Plans for the 400-sq.-ft. addition looked straightforward: a new dining room, a pantry, and a full bath stretched out along an existing wall of the house. Ordinarily, the wood-frame structure might have gotten concrete footings and stem walls if not a full foundation, but designer Michael Maines decided to build the structure on helical piles instead.
The 10 hydraulically driven steel piles will cost the homeowner $3000. Maines, a builder and designer as well as a contributing editor atFine Homebuildingmagazine and a GBA Expert Member, didn’t price out the concrete work, but he guesses it would have cost twice as much as the piles. Then there’s the excavation and related issues he’s also avoiding.
Maines’s decision to opt out of concrete in favor of helical piles neatly sums up their appeal on both economic and environmental grounds: They are faster, less disruptive to the building site, and often cheaper—and with none of the carbon baggage that comes with concrete.
Those advantages are helping to propel the industry into a new era, 182 years after the first helical piles (then called screw piles) were used to support a lighthouse on the coast of England. While builders like Maines may choose them for new construction, they are more often used in residential work for foundation repairs and reinforcement. On commercial and industrial projects, helical anchors and helical piles have a variety of uses.
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hi, thanks for posting. i dont quite understand this statement
"When piles are not cut off at or near grade, a structure built on top of them may have a tendency to wobble. The problem can be corrected with bracing that’s welded to piles, or by leaving the tops of the piles closer to ground level."
Max, because helical piles have a small diameter, they don't have very much resistance against lateral movement. If you're placing girders directly on them it may not be an issue, though I know of a project nearby with that situation and when you walk on the floor system it shakes a bit more than it would on a regular foundation. When the floor system is built up on posts, as mine is in the project Scott photographed, there needs to be angle bracing to keep the posts from shifting. On my project we'll add diagonal 2x4s, but if you wanted to you could extend the metal piles higher and weld or clamp a metal brace instead.
查理,项目过程中,我们只是站在exterior walls yesterday. It's attached to an existing house so lateral resistance is not as important. But after we drop 2x4 sub-joists below the 2x10 joists to get a 13" insulation cavity, and cover that with plywood for air and critter resistance, we'll add diagonal 2x4 knee braces at each post. It's definitely a more pleasant space to work than a sealed crawlspace, aside from the fact that we put down 3/4" crushed stone and I keep forgetting my knee pads. We'll eventually wrap the space with vertical board skirting.
如果我正在设计一个全新的房子，完全靠在码头上，我会参与一名专业的工程师。Techno Metal Post还有能够回答很多问题的工作人员的工程师。
To me the two photographs illustrate how many of the weaknesses of the system can be designed out. The floor of the outbuilding supported directly on the piles would be difficult to work on, leaves an awkward space underneath, and the exposed piles, although structurally adequate, look unfinished, flimsy, and temporary.
That airy underside of Micheal Maine's addition avoids all those issues. If the floor, and attachment 0f the walls to the existing house, provide adequate shear-resistance, I'd be inclined to try and not add bracing to the posts.
Michael, what size metal braces do you recommend for lateral bracing, and how extensively do the piles have to be braced? thanks!
Hi Max, my only experience is with wood bracing--I'd talk with the helical pier company, and/or a licensed engineer. The Techno Metal Post website includes this image, which looks like probably 1" diameter bracing.
Thanks for the info Michael.
Do you have any information on the plumbing chase below the structure?
Edit: I just re-read and realized I was confused. Sounds like there was existing plumbing under the addition, not new.
Chris, we are adding a bathroom so there will be plumbing in the floor assembly. I was careful to lay out the joists so the toilet drain can go straight back to the house, and the shower and sink drains can be drilled through the 2x10 joists to tie in with the toilet drain. The 2x10s are larger than structurally necessary, partly to allow for drilling.
Yesterday we gusseted 2x4s to the bottom of the 2x10s so we have about 13" in the floor cavity. More than half of the insulation will be below the drain so I'm not worried about freezing. My insulator does a lot of floors on piers for seasonal lake homes, and he likes to make a removable polyiso foam panel below plumbing chases. We may do that here but I'm not sure yet.
Another idea I designed for a current project before the builder decided to go with a slab system for time and budget reasons (WarmForm by Bygghouse) was to make a small crawl space, about 10' x 10', and put the rest of the structure on piers. That would have given us a place to make plumbing connections and also would have braced the entire floor system against lateral movement.
What are your ideas?
Thanks for responding! I'm planning a build on piers, which I'll hopefully start next summer.
I'm thinking web joists for the first floor & pack with dense-packed cellulose. If they're deep enough, I don't think I'll have to worry too much about the lines in the floor.
What I'm stuck on is how to get the well & septic lines into the house, and how deep to go with that detail.
I thought of just many layers of foam board with some sort of wood-walled "basement". Maybe a 4'x4' or something smaller.
I've also considered a small concrete chase, then insulating. This would help with lateral strength of the house (something I'm still not sure how to accomplish well on a building entirely on piers).
I built that addition for a friend many years ago in Burlington, VT. I'm fairly certain it hasn't had any issues, yet.
I've done a couple of insulated cores. After working out the kinks (the first was too small relative to the height from floor to grade and kept freezing), on the last I poured a 4 ft x 4 ft square of concrete stem walls. with foam interior insulation continued down to the frost level. I located it under a utility room, and left most of the top open so that it relied on the heat of the house, rather than supplemental heat. That meant that if it froze, the rest of the house had too, and you had bigger problems to deal with. Once done it is vitally maintenance free and can be forgotten about.
谢谢马尔科姆！I'm in Maine, Zone 6a (wet). Frost is 5-6ft. I was thinking something similar to that. You found that 4x4 worked well, it sounds? What size was too small?
My advice is all based on my experience here on the milder West Coast where the frost level is around a foot. There may be more efficient ways to deal with protecting the core when it has to go as deep as you would have to. Perhaps using wing insulation as they do with Frost Protected Shallow Foundations? I hope Michael or some others will chime in with their thoughts on that aspect of the design.
Chris, on a new home on piers in Harpswell that I was involved with we used thick sheets of EPS foam to make a transition box for utilities--kind of like a mini-basement. Pretty much like Malcolm describes except without the concrete. I think the carpenters ended up wrapping the foam with pressure treated plywood, which would help with UV and critter resistance.
Thanks Mike! That's kind of what I'm hoping to do. When I do basement/dug-out egress windows I usually box it in with 6x6's. I was thinking the same thing, just lined with several layers of EPS.
Michael, All: Very happy to read this article. For an upcoming Passive build, referencing Mr. Maine's excellent article on minimizing concrete in a slab on grade foundation vs optionally a foam-encapsulated raft slab foundation a la Warmeform. In a variant of your stem wall or perhaps an improvement to a thickened edge raft slab, I've been pondering for a while using helical piles to improve both anchoring and support while reducing total cement required. General idea was scrape topsoil, insert helicals and then tie their post caps to the ring and intermediate support beam's rebar before pouring with presumptively minimized concrete. Same idea for the EPS-encapsulated raft slab: screw in the piles before dropping the foam on top of them, then proceed as normal. Solves the problem of cross-bracing. Not sure this makes sense when I see the linked installed costs survey results. However, would welcome thoughts or comments. Thanks in advance.
We did a guest house in a floor zone a couple of years ago on piers. Built an insulated core box for water and waste. Put in some heat tape just to be safe. No problems yet, and we've had a couple of very cold winters in between.
Interesting article. Bravo to Mr Maines for looking to an alternative way to build.... I have owned a home on Long Beach Island NJ for 50+ years now. Part of the home is on helical pier reinforced spread footings and a different portion is on wood pilings driven into the ground. Both performed well during Hurricane Sandy. For the last 50 years almost all new homes on LBI have been built on wood pilings although helical piers are now sometimes used. It is hard to justify the helical piers since the solid wood piles do not create a hinge point and are cheaper. Despite the marine environment, there is no evidence wood pilings with the proper treatment levels have rotted and there are thousands of houses built on them.
Concrete is the greatest construction material ever invented-it is almost perfect....except for the imbedded carbon...I am having trouble justifying using dozens of yards of concrete in a residential home to build basements, crawl spaces, stem walls and slabs....when there are perfectly good alternatives..
For a chase, try a large plastic conduit-the black ribbed kind or corregated metal, 30 inches diameter, filled with rock wool with the pipes running up the middle..
我是打算将螺旋桩但我m building close to the grade - only 15" from grade to finished floor height - So even if i can get it to work structurally, with my insulation, etc I still am only a couple of inches above grade - seems like I am just inviting a problem... so slab on grade seems the only option... This seems like an important aspect to note...
Jamie, that is a logistics problem, and also a code violation if your location uses the IRC, which requires 18" clear except at beams.
I framed one free standing addition on piles last october here in northern vermont. the piles were all out of line due to the rocky nature of our "soil". the three girders were built on top of 6x6 posts to level out the building as it was sloping with 4' of drop over 24 feet. the girders were not square, and we framed the floor joists square on top of the girders.
after my one experience on a sloping site I wonder if there was much of a cost savings versus concrete columns. there was a lot of extra labor and materials building up the piles to get to a place we could frame the floor.
在这里，很难看到螺旋杆在木柱中结束。相反，人们经常使用2 7/8或更大直径的圆形码头/桩，并简单地将其延伸到光束 - 无限制的一点和一些劳动力。
经过the way, in residential use we talk a lot about helical piers or piles, but there are also a variety of push piles and other driven piles and, of course, wooden poles, pilings and piers installed a variety of ways. Last but not least there are interesting prefab concrete items like “Perma Columns” that may be cost effective for those who do not want to put wood in the ground
我的客户规范螺纹护套的成本节约measure. he works for a large commercial builder in southern New England and they use them on big projects regularly. he didn't want to spend the extra money to extend the the steel posts.
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