Tag Archives: Design

Curved Walls

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Posted on March 30, 2013 by

Curved walls are not very affordable for wood construction, but they are a somewhat natural choice if you are working with shotcrete, particularly in an earth sheltered application.   But even if the curved walls are easy, many other aspects, from surveying to carpeting, are much trickier.  Tricky translates into expensive.  I will keep track of curve related issues as I build and put them here.

Damns are curved to better hold back the enormous pressure of the water behind them

Damns are curved to better hold back the enormous pressure of the water behind them

If you try to balance a playing card on its edge, it will fall over, but curve that card and it will stand.   When building a concrete wall, a curved wall is self bracing.   Damns are curved because it allows them to hold back much more water pressure.   Earth sheltered homes with flat roofs need at least 12 inches of concrete, but curved roofs can be as thin as 4 inches.

Curves also look and feel very appealing.  Humanity has only been living in wooden boxes for a few hundred years.

“The idea of putting a square home under the earth made no sense.  Caves are not boxes, and the box is not a shape that lends itself to the immense load of earth above.”  ~William Lishman

 

On the other hand, curves bring lots of issues.   While laying out our curvy house, we had lots of issues making things work.  It is just not as easy to lay out a wedge shaped room as it is to lay out a square one.  It also added lots of difficulty for the architect.  In fact, if my house were rectilinear  I might not even have needed an architect.

Looking ahead to construction, I am sure that siting the house will be much more difficult due to the curved walls.  I can’t just string a rope to make a straight line.  Digging a curved trench will be more difficult than digging a straight one.  Framing will require curved track which costs more per ft than straight track costs.  Placing floor joists is more difficult because each joist is a different length and angle from the wall.  Some constructions systems (like pre-stressed concrete planks) are out of the question, and others (like curved ICFs) just get a lot more expensive.

TorsionRectilinear homes rely on the principles of the post and beam, but when the beam between two posts is curved horizontally, it results in torsion.  the weight above the beam doesn’t just push the beam down, it applies a rotational force to twist it off its posts.

In a curved wall, window lintels are not just a simple beam.  They need to be specially fastened to the posts to resist this torsion.   I only have windows in the curved front wall of the house.  Here the curve is really just to be continuous with the other earth sheltered walls.  To reduce this torsion effect, I have kept the wall above the windows as light as possible.  It is the only section of wall made of steel studs without shotcrete.  I also put beams between each 40 inch wide window so that the max deviation at the mid point between supports is only about an inch.

The Formworks earth sheltered homes all use curved back walls to support the earth.  But most have very simple layouts and simple flat front walls.  I am treading into dangerous territory with my curves, but at least I am aware of it.

Dangerous-Curve-Ahead

March Update

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Posted on March 30, 2013 by

Lets review March…

The plans…

As I mentioned in my earlier post, I had met with the architects and engineer at the start of the month and reviewed a bunch of stuff.  Most importantly, we came to agreement on a few things, including some changes they wanted and some that I wanted (and had already asked them for months before).  I came home with a new set of prints that included the 12 sheets of house plans, plus 6 sheets from the engineer.    I could see that the architect had already made a good effort to target the issues I had reported in my big “catch up” review…  Of course, I found some new issues, especially as I got to the later pages, but it wasn’t too bad.   I carefully went thru sheet by sheet and itemized all the issues over several emails.

Mean while, I was trying to get a meeting with a shotcrete company in michigan (who has since asked to have his name removed because of negative comments on youtube about his work).  I figured I would run the plans by him to make sure it made sense to him while I still had the architect and engineer under contract.  In had been a few weeks since I had received anything from the architect, so I asked for an update of the plans to show the shotcrete contractor.   Not many of the corrections I had asked for were implemented yet, but they had added two new and interesting sheets.

One of the sheets included images of the sunshade…  The sunshade had been hard to see in the elevations, but now that they had done a detailed view, it was clear that they had not understood what I meant when I said the front corners would sit on pilasters between the windows on the side walls.  Hopefully we will get all these details sorted out soon.

Sunshade2

This month, in prep for my meeting with the shotcrete contractor, I did a lot of planning the order and process of construction.  It suddenly occurred to me that the large concrete ribs were sized as if they would be set on the finished slab floor, but in order to keep it from being damaged, the floor would not be added until long after the ribs were in place.  The foundation drawings showed footings for the ribs, but nothing was indicated between the footings and the ribs.  This was particularly bad on the half of the house with a basement.  Similarly, the walls (and the steel ribs within them) would need to start from the footings, which most of them already did.  The problem was that the exact depth of the footings is not known until they are poured, so if we based the arch heights on the drawings, they would almost certainly be wrong and require us to build a stem wall which would weaken the structure.  I contacted the architect with solutions to both problems and he agreed.  We would add pilasters to support the ribs, and extend the bottom of the ribs down 6 inches below floor level so we could later pour around them.  For the steel arches in the walls, we could order them a bit long and cut them down to shape.  I will also try to delay ordering those as long as possible and will perhaps have the actually installed footing depths at that time.

I plan to "frame" the vertical portions of the walls with these metal studs with metal lath backing and rebar reinforcement, then I will get the shotcrete guys to encase it all in concrete...

20 gauge steel studs with open web, $0.47/ft

I also noticed that some of the drawings still specified steel studs in the vertical walls.  This idea had come up in November, but one of the concrete guys (Ken Veera) had been worried that the steel studs would be flimsy and deform under the impact from the shotcrete.  They would also cause weak planes in the concrete (like cold joints).   The idea of using metal lath should stiffen the wall structure up a bit.  But before asking the architects to change this again, I figured I should come up with a better idea.  I decided to try and find more suitable metal studs.   Previously my metal stud research was based on reducing heat loss thru the front wall.  Now I shifted my focus and my search terms to look for stronger studs that would resist deflection.  I ended up discovering studs from Marino Ware that were 20 gauge structural steel studs, and had the cutouts that would reduce heat loss if used on the front wall.  Also, the frequent holes allow the shotcrete to pass thru reducing deflection and preventing the cold joint effect.

Anyway, back to the shotcrete guy.  He is a busy guy and was somewhat hard to get a hold of.  I guess that could be a good sign (I don’t want the contractor who is just sitting by the phone).  That week, he was actually putting in the Beaver Habitat at the Detroit Zoo.  Eventually he squeezed me in between a day at the zoo and an evening at a pool show.  I just had 50 minutes to chat and show him the plans.

He seemed quite comfortable with the plan I presented, which included 20 gauge studs to frame the walls.   He was also fine with shooting the basement from the outside, so I could have the nice planar specfinish over metal lath interior walls; as long as the slope of the excavation outside was greater than 45 degrees for at least 8 ft. We talked about the shooting tower, the bedrooms, the garage, the “light well” and the eyebrows.  We talked about order of operations including how his guys would handle working without the floor in the main living area. We talked about storage for his equipment, as well as what equipment I would need to rent (articulating man lift, crane, etc.).  I asked what other aspects of the job he would like to bid on and he said he was interested in all the steel frame work and the floors.

I asked him several times if any of this scared him, but he said it did not.  Like me, he is an optimist with a “can do” attitude, so I am not really sure if he should be scared, but just doesn’t know it yet. 

 

We also talked a bit about when we might start. I told him that I hoped for a June start, but that means the architect would need to be finished in the next 3 to 5 weeks (end of April).  I emailed the architects an update and asked if they thought they would be ready, but they have not responded for over a week now.  I will call them next week.

 

Sourcing

Since I finally had some final drawings for the ribs, I took another shot at getting quotes on getting them precast by professionals.  The last time I had looked for quotes, one of the replies told me that they didn’t feel they had the right PCI Plant Certified or APA Plant certification.  I used each of those terms as a Google search and found a lot more precast concrete companies that did carry that certification.  While browsing thru these sites, I learned about the different finishes (I am interested in a sand blasted or acid etched finish), terminology, etc.  With this new info, I sent off requests for quotes along with some details and drawings to half a dozen companies.  One replied the next day and quoted me $4K per rib.  I have 10 of them, so that adds up to more than I want to pay.  The majority of the companies never bothered responding.  Another company in IL called back to tell me that they wouldn’t ship that far.  But a couple days later, I got a call from a company in Wisconsin that I had not contacted because I thought they were out of my area.  Apparently, the one in IL had passed my info on to them.  This Wisconsin company is very organized.  They have called me a couple times to discuss finishes and immediately sent me a 7 lb box of concrete color samples (Sherri and I agreed on “sandstone”).  However, it has been a couple weeks and I have not received a quote yet.  I suspect that the shipping will be relatively high (~400 miles).  Since doing that search (which didn’t get me a lot of call backs), I noticed that some of the companies were in the Architectural Precast Association, which gave me a bunch more companies to try eventually.

If I can get each rib for a reasonable price, I would rather pay someone else, but if not, I will make the forms and precast the ribs myself.  I figure each rib requires less than $500 of concrete and rebar. Each form may use a few hundred dollars worth of supplies, but those can be reused.  Check out this page for more info on that.

This house was framed with Steel studs

This house was framed with steel.  Click on it for a closer look at the open web studs and joists.

This month I also spent some time at drywall suppliers…  I was not looking for drywall, but just those steel studs.  These out of the way suppliers have much better options and prices than Home Depo.  Presumably, they save money by hiring unhelpful people and I faced the same sort of product ignorance and lack of interest I found in my other sourcing adventures.  The guy behind the desk would tell me they didn’t sell something or such and such a product didn’t exist, so I would give him the part number to look up in his computer.  One guy actually argued with me for a while before actually entering it.  He told me it didn’t exist, but I noticed a poster of it on the wall.  He didn’t even believe the poster.  He just kept saying I could drive around back and look for myself.  Eventually he entered it and I got my prices.  Other guys just asked me to write it down and they would get back to me.  Guess if they did?

While researching steel studs for the walls, I also got interested in steel studs for the floor joists over the basement area.  The drawings specify 2×12 lumber, but I found I could also switch to wood I-beams (straighter and lighter  or steel joists from Marino Ware.   The 2×12 or wood I-beams cost about $1.50 per ft.   The steel ones cost about $3.50/ft, but would never burn or rot.  I only need 65 beams totaling 605 linear ft, so the price difference isn’t that much in the big scheme of things. The advantage of steel is that you tell them all the lengths up front, so they do the cutting for you and there is very little waste compared to buying a bunch of 16′ or 24′ wood joists.  I am still thinking about it and will research more.

I also spent some time looking at spiral stairs and steel grates and a few other things…

Eye Candy

Everyone’s favorite part of the site…

 

March Update

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Posted on March 6, 2013 by

Well it has been a while since I got on to the website.  I had some work travel, a bit of a vacation, but mostly I was just really busy with work and school (MBA).  However, I did find time to work on the house and things have not been standing still.

The engineer and architect have both moved forward.  The new storm room design has finally made it into the plans and we had a meeting last week to resolve a number of the engineering issues including issues with the design of the the concrete sunshade and the roof structures for the entry and green house.  We are still going thru the plans and cleaning up little details.  The windows have not been updated in the drawings yet, but I expect that will be taken care of eventually.  We are also adding some details like stone veneer to the design in key locations.

This is how the plans looked last week... You can see the new Storm Room, but the sunshade and rail are changing...

This is how the plans looked last week… You can see the new Storm Room, but the sunshade and rail are changing…

 

While on vacation, relaxing after a day on the beach, I solved the problem of the chord windows.  These high windows were placed on a curved wall.  each vault spans a 30 degree section of the vault and we knew that the chord deviation would be too large to span with one piece of glass.  We broke the    chord window into 3 partial chords as a solution, but when I got the quotes I found that actually tripled the cost to fill the same area.  The cost was so high that we actually considered dropping the side windows and just having a 40″ wide arch top in the middle.  The epiphany on the beach was that the windows were not spanning the full 30 degree segment of the wall, but rather a much narrower section near the top of the vault.  I did some quick trigonometry back in the hotel room and worked out that the max deviation of full chord window from the curved wall would be less than 4 inches…  That means it fits on the 6 inch thick wall (sort of) and I could go with one large chord instead of the more expensive 3 part window.  Seems kind of obvious now…

This is a detail of the 3 part chord window that I had in the top of each vault...  The yellow line represents where a straight window would lay...

This is a detail of the 3 part chord window that I had in the top of each vault… The yellow line represents where a straight window would lay…

 

You may recall that the “Storm Room” has a 6ft round hole in the floor.  I had wanted to put in a glass floor, but that was very expensive (over $6K), so I was settling for a safety rail for now.  I figured I could always replace it later if I found a good deal on the glass or struck oil.   But then the “temporary” safety rail cost was estimated to be $2K, which sounds a bit high to me.  The architect came up with the idea of putting down a steel grate.  Sherri and I both liked the idea, although I think what is in our heads may be a bit different than the architect was thinking.  Instead of an industrial steel grate, I will work on getting something a little more residential.  Hopefully, I can find something to match the spiral stairs and ship ladder that lead up to the storm room, perhaps made by the same company…

Much of the rebar layouts have been done, and I already put together a spreadsheet to calculate the quantity and cost of rebar required…  it is not too bad, but I will be looking for a bulk discount and a big truck to deliver it.   I will also want to get a bulk deal with the concrete company.  The engineer prescribed 3 ft wide footings to support the central tower of the house and there will be a lot of foundation in other areas also.  There are also some larger steel beams in a few areas that cost a few hundred dollars each, but I convinced the engineer to remove the really expensive compound bending beam that had been in the design for the sunshade and replace it with a much simpler post and beam design.  I am already getting quotes on the components that are fully designed, such as the precast concrete ribs.  I am waiting on the architect to complete the detailed plans on all the steel arches.

I re-initiated the relationship with the building inspector and gave him a copy of the plans in progress.  He decided to call my architect and reviewed the plans with him directly.  I wish I had been in on that meeting because my architect isn’t good about sharing the details.  I know he talked to him about stairs (not sure what about) and also told him to change the “Storm Room” label to “Light Well” so he could go a lot easier on the inspection.  I thought that was a good sign that he plans to be more helpful than difficult.

Next I plan to meet with the likely builder and go over the plans with him one last time while the engineer and architect are still under a fixed price contract.

We have started the process of getting our current house ready to sell… Or I should say Sherri has started patching and painting over the past decade’s worth of kids vs. drywall damage.  I helped by spilling some of the paint on the carpet while trying to help.  I am sure my turn will come, there are lots of fun jobs to do.  The good news is that the market is picking up a little around here and we may even be above water on our mortgage.

Even with over a month of no posts, the website is up to nearly 10,000 visits, but my views are down to 20 or so per day.  Things should get much more interesting once we start building.

And now some eye candy…