Metal building condensation (help please)!

[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.