Plumbing for Tiny House on Pier Foundation
I am planning on building a 200 square foot tiny house thing before I build the actual house I want to build in Climate Zone 7 in Wyoming. I have no building experience and this is more of a cabin to buy us time to figure out what we actually want to do. I’ve done small house renovation before and watch a lot of youtube so I’m basically a pro now (sarcasm)
Anyway I don’t trust myself to poor a good foundation for eithier a basement/crawlspace or slab on grade, however, a pier foundation seems like it tolerates a more novice-friendly approach. I’d like to have water and sewer run to this. I will have electricity and am debating in putting in a propane tank (no natural gas lines).
Is there a best practice for detailing a water and sewer chase down to ground in climate zone 7? Or is this as a whole a very bad idea. I’m open to any suggestions and I’d like to do it right.
Thanks!
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Sorry I don't have a tried and true solution for you. This is one of the problems with pier foundations (besides insulating the floor properly, and isolating the underside from bugs and squirrels, and air sealing, etc.). Not saying it can't be done, just seems to be more work than its worth whenever I think about it.
I live and work primarily in Zone 7, and have considered pier foundations for hillside lake houses, but I always come back to full stem wall (or basement) with footings.
Don't be afraid of the concrete pour. For the most part, you need to make sure you have 2 main things: 1.) Adequate bracing, especially for ICF walls, and 2.) 1 good concrete finishing guy for slab pours - someone who does it a lot. Hire a guy after hours for the day. Other than that, you can do as good a job as most concrete contractors in my opinion.
Great approach building the tiny cabin first!
I love concrete, but given the enormous embedded carbon in concrete I am thinking more about no concrete or low concrete residential structures with no basements or concrete crawl spaces. So structures built on wood or concrete piers or pilings or even helical piers interest me.
I have owned a home on Long Beach Island NJ for 50+ years. There are thousands of $$ million houses built on LBI and other Jersey Shore towns on wood pilings above ground (zero concrete) that run the plumbing stack and water through a chase. Climate 7 is a bit colder but why shouldn't that just require more insulation? These days many people close in the entire bottom floor around the pilings with wood breakaway walls (flood zone); but many still use a small insulated square plumbing chase (e.g., 4x4) built out of pressure treated studs and hardie board sheets, insulated with rock wool. The pipes run up the middle.. You can also do this out of concrete block or even poured concrete-insulated with foam. It is important to protect the pipe from the bottom of the trench up into the floor.
If the structure is at least 5 ft above ground, an exterior sheetrock with fiberglass face (e.g., Dense Armor Plus for instance) is often used to seal the bottom of the floor, taped with fiberglass tape and finished with mold resistant compound (if cars can be parked under the house, fire code requires double 5/8 sheetrock). If you are closer to the earth, use hardi board or even pressure treated ply with taped seams. In all cases a good gloss latex paint helps to finish it.... keep penetrations to a minimum and seal them with tape. Also, covering the ground with two 6 mil layers of plastic helps manage ground moisture. You can enclose the sides with louvers or lattice panels to keep bigger animals out. If there is a prevailing wind on that side you could make a solid wall out of hardie or louvers to block the wind. Shrubs or a rock wall can even do this.
Recently I saw a picture of someone building a chase out of plastic conduit-the black ribbed kind used for piping a stream under a road. I suspect 24-30 inch diameter, filled with rock wool insulation and the pipes running up the middle from the bottom of the trench into the house. looked easy and cheap....
In all cases, if you are in termite land, you will need to consider how to address these pests, but how is that different from keeping them from crawling up a full foundation or crawl space??
>" So structures built on wood or concrete piers or pilings or even helical piers interest me."
Don't go the wood foundation route. If the foundation fails, you have two options: hugely expensive foundation repair work, or tear the house down and start over. I would argue that rebuilding more than offsets and supposed "green" advantage of a wood foundation. Use concrete where concrete is needed, and a foundation is one of those places. There are other concerns than just the initial impact of the material, and to truely build the greenest building you can, you have to consider the entire system and the building's lifecycle.
Helical piles are another option, but will requier a lot of changes in the rest of the structure to distribute the load. This is entirely doable, but will require a lot of work that many contractors won't be familiar with so be careful -- anyone doing this for the first time is prone to make mistakes. You'll have more issues with detailing too. I don't mean to try to discourage the use of helical piles, just be aware that they will complicate some other things so you'll need to modify your details accordingly.
Bill
I don't know about national codes, but the two places I'm familiar with no longer allow wood below grade, even for decks. Concrete to grade, and then a post bracket and a post above.
I don’t understand the fear of wood in ground. In San Diego by my daughter they have a fishing pier built in 1930 of wood that still stands in huge waves. Virtually every house built at the Jersey Shore South of Seaside Park in the last 40 years is built on wood pilings. None are under $1 Million. They started building like this where I am in LBI in the 1960’s and I am not aware of a single house that has had the foundation replaced except those that were knocked down to build a bigger monster house. In places where there is flood risk the pilings are best because they allow water and waves to pass through, just like fishing piers.
In rural areas they have been building pole barns for generations and the wood poles last a long time so long as the wood is properly treated for ground burial, not ground contact and it is not exposed to animal excrement.
I'm not a particular fan of wood foundations simply because I've never focused on them, but I'm pretty sure there are ways to build them every bit as good as concrete foundations. In Australia and New Zealand wood foundations are very common for most new houses.
Kevin,
Frame an insulated core from the underside of the floor down to below frost level, much as though you were building a preserved wood foundation. Make it about 3 ft x 3 ft and leave the top open so that it draws heat from the cabin above, rather than a separate heat source.
It's a very frequent topic here on GBA, and there has been a lot of discussion of how to detail the core. It might be worth searching the site to look at other threads.
A bit warmer in zone 6, by my cottage is built on piles. The drain and water line was wrapped in thick fiberglass insulation for steam pipes. The water line also has a heat cable on it, seems to be needed as it will freeze when not there.
Be careful with sealing for critters where these go through your floor.
I'm in climate zone 6 and for my small cabin on piers I used a 12" plastic culvert (which could've been a smaller diameter) that extends vertically from where my buried waterline 90's upwards (6' below grade), to the floor. I made a box with walls 4" thick of foam insulation that fits around the culvert. It extends from the underside of the floor to a foot below grade, and the perimeter of my cabin is also enclosed and insulated (treated plywood and foamboard.) We get winter lows that may dip to 35 below, and in 16 years have never had a problem. Sched. 40 sewer line isn't in a chase. Exits straight down to it's long sweep 90 that's below grade.
By culvert you mean the corrugated black conduit pipe that you see used for irrigation and drainage? That is a great idea. That stuff is tough, and comes in big sizes (36 inch diameter and bigger is not that hard to find) that can hold a lot of rock wool insulation around the water lines.
Yes, it's double walled black plastic culvert/drain pipe. The interior is smooth and the exterior is corrugated. Meant for under roads, so it's heavy-duty. Not cheap though. Local railroad maintenance crew sold me a leftover 20' section for a great price. I didn't insulate the interior because I wanted the heat from the ground to be able to migrate upwards and keep the waterline warm. That's why I built the enclosure around the culvert pipe.
Daniel,
That's a great idea. Kills a lot of birds with one stone.
Hi Daniel,
Quick question for you. I'm considering a similar approach here in Maine, however, I won't have a skirt around my structure which is 2 feet above grade. Above you reference that the perimeter of your cabin is enclosed and insulated. Are you referring to a skirt (i.e., the underside of your cabin is not exposed to ambient air)? My floor system will be insulated and enclosed, but the space between the bottom of the joists and grade will be open to the sides. This makes me think I may need to extend my insulation around my pipe further down than the 1 foot below grade that you did. I'd appreciate your thoughts.
Thanks,
Josh
Hi Josh,
Yes, I installed an insulated skirt so there's acutally a whole other layer of protection for the waterline that's already protected by the culvert and insulated box. The crawl space always stays above freezing. The culvert pipe being installed below frost will offer warmth that should keep the waterline above freezing in the section above grade if you insulate well enough around the culvert, and starting the insulation deeper than 1' would surely be a good idea I'd think too.
When we first moved in I hadn't yet put the insulated skirt on, so I didn't close off where the culvert enters through the floor hoping that the heat from the house would help. I also wrapped the top few feet of waterline with heat tape which I'd turn on for only the coldest nights. I've not used it since that first winter, and not sure how necessary it even was: I'd lower a thermometer down and though it got close, it never hit 32f. That first winter here all I managed to do was put up a crude roofing felt skirt to help keep the wind from blowing through.
Rather than worry about building a chase between the ground surface and the underside of the house (and then keeping it heated inside so the pipes don't freeze) do what I did and build a small utility shed attached to the side of the house on a small slab on grade concrete foundation (i know it's still concrete but you can probably manage a slab for a shed rather than for the whole house). Now you can bring all the pipes up out of the ground into the shed and run them through the connected side walls into the house. You can put all the water purification and heating equipment out there too (make sure the underslab and walls/roof are well insulated).
Scott,
You described that in a previous post. I'm puzzled as to what advantage you gain? It's essentially an insulated core located next to the building you have to put a roof on, which also needs supplemental heating.
I just realized how small your sq. footage will be and thought I'd offer what I did, being in a similar situation to yours: I built a small cabin to get on our property and have a place to live while we planned and then built the main house right next door. Cabin then converts to my shop.
With space at a premium and the need for a large pressure tank due to our off grid electric system and a low flow dc submersible pump, I installed a "service pit" between the cabin and main house site. The pit is 6' deep and made using 3) 2'h x 4'w well tiles. The manifold with pressure gauge, switch, and tank are housed in the pit, and a simple shut off and drain allows me to drain the cabin to it if we travel during the winter. I can leave the pressure tank full since I'm confident that the service pit will never dip to freezing temps. Without a proper basement I don't trust the cabin to maintain temps above freezing for more than a day or two if the heater were to quit during a deep cold snap. I provided two supplies off the tank manifold: one for the cabin, and one for the main house. I could've moved the manifold, tank, etc., into the new house, but like the idea of being able to drain the house down if I want while maintaining a live system to the pressure tank. The new house is a slab-on-grade and the pit provided for a drain point. If we travel leaving the main house I would have had to otherwise drain my tank, and it's a 25 gallon drawdown that's precious in my off grid electrical situation. The water is also nice and cold through the heat of summer.
After reading all of the above (including some good ideas), I still say ... concrete.
Even for a backyard shed, I would never build a wooden floor with a ramp up to it. I realize that's what most people do, but to me it's ridiculous. Assuming you want to build it properly and to prepare the base properly for a cold climate, it's going to cost you 75% of what it would cost to build a concrete foundation/slab.
Malcolm, sorry for the late reply. The rational for the utility shed attached to the side of the building came about from the fact that I was building out in the middle of nowhere so getting a concrete truck onto the site (even if there was a concrete plant nearby) would have been impossible.
The lack of access to lots of concrete typically means building on piers which still requires some concrete but it can be mixed by hand onsite and placed in tubes yourself. However, the problem now is getting the water from a well up into the building and then getting the waste water down to a septic field. Since I am in a cold climate I thought "why not see what people do in this situation in really cold climates like the arctic".
I went onto a research site that studies buildings built in Alaska and they all use an insulated chase from the ground to the underside of the building but every one of them required supplemental heat (usually an electrical tape) which runs 24/7 throughout the winter. I didn't want the extra electrical load so I decided to expand the chase idea into a full shed.
I figured that since I also needed a space for the pumps, the water storage tank, water purification, etc and didn't want these things taking up space in the cabin I'd group all the equipment together on the ground on a small concrete slab. The slab is insulated underneath and at the edges and the well pipe comes up through the slab into the shed. Then the water is heated, cleaned and stored before coming into the cabin through the adjoining shed and cabin walls (under a false floor in the cabin). Waste water and sewage exits the same way, out through the adjoining walls and down through the slab to the septic system.
The shed is insulated and the excess heat from the water storage tank and other equipment helps keep it warm inside but I did add a very small direct vent propane heater on a thermostat that kicks on if the inside temp gets close to freezing.
I guess the biggest benefit to the shed is that it groups all the mechanical equipment together and outside of the cabin and yet it's still easily accessible. I also have space in case I ever need to add more equipment in the future.
I would do this even if I was building a new Big house. No moving equipment down to the basement or up to the attic. Do this.
Use a foam and plywood floor instead of a slab.