I am building a home with a walkout basement constructed of 12″ CMU – wood framed top floor – exterior walls are damproofed and backfilled with 2B stone in NW Pennsylvania. I placed 1/2″ tuff foam insulation against block walls with shiny side on interior, then used metal studs and installed R11 fiberglass insulation. After installing and turning on heat, but before it has been drywalled I have found moisture on the foil side of the tuff – some bays are dry while others are quite moist. Any suggestions as to why this is happening. Drywall is set to be installed next week. thanks
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Moisture condenses out of air when the temp. is reduced.
Obviously warm moist air is reaching the face of the foil which is cooler and condensing. Tell us where is the warm moist air is comming from and solving your problem will be easier.
Thanks for your response. I suppose the warm moist area is due to the fact that the temperatures have been around 0 - 15 degrees outside and the home has not been heated until last week. The condensation did not form until we turned the new heater on (propane forced air). Will the problem stop once the drywall is up or do I need to remove the foiled foam insulation and use only the fiberglass? The temperature is set at 70 degrees during the day, but is turned down to 55 at night.
A new house makes a lot of moisture from lumber and crete still drying out. By not heating it, not much drying was happenning. You kept all that moisture in the ice form. There is a strong variance between the extremely cold concrete in floor, CMUs and the suddenly warm air. You need a few weeks of heat before things stabilize. I would make sure to ventilate a bit. Maybe leave a couple windows cracked open an inch and turn the heat up to let some moisture out. Some new hopmes take a year to stabilize. You will nbe adding even more water with the sheet rock mud and paints.
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This subject has been of interest to me. I am pondering the feasability of different construction methods before finishing my own walk-out basement.
I found some interesting reading on the subject:
http://www.buildingscience.com/resources/foundations/basement_insulation_systems.pdf
Hope it helps you better understand what is happening.However beautiful the strategy, you should occasionally look at the results. Winston Churchill
The propane heater is a source of H2O. The products of combustion are CO2 & H20.
Enclosed space with cooler surfaces = condensation
"The propane heater is a source of H2O. The products of combustion are CO2 & H20."
I agree that using a portable propane space heater sources a great deal of moisture. There are a number of factors in the construction of a new home that contribute to high levels of moisture.
Insulating a home has its benefits and drawbacks. Ventilation and vapor barriers are controls for moisture in the upper floors. Typical interior construction does not allow for moisture moving both ways through concrete or block.
However beautiful the strategy, you should occasionally look at the results. Winston Churchill
My neck is bent forward from reading a bunch of material downloaded from the Building Sciences web site concerning insulation techniques in new construction basement.
Maybe you need to hold off until most of the moisture present in your block wall has dissipated.
It probably still contains quite a bit of moisture from the new construction, especially if the voids were filled.
Same thing from the floor slab.
Operate a dehumidifier draining to a floor drain and monitor the humidity level for a while before finishing the basement ?
Tarby,
I just had a large reply dumped by my computer before posting it.
Here's the recap.
Non vented propane heaters dump alot of moisture in the air, so if this is what you're using then that is a big source of the condensation. If it's your furnace (vented) doing the heating no worries.
New homes have large amounts of moisture that will be released from concrete, lumber, paints, finishes, etc. You will need a little time (maybe a full heating season) to dry out the above.
Read the basement insulation PDF at Buildingscience.com. Make sure that your 1/2" foam is has enough R value for your climate to raise the interior side of the foam above the dew point under normal conditions. I don't know for sure, but I think R3.5 might not be what you need for NW PA.
Good luck.
Jon Blakemore
I don't know for sure, but I think R3.5 might not be what you need for NW PA.
Jon has a good point. I did not pick up on the fact that the foil sided foam was only ½" thick. Top another 4" of fiberglass batt over that and the vapor barrier (foil) is now on the cold side of the wall. Unless of couse you have insulated the block cavities. Perlite is one product, it would raise the insulated value of an 8" block wall to R-11
I can see the foam as a barrier to keep the batt off of the block wall, was the foil sided foam considered an improvement over extruded or expanded foam?However beautiful the strategy, you should occasionally look at the results. Winston Churchill
My take on this is that the reason you have moisture condensing on the foil faced insulation is that you didn't place a sealed interior side vapor barrier before cranking up the heat. Or at least I didn't see any mention of one.
If I'm reading this correctly, that foil face should be preventing moisture from the CMUs from entering and the studs are metal, so they don't need to dry out (lol).
No significant amount of moisture would have been able to get to the foil-face if there was a well-sealed/taped plastic vapor barrier in place. As it is, water vapor has migrated thru the FG and made it's way to the foil where it has condensed.
Sounds like you'll have to take appropriate steps now and then wait for things to dry out before closing it up.
Goldhiller,
I disagree.
You do not want a vapor barrier in your basement because you want to dry to the inside. Remember the foam is up against CMU's, which are porous. They will develop moisture no matter what you do. Non-faced foam (eps and xps) will allow them to dry to the interior. A good vapor barrier on the inside will trap the moisture, causing it to condense in the FG batts. A vapor barrier on the foam (foil face) will hold the moisture between the block and foam, with potential rot problems. 2" of XPS would bring the interior condensing surface up to above the dew point but still be permeable enough to allow for the escape of moisture.
Now that I think more about it the foam is a very bad idea. Hopefully the Tardy might still be able to fix this before it's too late.
Edit: I read the first post again, and I think the "shiny side" might not be foil, rather just the facing that you will typically see on polyiso board. If this is the case, the problem is not as bad.
Jon Blakemore
Edited 2/19/2004 11:42:15 PM ET by Jon Blakemore
Upon talking to a local insulation guy, he recommends putting an additional layer of the Tuff R insulation against the existing rigid foam insulation and removing all fiberglass. He doesn't recommend using fiberglass in basements because of potential problems, like these.
In response to other posts, we can't wait to finish the basement for a year because this is living space. It is a mountain cabin with a walkout basement. In the basement are the bedrooms and main bath as well as the utility rooms/wash rooms. The top floor consists of living/dining area and kitchen with loft.
Thanks to all who responded.
No disagreement on my part about the principles involved. The way I perceived the situation is that foil-faced was put against the CMUs (foil to interior side), then the steel studs and then the FG was installed. I'm also assuming the foil-face was carefully placed and taped so that no moisture from the outside can enter thru the foil. Probably not the case.
I wouldn't do it this way myself either, but the question IIRC was "what is causing this"?......not "what should I have done"? And consequently, my response as to what is causing it IMO. Moisture from the house has made it to the foil-face and is condensing there. A carefully installed interior vapor barrier would probably have prevented this occurrence. But since/if that foil face is present, you've then just started a procedure that pretty much demands that the insulation is hermetically sealed on all sides to prevent other future problems........and that usually isn't or can't be done successfully for the long term. Maybe that bagged/encapsulated FG? I've never used it, but it doesn't seem like you could get it to fit as tightly as would be desirable.
It seems the appropriate methods of insulating a basement on the interior side of the wall is another one of those highly controversial issues. I've seen all manner of notions touted as "the way" to do it. But it also seems what works fine in one situation just simply won't in another. Differences in foundation materials, soils, water tables, drainage, climate, etc. will all play a role in success or failure.
We're facing an elaborate basement remodel in the very near future and so I'm also wrestling with this insulation and venting issue, among others. Although it's been a long time since there was any moisture problems in this basement and it's currently lined with 1"x6" knotty pine directly against the concrete walls (which will all be removed) with no signs of even any cupping of the wood, I think I have to assume that sooner or later the moisture will come and engineer things accordingly. It's my butt in the sling this time. <G>
Knowledge is power, but only if applied in a timely fashion.
Agreed, but I think a vapor barrier (or diffusion retarder) would only be worthwhile when the interior humidity levels are elevated from the construction process. No point in installing carefully only to tear out later.
I would strongly recommend that you read the articles at http://www.buildingscience.com I've learned alot from spending time there.
Jon Blakemore
Agreed. Tearing it all out again when the RH lowers and levels out would not be a good feeling. But.....it would have prevented the condensation on the foil-face, I think. Seems like removing the FG until things settle down is the thing to do now and then implement a different system. The rush to finish up the DW now is apt to cause some future problems I fear.
Thanks for the Building Science link, but......... I've already read scads of stuff there on basement insulating.
Knowledge is power, but only if applied in a timely fashion.