The Engineering Bid

Perhaps the most important aspect of building with containers are the modifications of the boxes themselves. I assume that if your reading this blog that you are already familiar with the characteristics of conex boxes. Forty foot hi-cube conex boxes are capacity rated to carry over 80,000 lbs. They stack full containers aboard ship at least five high, so they have both solid floors and virtually crush proof corners. Both sides and top are really just curtain walls, however, they provide enough shear wall strength to keep the whole from racking and the floor from sagging.
Every engineer that I've spoken to about using containers always refers to them as box girders. Their calculations concerning the removal of sections of the curtain wall, whole lengths of wall as well as windows and doorways, come down to proving that modifications do not violate the integrity of the box girder.
This is a section drawing of an interior container wall in one of the pylons of the house on Bethel Island. Where the curtain wall was removed a steel square tube 2x4" header on 2x2" square tube posts re-supports all the loads. These were the engineered modifications used on the Portland project when joining two containers side by side with open walls. Since we are modifying standardized structures we can design using standard pre-engineered modifications. The steel 2x5 1/2 square tube at the bottom of the container has yet to be engineered. It has welded clips attached to receive glue laminate beams that will carry the center span between the container pylons. They are supported underneath by 4x4" steel posts to carry the point loads down to the foundation.

Our preliminary report from the soils engineers is that their foundation recommendation will be for the use of grade beams set on driven piles. When I have built previously with containers the foundations consisted of grade beams that spanned only the ends of the containers but included footings to support the point load of the posts. I expect that will be how the structural engineer will handle this project. I have never worked with driven piles before so it's inappropriate for me to present a foundation sketch. As you can see these sketches could easily have been done on cocktail napkins. I've hired a real draftsman to put this idea across to the engineers that are about to receive my Request For Proposal.

I've collected other appropriate modifications, such as welding the corners together and how to design embed points in the foundation footings to weld a project to the ground. These will come in handy, too. The better you can explain what you want to do to an engineer the more helpful and efficient they are going to be. You are going to want to make sure that they are looking at the type of containers you are building with. I once hired an engineer that used as his model containers that did not have a square tube top rail. The modification that he designed used custom steel headers that would have cost five times as much as off the shelf steel. I ended up paying for the redesign, it was not cheap either.

Professionals

You can only go so far with Google Sketch Up. In order to build the kind of documents that you need to pull permits you need to go to the professionals. While you aren't legally bound to use an architect to design a residence when you get ready to summit your design to the planning authorities clear understandable drawings are a major asset. It's also going to help when you hire structural engineers. Clear drawings are going to save you money with these guy's, they charge by the hour, the quicker they understand where your going the better.
Last week we hired Jeffrey McGrew as project draftsman to produce planning sheets. Jeffrey is an old friend of mine that works out of Oakland, California. He wrote his masters thesis on the use of cargo containers as modular building components about eight years ago. Other friends of mine had been using containers for art studios in San Francisco by that point but Jeffery gave it that academic gloss that got me to take them seriously. We've hired him to produce regular two dimensional drawings and electronic files that will transfer easily for use by the structural engineers.
He'll initially produce the elevation and plot plan drawings needed to apply for permits from the Contra Costa County Planning Department. They will check that the zoning is in order and that the building conforms to the restrictions applicable to building on Bethel Island. These restrictions include all the requirements for building in a flood zone. We will have to get a civil engineer to confirm grade height before construction begins and recheck afterward that the habitable space is above flood level, After we receive plannings permission we will develop the detailed construction plans.
We hired soils engineers this week. Before you can build a house you have to build a foundation. Before you can build a foundation you need to know what the ground is like beneath the surface. We are particularly challenged by this building site. Bethel Island owes it's existence to a levee that was first built around the island by the US Army Corps of Engineers. Without the levee the island would now be 12 feet under the waters of the Sacramento River. Before the Corps decided to control and channel the flow of the river Bethel Island was already very soggy marsh land. Repeating over the centuries the plants on the island died and were pushed down by new growth. All that plant matter turned itself over time into what's known as peat moss. Peat has the consistency of a really old kitchen sponge. This peat bog is on average about 34 feet deep on Bethel Island. Everybody knows this, the county building department, the municipal district and the old guy that lives next door to the site that used to be a soils engineer before he retired. The thing is in order to plan the foundation you need to have an up to date soils report. We went out to bid with two different companies and selected the company that used the least intrusive test bores. The losing bidder wanted to use a very expensive drill rig that he didn't own. It's cost was in addition to his fee for the report. His proposal estimated total cost ranging from $7000 to $11,000 depending on the number of holes drilled. Berlogar Geotechnical Consultants of Pleasanton, California was selected based on a total price of $6800. They use a drill method called CPT and they own their equipment. As the soil conditions in the area were already well documented I wonder what the first guy thought he was going to find in the extra bore holes.
All that we have done to this point is called the site work. If we had needed to cut a road or seriously graded the site that would have added additional expense not just in actual work but in the production of professional reports that cover everything from protection of riparian habitat (bird nests) to water runoff control. Depending on where you want to build you can easily go through many tens of thousands of dollars completing your site work. It's pretty laid back on Bethel Island. I think they have figured out that if you really want to build a house on a peat bog you've already got enough problems.

Preliminary Design

Our design consists of two pylons of four forty foot long hi-cube cargo containers with a span section separating them by sixteen feet.
The lower levels provide parking and storage. It also raises the habitable spaces above the flood plane, a requirement for building on Bethel Island.
The third level contains the living area, kitchen and a half bathroom. It is entered by way of an interior stairwell . There are decks both fore and aft between the pylons. The rear deck connects by footbridge to the top of the levee and the boat dock.




The forth floor has three bedrooms. The master bedroom has its own separate bathroom with the two remaining bedrooms sharing a bathroom.
The center span connecting the pylon sections will be built as a steel framework supporting glue laminated beams and decking. The span walls will use as much glass as is practical to provide stunning views of both the island and the delta as well as interior day lighting.
As the design progresses we will add windows to the exterior container walls to provide both cross ventilation and lighting. The roof is flat across the whole structure with a slight slope to manage runoff. It's currently planned to pour a light weight concrete roof topped with a waterproof membrane.

From The Ground Up

I have a client. Since looking at the property in Santa Cruz last year things had been slow. But I've been seeing sure signs of economic life coming into bloom. People aren't as shell shocked about life as they seemed last year. All the fear that was poured into society didn't poison the well. The most common response to all the dire predictions that I saw, and I traveled a lot last year, was the planting of gardens. Everywhere I went I saw people building raised beds and turning compost into the soil. I thought "What a marvelous response. I'm glad I live among a people of such grace". As Voltaire wrote "We must all tend our gardens."

This blog, by the way, has been very effective at getting information to people who are interested in actually building. My new client is a guy that retired from the petroleum processing business and lives for at least part of the year in Panama. He owns a piece of land in a community called Bethel Island on the Sacramento River delta in northern California. He and I are into about a 250 email relationship at the moment. We exchange drawings using Google Sketch Up and have produced a design that's ready to develop.


This is the building site, the view is looking back at the island from the top of the levee. The lot is 50 feet wide and about 200 ft long from the levee to the road. There's a drop of about 5 feet from the road to the lowest spot on the property. From the road height to the top of the levee is 16ft. The design that we are working on is three stories tall. We are using two stacks of three containers with a span of 16 feet between them. The span connecting the stacks is built of structural steel and glue laminated beams. The first level contains the garage and will lift the habitable parts of the building above the flood level. Most other houses on the island are built on top of pilings to raise them up, we are going to use hi cube cargo containers that sit on grade beams which are in turn set on helical piles.

When I visited the site for the first time I met with Steve from the Bethel Island Municipal Improvement District. He is in charge of maintaining the levee and is the first authority that must approve building plans. I asked him about the soil conditions and he said "So you don't know already?". This is always a very bad sign. He explained that below the topsoil was a layer of peat moss that was on average 32 feet deep. Peat has the consistency of a wet sponge and is so unstable it cannot be built on. Below that, however, was a bed of compressed gray sand that would support piles. Pile driving, as you might imagine, is very expensive in itself. But when you add the associated costs of civil, soils and structural engineering just to get you to a workable design the costs really add up. Steve did say that it was legal to build on a concrete slab directly on the ground but then pointed to a neighbors garage that had been built a couple of years before. The garage was nose diving about 5 degrees already. He added that the soils subsides about an inch and a half a year.



And so it's time to start the site work. The house is designed so that the habitable space starts close to the level of the top of the levee. The whole point of building here is the proximity to the river. Almost every house on Bethel Island is built along the levee, each with it's own dock. The building code dictates that no building can be higher than 35 feet from grade. Say the gray sand layer is currently 34 feet down. You start this process by hiring a soils engineer to bore test holes in the ground to determine the depth of the bed that you can build on. As every house on the island has had to do this you would think that this depth was a known quantity. The short answer is no, the process has to be repeated with each job. I've asked for proposals from two firms that have some experience of the island and am waiting for the bids. They will show up with a quote for the report plus whatever it costs to bore the holes. There are several methods to do the drilling and each has its own draw backs and features and they are all expensive. In the next installment I'll be discussing what we find. I'm willing to bet you right now that the learning curve is going to be sharp and expensive.