Hi, this is my first post, and I'm no expert...but I've been researching for a while now regarding our floor issues, and found this incredibly informative site! This is our situation...We have been in our home for 4 years-It was built in 1960, brick on piers and an addition on a slab added around 1980 ish??
The house is bricked to the ground, with vents about every 6 feet, only about 1' wide each(my husband could BARELY squeeze through one) and there is no Vapor barrier at all in the crawlspace. We realized we had a problem when our floor in our hall started to rot, just soft spots that eventually spread down the hall. We thought we had a leaky pipe or something, so went into crawlspace and found no leaky pipe, drain or anything,but the joists under our dining room, hall, and a bedroom all had water droplets just hanging , like condensation, and the crawlspace was really wet,puddles, etc....So we've determined that we have a moisture problem, but when I pulled up some carpet and old linoleum in the dining room(which leads to hall) the plywood underneath was moldy and rotten.Even some mold on the baseboards and wall.So now we're looking at having to replace almost all the floors in our house, but we'd like to know why they rotted in the first place, and what to do about our crawlspace. It's our first house and it's so overwhelming, and my husband's not the handiest guy, butit seems like an expensive and labor intensive task...We just really need advice.

The previous owners also had a big dehumidifier in the house, which they left, and were very nonchalant about "Oh, sometimes we run it in the summer...Blah Blah Blah..." ( Now we know why) And it looks like they had just changed out the hall floor (we found remnants in the attic)and dumped the house on us!!!
Where do we start, and what do we do??????

 

RELATIVE HUMIDITY (RH%) - Means the percentage of moisture a certain object can hold under different temperature conditions. Warmer objects can hold more moisture than cooler objects. This is because when an object is warm the molecules become excited and move further apart and when they become cooler they become less excited and move closer together. It is the space between the molecules that the moisture vapor molecules occupy. For example, a piece of wood or a certain volume of air RH% will go down as the temperature goes up even though the amount of moisture has not changed. This is because the rise in temperature causes the wood or air molecules to move further apart which provides more space for the objects to hold moisture. Another way of putting this is when the temperature of a piece of wood increases, the wood expands and when it cools it contracts. Clearly the wood that is expanded can hold more moisture than the wood when it contracts. The same is true for air or any object for that matter. So RH% represents the amount of moisture an object can hold under different temperature conditions. For those who are interested under Physics this is known as Psychometrics. This also explains why people say, “Warm air condenses on cooler surfaces”.

MOISTURE BARRIERS – Also have a low Perm Rating just like vapor barriers. This is why people have the tendency to interchange the two terms. Moisture Barriers are used to prohibit the retention of moisture inside the crawl space. Whereas vapor barriers are used to reduce the amount of moisture inside heat before it enters insulation and are only used with insulation. Moisture barriers over dirt floors should be applied to both ventilated and sealed (not ventilated) crawl spaces. It addresses two sources of moisture, which are capillary action and recycling. Capillary action explains how the ground acts like a sponge. When it rains outside, the dirt inside the crawl space floor will absorb the water from the outside. What Moisture Barriers do is provide enough time for the ground outside to expel the water either through draining and/or evaporation. Without the Moisture Barrier over the dirt floor, the objects in the crawl space with a lower humidity level would absorb moisture from the ground before the ground outside could expel the moisture. Recycling is when the dirt floor in the crawl space expels the moisture in it through evaporation and absorbs it and then does it again. Moisture Barriers prohibit evaporation with the moistrure in the dirt floor, which dramatically reduces Recycling.

Unlike water shedding systems, the confinement inside the crawl space makes it difficult for moisture to move away from the house. The same is true for attics. So to extract the moisture from the crawl space, air exchange is used. There are a considerable amount of variables concerning the crawl space and moisture. So I am only going to use one scenario, which will probably omit several factors for this explanation.

During the winter, heat with a precentage of moisture (RH%) travels from inside your home to the outside through your ceilings, walls and floors. The moisture in the heat is absorbed by the cold air outside that possesses a lower humidity level. This is referred to as Equilibrium Relative Humidity (ErH%). This states that an object with a lower humidity level with absorb humidity from an object(s) of higher humidity level(s) unitl the humidity levels in all the objects are equal and not vice-versa. Your attic have vents to provide air exchange so that ErH% can occur to remove moisture from the confines of the attic. The same is true for your crawl space.

A moisture problem occurs, like in your crawl space, when the introduction of moisture is greater than the ability of the area to absorb and expel the moisture. For example, if your attic hatch/door was not closed during the winter, the heat inside the house would flow into the attic at a rate that your vents could not provide enough cold air outside to absorb it. The result would be condensation would be present throughout your attic.

With your crawl space a major contributing factor to your moisture problem is the dirt floor. The moisture in the ground and the ability of the ground to retain moisture is resulting in high humidity levels in the crawl space. So as the heat from the house goes through your floor and loses temperature as it enters the crawl space, the moisture in the heat condenses immediately inside and/or under the wood floor. So providing a moisture barrier over your dirt floor will dramatically reduce the humidity levels inside your crawl space.

You must address the source of the moisture problem before you repair your floors. Since the first floor framing and the flooring itself (no sub-flooring) are structural, I would recommend you contact your insurance company to see if it is covered.

 

Thank you so much for your reply.It was by far the most thourough explanation I've gotten from anyone I've questioned about this. We are in the process right now of making sure no rain water can get under there, and then we will tackle the moisture barrier..I am thinking 6 mil poly under the whole house covered with sand and/or gravel...Others advising us and helping seem to think a good heavy layer of sand over the dirt will do the trick.(I'm not too confident) And I really don't want to have to do this again in a few years because we took a shortcut. We've also had a carpenter say he thinks we could lay new floor right over the old dining room sub-floor because it feels like it's still solid, but I don't know about laying over that moldy wood..and if I try to rub it clean, it just shreds and rubs off. It is going to dry out after it's that far gone??? I'm just one of those people who needs a cut and dry solution to a problem, and with our moisture problems, it seems like eveything we do will be a "Wait and See " thing...and in the meantime one thin layer of vinyl seems to be the only thing keeping us from falling through the floor!

So how do I lay a moisture barrier under a house on piers, does it have to be sealed at every pier? And around the edge of the house just weighed down, taped at the seams? Is it possible under a house with literally 1' of wiggle room ???

 

Might go look at http://aboutsavingheat.com/crawlspace.html

Like said you have to work the out side first gutters and down spouts first with new grade of the ground.

Out of the box here but have done it. Take up all the old floor like one room at a time .Check all joist put down a 6 mil polyon teh ground and seal the walls at this time with insulation then new floor it works room by room best if you cant fit under the home. Id also at this time check all wire and plumbing.Yes the poly over lap it 2' and tape seams make tight around any of the piers also.

ED

 

Thanks so much, all suggestions greatly appreciated.I had actually considered doing it that way, it just seems to make sense to work from inside the house because of the tight squeeze under house. Should we try to make our vents bigger and install a couple of fans first to suck that moisture out or are we better off with the poly???

 

Dont know where you are are what is the temp there. We close and seal up all vents in a crawl space. Most of the time when you pull outside air into a cooler crawl space it will just make things wetter under there. Run that dehumidifier while you have the whole floor up in a room will help more.

ED

 

Save that moisture barrier until the last thing. By the time your repair crew

gets done doing all the structural repairs, that nice new plastic sheeting will

be ripped and torn to shreds and there will be lots of debris on top of it.

 

Thanks again , we're in lower central Louisiana, so needless to say...it's really boggy here, and to make matters worse we live next to a canal, Water, Mosquitos, the works...We'll surely wait and put the poly last, especially since we're not even sure how much floor will have to be changed out yet. My husband suggested sealing off the crawlspace altogether, but I just thought that if we missed one tiny way that water was getting under there, we'd be even worse off because we will have trapped it in there.We also found that our relief valve on our hot water heater has a tiny leak, but it's no where near the rotted floor...but our dryer vents under the house into the crawlspace, with a small, seemingly inadequate vent near the laundry room.So we have alot of little solutions we we hope will eventually solve our really big problem...