Steel decking sweating

timswi · Dec 15, 2009

I have a 48ft storage area under my front porch that is covered with 7" of concrete with steel decking underneath. It's turning into a rain forest in there from water dripping off of the steel. Only really happens when the temperature drops.

Has anyone tried putting styrofoam on the steel to insulate it? If so, what thickness, what kind, and how well did it work?...Gotta fix this, SWMBO is running out of patience. It's a newer house, so want to get this taken care of....Thanks.

randy41 · Dec 15, 2009

what is the flooring in the storage area?

timswi · Dec 15, 2009

randy41 said:
what is the flooring in the storage area?

Block walls and concrete floor...unheated space.

sawdust_maker · Dec 15, 2009

timswi said:
I have a 48ft storage area under my front porch that is covered with 7" of concrete with steel decking underneath. It's turning into a rain forest in there from water dripping off of the steel. Only really happens when the temperature drops.

Has anyone tried putting styrofoam on the steel to insulate it? If so, what thickness, what kind, and how well did it work?...Gotta fix this, SWMBO is running out of patience. It's a newer house, so want to get this taken care of....Thanks.

The problem is moisture in the enclosed space. It contacts the cold steel surface, and you get sweat. The solution would seem to involve:

- stop the moisture from getting in there
- remove the moisture
- isolate the moist air from the cold steel

You can stop the moisture from getting in by laying down a thick plastic membrane on the ground. This might be difficult to do, you need to seal it off.

Removing the moisture will mean either putting a dehumidifier in the enclosed space (expensive), or putting in adequate ventilation. Good cross-flow of air will stop this problem.

Insulating the steel is an option, but you would need a spray on insulation, probably polyurethane based.

Even if you do go with the insulation approach, I'd still definitely put in some ventilation. The moisture stuck in there will cause mold and mildew, nasty things to have around a home.

John

timswi · Dec 15, 2009

sawdust_maker said:
The problem is moisture in the enclosed space. It contacts the cold steel surface, and you get sweat. The solution would seem to involve:

- stop the moisture from getting in there
- remove the moisture
- isolate the moist air from the cold steel

John

Thanks John...Ventilation in there would be impossible at this point. It seems that the temperature differentials that we have been having (15deq one day and 50deg the next) is causing this. When it's not cold, it's bone dry in there. It appears that the steel is reacting to the temp changes, that's why I was curious about insulating it.

I put an oil heater on one end this week, and that end dried up in a day. I really don't want to run a couple of those, the electric costs around here are insane.

Steve C · Dec 15, 2009

timswi said:
I have a 48ft storage area under my front porch that is covered with 7" of concrete with steel decking underneath. It's turning into a rain forest in there from water dripping off of the steel. Only really happens when the temperature drops.

Has anyone tried putting styrofoam on the steel to insulate it? If so, what thickness, what kind, and how well did it work?...Gotta fix this, SWMBO is running out of patience. It's a newer house, so want to get this taken care of....Thanks.

Anytime a surface becomes colder than the dewpoint of the air, condensation will form on the surface. If the deck is corragated, putting solid styrofoam sheets on the surface will help, but it will still condense moisture in the voids where the insulation isn't contacting the deck. It may or may not run out and drip, but it will be there. A better solution would be to install a sprayed on foam that will completely insulate the deck and more importantly isolate the cold surface from the air containing the moisture. Then you can put additional insulation in the form of fiberglass batts or ridgid plastic sheets up on the cieling. You need a vapor barrier on the warm side of the insulation to rob the cold surface of its source of condensation. You can install plastic sheeting as the bottom most layer , fastened at the walls with cleats to accomplish this. It will want to be continious without any seams. You can then put up a finished ceiling if you chose and the problem will be long gone.

Never to see a drip again, and it will be much warmer.

timswi · Dec 15, 2009

Thanks Steve,

Was trying to avoid the spray-on stuff but it's looking like it might be my only option. This will never be finished, just storage. So I kinda want to keep this under control cost wise...Oh well, guess that's how it goes sometimes. Should have filled it with gravel and sealed it off when I built it.

sawdust_maker · Dec 16, 2009

timswi said:
Thanks John...Ventilation in there would be impossible at this point. It seems that the temperature differentials that we have been having (15deq one day and 50deg the next) is causing this. When it's not cold, it's bone dry in there. It appears that the steel is reacting to the temp changes, that's why I was curious about insulating it.

I put an oil heater on one end this week, and that end dried up in a day. I really don't want to run a couple of those, the electric costs around here are insane.

Then spray on foam is the way to go. Make sure it is dry first of course.

John

EddieWalker · Dec 16, 2009

The sweating, or moisture is condensation. It's caused from the moisture in the air, and the temperature of the metal. All air hold water. It's measured as humidty. When the humidity level is 100%, you have moisture. Below that level, it's still part of the air. Air can only hold so much water. The warmer the air, the more water it can hold.

So at a given temp, the humidity level will be at one point. When the temp increases, the abilit for the air to hold water increase too, and the humidity level decreases. When the temps decrease, the ability for the air to hold water also decreases. When this happens, any areas of that air that decrease to the point of 100% humidity will result in moisture appearing.

Metal is very prone to this because it gets colder faster then most other materials. It's only the air right next to the metal that is affected, but because the metal is cooler then that area of air, the humidity level increases to more then the air can hold. The result is condensation.

A foam barrier works great to stop this, but so does other materaial. Bubble wrap and wood work too. Creating an air pocket behind the foam or wood will actually allow that space to be warmer then the outside air, and you'll have less condensation.

Eddie