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

 

[AGGIE00]

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

What you are refering to in laymen terms is plasticity index which is calculated by a geotechnical engineering firm and then a recomendation is given to the structural engineer on how to design the slab and pad. The geotechnical engineer then performes inspections by measuring moisture content and density in the field against a proctor that was taken from the pit where the borrow comes from, assuming the existing soil has a plasticity index above what is considered acceptable. Here, we want the PI to be between 7 and 15. I spent ten years as a superintendent building these pads for commercial construction and too much time defending our construction when there is a failure. It was not our job to design the pad, but to follow the plans as they were written. When the failure happens, usually caused by water infiltration, the finger is first pointed at the dirt contractor. The slab is then cored and depth checks are taken to verify that the minimum requirements were met for stable fill. Moisture content is also checked at the core locations and 9 times out of ten, the moisture level is much higher than the test reports showed at the time of construction. I'm not failing to understand anything, as this was my profession.

Also, compaction is relative to moisture content and anyone can exceed 100% compaction if the moisture content is below optimum, usually 4 points. Modified density curves do require 99% to pass, but also allow for less moisture which is never desired under a building. The amount of compactive effort needed to pass a modified density test will never be found on a residential slab and will eat your lunch on stabilized soil using 14ton pad foot and smooth drum vibratory rollers. Standard curve proctors require 95% density and a moisture content between -1 to +3.

 

[EddieWalker]

What you are refering to in laymen terms is plasticity index which is calculated by a geotechnical engineering firm and then a recomendation is given to the structural engineer on how to design the slab and pad. The geotechnical engineer then performes inspections by measuring moisture content and density in the field against a proctor that was taken from the pit where the borrow comes from, assuming the existing soil has a plasticity index above what is considered acceptable. Here, we want the PI to be between 7 and 15. I spent ten years as a superintendent building these pads for commercial construction and too much time defending our construction when there is a failure. It was not our job to design the pad, but to follow the plans as they were written. When the failure happens, usually caused by water infiltration, the finger is first pointed at the dirt contractor. The slab is then cored and depth checks are taken to verify that the minimum requirements were met for stable fill. Moisture content is also checked at the core locations and 9 times out of ten, the moisture level is much higher than the test reports showed at the time of construction. I'm not failing to understand anything, as this was my profession.

Also, compaction is relative to moisture content and anyone can exceed 100% compaction if the moisture content is below optimum, usually 4 points. Modified density curves do require 99% to pass, but also allow for less moisture which is never desired under a building. The amount of compactive effort needed to pass a modified density test will never be found on a residential slab and will eat your lunch on stabilized soil using 14ton pad foot and smooth drum vibratory rollers. Standard curve proctors require 95% density and a moisture content between -1 to +3.

I was a C student in High School and never went much farther then that, so I had to look up some of the words you used.

Plasticity index doesn't seem to fit what I'm refering to at all.

ftp://ftp.dot.state.tx.us/pub/txdot-info/cst/TMS/100-E_series/pdfs/soi106.pdf

I'm talking more along the lines of how much weight a given soil type can hold. And designing a foundation based on identifying that soil type and knowing what it can suppport and also how much movement it will have.

Back to the original reason for this thread, I'm lost as to whether we agree or disagree with the cause of the condensation on the metal roof.

It is my position that all moisture inside a building is from the air. Moisture does not travel through a cement slab and add moisture to the air that is already there, or form water on the surface of the slab.

If there is moisture under your slab, it is because the ground was not properly prepaired before pouring the slab, and/or the slab was not designed properly for the soil type that is there.

As to exceeding 100 percent compaction, I'll have to take your word that it's possible. I only worked one season doing this, and it was back in 1988. We failed a few times and had to remove the dirt and do it again, and we did some lifts that where pretty significant that passed. I also did quite a few pipeline jobs that we only had to deal with a trench that was a couple feet wide. Maybe CA tests are different then what you are used to? or maybe my experience is just too limited compared to yours?

Eddie

 

[beppington]

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.

I'll volunteer to do this test & report & take pics. How deep do you want the water to start with before I put the brick in?

I think water will indeed soak into the brick, above the water line, much like it would soak into wood. But we will see.

 

[Garybake]

What is the atmospheric pressure going to be for the test...:laughing:

 

[Willl]

Able to leap tall buildings in a single bound,,,,

 

[AGGIE00]

There are dozens of types of clay. Saying that clay is not stable is admitting that you don't understand compaction or soil types.

Eddie

I wasn't trying to sound like a know it all, but with statements like this directed my way I feel the need to qualify.

 

[jejeosborne]

Ok I will add my two cents. Condensation will form anytime you have a differential temperature great enough to cause the air to no longer hold its moisture. The only way to prevent this is through a vapor barrier or stopping the differential in temperature.

To tell someone to heat this building may create more condensation because that will allow the air to hold more moisture which will then come into contact with the cold metal on the roof. It is similar to heating your house and having condensation form on your windows. The greater the temperature differential, the more condensation. You must provide a thermal break to prevent this condensation. This is why double pane windows work better. This only applies if you have a source of moisture inside the building like wet or snowy vehicles brought in or fancy shop with a shower.

Also it may be bad advice to tell some to add fans. Basically what you have created is a super larger dehumidifier. Blowing more air over this cold metal is just how a commercial dehumidifier is built and that is what this building is acting like. You will not be able to warm the metal enough to stop this unless you can heat the entire county.

If there is any place on the insulation job where the vapor barrier or thermal barrier is broken, it will allow the moist air to contact the metal. You always place your vapor barrier on the heated side of the insulation in cold regions. These barriers must be sealed tight. This is why foam adhered directly to the metal is so great, it is both a vapor and thermal barrier in one.

The sweating tools and floor are caused by large quick temperature swings inside the building. The air temperature will heat quicker than anything with mass causing your beer can effect. Step outside of an air conditioned house on a warm muggy day and your glasses will fog over because your lenses are still cold. Opening my barn door after a cold night will make my tractor sweat.

 

[Willl]

I'm in western Washington. I've seen 'wet'.

My pole building only has roof insulation just under the metal. Don't know the thickness/r value.

Never had a sweat problem. Wish I knew the dif.

Didn't see this in earlier posts, this concrete floor ? (never mind, I found that he does)

 

[clemsonfor]

I do have a full slab, with sheeting underneath it.

Reckon what it would take to heat this huge building up to prevent the issue. I could probably source some used poultry house propane heaters, but I have heard that those contribute more moisture to the air, and those units are far from efficient.

I am thinking two cupolas, maybe 30"x30" with exhaust fans in them would pull out alot of air, and outside air could come in thru all the gaps above the roll up doors.
It seems to me that this would move alot of air thru the building. But as you can tell, this definately isn't my area of expertise.

Only on about page 3 but why not pull the ridge cap and get a vented ridge cap, this would be way cheaper than 2 coupalas.

You could also insall around the base those house type foundation vents that you can open or close or the kind that auto open.

 

[slowzuki]

Eddie, vapour barrier is extremely important in wetter climates to control migration of ground moisture into a building, especially one that is climate controlled. In a dry climate and hot weather yes it is important for curing the concrete too but there is an amazing amount of water in the soil that will be drawn into and evaporated off the surface of a slab with no vapour barrier. I know in Texas there is a lot of impermeable clay but it isn't the same elsewhere. In our soil, the moisture in soil will "pull" 20,30,40 and more feet past the drip line of a building to keep the soil under a building wet. The areas with holes in the vapour barrier aren't wet per say because it evaporates off the top of the slab faster than its being let in.