Metal building condensation (help please)!

[slowzuki]

I'm assuming here this happens mostly in near freezing weather and the sun is melting the frost that formed on the underside of the metal roof?

I have a corugated metal roof on my garage at home and the building is prety well draught proofed with no vents.
The garage has been built for 26 years and I have a condensation problem.

the roof is about ten feet off the floor and if the sun gets on the roof after a cold night condensation drips from the metal roof quite badly.
This soon drys up if the weather is nice and is not realy a problem unless I have just painted something and left it overnight to dry.

Anyway the reason I am posting is because we have just put a corugated metal roof on a building at the farm and we are worried that it may have a condensation problem just like my garage.

The metal sheets are plastic coated but we haven't had a sunny morning yet so not sure how bad the condensation will be.

We were thinking of insulating the inside of the roof but not sure if that is nesessary , we have put vents in the gable end at the top and about two feet down so as the air will flow in and out just like the wasps will do

Any ideas ? I have read the full thread but its not quite the same problem.

 

[Sutol]

Do get more drips with sunshine after a frost but sunshine on a cold morning still creates drips from the roof.

 

[forgeblast]

Thanks for explaining Eddie!

 

[SandburRanch]

I can see there are a great many people that would benefit from a short course in meterology. It would save a bundle on plastic that is put down in advance of a concrete pour.

 

[EddieWalker]

I can see there are a great many people that would benefit from a short course in meterology. It would save a bundle on plastic that is put down in advance of a concrete pour.

There is a HUGE misunderstanding on what plastic is used for on concrete slabs. Water does not come up from the ground, throuch concrete and into the air.

If that happened, every house would be soaking wet around their bathtub drains, where the trap is open and the slab is usually a foot by half a foot wide, and open to the dirt. If you ever do a remodel, you will notice that the dirt is hard as a rock, and very dry under a slab.

What the plastic does is keep the moisture level in the concrete consistant through the slab when pouring. Water levels in the slab are very important. Too wet and you lose all your strength, too dry and you lose all your strength. If the soil is very dry, or very pourous, the moisture in the concrete will leech into the soil and dry out the bottom of the slab, giving a very week slab that will crack quickly and often.

Since soil does not contain air, there is no humidity in soil. Air contains massive amounts of air. Even the very dry air of the desert is full of water. Humidity is measured in the amount of water in the air at a given temperature. When the temperature of the air changes, the level of humidity changes. Warmer air can hold more water vapor and if the water vapor stays the same, the humidity level will decreas when air temperature gets higher. The opposite is true when air temperature lowers. This happens all over the place, especially next to a metal building when air temperatures are different inside and outside the building.

Soda cans are good examples, except when you notice the condensation, it's on the inside of the building. It happens on the outside too, but it's not a problem then.

Eddie

 

[beppington]

Here you're required apply termite treatment (poison) to the fill dirt below the slab first, put visqueen down over that, then pour. I think the visqueen is also to block the poison from seeping thru the slab into the house.

... Air contains massive amounts of air.

 

[AGGIE00]

There is a HUGE misunderstanding on what plastic is used for on concrete slabs. Water does not come up from the ground, throuch concrete and into the air.

If that happened, every house would be soaking wet around their bathtub drains, where the trap is open and the slab is usually a foot by half a foot wide, and open to the dirt. If you ever do a remodel, you will notice that the dirt is hard as a rock, and very dry under a slab.

What the plastic does is keep the moisture level in the concrete consistant through the slab when pouring. Water levels in the slab are very important. Too wet and you lose all your strength, too dry and you lose all your strength. If the soil is very dry, or very pourous, the moisture in the concrete will leech into the soil and dry out the bottom of the slab, giving a very week slab that will crack quickly and often.

Since soil does not contain air, there is no humidity in soil. Air contains massive amounts of air. Even the very dry air of the desert is full of water. Humidity is measured in the amount of water in the air at a given temperature. When the temperature of the air changes, the level of humidity changes. Warmer air can hold more water vapor and if the water vapor stays the same, the humidity level will decreas when air temperature gets higher. The opposite is true when air temperature lowers. This happens all over the place, especially next to a metal building when air temperatures are different inside and outside the building.

Soda cans are good examples, except when you notice the condensation, it's on the inside of the building. It happens on the outside too, but it's not a problem then.

Eddie

Not trying to argumentative, but this makes no sense to me. Dirt may not contain humidity, but contains a tremendous amount of water that fluctuates and is called saturation. Plastic does ****** the tranfer of water out of concrete when curing, but it's not a big enough deal to warrant. If this were the case, then all concrete paving would require plastic or some sort of vapor barrier. Dry air, zero humidity, contains no water so I don't know what you mean by desert air containing massive amounts of moisture. We have sprayed foam to the underside of structural concrete panels in houses to create a vapor barrier where proper ventilation holes were not installed. This was an engineered fix, not our solution. We could start another thread about the proper curing of concrete.

 

[EddieWalker]

Not trying to argumentative, but this makes no sense to me. Dirt may not contain humidity, but contains a tremendous amount of water that fluctuates and is called saturation. Plastic does ****** the tranfer of water out of concrete when curing, but it's not a big enough deal to warrant. If this were the case, then all concrete paving would require plastic or some sort of vapor barrier. Dry air, zero humidity, contains no water so I don't know what you mean by desert air containing massive amounts of moisture. We have sprayed foam to the underside of structural concrete panels in houses to create a vapor barrier where proper ventilation holes were not installed. This was an engineered fix, not our solution. We could start another thread about the proper curing of concrete.

There is no such thing as air with no humidty or moisture in it. What you have in dry desert air is a low humidty level, but early in the mornings you will still get dew, and anytime you have a cold drink you will see condensation form on the side of the glass or can on a warm day.

While you are right that dirt contains massive amounts of water, it doesn't store massive amounts of moisture near the surface. In fact, it can be just about impossible to find any moisture in the soil under a slab foundation, or even a dirt floor barn that doesn't have a leak in it. Have you ever tried to dig in the dirt after removing a slab or part of a slab?

Depending on the soil type, temperature, concrete mix and requirements, plastic can be VERY IMPORTANT in keeping the proper amount of moisture in the concrete.

If you think that the moisture in the earth comes up through the soil and then up through the concrete, why doesn't water in the dirt do this for lawns? Why doesn't the moisture in the soil do this on open dirt?

Are you confusing condensation on a slab with the impossible feat of moisture in the earth coming up and out of the soil to make the concrete wet? Why would it do this and not make the soil around the slab wet? Why does this only happen when water has to force it's way through solid concrete, but never out in the open?

Do a littl test. Put a brick in a bowl or pot of water that's about an inch deep. I don't care how long you wait, water will never work it's way to the top of that brick. Just like it will never work it's way through solid or cracked concrete and into a house or shop floor.

Eddie

 

[AGGIE00]

If you think that the moisture in the earth comes up through the soil and then up through the concrete, why doesn't water in the dirt do this for lawns? Why doesn't the moisture in the soil do this on open dirt?

Eddie

You don't see it in lawns because of the evaporative effect that takes place. Moisture can not evaporate from under a slab due to lack of airflow to pull the moisture out. This is why we replace clay with a more stable select fill that will not shrink and swell with varying moisture content. Where we are, many slabs are falling apart from the drought causing moisture to escape and then be reintroduced from rain. If there is no moisture in the soil there would be no heaving. The slab in our church heaved 4" in places because of water getting underneath mostly due to irrigation. The new method being used is moisture conditioning to saturate the soil before the slab is poured so that it will not heave from excessive rain. Gander mountain uses lime stabilized subgrade 5' deep below the slab to stabilize against moisture fluctuation to an elevation where moisture content stays constant.

 

[EddieWalker]

You don't see it in lawns because of the evaporative effect that takes place. Moisture can not evaporate from under a slab due to lack of airflow to pull the moisture out. This is why we replace clay with a more stable select fill that will not shrink and swell with varying moisture content. Where we are, many slabs are falling apart from the drought causing moisture to escape and then be reintroduced from rain. If there is no moisture in the soil there would be no heaving. The slab in our church heaved 4" in places because of water getting underneath mostly due to irrigation. The new method being used is moisture conditioning to saturate the soil before the slab is poured so that it will not heave from excessive rain. Gander mountain uses lime stabilized subgrade 5' deep below the slab to stabilize against moisture fluctuation to an elevation where moisture content stays constant.

What you are doing is using a failure of construction and assuming that it has something to do with another thing.

There are dozens of types of clay. Saying that clay is not stable is admitting that you don't understand compaction or soil types. Some clay is terrible to build on, other types are ideal. What has to happen when building is that the type of soil needs to be identified. Each soil type and each type of clay has a rating on what it can hold. Depending on the rating, the footings for the foundation are calculated. You can build on just about anything if you plan for it. When there is failure, it's not the soils fault, it's the builders fault.

When building, you either want to build on undisturbed soil or fill that is compacted. To compact soil, it needs a certain amount of moisture to hold it together. Too much and you have mush, not enough and you have powder. Compacting requies different techniqued depending on the soil type. Testing is done with a radiocative beam that is very similar to radar. It goes into the soil and bounces off. When I did this commercially, we had to be at 99 percent compaction to pass inspection. Nobody can do this with a farm tractor, but most can get fairly close and most houses are just fine. Some are not.

Once the slab is poured, no more water should EVER get under the slab. Over time, the moisture level in the soil will lower to just about nothing. This is why water does not come up through a slab.

As for evaporation on lawns, you missed my point. The moisture that you see on grass is dew. It is caused by condensation because of the air warming up faster then the ground. That dew remains as water on the grass, and then evaporates as the air warms up,and like you said, the wind dries it out.

My point was that the grass cannot get water out of the ground in it's roots to live because water in the ground does NOT come up to the surface.

Eddie