What I’m Working On

No construction projects on my plate right now. Colin’s house is very nearly complete, with a few finishing tasks that Terry will perform unassisted. Bob has a gorgeous upstairs to come home to; the rest of his house is on hold while he attends to some personal business. That means I can turn my attention fully to my nascent civil engineering practice, PERCH.

I have one client near Montpelier who plans to lift his existing house 7 feet while maintaining the foundation. The goal is to elevate all habitable parts of the structure above Base Flood Elevation, or BFE. I love this project because it’s the perfect marriage of engineering principles and construction reality.

Why was the house built below BFE? Well, it wasn’t. BFE is based on historical data, just like snow load and ground acceleration (i.e. earthquake strength). But how do you set a 500-year flood elevation when reliable data only go back a couple hundred years? You can use statistical models to estimate the likelihood that a future flood will surpass any flood on record, but the result feels a bit hand-wavey… like adding a random volume of water to the worst hurricane anyone can remember. Each passing year provides new recordings and makes the picture less blurry.

Irene, 2011. This actually happened. (picture from The Valley Reporter)

Irene, 2011. This actually happened. (picture from The Valley Reporter)

When Hurricane Irene blasted New England and upstate New York in 2011, it created a new historical data point. Though my client’s house weathered the storm just fine, the new data altered local flood insurance rate maps to reflect that a flood was more likely than previously thought. This change put the house underwater, so to speak, and threatened to increase the flood insurance premium by a factor of ten.

Instead, my client applied for and received a FEMA grant to bring the house back into compliance by elevating it a foot above BFE. And that’s where PERCH comes in!

Postholing

Colin checks level on a porch post, embedded 42 inches deep in a posthole.

Colin checks level on a porch post, embedded 42 inches deep in a posthole.

Time to build the porch! We were waiting for Pillsbury, our excavation contractor, who finally returned yesterday to do some essential sitework. In particular, Todd and Tim graded around the house and the future breezeway where the porch will go. To give them access, we had to switch our temporary shed roof supports, bracing diagonally from the house exterior wall instead of vertically from the ground. Todd also let us borrow his trailer to pick up a hefty order of 6×6 lumber and bags of Quikrete – essential supplies for the porch foundation.

We installed ledgers to support the porch before Pillsbury Excavation arrived.

We installed ledgers to support the porch before Pillsbury Excavation arrived.

To start, the excavators augered a series of holes for the porch’s supporting posts, at locations Terry laid out. Then we measured the depth of each posthole and used hand tools to dig out any clay that caved in, for a uniform depth of at least 42 inches. Our chief implement for this job was the posthole digger, possibly the most aptly named tool on site. It’s basically a pair of shovels facing each other, connected with a pivot. You reach way down into your posthole, spread the handles to make the shovels chomp down on a clump of dirt, then lift the assembly up and out. We removed a whole lot of dirt this way to guarantee a proper embedment depth for the posts.

Digging a posthole with a posthole digger.

Digging a posthole with a posthole digger.

After checking the location of each hole, in went the 6×6 posts. Next came the tedious business of getting the posts square and plumb. When possible we braced the post with a 2×4 screwed into the ledgers Terry and Colin installed along the base of the house. That took care of alignment in one direction. We got the top of each post in exactly the right spot, held up a level, and pried from the bottom until the post was perfectly vertical. Then we rechecked the post’s location… because our next feat would make it a whole lot harder to move.

Into the hole goes an 80-pound bag of Quikrete.

Into the hole goes an 80-pound bag of Quikrete.

The postholes were much larger than the posts themselves, enabling us to anchor the posts with Quikrete and then backfill around them. We compacted the fill frequently by tamping it down with Sluggo or a smaller stick. Here I encountered a technique that I’ve never seen before, and that’s certain to send shivers down the spine of a commercial engineer. Instead of adding water to the Quikrete, we simply poured the dry mix under and around each post. As the logic goes, this powdery mix will eventually react with groundwater and harden into concrete all on its own.

I’m skeptical. How do you know when the concrete reaches full strength? Won’t the outer edges set first and prevent water from ever mixing with the inside? But here’s the big picture: each post ALREADY has a solid connection with the ground, buried in 42 inches of compacted soil. Adding any concrete at all is overkill, so when it comes to structural integrity I don’t worry.

Backfilling the posthole.

Backfilling a posthole.

Todd and Tim did additional sitework in the meantime, namely trucking in lots of gravel and re-grading the driveway for drainage. The level of this gravel finally matches the Barn slab, enabling vehicles to easily drive into the garage for the first time. I think Terry’s going to take advantage of the shelter this weekend to repair his truck!

The latest & greatest. All the posts are installed and the driveway is properly graded.

The latest & greatest. All the posts are installed and the driveway is properly graded.

Heat

It’s hot and humid this week, with highs around 90 and scattered thunderstorms each evening. And working down inside the basement, where white foam walls reflect the sun and no breeze can get through, is particularly grueling. I haven’t sweated this much since I worked as a mover nine years ago. Fortunately we finished all the load-bearing basement walls early this week and raised first floor joists, so we’ll be out of the oven soon.

Everybody makes sure to drink plenty. Each day we pack a giant cooler bag full of reusable water bottles and ice packs, plus a 3-gallon canteen for refills, and we pretty much finish it by day’s end or run for more in the afternoon. We replenish electrolytes with sugary drinks and we always refuel at midday with a proper lunch. For all the discomfort, there’s remarkably little whining. Seems to be an unspoken code of construction conduct: get the job done, take care of yourself, and don’t bother anyone else about it.

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End of Monday. Terry, Carson, and Colin reflect on their work… or dream of jumping in a pool.

As I’ve mentioned, the first floor joists are prefab trusses. Getting them in their proper place took several steps. I set up the transit and surveyed top-of-wall elevations. At high points, Colin used a planer to shave sixteenths of an inch off the double top plate until we had a level surface for the floor joists. Some joists we cut to fit; others overhung the supporting wall on one end. Carson and I raised each joist one end at a time with the help of a ladder, same method we used in the Barn. Meanwhile, Terry and Turner installed rim boards along the edges, laying out the correct joist locations as they went. Finally we nailed the joists to the rim boards, and the rim boards to the top plates, checking that the whole assembly was straight and square.

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Colin planes down a top plate.

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Terry and Turner install rim boards.

A few unique conditions varied our sequence. The main interior load-bearing wall contains one full-height opening, and we built up a header beam to sit atop the wall… which prevented the floor joists from bearing there. Terry solved this problem elegantly by installing joist hangers, metal corbels which nail into the header beam and provide a platform for the joist ends. He doesn’t like to use joist hangers when he can avoid it, but we definitely wanted the high header beam here to keep the basement open and airy.

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Nailing joist hangers into a high header beam.

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Blocks let two adjacent joists share their load. They’re made of scraps cut from the truss ends.

As we build, we need to think ahead, or rather above. Any point load from the roof or upper floors needs a path to the ground. Terry built a beefy column into one of the basement stud walls after careful consideration of a roof line. And I spearheaded a surprisingly time-consuming project installing blocks between the two outermost floor joists to help them share the exterior wall load. Meanwhile, Pillsbury continues grading and landscaping around us, improving our access to the basement every day. The walk-out looks splendid.

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Todd from Pillsbury masterfully stacks boulders into a retaining wall.

By the way… if you think I shouldn’t complain about the heat, if 90 degrees doesn’t sound so bad compared to where you come from… then great, come on over! We’d love your help!