would put something down on top of the concrete before tiling. A lot of people in my area use the plastic dimple membrane designed for the exterior of a foundation (black roll product - delta MS) and then put plywood on top. Drive tapcons through the plywood and and membrane, and then you can use whatever floor you desire.

[Trip]

==>and a tile floor

if the moisture is coming through the slab, you'd need to mitigate it prior to laying a floor...

 

First things first... identify source(s) of moisture, then mitigate, then finish...

[Tpt life]

Radon mitigation is going to move air from under your slab and create a little suction. If below the slab is a decent sand gravel base, you may significantly reduce humidity migrating through the slab. I would be curious to see how you fare post radon mitigation.

[krtwood]

You say the dehumidifier runs constantly, but how often do you have to empty it?  Or is it hooked up to a continuous drain?  I only ask having had my current dehumidifier fail to actually get cold enough to actually do anything after 1 year and the previous one after 3 years.  Just because it's "running" doesn't mean it's working. 

[pghmyn]

I have it hooked to a hose, so it's just draining. But I'd say it took about a few hours to fill up the bucket. Not long at all.

[jHop]

My parents have a humidifier running 24/7 in their basement.  The windows are usually closed in the house, although there are plenty of leaks.  They don't have A/C right now, due to the rising costs of equipment.  (Sometimes, my family takes a really long time to make decisions.  The A/C has been on the fritz for 20 years.)

 

They've got a cinderblock basement with wood paneling (furring strips only half way up the walls) with a basic tile floor directly over the concrete.  They've also got moisture issues.  Some carpet remnants were placed on the tile (only the basic non-slip underlayment) to act like an area rug.  

 

My dad keeps his inventory of used books down there, as well as the family library and much of the audio visual collection.  There's not a lot of walking room, but the inventory is cleaned out periodically.  On the other half of the basement is a mildly finished room (painted cinder block) that has the laundry, the workshop, and the fabric collections.

 

This dehumidifier runs constantly, and gets drained usually every 24 hours.  I'm not sure what the rating on the dehumidifier is, but the bin is at most a 5 gallon bin (probably only 2).  The air downstairs is easily 20 degrees cooler than the rest of the house.  (I know this is because there's less moisture in the air.)  My point here is that this is all without intentional air flow.  The books are not falling apart due to humidity issues, they are under attack from the occasional invading moisture issues.  The tiles, before the humidifier was put into the finished side, would just pop off the floor because there was no treatment to them.  These were the basic vinyl tiles, which you can usually find around $1-2 each.

 

My rule of thumb has been that buck to buck-fifty per tile (in the 12" by 12" square).  Then again, I'm cheap.  (Maybe not as cheap as my parents: I would have had work done on the A/C and foundation waterproofing within that 20 year span.)

 

I provide this example not as proof of what I can do better, but as what not to do.  Sure, the humidifier keeps the pages from sticking together.  But it's too cold down there for most long visits.  You need an afghan or throw blanket just for a simple TV show, and just because there's a humidifier doesn't mean the problem has been solved.  The humidifier is more of a bandage; the real medicine is in limiting the amount of moisture that gets into the space in the first place.