closed cell spray on foam insulation

[MFWD]

Hello,
I have a question about spray on closed cell insulation. I have a metal carport that I have enclosed both ends, put on a garage door and have metal the whole way down the sides. It was the first thing I built when we moved into our new house. I needed a place to store outdoor stuff before we built a garage/workshop combination. It is a double car size. I have a problem at certain times with condensation on the under side of the roof and it drips all over the things I have stored in there....skid steer. 4-wheeler, lawn tractor, log splitter etc. I think I read somewhere that if the ceiling is coated with a closed cell foam that all that condensation stops. Anybody here ever do this? Anybody here have any knowledge about this idea ? Can you help a brother out? Thanks in advance !!!!


MFWD

 

[RNeumann]

You need to understand scientifically why condensation is occurring. It’s the temp difference that is causing the condensation (different than dew). Spraying foam is about the most expensive “solution”.

Moving air through the building so the inside and outside air has the same moisture content and temp will go a long ways with regards to condensation issues.

 

[RayfromTX]

RNeumann, you are close but missing a key ingredient. The condensation is caused by a condensing surface that is colder than the dew point of the air. Dew is condensation. The reason condensation forms on the underside of the roof is the same reason it forms on the top side. It is because the metal is colder than the dew point of the air. Here's the really cool thing.

On a clear night, the roof metal is colder than the air. This is caused by the metal radiating it's heat to the night sky. Everything radiates heat at some rate. If you and I are facing one another then we don't notice it because we are about the same temperature and have a similar emissivity. If instead you are sitting and talking to a snowman you would feel cold. The snowman isn't radiating cold. That would be against the law. The second law of thermodynamics teaches us that cold doesn't radiate. What is happening is that you are radiating more heat than the snowman so what you are feeling is a net heat loss. The roof is facing deep space. It radiates it's heat but deep space doesn't have much heat to radiate back in return so the roof experiences something called radiant overcooling. The roof may be as much as 10 degrees colder than the ambient air temperature.

If you check the roof of your car there may be condensation in the morning but the sides are dry. That isn't because dew falls. Dew forms. It is because the sides of the car see other things that are also radiating heat like walls and plants so there is little or no heat loss. The roof of the car is colder than the sides. Another thing that is caused in a same way that you may have noticed is when the temperature is above freezing but there is frost on your roof. The air may be 35 degrees and the roof is 27 degrees because of radiant overcooling. Frost doesn't fall either. It forms in the same way dew forms. Cool stuff, eh? On a cloudy night the bottom of the clouds are significantly warmer than deep space so radiant overcooling isn't a factor. Almost no dew on a cloudy night. There may be drizzle but not dew.

Here's how this matters to the question asked by MFWD. If he sprays closed cell foam on the underside of the roof the topside will still be cold and form dew but the surface that the air will see on the underside will be the bottom of the foam. It will be facing the things in the carport and won't over cool by radiation. It will stay warm enough to not condense out the water vapor in the air because it resists the movement of heat to the cold topside.

There is however a condition when things can still get wet in that carport. That is when the temperatures have been cold and a warm humid mass of air moves into the area that has a dew point that is higher than the temperatures of the surfaces in the building. We see that happen when our porches and other things under cover are soaking wet after humid air moves in. It isn't the fact that the air is warm that causes it to condense. It is the fact that it has a dew point that is higher than the condensing surfaces that we are concerned with. Warm DRY air won't condense on cold surfaces until the surfaces are colder than the dew point of the air.

If you spray closed cell foam on the underside of the roof it will be like putting a coozie on you soda can. At least with the temperatures we deal with. Now if you fill the beer can with liquid hydrogen and call it a fuel tank and hook it to a rocket booster it won't work as well. The difference in temperature is too great. At <-423 degrees f liquid hydrogen is so much colder than the air in florida that the vapor pressure is powerful enough to cause water molecules to move through the foam on the tank and form ice between the tank and the foam, separating the foam from the tank. On takeoff the vibration shatters the ice and the foam and ice fall off and strike the space shuttle, eventually dooming the brave astronauts inside. The second law is to be always respected.

 

[Coyote machine]

You can buy spray foam from lumber yards. It comes with two filled chemical tanks filled with parts A & B that mix in the tubes that attach to each tank and a special nozzle to spray the foam with. The price is now way down from what it used to cost. I've used it a couple of times and it's worked flawlessly for my applications, which were for a new bathroom retrofit, and basement sill plate sealing.

Overhead use you'd want a Tyvek suit and hat/ mask and goggles and gloves, taped to the suit at your wrists. If the foam gets in your eyes or any skim it can do serious damage, including possibly making you blind.

I would also consult with a professional spray foam company as to any specifics regarding your application and other possible hazards, and best conditions under which to apply to your ceiling: i.e. temp/humidity/and dryness of the ceiling surfaces.

 

[texas42]

MFWD - the quick answer is YES. 10 years ago I had a 40 X 50 x14 high metal building built for shop/storage. Having had metal buildings before and having the condensation problem I had the interior sprayed with a one inch layer of closed cell foam. It has worked great - no condensation in 10 years.

 

[MFWD]

Hey RayfromTx andtexas42,
Thank you Ray for all the technical info and texas42 for the answer from experience.

MFWD

 

[forgeblast]

Foamitgreen.com has kits I have used them and would recommend them.

 

[ArlyA]

MFWD asked a interesting qestion. I've wondered about this myself but yes, if the tin is insulated, then you'd not see the moisture or sweating ever occur. A related question might be..... if you add this spray-foam to your tin wall or roof, what then happens at the joints when tin is overlapped? Seems like the foam would crack there from the temperature fluctuation and the metal is expanding and contracting???

Arly,,,, small minds like to know,,,, A

 

[RayfromTX]

Spray foam expands more with temperature variation than metal does.


This is an interesting article about thermal properties of spray foam related to nasa projects.
https://www.google.com/url?sa=t&rct...70008201.pdf&usg=AOvVaw27vGh7vbbJYy28dwIY8YJQ

On another note; Allison Bailes is a really brilliant person. He writes here about ignition and thermal barriers.
Does Your Spray Foam Insulation Need a Thermal or Ignition Barrier?

 

[astrohip]

While I knew most of what RayfromTX said in his post, I've never seen it explained so well. Thank you!

I have a 50x50 metal fully-enclosed barn. I sprayed closed cell over every surface except the overhead doors. I have -zero- problems from condensation, and the barn stays relatively cool even in our triple digit summer days. You can put your hand on a west facing wall in the summer, and it's not even hot. Put it on the overhead door, and it can fry an egg. Love my foam!

I do get, on rare occasion, the condensation on the floor, from the condition RayfromTX described as "temperatures have been cold and a warm humid mass of air moves into the area that has a dew point that is higher than the temperatures of the surfaces in the building". There will be small areas of condensation. We also have an attached covered patio on our house, screened-in, that has the same problem on rare occasions.