Hello – I searched and didn’t find any matches to my exact situation. I’m in the process of finishing my basement and am trying to decide how to handle the floor. Headroom is 7’2″ from concrete floor to bottom of joist and I’d like to preserve as much as possible. The main issue I’m trying to address is condensation forming on the floor in the summer when the windows are open but I’d also like to take some of the bite of the cold away in the winter. I live in NJ and the concrete floor will get to about 58 degrees in the winter. Finish floor will probably be some kind of laminate, haven’t decided yet. Water isn’t an issue. Slab has no insulation or poly under it, house built in the 50’s and already had to cut through it to install a sewage ejector. I’ve thought of a few different options that I’d like opinions on but am open to any others.
Scenario 1 – Poly then 1/2″ Foam (R3.3) then 5/8″ OSB floated over the foam joined by plastic spline type of thing. I’d like to avoid having to use tapcon’s. They are just a PITA. Think this would be enough to get the floor above the dewpoint and avoid condensation? What about the floating OSB joined with the spline, will that work?
Scenario 2 – Similar to scenario 1 but use 1/4″ fanfold foam (R1) instead of the 1/2″. Think that is thick enough to avoid condensation?
Scenario 3 – Use Delta-fl and float the laminate right on top of it. I’m not sure if that would be enough to avoid condensation.
Thoughts? Do any of these sound feasable? Sorry for the long read.
Thanks,
Rick
Replies
Why not fix the problem first?
Your problem is ... condensation. You fix that with ventilation. That ought to be your first step. This means heating and cooling the basement completely separate from the house above.
Your second problem is that the condensation pools, rather than drains. You fix that with a floor leveling material, such as Gypcrete. You'll lose about half an inch of your headroom. The simple fact is that basement floors are not nearly as flat as your typical driveway.
If the water is coming through the slab -concrete is porous - you need to trench & drain the water away from the basement before it enters the house.
FHB has run at least two articles advocating covering the floor with plastic. Mike Holmes and I oppose this practice. IMO, all plastic does is make a mold farm. Fix the underlying problems - uneven floor and high humidity - first.
Floordrainage is so important I favor "floating" a new subfloor over the concrete, leaving space for water to drain to the sump and air to circulate. This suggests using a waffled plastic sheet (like Ditra) or metal 'hat' channel, rather than solid foam panels.This space will also provide that thermal 'break.'
Headroom is nice, but consider this: All basements flood at some point - and those floods are often quite shallow, as in less than 1". Why not raise your floor above the water level? Deeper water? A floor that can drain / breathe will drain and dry out much faster.
Imagine this: A floor mounted 3/4" above the concrete. Fresh incoming air directed by a duct to flow under the new floor at one side of the basement, and the moist air pulled out a duct on the other side-to be exhausted out of the basement.
a. go on craigslist and get a bunch of free latex paint, apply it thick, very thick, a few coats at least, apply thick with a push broom. Since you can always find lots of free latex paint on CL, pour it on, about 1 gal per 25 or 30 sq ft.
b. install a dehumidifier for finish basement, or really cheap, hang pantyhose legs full of of calcium chloride over a bucket, that will fix the condensation problem. Note, used the calcium chloride trick back in the 1950s in the coal bin, a modern dehumidifier is a lots nicer <G>
c. install floor of your choice after everthing has dried out and no more condensation.
58F in winter, say you keep the room temp at 68F? Set your dehumidifier to keep Rh below 55% and no condensation - refer to psychometric chart for other temps.
renosteinke - Yeah, I think also think condensation will be the first problem. It will have a seprate heating zone (baseboard hot water) and cooling (windows air conditioners) although the air conditioners probably won't get a lot of use, I probably won't run them much. I lean towards just open windows in the summer. My wife calls me cheap but I like to call it fiscally responsible... I also have a dehumidifer I run but once I open up the windows and let it in the humid air it kind of defeats the point. I may just need to be not as cheap..
No floor drains or perimiter/sump pit for any potential water infiltration to drain to. It's always been dry though, been here 12 years through some record setting rains.
It would be interesting though to use a ditra type undelayment like you mentioned and hook up a radon type of centrifugal fan with a duct mounted to it so as to pull the air from under the ditra to exhaust any moisture coming up from the slab out. Don't know if that would really work or not but intersting to try. Ideally I probably would have wanted to do that before framing any interior walls but that ship has already sailed..
junkound - Is the idea with the latex paint to create a continiuos vapor barrier? That would avoid any mold under the plastic. Ideally you wouldn't have anything organic under there for it to eat anyway.
I do have the dehuimidifier that I'll use but it's funny you mention the calcium chloride. I actually have containers of that in my closets in the summer to help with the humidity. I figured out after buying a couple of those Damp-Rids that is was just calcium chloride. Now I just steal some from my 50 lb. bag I buy for the driveway. I can usually keep the basement 50-60% in the summer but once I open a window that humid NJ air comes pouring in. I just hate the windows closed up in the summer but maybe I should just get used to that.
I'm thinking I may just go with the Ditra and use a floating laminate right on top of it. If it ever does get wet I can always just pull it up and replace it. You can get some cheap laminate that looks pretty good. I also plan on keep the drywall an inch or two above the floor and covering the gab with baseboard, just in case. I just hope the ditra provides enough of a thermal brake to avoid the condensation from forming on top of it or the laminate
Thank you both for the input.
Rick
Solve the condensation issue first.
As stated above, you need to increase the air circulation in this space and install some sort of dehumidifier.. If you have that much humidiity in the space, you risk all sorts of other issues (mold, warping the floor material, etc).
I am at a loss as to why the responder above would require it to be completely separate from the home's existing system (no mention of the heaty/cooling system type). For example, if it was forced air, simply adding this to the existing system may be quite simple. If you have baseboard heating everywhere, then some sort of air circulation sytem would likely be required (basement area exhaust fan tied to humidistat? air to air heat exchanger?)
If you solve the excessive humidity issue first, it makes all the other choices are much easier..
Close the windows
In NJ, in the summer, opening the windows brings in very humid air. It's almost certain that the cool basement will be below that air's dewpoint. There is no treatment for the floors that will eliminate condensation if they are cooler than the dewpoint. You need to close the windows and dehumidify.