We have a very conventional house at our community, that acts as our primary communal building here. It is one of the only finished buildings on site and we are trying to figure out what to do with it.  The problem with it is terrible mold and water retention. When it was built, long before we inherited the community, it was intended to be a garage! Do we keep it as a primary living space and make all the adjustments needed for it to be livable? We would prefer to build tiny houses and live in those, and convert this building into something else. We have a couple ideas which I will share later.

First some specs - it' has an unfinished concrete slab sitting on top of limestone slab rock in the living area, kitchen and office. The two bedrooms and pantry were additions and they are just a raised wood floor, with support beams under sitting on top of the earth, sort of like how people build patios, but they are bedrooms. The inside walls are drywall and the exterior is sheet metal, as well as the roof. The ceiling is also sheet metal and there is fiberglass insulation between ceiling and roof. The problem is that the house sits on slabrock near the bottom of a large hill where water collects really heavy. On the south side is a forest, keeping it shady, cool, and very damp. There is little airflow. The eaves are very short, to non-existant. We do have rain water collection on the north side/ uphill side of the building which helps to divert some of the water. But we still have all the water flowing down the hillside that settles in front of the house like a pond.

Last year the mold inside was so bad we had to throw away and burn a lot of the rugs, mattresses, clothes, etc. and we painted the walls with kilz and standard indoor paints. The mold isn't as bad this year as it hasn't been as wet, but we have some mold and fungal colonies creeping back in. We want to fix the problem this year. The kilz and paint just covers up the symptoms, but the issue is that there is the location, the fact that the floors were never finished, and very little ventilation. This year we have been keeping windows and doors open, and running a fan 24/7. We prefer a passive solution. And natural solutions.

One of my ideas is to convert this building into a three season building. Take out some of the exterior walls and put on screen instead, so we could use it all year except winter. Then we'd have plenty of ventilation! Ideally, all of us want to start building a tiny house this year. We have experience with cob and roundwood framing, so we can make it happen. We want to keep this house to be used for workshops and interns to stay in. Should we make the dramatic change to open up this house? Even if we do that, we will need to continue living in here until the tiny house build happens. So until then... do we seal the concrete floors with conventional sealer? Do we pour concrete over the floating wood floors? Do we divert the water somehow? How do you divert water for a large hill? Can we seal the floors with wax or some other natural sealer? Can we slap some clay slip on the drywall? It's a huge building so I don't know what is feasible for us to invest time and energy.

Thank you in advance for your time!

You are going to have to get the water under control before you do anything else, I would do some research into French drains, as it sounds like they would be suitable to your issues. Essentially what you are going to do is dig a trench on three sides of the building and fill them with rocks, so they create an underground drainage system that can flow the water from the hill around your structure. The Straight lines in the diagram represent the French drain...

    ^^^Hill^^^
     
   ___________
  | .................. |
  | .....House.... |
  | .................. |

EDIT ... Oh well the ascii art doesn't work well here but you should get the idea

The probability of you salvaging the interior materials is questionable. Killz may limit future mold development, but it's far from ideal. The interior drywall and wood will contain mold spores which endure. Mold is a cause of many health issues; it is known to cause lung capacity to deteriorate. I don't recommend you mess much with it. If the building's structural materials are significantly compromised, as your original post seems to suggest, then these materials must be removed. As to saving the structure, I would encourage you to analyze the condition of the framing. Is there rot from the moisture? Are any timbers black from mold? These would be primary concerns that suggest a high salvage cost. If these are problems, you may be better off building a new structure and utilizing the metal roof, appliances, and other uncompromised contents within (after extensive cleaning).

There are materials you can use which are naturally mold resistant. The old lath and plaster walls contained non-hydraulic lime; the ~13 pH level of the lime proves effective as an anti-fungal. If you are up for a major reno, some research into mold resistant materials could provide you many options. You may wish to use such materials in your tiny homes as a means of preventing mold issues from developing in the new structures.

If you intend to salvage the structure, I would immediately invest in a couple of dehumidifiers. Draw the moisture out of the air and building to limit further damage. Provided you keep your moisture level under control from that point, your issues will stabilize and you'll be left with refurbishing as your primary concern.

We have thought of and attempted to trench the perimeter of the building. The problem is that we are sitting on limestone slab rock, and it's relatively impossible to dig in. We have used a pick axe to make some trenching in the past, but osmeone pointed out that we might ruin the whole foundation of the house because the concrete sits on the slab rock and if it cracks, the whole foundation could ruin. Not sure how to move forward with trenching.

The drywall certainly contains mold spores. We have some exposed wood in the house and those have not had a visible mold problem. Last year the mold seemed to live all over the walls and fabrics of the house, but the door frames appear fine and the exposed wood sills on the floor and windows seem to be fine. No visible mold. The spores still live here, the place smells like a damp cellar, but I think a lot of the building is salvagable. We just don't want to live in it and we need to figure out a solution. Fix the problem somehow, and get rid of contaminated stuff. Is there a passive way to run a dehumidifier or one that operates with low energy input? The building is big, so we'd probably need two or three of them. We run on mostly solar with grid back up for our deep freezer and a couple other things, but we are working on upgrading our solar to power all the things so we can be totally off grid.

That does make things quite a bit more interesting...  Is it possible to collect the water uphill before it gets to the slab rock?  Possibly something like a drainage ditch  in the hillside with deep dry wells at each end, would not catch all the water, but should certainly cut back on what comes down the hill into the front of the house.  I would also divert all roof water to some other location, and possibly install some sort of sump pump in a lower spot (maybe make a 'true' sump, by burying a barrel with holes drilled in the sides) in the front yard to pump excess water away.

Desiree Fleck wrote:We have thought of and attempted to trench the perimeter of the building. The problem is that we are sitting on limestone slab rock, and it's relatively impossible to dig in. We have used a pick axe to make some trenching in the past, but osmeone pointed out that we might ruin the whole foundation of the house because the concrete sits on the slab rock and if it cracks, the whole foundation could ruin. Not sure how to move forward with trenching.

Wood heat will remove humidity quite rapidly. Do you have a wood stove? How do you feel about installing one?

How thick is this layer of slab rock? How close to floor level is the slab rock? Is it fractured at all already? If you can break it with picks, it is not likely to be significantly structural more than a foot or two from the walls. You would benefit from having roof overhangs that large anyway, keeping water from hitting the ground close to the house. Even chipping a channel in the top of the rock that slopes to drain and lets water move away underground would help significantly. An uphill drain that moves the bulk of the water away from the vicinity of the house would aid in mitigation.

DON'T live or have anyone live in a moldy building; it will wreak people's health. Ask me how I know . . . And health is not always rebuildable.

I'd stop what water I could from draining downhill then drain whats left into a surface drain channel sloped & plumbed to day light with perf tubing  if my soil drained well or solid if not. I would not chip away at the foundation it could probate cracks, build up the grade.

It be interesting to see whats inside the walls and roofs. Sheet metal siding I bet has a plastic barrier, is highly conductive fungi lives in your hot humid days, and you added kiln and latex to the interior, with FG in it. That my friend is the worse microbial nightmare in building history. Vapor trapped FG or walls a whole house dehumidifier will do no good, add a concrete surface sealer/barrier now the slab can't dry and is vapor locked. Siloxane would be a better choice if the interior humidity could  be controlled at all times below 35% DC desiccant wheels driven by solar panels are best. Wood floors over a insulated crawl w/damp soil not good. Opening up the walls a little will not work, not with that little air flow. Passive natural solution = Tear it all out start over.  

There are pros that do microbial cleaning, in most cases it all has to be removed along with a permanent solution by qualified pros.

Although not a good idea to live in mold we are exposed outdoors too. As far as I know there is no known exposure limit to be classified as a carcinogen, or proven links to cancer, just like formaldehyde all over your design. If there is I'd like to see it.

Hi Desiree,

Lots of helpful comments on drains; this is priority one!

Once the water is diverted to go around the building instead of through it, then you must tear the thing apart. Remove everything and save what you can. This is the only way to remediate the moldy internal framing and fg insulation. Then wash down with oxiclean and rebuild in a more suitable fashion that can handle water, just don't seal things up.

All Blessings,
Bill

Such vast knowledge here, thank you all so much!! So here's a plan we have come up with and talked about in the past that we think it makes good sense to act on. In front of the building, the uphill north side, is the slab rock where water pools. We don't want to attempt making trenches in it as it doesn't really work anyways. Our idea is to build a patio on the slab rock with rocks from our creek and pour some concrete in the cracks and a concrete berm in the front of that (uphill) to move the water around the building and down the hill past the house. We spoke to a friend who had similar problems at his house, and he put a simple concrete berm in front of the house that diverted the water down the hill. It's been working for years. Seems like a simple fix, and we would have a lovely patio. We have attempted to build trenches in the hillside that does divert some of the water, but it seems like to be the most effective, we need to divert right in front of the house because this is where it pools. After diverting the water, we will need to assess how and when we can gut and replace whatever is inside these walls and ceilings.

Should we put a sealer on the concrete or do you think that would just seal in the funk and make matters worse eventually? My dad and husband (who both live in the house with me and my son) both think it's a great idea to seal the concrete floor.

What I envision you building is essentially a retaining wall on the downslope to your building, please correct me if I am wrong.  

Now I am far from either a concrete or water hydraulics expert, but I would imagine the water setting on the outside of the wall would eventually permeate/penetrate the concrete.  If I was going to attempt something like this I would excavate down to the slab level everywhere I was going to apply concrete, I would drill/jack hammer down into the slab to secure my concrete, and pour at least a foot of pure concrete at that level before stacking my rocks.  I would also line the created wall and at least several feet up hill of it with some sort of impermeable barrier and put a 'french' drain of some sort at the base to direct standing water from the 'wall' to lower areas.  Otherwise you are going to end up with something very similar to the problems with basements in the wetter areas, where the water eventually forces it's way through the concrete and seeps through the other side.

If I am incorrect on this issue I bow to those that know much more about concrete and water hydraulics than I, but this would be my first guess at the issues that you could expect.

BTW I envy your issue with excess water, I would love to have to decide how to dispose of standing water.  

Also I have flagged your post for more attention in hopes of getting you more 'professional' or knowledgeable input on your situation.

If you want some nice looking breathable concrete floors polish them with a 400 grit for low gloss, 800 for semi, 1500 for high gloss I do. Add a deep penetrating lithium silicate densifer and acetone for transport that evaporates fast. You can add natural earth or iron oxides, reds have the highest VOCs. As a finish sealer add a 100% + permeable siloxane/silane w/40% natural silicone_sand solids that is n/a to low MVOC, deep penetrating. Get a test sample, water should surface bead & not penetrate so it can evaporate. If not use more solids. It will also reduce efflorescence, resist chemical spills, salts, freeze-thaw on exterior verticals.

I'm guessing good that your slab cannot dry down due to a torn plastic or other vapor barrier and wet soils, drying in is the only choice to avoid vapor lock. The last thing like the walls needed is a toxic vapor interior barrier/trap as in high VOC/formaldehyde fungi producing epoxies, acrylics, asphalt based sealers, or harsh solvent transports. A water based transport siloxane will do to deposit soilds, it is usually milky white but dries clear, no residual oder.....The manufacture should spec out the perm rating, I have seen as high as 110%. Get all materials at most concrete supply places or kits: http://www.runyonsurfaceprep.com/Ameripolish-Products.dept

As I said above, in conjunction, the RH of the indoors needs to be maintained at all times to 35-40% for a healthy building. Come back for tips on how to design hygrothermal interior mass and passive humidity buffering w/o overheating. There should be no need for an active system if designed properly your interior should maintain a comfortable level despite your high heat/humidity indexes.

Burms do little to stop gravity drainage under foundations, where ever there is field lows water will drain through soil to that area and due to hydraulic pressure and temperature differentials, capillary actions, wick right up into concrete, especially if the lower plastic barrier has failed and you have a low RH interior. The best defense keep water as far away as possible.

Good luck!

Terry you really seem to know what you are talking about and I thank you so much for taking the time to help out. To be honest, I'm having difficulty understanding some of what you are saying, but we have a friend, engineer-minded guy helping us tackle some issues, so I'm going to have him read your advice and decipher it for me.

Desiree, as you have been advised you need to get the dehumidifiers, but if you have not done this yet you can buy a product at Walmart or other hardware stores called Damp Rid.  It is a temporary solution that you can put one in each room until you can get the dehumidifiers and may even help after getting the dehumidifiers.   It will also help in the tiny houses.

This is how we have responded the problems so far...
We ordered a dehumidifier which will arrive this week, a pretty high capacity one, and we may get some small ones for the bedrooms. We got damprid for now, to help slightly. We took out all the carpets and extra fabrics, because even our couches are collecting lots of moisture. We keep the windows and doors (with screens) open all the time for air circulation. We are going to make more screens for the rest of the windows. We have a fan blowing all the time. I took out all the overgrowth in front of the house so I could see what we are working with, it's about 2 inches of soil and then bedrck for several feet in front of the house, and then there begins the hillside incline which is full of rock rock and more rock. We are going to get some concrete and put it up against the house so the surface water doesn't get underneath the hous e as easily. We are going to install two sliding glass doors on the north uphill side with screens, this is the most open side of the house, very wooded on the other three sides. We also have a attic turbine fan we will be installing soon. And we are in the middle stages of developing a plan to landscape the uphill landscape to divert the water before it gets here. We are still unsure of exactly how to do that.

I'm not sure that concrete next to the house is a good idea. Yes, it will divert surface flow, but it will let seepage underneath unless you get a much more perfect seal than I've seen in similar circumstances, and it will hold dampness against the edge of the floor.
If you make a mini-dam of concrete a foot away from the foundation, so that any seepage has a chance to evaporate before getting to the house, that might work for you.

Okay, we will consider making the berm a foot away from the house. And we will begin a trench upslope. The serious issue lies directly in front of our home where the water just pools. It comes off the hill and our stone walkway and lands on soliid bedrock,.

I would suggest you don’t assume the surface water around your building is causing high humidity levels in the entire house, or foundation issues.

It is not clear to me if the house is built on bedrock and/or where the water table is. If I have it correct the north side facing a hill is an addition that it is not clear to me what the foundation design is. A complete understanding or section cut drawing and plat drawing is needed for starters along with pics for any advice to be given.

Before I spent any time or money on this building, I’d hire a Geotech to provide a report of the moisture & plastic limits of the soils that could potentially be compromising the foundation and identify where the moisture/liquid is coming from. They know how to extract samples. If built on bedrock perhaps n/a. If the soil plastic index is being exceeded or is too high then it would make no sense investing money into a building sitting on foundations that could fail in time that may or may not be being encroached upon by surface water that can easily be diverted by grilled drain channels. I did not mean to suggest above that water diverting walls will always allow water to get below a house and under a foundation and/or is the underlying cause for high relative humidity and rot.

Before you start dehumidifying the place I’d suggest getting a humidistat and taking some readings in your hottest months which is now and August? With the temp and relative humidity known, go online and find your interior dew point temperature. In your climate exterior dew happens at high temps, and like your skin that gets that muggy feeling the building can’t dry/vapor breath and condensation occurs that incubates microbials.  Taking some slab moisture content reading would be a good idea too. Use this baseline so that when whatever is causing high levels, the location(s) are found and you can quantify. Try adding active or passive wind, diverting water, etc.

IE: 100F @ 35% RH (recommended) = 68 F Dew, 100F @ 80% RH = 93 F Dew,

Wind may help but it could make your interior RH higher if the intake wind has a higher RH, some exterior wind quality is so low it can cause microbials. Wind can dry out surfaces by changing where high/low pressures are you have little of, but, does not change dew point and it may not be able to keep up with dew/condensation rates and/or prevent fungi/bacteria/allergens/carcinogens. Hence why some are opting to active mechanical ventilation systems with merv 14+ filters such as hrv/ervs (if you rebuild to passive house standards you’ll need, ervs manage RH), or whole house dehumidifiers and/or high cost active air conditioning evaporation, since their envelope like yours is not designed properly to the passive climate zone.  In addition, wind speeds/pressures/RH/dew point will be critical to any breathable wall/roof redesign, evaporation of ground water/moisture, further coupled with the drainage issues, begging the question whether or not the building is habitable or salvageable at a reasonable cost.