Help! High water table, foundation type, and drainage. Almost no information for this situation!

Hello,

Thank you for any assistance or knowledge you can provide.

I purchased land outside of Ithaca, NY, and I’m planning to move onto the land next year in a yurt. I would eventually like to build a strawbale house but am having trouble finding information and understanding a few things.

I want to build a pier and beam-style foundation for ease of repair and cost. I’m considering a rubble trench-type pier system where, instead of pouring concrete, I fill the holes with rubble and then place a concrete footer on top. From my research, this seems possible, but I haven’t figured out or fully understood how to handle the high water table in the area.

The only solution I’ve found to prevent water from infiltrating the piers is a perimeter drain. Would a perimeter drain work for the type of foundation I’ve described, and how does it work? If the foundation area is surrounded by a drain but the ground has a constant source of water from all sides, wouldn’t this be ineffective?

Rubble trench piers, if carried down below the frost line, should not be impacted by the water table. If you have sloped land, making drains that slope from the bottom of the pier pits to daylight would be a very good idea. A perimeter drain only works if there is someplace for the water to drain to. If you have flat land with no place to drain and a high water table, I would not consider that good land to build on. It would likely be very susceptible to flooding, and I would investigate ways to raise your building site if you must use it.

Welcome to the forum!

Pier and beam would be good for a foundation with a high water table.

The piers might need to be taller to keep from flooding the beams.

Also it might be good to find the highest spot on the land to build and it might even be necessary to bring in fill dirt to raise the level of the site.

We have used what you are describing as a perimeter drain on several of our properties and this works well if the are deep enough and can get the flow of water away from the site.

Think about how houses are build along the coast in Florida and Louisiana.

Thank you both for confirming my thoughts. However, I am still having trouble finding adequate examples or even descriptions of what I am envisioning in my head. To clarify:

I want to build a foundation using the rubble trench method, but instead of a continuous trench, I want to use individual holes filled with rubble. These holes would then be topped with a high-strength concrete footer, with a wooden pier on top to support my floor. Does this seem correct?

Hi Eric,
I also welcome you to Permies!

I agree with Glenn that it should not be a problem if they are deep enough. What sort of concerns do you have with the rubble trench piers? Are you worried about freezing and heaving in the winter? Or is it more of a concern that the high water would soften the ground around the piers and cause them to collapse?

Also, do you know how high the water table is? Are we talking that you could dig a foot in the ground and find water?

Maybe this is what you have in mind:

Rubble Trench Footings

https://wrightchat.savewright.org/viewtopic.php?t=5432



https://www.hansenpolebuildings.com/2022/09/rubble-trench-foundations/

I understand the question to be about rubble trench footings in short disconnected sections, each supporting a pier. There is no reason they would not work as well as a continuous rubble trench footing, or individual concrete pier footings, given appropriate loading. The presence of a high water table is a similar concern no matter the footing style, and needs to be dealt with appropriately, usually with drains sloping to daylight.

Matt McSpadden wrote:Hi Eric,
I also welcome you to Permies!

I agree with Glenn that it should not be a problem if they are deep enough. What sort of concerns do you have with the rubble trench piers? Are you worried about freezing and heaving in the winter? Or is it more of a concern that the high water would soften the ground around the piers and cause them to collapse?

Also, do you know how high the water table is? Are we talking that you could dig a foot in the ground and find water?

Thank you for the welcome. yes I'm worried about what you mentioned as well as how to adequately drain the piers. Would installing a French drain around the perimeter of the piers be enough to drain the ground water?

Hi Eric,

I'm also building in a high-water table area. My build, which will doubtless be much smaller than your as it is a little barn in our woods, sits on top of continuous "rubble" trench foundations (actually it's 40mm "drainage stone", washed pieces of limestone). The spoil from digging the foundations was mounded on the uphill side of the property to form a low bank and to absorb and redirect any surface water around the building.

The bottom of the continuous trench slopes towards the lowest (most downhill) corner and then continues about 4m (~12') beyond the footprint, into a soak-away near a natural, seasonal stream. This allows any water that flows, in the ground, into the foundations, to be directed around the building and away from it to safely drain into the soil. I had a length of French drain pipe (perforated, 6' wide plastic pipe) and I used this in the bottom of the downhill foundation and into the soak-away. I don't believe this is required but, as I had it, I wanted to make use of it.

To protect the fabric of the building, I'm using a low (~60cm / 2') stone wall (mortared with breathable NHL 3.5 lime) directly on top of the rubble trench. No concrete pad required. The stones are large and will spread the weight of the building fairly evenly. The lack of concrete allows surface water to drain into the foundation trench (and to flow around, as above). I will thicken the wall into square piers where a post is required to further spread the load of the building.

Generally, a generous eave/overhang on buildings that are not water tolerant is a good design feature. A friend of mine has built using straw-bales and has an overhang of around 1m/3'. He has also limewashed the straw (and will do so every year or two) to protect it from water and rodents (who hate lime!).

Thank you for your reply Luke. yes, I'm familiar with the perimeter drain on a continuous rubble trench drain. my concern is drainage for individual piers in a high water table and issues that Matt brought up earlier.

After a bunch of research I think I've come op with a solution for my foundation. Ill still need to dig a French drain eventually but I think this solution will work.

Can anyone tell me if the image below can be submitted to building code or whatever to get permits.

You need to find your local/county/whatever building inspector or code enforcement official. Someone in government will be able to tell you who to contact. That official can tell you what is required to get a building permit, and what drawings or other information will be acceptable. Different localities have different degrees of strictness, and nobody else can tell you what is sufficient.

Steel rebar that is not encased in concrete, especially in a high and possibly variable water table, will corrode fairly quickly and is not likely to be useful for long. I am not sure what use it would serve to begin with, actually. All you need to support your load is a well-built rubble trench or pier capped by a concrete pad (possibly reinforced) which is high enough to keep the supported structure dry. If there is a measurable frost depth, your rubble needs to extend well below that. What your locality may require beyond that is up to them.

Glenn Herbert wrote:Steel rebar that is not encased in concrete, especially in a high and possibly variable water table, will corrode fairly quickly and is not likely to be useful for long. I am not sure what use it would serve to begin with, actually. All you need to support your load is a well-built rubble trench or pier capped by a concrete pad (possibly reinforced) which is high enough to keep the supported structure dry. If there is a measurable frost depth, your rubble needs to extend well below that. What your locality may require beyond that is up to them.

The rebar will be imbedded in the top concrete footer and in the stone. I figure that this will help to secure the entire structure of to the ground for wind load. to stop the rebar from coroding I'll install a French drain at a later date.

If the soil is moist enough to need a French drain, it is moist enough for underground rebar to corrode. I have heard of basalt rebar and other types of corrosion-proof materials. What wind conditions might your location experience? If uplift of a whole structure is even a consideration, I think you need an actual concrete pier embedded in the ground.