Building on Piers in a Cold Climate
Hi All.
Preface-I’m new to all things building.
We just purchased 16 Acres of woods in Western Massachusetts from our neighbor. Winters are cold, summers can be very humid. We are planning to build a small house approx 20×30, with 1.5 or two floors. No basement.
We are people of the student debt generation and have relatively low joint income, and we are dreaming of the possibility to build a small and simple home without going into “normal” American levels of debt. We’re living in a rented small cabin in the same area, that was converted to a full time living space years ago. Its plenty warm when the wood stove is going but does not retain heat well, and the floors can be cold when the fire has been out for a while, which doesn’t cause us to weep and moan much because its affordable to live here and that’s our main goal.
Is it possible to build a small full-time residence in cold climate, on piers, that is comparable in warmth and function to a house with a cement foundation or insulated slab? – I’m imagining PT 2×12 Floor joists being sprayed with foam or the cavities filled with another method or insulation. Putting up hardware cloth mesh to keep out the critters. Then sealing the underside with a plywood.
Thoughts on containing and insulating the plumbing underneath? Is it possible without skirting around the perimeter? The concern is that the skirt will become it’s own contained environment in humid summer and get moldy and invite more critters.
We would like to heat primarily with wood, as we have plenty of it around. We will have full southern exposure once the trees are cleared. Secondary heat source can be whatever meets code, is affordable and keeps the pipes from freezing when we can’t feed the wood stove. Thoughts on a 2nd heat source system for when we’re away from the wood stove? Preferable the smallest sized systems as to not take up space in mechanical room in small dimension home.
A neighbor friend who is a retired builder, is all for the piers, but most people I speak with in Western Ma have basements and think it’s a bad idea. Is paying more money for an insulated slab really going to make a large difference worth the expense?
General and or specific thoughts on building on Piers in cold climate?
Thanks!
MD
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Replies
Your water has to come in underground and your sewer has to leave underground. The usual way to do that with a house on piers is to build an insulated column from the ground to the underside of the house.
Have you really priced out that piers are cheaper? Just as a for-instance, near me pressure-treated 2x12's are about $36 and untreated are about $18. In general whatever is conventional construction for your area is cheapest, that's why it's conventional.
If you build the house from the ground up to have thick insulation it really doesn't cost any more. You will never regret having a well-insulated house.
Basements are conventional in this area. Is concrete, excavation and labor for a basement cheaper than piers? It's just got to be. I could dig the holes for the piers, build forms or buy sono-tubes, borrow a cement mixer and pour the piers myself or pay for the concrete to be poured into the forms, I'd still have to think it would have to be much cheaper than a full basement. Not to mention piers are much less invasive to the site. I'm all for a well insulated house, and have to build to code regardless, and hope to insulate above code if possible. But the question is, is there such thing as a well insulated house on piers in a cold climate?
MD1986,
Yes, there is nothing that precludes a house on piers (concrete or helical) being well insulated. The usual way is to install a continuous layer of foam board on underside of the floor joists covered with plywood for protection, and fill the bays with batt or cellulose insulation.
There are a couple of complications. You need to keep the house high enough so that you have access to the underside to work - and the work there isn't pleasant. As DC said, you also need a small core of either insulated concrete or PT wood that extends down far enough to keep your services from freezing. My preference is to keep the top of this open and connected with the living areas above to prevent freezing, rather than relying on a separate heat source.
For a secondary heat source I'd suggest a mini-split heat pump.
Thanks for the reply. I've read about the idea of the core, and I think I can visualize it. It is essentially an insulated box that goes down to where the water line is below frost, is that correct? And when you say the core is connected to the living area, how do you mean? I have yet to hear that idea and am curious.
In order to keep a pipe from freezing insulation is not enough, there needs to be a supply of heat. The idea is the core is not insulated at the top but is exposed to the living area so heat from the living area keeps it warm. It's not a gaping hole in the middle of your living room, it's a cabinet or closet that is open to below.
What's hard with raised floors is running the drains so they don't freeze. Running drains is hard under the best of circumstances.
MD,
You and DC have described it very well. I prefer to use the heat from the building above, as you then never have to worry about the heat source for the core failing. If the heat for the whole house goes out you have bigger problems than the core to worry about.
To your question, "is there such a thing as a well-insulated house on piers?", the answer is yes. If you go far enough north, that's the ONLY way to do it. Building Science Corp has a fascinating article on the subject: https://www.buildingscience.com/documents/insights/bsi-031-building-in-extreme-cold
What kind of foundation makes sense (e.g., slab-on-grade, full basement, walk-out basement, or house-on-piers) will to a large extent depend on your site and its geology/hydrology. Figure out where on those 16 acres you'll be building, how any services will get out to the site, and what things look like under the surface. You may anyway need to have excavation equipment on-site for infrastructure (i.e., driveway / septic / drainage), in which case the additional cost to excavate a foundation may be almost reasonable. Another option might be to look into helical piers.
Finally, some advice: tempting as it may be to play the "we'll do this ourselves, too!" game (trying to save money), be VERY careful in evaluating what makes sense to do yourself. There's a real cost to delays, stress, mistakes, and your time (ask me how I know). Save your time and energy for the things you enjoy.
Thanks for the link, wow, that's alot of insulation! We certainly will need excavation equipment on site for septic, driveway. etc Even if the extra cost to excavate the foundation while machines are on site was reasonable, I'd imagine the cost of the concrete for a full basement to cost a whole lot more. We are pretty much against having a basement, but are considering a slab on grade if not piers. But I don't yet know the soil specifics. Ill look into the helical piers.
That is good advice, but hard to take, as a frugal new englander! Thank you
"Is concrete, excavation and labor for a basement cheaper than piers?"
You have to look at a house as a system. Yes, piers require less material and less labor than a basement. But they introduce costs elsewhere in the project. Costs vary enormously by region so there are no general rules.
If you are doing piers, look into helical piers instead of blocks or concrete. I plan to build a 20x30 studio on piers in my yard in coastal Maine. I like piers, they give me flexibility to add plumbing later, not to mention I skip the stress and time dedicated to working with concrete. Plus I grew up in the South and most older homes there are built on block piers, it's not an unfamiliar thing to me.
Going by the articles on this site, the floor will require some detailing to add enough insulation to get decent performance, but it's not a deal breaker.
To answer your first question, yes you can insulate a raised floor to a good level of comfort.
The reason basements are popular is snow load. I have a house in RI, I assume where you are in MA is similar. We have to design for 35 lbs/sf snow load and 20 lbs/sf dead load for the roof and 50 lb/sf for each interior floor live and dead. With a 2-story house that's a total of 155lbs/sf. With a 600 square foot house that's 93,000 lbs. We're allowed to assume 1500 lbs/sf soil bearing capacity without soil testing, so that house requires 62 square feet of footings. You may as well just do a 12" trench footing down each of the 30' sides to get that. We have to go down 48", you probably have to go deeper. If you're going down that deep it's not that much more to dig out the basement.
I understand the appeal of piers in that it's something you can do yourself, and in stages. The traditional way to do that is concrete block, although I'd say that requires more skill than piers. But if your soil is like my soil it's going to be an enormous job to dig those piers by hand. A 14" sonotube is just about exactly a square foot, you'll need 62 of them.
I realize you're just in the exploratory phase right now, and you're asking the right kind of questions. If you're planning on doing most of the building yourself there are design decisions you can make to simplify the construction. At the same time, you have to realize you're not going to be able to do everything by yourself and part of the design discussion has to be what parts you're going to hire someone else to do. I think the foundation is a good candidate, because it is crucial to the house and requires special skills and equipment.
Thanks for the replies. While I'm still ignorant to things like snow load details, I have seen 2 houses going up in the general area that are on piers, and while I didn't crawl around underneath, I sure didn't see anything near 62 piers. What about a row a few piers (whatever # required) running lengthwise, with brackets on top of them, and beam laying across them.
You're exactly correct about the exploratory phase. I can't and won't do everything myself that's for sure.
MD1986,
Your pier spacing will be determined by the best span for the beams above - probably in a grid of about 10 to 12 feet apart. The footing pads under the piers will be around 2.5x2.5 ft (6.25 sq ft), so it doesn't take many piers to end up with adequate bearing for the whole house loads.
The other thing to look into is boring stuff like permits and insurance. MA is pretty strict about permits and what work a homeowner can do. If you ever want to insure the property the insurance company is going to have requirements too. It's getting harder to insure a house with a wood-burning stove.
My last house was on piers. It was also on ledge, making the water line interesting.
The water line was wrapped in a 6 inch diameter foam sleeve, with heat cable that was turned on in October. The heat cable continued down 10 feet or so until the ledge dropped off and it could get to a proper depth. There was foam board above but not below the water line, which was wrapped all around with thinnish foam. Never caused a problem and the electricity use was not noticeable.
When bought the floor was 12 inches of fiberglass with foam board under. Heaven for red squirrels.
Had it spray foamed
Drains were never a problem, well, perhaps once the shower drain froze, as that part they had not insulated as well originally.
I have seen many people build there own houses with the thought of keeping costs down, I have done it myself several times. Yes, money can certainly be saved by the sweat equity you put in, but it is never as cheap as you think or hope it will be.
Most projects can be roughly estimated for cost by assuming 50% materials and 50% labour, so putting in the hundreds or thousands of hours yourself will add up big time. However, some items are simply best left to the pro's, like electrical and perhaps plumbing.
Designing the house so its various components can be built by yourself is great, just make sure you are getting good advice from knowledgeable people around you. Find a good carpenter/contractor that you can have over to ask questions as they arise.
Good luck, and avoid that debt if at all possible.
plumb_bob,
"Find a good carpenter/contractor that you can have over to ask questions as they arise."
I've been that guy on a few builds. I generally end up running the job.
If you have only a certain amount of time to contribute to the project you want that to be as high-value as possible. If you look at a typical construction project the highest rates go to guys with specialized skills and equipment like excavators, plumbers and electricians, but also to guys who spend most of their day sitting at a desk. A project like this takes a considerable amount of administration -- sourcing materials, coordinating and scheduling sub-contractors, applying for permits. The lowest-paid guys are the ones doing unskilled labor.
So while it may be romantic to think of yourself out there with a shovel digging footings for piers the reality is that your time may be better spent on the phone calling around to lumberyards getting the best price on a framing package or sitting in the office of your local permit officer.
I wouldn't be digging holes by hand, I have a neighbor who is generous with lending his tractor which has a small excavator bucket.
As far as lumber. Ive already pulled just shy of a log truck load of hemlock and pine out of the woods, with said tractor. Ive got a friend willing to mill it all if I trade him some labor and some pine.
I do have a hard time with organizational skills and communicating with other people. That will be a challenge for me.
I worked on a story about a high-performance house built on piers in Massachusetts. It was designed and built by South Mountain Company (a good resource for you). Take a look at the illustration in the attached PDF to see how the water supply--among other things--was handled.
Kiley,
That's a nice clean detail for the core - and although it uses a bit more material, I bet the 2"x4" "underfloor" pays for itself in the reduced labour involved in not having to work from below, or flip the floor panels.
This is both helpful and inspiring, thank you!
Wow. these guys are talented! This is the wave of the future for new homes: small, well built, low embedded C02, low(ish) environmental impact (almost as good as renovating existing structures). Now we need to work on cost and mass production (so the masses can afford it!).
That is the most thoughtful piers design I've ever seen.
wow this is solid gold, thanks for posting!
Excellent article, and great job on taping the seams to keep water out of the floor bays during construction. My on-helical pier house (most of first floor) was not protected for a period of time, which resulted in having to tear up the subfloor to replace soaked fiberglass insulation in the 3" spray foamed bays. The closed-cell spray foam sealed the bays so an inch or so of water collected. Removal of subfloor, drying out and replacement of fiberglass set the project back over a week. The frame is pressure treated solid joists with pressure treated plywood toe-in screwed from the top side as clearance was tight from below, then the closed-cell foam was sprayed in, followed by fiberglass and subfloor. Water/sewer come up through a 10'x10' by 3' deep crawlspace with foam sprayed walls and concrete floor. 11 F last night and the floor always feels sufficiently warm (10" wide engineered white oak planks).
Malcolm,
Next time I build a house I will give you a call!
MD1986, not sure how much construction experience you have, but if you read between the lines of Malcolm's comment he is saying do not bite off more that you can chew. Good advice! Nothing worse than a construction project gone bad. But if you feel you can reasonably complete the project, go for it. It will be one of the most challenging, but rewarding, experiences of your life.
I like this thread because it reminds me of my first projects. However, when I started my first house I was a young carpenter, so had some skills and experience. My first house was a dove-tailed log house with custom everything. Great experience, but I had PTSD for a few years after...
p_b,
"I had PTSD for a few years after..."
I had been practicing architecture for five years and done a lot of on-site inspections, but was still pretty unprepared for many of the tasks involved when I built my first house. It took longer and was more stressful than I had anticipated. It was as you say though a really fulfilling experience - and the psychological damage fades with time.
Literally the first thing I ever built was a house. It took forever. I made plenty of mistakes. But it was something I'm glad I did and was immensely rewarding. I went to look at it a few years ago. After 50 years, it hasn't fallen down.
This week, I'm building an outhouse.
I don't have any real construction experience, though I've worked as a grunt guy on a few jobsites here and there, and have built plenty of rabbit hutches, chicken coops (ha!) and built handful of stringed musical instruments. I, absolutely, plan on having other people do plenty, of the work.
Around me any building on piers is considered a cabin whereas anything with a foundation is a house. Even if two buildings are side by side, there is a big price difference between the two, enough to easily offset the initial costs.
As an option you can also look at something like a shallow wood concrete free foundation. This is something that you can mostly DIY. It avoid many of the issues of building on piers and needs minimal concrete work.
https://www.greenbuildingadvisor.com/article/minimizing-concrete-in-a-slab-on-grade-home
I really like that.
Unfortunate that psychology plays such a role. Here in Montana, a house built on the side of a mountain with piers is no cabin. Engineering-wise, piers make sense. Piers are ancient technology and cost effective. Helical piers find widespread use across the globe.
There is lots of good advice you have received that says this is a difficult task… but far from impossible!
There are perhaps a million homes up and down the Atlantic and Gulf Coast built on piers (aka wood pilings). My neighbor just built one that sold for $5 Million on LBI. These types of homes share many similarities with your project. They have all figured out various ways to insulate the waste and water lines (e.g., a heavily insulated chase or even 24 inch conduit pipe); keep critters out (e.g., wire mesh screens all the way around) and insulate floors (I like open floor trusses or a false floor under the main joists). Sheathing the underside of the floor is tricky, particularly if you are close to the ground ( perhaps painted ply or hardieboard). If you are more than four feet off the ground look into commercial grade paperless exterior sheet rock like dense glass plus.
There are also probably a million post frame barns and even some post frame barn homes all over America built on poles (though most also have concrete slabs). You might ask a post frame company to build the shell leaving the rest to you.
There are dozens of YouTube videos by who built there own modest homes in rural areas, many on piers. Check them out. Some are very well done.
Personally I believe that if we are serious about fighting climate change we can’t keep building stand alone homes that are 5000 sq ft and use dozens of yards of concrete. I also think that in many areas ( particularly the Northeast) radon is an under-appreciated danger. Thus your idea of building a modest home on piers makes a lot of sense. Good luck!
Agreed!
MD,
I started 40 years ago with the same inspiration you feel now. I still have it, despite the constant sense of doing it wrong. Not only do you learn from your mistakes, you learn from everyone else's too. Building Science was just science fiction decades ago, and material choices have changed just as much.
The rest of the building industry hasn't gotten the message yet, but a full basement is on it's way out. It was never necessary, and now it is obsolete and way too environmentally expensive. I would build first on piers, second choice on a slab. Details are easy enough to find or figure out.
I rarely speak to someone who is happy with the conditions of their basements. Wet, mildew, moldy, and very expensive. Not to mention it incentivizes you to hoard a bunch of shtuff. The only part of the basement I like is it being a place to house the mechanicals. Which I'm also wondering, how much area an above-grade Mechanical room would likely need to be. I'm sure it depends in what systems you have, but in general..?
Your question about a "mechanical room" reminds me of when I lived in NYC in a 200 sq. ft. studio. The "mechanical room" consisted of a closet with a small water heater!
Seriously, if you use ductless mini splits, the only thing in a mechanical room would be the water heater and maybe a water softening system. My 50 gallon AO Smith and water softener could fit in a medium sized closet, although because it is a heat pump it needs air circulation so that might complicate placement.
In the next year or two I expect air to water heat pumps to become more useful and that may be another source of heat and/or hot water that will take up very little interior space.
With a tankless water heater you don't even need a tank. Although on 16 acres MD is likely to have a well which probably means a pressure tank somewhere inside the building envelope.
But in general, the idea of a mechanical room dates from an era when people had oil or even coal-fired boilers and needed a whole room for them. Although the Levitt houses on Long Island are all build on slabs and just have the oil boiler in a cabinet in the living room.
I know a number of folks who grew up in Levittown houses on Long Island. In some respects they were amazing-inexpensive, easy and quick to build. for many they were the ticket from the City to the suburbs....
I agree. Spend the money a basement would have cost on additional above grade conditioned space if you need it.
One additional point. Check out building or building supply auctions for cheap construction materials. I often go to Peak Auctions (peakauction.com) when they are in my area, but there are usually local auction companies who occasionally hold building auctions. I also get cheap or used building materials online (craigslist and facebook marketplace). And look for local demolition sales in high end neighborhoods-it is amazing what gets trashed in wealthy remodels and teardowns. I once bought my dad an entire kitchen with most appliances and quartz countertops for $1,500. It was less than 5 years old....Finally check out the local Habitat Reuse store....Reusing used stuff is good for the environment.
Also look to minimize your framing sizing. You mentioned 2x12 floor joists, for a 20x30 house you could possibly use 2x6 with a mid span support. 2x4 wall framing with continuous exterior insulation, look into advanced framing techniques. All of my exterior finishing now is with un-stained western red cedar, this saves lots of time and money. Cedar shingles are a low material cost, high labour cladding, perfect for a DIY. If you are smart and flexible there is certainly money to be saved.
I have yet to figure out our insulation/framing systems yet, but my thought was 2x12 joists would allow to really pack in the insulation, and even if I didn't insulate the entire cavity at first, I could add more if the floors turned out to be too chilly. I like the sound 24in on center, 2x6 framing, with walls filled with insulation and also at least one continuous layer of exterior insulation. We hope to side the house with simple board and batten, using the milled pine from our property. We love the look of a weathered pine siding, not to mention the full circle idea of the pine trees remaining on the property for a while longer. I'm hopeful we'll be able to harvest enough hemlock for all the framing, too.
My wife and I built a small house ( 800 sf footprint, 450 sf second floor) on 14 helical piers in the woods on the border of CZ4 and CZ5.
We did not want basement or attic to begin with, and also we had a site with clay and huge boulders. We got ridiculously expensive quotes for a slab or concrete piers, not to mention that everybody wanted to cut the old trees to make the job easy. So we decided on helical piles.
This was the only job we outsourced on the whole construction.
The piles were installed in two and a half days ( the clay and the boulders slowed it down - otherwise would have been a day) with minimal site disturbance. On the fourth days we had a complete floor deck. The build took us 9 month full time, and it was much more fun than frustration. BTW I'm not a builder by trade.
PM me and I can send you a link to our day to day construction blog.
That is a great looking place. Nice job. I love small houses
Nice ! I love how the house seems to fit in nicely with the surroundings, as if it grew there.
I am surprised it took so long to put in the helical piers. The last time I drove helicals we put in four in less than an hour-all to about 15 feet. I guess rock can make it complicated. They are versatile to be sure.
Looks great! I'd love to check out your building blog. But I can't seem to figure out how to PM you.
Nice!
One of the things I've learned is that it's hard to save money on a house build once construction is underway, a lot of the costs are built into design decision that you've already made -- implicitly or explicitly -- by the time you break ground.
What would be fun would be to have a broader thread on design elements that are appropriate for simple, economical but energy-efficient construction. By the way, I would say the structure outlined in the original post -- 20x30, 1.5 or 2 stories -- is a very good starting point. You want something close to a cube, no crazy shapes or angles.
Yes, just a rectangle is all we want. We're back forth about doing a saltbox shape, with the tall side facing south. We will have direct full southern exposure so would like to maximize on that. But we have yet to figure out how much money/labor/materials that would be as opposed to a 1.5 story with a single south facing shed dormer in the master bedroom. Floor plan to be mostly all open on first floor, with the exception of a couple closets, a very small 1/2bathroom and the mechanical room. Hopefully one of those can be designed to use the underside of the tallest part of the staircase going up. 2nd floor will likely be 2 bedrooms, storage spaces/closets and a full bathroom.
The two biggest problems with building on piers are how to keep the pipes from freezing between the ground and the underside of the floor system and how to keep the pipes running within the floor system from freezing.
What I did (in zone 6b) is put in a 12 1/4" thick SIP floor on top of the foundation beams and then a 2x6 false floor on top of that (the false floor system is contained within the exterior walls) in which to run the pipes.
Then I built a utility shed on a concrete slab next to the cabin on piers (their exterior walls touch) and brought all the well and septic pipes up within the shed. Then they pass through the cojoined walls and under the false floor system. At no time are the pipes ever exposed to the outdoors, all the water purification and storage/heating equipment is within the shed and there is a direct vent propane heater in there that is set on a thermostat to only come on when the temp gets close to freezing (All the shed walls and roof are SIPs too).
That's interesting. Even if you're not using SIPS, and without the mechanical shed on a slab, the false floor idea sounds like a nice solution to running plumbing. Thank you for that information!
That is a good idea. if you scroll up and click on the article appended to Kiley Jacques response you will see a very good article by South Mountain Builders of a false floor style. A more expensive but easier version of this is to use open web floor trusses. What I like about these is that they can be designed to span long lengths, be virtually any depth and typically have wide flange top and bottom chords that make nailing or screwing the floor and bottom cover a little easier.
Scott,
Any chance of some pictures? As I recall you were proposing a few innovative features in your build.
Updated the drawing with more info
Malcolm, I anticipated someone asking so went and found this drawing I did at the start. Since the shed is on a concrete pad on grade all the pipes just come up through the slab. Since I'm out in the middle of nowhere that means a well pipe and septic pipe but I put the water storage tank, water purification equipment, water heater, solar PV batteries and all the other traditional mechanical room stuff in the shed.
The cabin on piers and the utility shed are two separate buildings that are "connected" by a "picture frame" box of 2x materials stuffed with insulation. The utility shed's SIP roof touches the cabin's exterior wall sheathing and the connection is flashed and finished like you would with a typical porch roof.
All the pipes pass through the utility shed SIP wall, the picture frame connecting box and the cabin wall and run through the false floor system (shown in yellow on the drawing). I used 2x6's for the false floor system to have enough space for plumbing traps under the shower and toilet.
Thanks Scott. I was sort of fishing for photos because I followed the various threads about your build and hoped to see how it turned out. So many of the projects posted about on GBA just disappear without us being able to see the results of all the discussions. It's very satisfying to see all the thought become something the owners like to live in.
I'm using a variation of your idea on a small project right now. It's a small outbuilding on piers that may eventually get plumbing put in. Rather than build a core, I'm planning to add a service bump-out in the future if that occurs.
I built a 22'x16' cape cabin on piers in zone 6 west central Adirondacks that we've lived in for 17 years. Sono tube piers were cheap and easy to excavate and pour. Joists are well insulated and instead of plywood against the joist undersides I "capped" them with foil faced polyiso. Plenty of rodents here, yet have never had one chew through. Tough to hang onto that surface upside down, I suppose. Well insulated as the floor is it was always cold until I installed an insulated skirt and poly sheeting on the ground. My water service enters via a vertical 12" plastic corrgated culvert pipe that's set 6' below grade and flush with the underside of the joists. Built a box of foam insulation with 4" thick walls around the portion of the culvert that's exposed. Temps in the culvert remain comfortably above freezing regardless of how cold the deepest freeze goes. Because of space limitations and the desire to be able to easily drain down the house if we went away at all during winter I put in a service pit: 4' concrete well tiles set to 6' deep with an insulated cover (I've since built a small "well house" above that makes winter access easier.) This houses my pressure tank and lines out to house, garden, etc. Sewer lines are uninsulated and are fine that way. Our situation was similar to yours, and while we didn't have money or desire for a mortgage, we did have time.
Nice! I am curious why your floors stayed cold until you put in skirts. There are so many homes high up on wooden pilings on the coast that seem to be able to have warm floors. Perhaps they just need to go deep enough with insulation (e.g., 18 inch open web trusses). I suspect another issue is that most of these coastal homes have two layers of 5/8 drywall covering the bottom of the joists (required by fire code if cars can be parked underneath). That does a pretty good job of keeping the very high winds out. Of course most of these homes are not in zone 6 like you are. But winter nor’easters can drop temps and put a lot of wind under these floors.
My thought was that, well as the floor is insulated, the skirt and poly sheeting keep the space under the floor comfortably above freezing through the coldest temps, and that's got to make a difference in the floor. Instead of 20 or even 30 below against the underside of the floor during cold snaps, it's closer to 40.
The problem with skirts is that from both a practical and building code perspective, once the perimeter is enclosed it become a crawlspace - with all the issues and requirements those areas entail. So unfortunately, what you really up with when you add a skirt is a poorly performing crawlspace, made from inferior materials.
That's a valid point as a generalization, and after I spent a lot of effort detailing my skirt (because I thought I'd see a financial savings) I was painfully (physically and mentally) aware that my efforts were likely greater than it would've taken me to put in an insulated block foundation with crawlspace, and the savings weren't significant enough to justify the additional labor. But I can attest that the materials and detailing I put into my skirt resulted in a high quality performing crawlspace. It's not a given that a skirt will result in a poorly performing crawlspace, but the quality of materials and level of effort and attention to detail are paramount for success.
Daniel,
I didn't in any way mean to denigrate your efforts, but rather just point out that if you are going to end up with a certain result, it's probably better to start out with that goal in mind. So either build on piers, or build a crawlspace.
There are two fundamentally different crawlspaces - conditioned and vented - and both are much harder to do right with skirts than with conventional methods. The one most amenable to a skirt is a vented one, which if the main point of adding it is to partially warm the area under the floor, sort of defeats that purpose.
No skirts on my helical pier floor under a 20'x30' section and another 20'x30' section. The floors are closed-cell spray foam with batts and I haven't had what I'd call cold floor issues. Perhaps a major concern is wind. Wind increases heat transfer and drives air leakage/penetration. I have a metal panel fence surrounding my house, I expect it makes a difference. Too much wind across the bottom surface of a raised floor is likely to make for a cold floor on a cold day. Too little wind, likely to be an issue too (akin to a poorly performing crawlspace).
Malcom, I don't feel that you denigrated at all, but instead offered sound advice. On my project I'd never planned to include the skirt, but once the deepest cold hit got busy adding it. Even though I detailed it meticulously, I learned the hard way - crawling around on my belly - that I'd be spending much more labor working backwards than I would have had I just built a full perimeter foundation from the get-go.
Daniel,
If it's any consolation, I did the same and didn't learn my lesson. I've done it twice!
The big problem with raised on pier floors are the plumbing pipes running within the floor system. Building with 2x12 joists means that the pipes are inches away from the cold underside of the floor system and no matter what kind of insulation you stuff into that joist bay there's always a risk of your pipes freezing.
On the construction side of things, I've never understood the reasoning for trying to assemble a whole lot of parts (top and bottom sheathing, air and water barriers and insulation) for a floor system when you can get all of those components in one product - a SIP panel. Order them sized so that any seams land in the centers of your foundation beams and slap them down. Tape the seams, add a fireproof covering to the undersides and you're done.
All the plumbing can run through a false floor system and your pipes are always inside a warm environment. For about $10 a sq' you can buy a 12 1/4" thick SIP panel but you'll save yourself a lot of labor costs installing these compared to cutting and installing a traditional stick built floor system.
A SIP panel floor sure would be easier. Is the plumbing that runs through the false floor accessible in anyway?
MD, not really, the floor is finished but all the water supply runs are made with one piece of pex from the water heater to the fixtures and the drains are standard pipes with typical connections and there haven't been any problems yet.
Surprised there hasn't been a suggestion for"frost protected shallow foundation", essentially an insulated slab-on-grade.
Slab on grade is something we have not ruled out as an option. However I've read that even a well insulated slab can feel cold in the winter too, unless you have radiant heating in the slab. Given that they both have the potential to feel a bit cold the two options have been competing in my head with their pros and cons.
In my mind being able to access the pier foundation from underneath would mean any foundation repairs would be less expensive and invasive when compared to concrete slab repairs, as well as easier access to any main plumbing. You could keep adding insulation under the piers if you had to, skirting too, but the slab is more final. Piers can work with the gentle slopes of where we imagine the house, slab would require a flatter spot, or to flatten the spot.
Can an insulated slab on grade be as warm as a pier foundation? Or maybe I should ask, can a pier foundation be as warm as an insulated slab? BUT without having to rely on in-floor radiant heating in the slab? We would like to heat with a wood stove, and heat pumps for backup. Would the cost to build the slab and the potentially costly/invasive repairs down the road, be worth the investment when compared to the seemingly fussier, but simultaneously more flexible nature of piers?
Would love to hear people's thoughts on the pros and cons of the two foundations. (with costs greatly considered)
Look at post #22 again. Slab on grade, but the slab is foam, no concrete. I think this is the sweet spot for simplicity and quality.
The only plumbing you want in the floor anyway is the drains and the water entrance, both would be easy with this method.
This looks like a fantastic idea. Having built both a cabin on piers with insulated skirt, and a slab on grade for the second build, I wish I'd been aware of this approach.
MD: Our slab on grade is insulated with 4" of reclaimed XPS. Concrete will always feel cooler on your feet than wood. But we've never wished we had heated floors.
The average temperature of soil in an insulted foundation is apt to be around 50 degrees F in western MA. Air temperature could be 10 below in winter. I'd rather insulate against the higher temperature. I've never designed a foundation with the idea that it would need to be repaired.
On "that it would need to be repaired", maybe specifically for western MA? (lived there for some years). Can depend on where you live, like places (South TX, lived there too) where you have to water a concrete foundation regularly (https://texasheritageforliving.com/texas-living/protecting-your-foundation/).
PBP1,
Foundations can be designed for expansive soil, it's just that most of the ones in Texas weren't. Watering the foundation is a remedial solution.
There seems to be a lot of resistance to building on a raised floor foundation. But most homes (hundreds of thousands) on the Atlantic and Gulf coast built in the last 30 years are built on pilings with the floor raised above mean flood and many homes in the Arctic are also built on piers. Some have full skirts around the pilings/piers; some do not. But they seem to have figured out how to keep floors warm and pipes from freezing even in bitter Nor’easters. Things like open web floor trusses make building easier. Personally, due to Climate Change concerns, I like the idea of eliminating most or all of the concrete.
Agreed, it's largely psychological. Many pros for piers/raised floor foundations, piers can be installed in winter (without having to heat the ground as with concrete). Though hard to eliminate all concrete. I'm next to an alley that serves about 10 homes/townhomes and the city forced me to pay for a huge concrete apron to the alley and to pave 80' of the alley, along with a curbed concrete sidewalk to nowhere (neighbors don't have sidewalks), all while the city complains about affordable housing . . . .
Well as an Italian American I love concrete and masonry and even in my 60's I l still like to work with the stuff... It truly is a miracle substance that is the essential physical ingredient in modern societies. But given the Climate Crisis, I find it hard to justify using so much concrete in residential (relatively) low rise buildings. Until they find a way to virtually eliminate the embedded carbon in making, transporting and laying concrete and masonry, I am learning to love wood.....