This thread is all about airformed, thin-shell, concrete domes. It’s what I built to live in and what I design for others to live in or work in. I love all types of houses, and have rehabbed frame construction, but this is my passion.
Thin-shells can span distances of 300′ and more–clear span! They require–to pick a round number–50% of the energy of a typical frame house to heat and cool. They withstand winds > 300 mph with their normal engineering (FEMA has rated them as providing “near-absolute protection” from extreme-wind events). With their normal engineering, they will cost what a comparably-equipped frame house costs.
The dome under construction in these pictures is not one I designed, but it’s close enough to me that I can get pix. (In the interest of total disclosure, I did a few 3D renderings of exterior treatments for the builder, but was not involved with shape, size, or floorplan of this one.) Both the domeowner and builder have said I could post this.
This particular home will be a three-dome configuration. The LR and K are in the center dome, a 42 x 16 (42′ diameter circle footer and 16′ height, which makes it an oblate spheroid). The other two domes, housing the bedrooms and garage, are 36 x 13’s. They overlap, or intersect, by some amount to allow people to move among the dome segments (i.e. they aren’t independent structures requiring tunnels or anything).
This builder is building the segments separately, but they can be built with one airform, too. Builder’s preference. The picture shows the Bedroom airform.
This airform is made of a 6 mil cross-linked plastic sheeting. Larger ones are made of, as with mine for example, a 22 mil vinyl/polyester. This airform is staked to the ground and the footer will be shotcreted. Others use a formed and poured footer and attach the airform with wedge anchors or tapcons. This airform is being inflated to just 3/8″ water column (some go up to 2″) and has already withstood 50 mph winds and a hail storm strong enough to drop a 18″ diameter tree on the site. That’s before the steel and concrete are added.
When you pass through the airlock, you get this inside view.
I always like the “bullseye” views.
Over the next weeks what will follow is the polyurethane foam insulation, rebar, shotcrete, windows, and exterior treatments. Then a regular GC will take over and finish it out with all normal subs. I’ll post pix as I get them.
Another dome, this one of my design, will start later this fall, and I’ll add a thread on that. Any question on airforming or thin-shell structures is fair game, and I’ll try my best with them.
Edited 7/13/2002 11:42:38 AM ET by Cloud Hidden
Replies
Why would they require only 50% of the energy to heat and cool?
Because they are a naturally passive solar design--the thermal mass is inside of the insulation and exposed to the interior (kinda like ICF's without the inside face of insulation). It creates a naturally temperature-moderating effect. Also, the airform and the polyurethane prevent air infiltration (and moisture, too)--a huge factor in many house's energy requirements. And the poly, of course, is a great, great insulator. We spec it at 3" or 4" and it'll beat any other insulation.
Two have been reverse-engineered and tested to effective R-60 to R-80. (I didn't do those so I'm going on faith.) My HVAC contractor regularly does heat loss calcs for all kinds of houses and has, on different domes, come up with 50% to 33% of the heating/cooling load of a typical frame house on the same site. This has been also calculated by Wirsbo and by Carolina Power and Light for my dome house.
My house is running at 9 btu/h/sf and one in TX is 8. (That's an after-the-fact calculation--both were speced with traditional heat-loss calcs.) That would be like a 1300 sf house requiring a maximum of 1 Ton of A/C.
It's things like that that make us comfortable with the 50% figure as a conservative guideline. Of course, every one is unique and gets individualized load calcs.
After being inflated, a dome is sprayed with up to four inches of polyurethane foam in approx 1/2" layers. After foaming, the dome is strong enough to stand on its own well in excess of 50+ mph winds. This house is a multi-segment dome. The builder chose to inflate and foam the segments independently. The airform could have been built as a single multi-segmented airform, but different builders have different preferences. Here's the overlap of one segment into another.
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They're initially connected with a shot of foam on the exterior. Later they'll be connected on the inside with rebar and shotcrete, while the outside foam will be sanded and coated. But the foam in this picture was strong enough that the foamer could walk up and over the dome intersection as he was foaming:
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After cutting away the area of overlap, you see the shape of the interior with the sweeping arch:
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And a closer view of the intersection, and the builder, before the edge is cut and shaped to the exact size:
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Edited 7/20/2002 2:22:39 PM ET by Cloud Hidden
To prepare for the rebar, you stick rebar holders into the foam. Lots of them. There is another patented rebar-holder on the market, but this one is the invention of this builder. It is the next guage thicker than tie wire, twisted and pronged. Start by setting a string in the center of the dome:
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Use the string and a pencil to mark concentric rings on the foam. Use the rings to space the rebar holders per the engineering requirements:
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The next step will be a 1/2" layer of shotcrete to secure the rebar holders and stiffen the dome, and then the rebar. That's next week, after the first inspection of the foam.
Edited 7/20/2002 2:19:26 PM ET by Cloud Hidden
Really appreciate this photo gallery you're putting together. I'd love to see one of these up close and personal!
Hey Notch, on Oct 19 there's going to be a nationwide dome open house. I can help find any near your location if you want. Also, I have a bunch of designs going up in the next coupla years. Any time you wanna get to one, I'll clear it with the builder.
How thick is the "thin shell"? Are there "thick shell" domes?
How does the construction cost compare to conventional homes?
The concrete is maybe 4 or 5" at the base and 2.5 or 3" up top. A thick shell would be a poured wall or a block wall, for example.
Costs for a comparably-equipped frame and dome should be nearly identical. Instead of wood framing, insulation, sheathing, siding, wraps, shingles, gutters, etc, we have an airform, foam, rebar, and shotcrete. Things with the design or the site can drive one or the other higher, but they're ballpark similar cost. Now if you insulate the frame house to the dome levels or beef up the structural components of the frame house for better wind resistance, then the economics of the dome will look even better.
what about seismic loads on the dome, how do they fair when slated against a sitck frame or block frame with all of the siesmic hold downs etc?
In an earthquake the dome would move as a whole unit, having none of the structural moments of a frame house with corners, roofs, and such. Since the rebar is continuous throughout the entire structure, there's no way for it to rack or twist. Recently went through an extended discussion on this with an LA builder, and it turns out that a thin-shell concrete dome actually needs a smaller footer in earthquake country than a frame house.
Thanks for posting this.
Bob
Windows in this one are created by making a buck to the rough opening, plumbing and levelling it, securing it, and using foam board to form the shape of the window box.
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Later today they were gonna spray foam over all the forms as preparation for the rebar and shotcrete to follow. I had implied with my last note that they anticipated being further along by now (at least one layer of shotcrete). Well, conduit for electrical gets run be/t the foam and the shotcrete, and it seems there was a tiff be/t the owner and the electrician and the sparky left the job. My builder friend kept his nose out of it, but it throws off his schedule be/c he can't continue until a new sparky is hired and finishes the conduit and gets inspected. Darn those homeowner/GC's anyway!
Here's my photo assistant...
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Here's my photo assistant...
Your silver lining?
My sunshine!
Do people typically install ceiling fans to move warm air down from those high ceilings? May not be required with RFH, I guess.
I love the shape of the dome intersections, what a feature!Close enough for government work
The shapes that can be created are what attracted me first, too. They are so fluid. You can definitely _feel_ a difference being in one compared to an angular building.
I put in ceiling fans with a winter mode to bring the warm air down, but then never used them for that. I measured the winter temps over several days and never found more than 1 deg diff from floor to 25' ceiling. I LOVE RFH!!!! If you use forced air, fans might help, be/c there's a large volume of air up there, and no point in heating it. But air circ is usually good in these be/c of the round, unless you cut it up with lots of full-height walls.
For the one's I have first-hand experience with, the ones with any kind of heating load are going RFH. The others are far south and heating is an after-thought to those owners. They usually have fans for the summer that do fine for winter circulation.
The windows and other openings are starting to take shape. Here's the eventual garage opening. Blue styrofoam scribed to the contour of the dome is held in place with polyurethane, where it will serve as a buck to keep the shotcrete where it belongs. This will also be a guide for cutting the opening after the shotcrete is applied.
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A close-up of the buck foamed in place...
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One of the window openings taking on a more refined look...plus, the electrical being roughed in via conduit and junction boxes...
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This builder sprays a 1/2" layer of shotcrete w/ 3/8 gravel over all surfaces, then ties the rebar, then sprays to necessary thickness. The first shots are of the window inserts, so that you can follow their progression from the prior photos.
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This is a nice example of a solid wall, showing the typical geometry of the rebar. A typical pattern might be #4 @ 14" for the first 8' and #3 @ 10" above that. Lots of latitude to do a little more or a little less. Note also the footer. The airform was held to the ground with stakes and he sprayed the footer later, making it totally integral with the shell. Often a footer is poured and a key is cut in, and the shell is sprayed latter. Every builder has his own methods--many ways to skin the cat, so to speak.
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I found this one interesting. Instead of renting a crane, this builder built polar scaffold out of regular frames, a pivot point, and at the far end, the axle and wheels of the back end of a Pontiac. He's wired a little motor to it, and it creeps around in a circle at the perfect rate for foaming or shotcrete.
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This was from this morning. Progress would be faster if they worked every day. But the builder is alternating weeks between projects in NC and CO--that's being a glutton for punishment, and a sore backside from the driving/flying if you ask me. But the people want to work with him be/c he's such a nice guy and he really knows what he's doing--haven't ever seen nicer foaming or shotcreting than what he does.
Thanks for this thread--One of the most interesting in a while!
Close enough for government work
Cloud:
Is there a web site or directory for the dome open house event in October you mentioned?
I'm at the very preliminary stages (ie, daydreaming) of planning a new house and I've settled on concrete as probably being the main material. I'd love to see one of these thin shells up close.
Where are you? I'll check with all my contacts and the keeper-of-the-list for good examples nearest you (there are some you might just as well avoid). I'm off for the weekend to a job site visit in the Lone Star state, so I'll check back Sun eve or Mon.
The builder is busy with the shotcrete this week. He alternates be/t CO and NC, so the pace is slow. But he's probably getting 8 redi-mix trucks this week. Goal is to have finished the interior shotcrete by Sat. The GC for the rest of the job is starting the rough-ins under the slab on Monday.
Tough to get good pictures of the shotcrete process. The concrete fog shows a haze with a flash and the lighting w/o the flash is hit and miss.
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The builder has an interesting way of getting helpers. He gets the owners of the next dome in line to "volunteer" on the prior job as an apprenticeship for their own. Obviously this doesn't work with all homeowners, but on this job 4 of the helpers have come to NC from CO to get their feet wet. They pull hoses and clean up and tie rebar and shovel, and all the things that it's hard to find someone willing to do these days. Clever!
The shotcrete for structural reasons is done, and all they have left is the finish coat. It's a mix with no gravel, so they can spray it, trowel it, and sponge float. Poor guys...just two of them to cover 3 yards of the mud on a truck. Took 8 or 9 yards to cover the 3 domes.
The floor has been poured, half the windows installed, and the sills for the interior walls in place, so the shapes are coming together to resemble something that might one day be a house.
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Edited 10/23/2002 7:48:02 PM ET by Cloud Hidden
Looks like the head of the windows is flush with the dome. Do you ever put the sill flush with the dome, like a dormer?
Absolutely. I have 4 of those on my house. I'm not fond of the inset windows such as in the pictures here, but it's a choice that was made before the builder or I were involved, so everyone made the best of it. In the thin-shell dome sub-culture, the preferences for "innies" or "outies" or the coupla other styles, can be as heartfelt and incendiary as a number of touchy issues here on Breaktime.
Cloud- that wouldn't be involving sheetrock screws for other uses than sheetrock would it?:) Let the thunder crack and the waves roar.
We're going on.
I think it's attic venting! Or maybe not, be/c we don't even have attics to vent!
Inside stucco is finished and first primer applied. The framers, sparkies, hvac, and plumbers have moved in. All making good progress...never fast enough for the homeowner, but that's typical. Various framing shots:
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A typical connection of the top plate to the dome is with a wedge anchor used as a slip-bolt. I don't know how this framer will do it. He's asked my thoughts, but will likely also have ideas of his own. There are varying opinions over how much it even matters. Some think a thin-shell can expand and contract enough to make tight connections to the dome worrisome..i.e. if it expands is could drag the top plate with it and pull loose from the sheetrock. I've yet to see evidence of any movement in an insulated dome and think it's mostly a non-issue.
Edited 11/18/2002 6:18:29 PM ET by Cloud Hidden
good series , cloud... keep 'em comming ...Mike Smith Rhode Island : Design / Build / Repair / Restore
What do you use for the top plate, and how do you accurately cut the compound curve?
I framed differently from this contractor. There are several right answers, I'm sure. He used PT cut to fit between the studs and snug to the dome. Being the pieces were that short, they were not affected by any compound curves.
Here's a shot of my framing in my house:
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I tended to build the walls in 4' sections on the floor. I measured the top plate to be 1/4" to 1/2" shy of the dome at the ends, and thus it might be up to a couple inches shy in the middle. Because the sill doesn't touch the concrete, I didn't need PT. A slip-bolt at each end held it awfully snug and stable.
Some of the effect of compound curves is avoided by appropriate design. If walls approach the dome perpendicularly, so the dome is at a tangent to the wall, there's no compound curve effect. Usually (not always, but mostly) this is coincident with a balanced look for the building, and so appropriate design leads to simplified construction. Sometimes it can't be avoided--usually on a side wall rather than overhead--and then I typically use shorter pieces attached to the dome walls with tapcons and then cut the end of the stud on my compound miter to match the sill's angles and nail it off. I have also "propped" the sill piece vertical, and cut wedges to make up the awkward gap from the funky dome angles, and then drawn that tight with a wedge anchor. Gives me a good vertical starting point for the rest of the wall. But regardless of method, a rotating laser is the best way to mark the wall so that the plates are positioned properly. Levels, eyeballs, and plumb bobs don't work so good.
Pictures of the early framing of a design of mine were posted in YahooPhotos. As I get the chance, I'll post them within this thread, but for now, this link'll show them. It is just too freakin' cool to watch a design come off the drawing board.
http://photos.yahoo.com/bc/theant00/slideshow?.dir=/Dome+Photos/Framing+begun&.view=t
nice slide show.. thanksMike Smith Rhode Island : Design / Build / Repair / Restore
That must be exciting watching it all come together like that.Half of good living is staying out of bad situations.
The other...proper application of risk.
I'm curious about how the windows get done: are they cut into the foam before the shotcrete?
Also, with what has to be very low air infiltration, do you use heat recovery ventilation units?
Any thoughts on how well these work with radient heating?
FWIW, I did an inspection the other day where the seller is starting to build a dome in Indiana. (Who sez retired Ohio farmers can't learn new tricks!)
He showed me the plans and some brochures. Seemed to be a slick system. Each of the dome panels is foam and concrete, with a depression along the edges, like an exaggerated drywall edge. As the peieces go up, they are wired and rebarred together and then moter fills the depression at the edges.
He's going to start construction of the dome itself in a month or so and has invited me out. If I make it, I'll take some shots.
The installation method used for windows depends on the slope of the dome at that point. Typically a vertical window buck is secured after the foam is shot, and gets tied in with the rebar and shotcrete. Then you cut the foam away, install the window to the buck, shape the foam edges to a nice shape, and bring your exterior coating to the edges of the window.
Fresh air considerations are part of the typical HVAC workup. Some use HRV/ERV. Some have CO monitors. Some just have good ventilation. The typical dome will have more volume than a frame house of the same sf, so the build up of stale air is slower. That's the case with mine with the high ceilings. Regardless, each is analyzed by the HVAC designer and addressed according to the client's concerns. FWIW, a large number of owners list issues of chemical sensitivities as a partial reason for their choice of a thin-shell concrete dome. Not me, but I hear it a lot.
RFH works great with these and is the heating system I am asked about more than any other. One of many reasons is the greater volume of space makes heating with forced air a more difficult job. Heat the floor, rather than the 16' or 20' ceilings.
I'm not familiar with the system you mention, with pre-fab panels. I'll look them up. The type I deal with are all custom air-formed, spray-in-place.
Fresh air considerations are part of the typical HVAC workup. Some use HRV/ERV. Some have CO monitors....
I think all home with any form of combustion applinace (including an electric stove with a self-cleaning oven) should have a co monitor - the type wiht a digital readout (they're more sensitive than the ones that just sound an alarm) or a low level monitor if the house has infants, a pregant woman, elderly, people with chemical sensitivities, people with heart problems, people with immune system problems or people with prior co poisoning (see, e.g., http://www.aeromedix.com.)
I seriously question whether a CO monitor is appropriate for monitoring all indoor ar quality issues, though.
Thanks for all of the info; great subject!
Edited 7/22/2002 7:19:23 AM ET by Bob Walker
Boy that's neat. Saw something like that on an HGTV show, extreme homes I think. Should watch for the repeat.
bobl Volo Non Voleo Joe's BT Forum cheat sheet
>Saw something like that on an HGTV show, extreme homes I think
bobl, can't tell if you're playing straight or joking with that comment. I'd answer it, but if I answer from the wrong perspective, I'll feel foolish.
Mike, I wanna make my post clearer. The framing is done by a contractor down in TX, and the pix were posted by the HO. My design, but their hard work.
sometimes the fish nibbles but doesn't take the hook.
dang!bobl Volo Non Voleo Joe's BT Forum cheat sheet
One of the reasons I asked was not even re my house, which I had a fair idea had passed within at least spittin' distance of your consciousness. :) Rather, another one is on Extreme Homes tonight at 7, I think. It's a really nice, and much earlier, example of a thin-shell dome built in Colorado. I know the archy. The owner from the episode--an ex-astronaut--is not the current owner, so that dates it back a number of years.
First time I've been back to this one in a couple of months. During the winter they pretty well finished the inside, but didn't want to mess with the outside. They're trying to finish in the next coupla weeks. Here's the update:
All the window "frames" are getting radiused edges. The foam is shaped and will be coated next week with eifs products
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The living room has nice opposing curves on the wall, and is open to the kitchen
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The hallway is also curved, and beyond the arch you can see one of the curves where two domes intersect
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Cloud: That is very impressive work.
Thanks Stan. Giving credit where credit is due...The dome and the outside work is dome by Mert Hull, of Colorado Springs, CO. The bullnose on the foam is absolutely perfect radius. Mine woulda looked more like hand finished adobe. He's gonna teach me how he does it. Wait till you see how it cleans up with the final sanding and eifs finish--it'll be a great transformation in a short time. The inside is framed and finished by Tim (I don't know his last name) who's in Western NC. I did some redesign on the interior to correct mistakes made by the original architect, and mostly take credit for getting the client to leave the front kitchen wall as a partition and to curve the hallway. And trust me, these little victories were the result of hard-fought battles! She's glad now that she allowed it to be done that way.
6" of rain this week slowed progress on the outside, but they are getting there. Here's a sequence of pictures showing how some of the decorative effects happen.
This house is getting an eyebrow of foam around most of the perimeter. It will provide shade, direct runoff, and provide a horizontal line to visually connect the three domes. It starts with blue or pink foam cut to shape and attached to the dome with polyurethane.
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Enough foam is added to create a wedge above and below for strength. The result is sanded and sanded to take the desired shape--one of life's least pleasant tasks.
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Details like outdoor lighting can be accommodated.
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Once everything is shaved and smoothed and primed, the results can look pretty slick.
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The big discussions lately have been on the color scheme, and we don't yet know how the owner will decide. Worried that she'll continue to push for something that's a little too much like pinstripes on a race car...we're trying to mellow the scheme a bit. Will find out this week what success we've had.
Also, this amount of foam sculpting is rare on a house. Normally we handle "decoration" in other ways. This builder has the equipment and skill, but even he was getting a little tired of foam bits in the eyes and mouth and...
picture links are broken...
:-(
brian
brian, they work for me - - maybe try restarting your computer? -
A stucco crew ran over the building the last coupla days and applied the mesh and base coat. Now the curves are really starting to show. Color coat to follow.
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That corner in the middle photo really shows off the fine lines you achieve on these structures. Great work. ...that's not a mistake, it's rustic
Cloud,
Now I finally know where architecture is picking up after the "Jetsons" was so cleverly designed more than 30 years ago.
We've got millions of visionless houses, McMansions designed by idiots, all over the country.
One decent, cool, interesting, whacked out place. Well, there are a FEW more, but...
Giving tours?
MD
Thanks MD. Actually, we do give tours. I show my house to people at least once a week (dw just LOVES that!) and have arranged visits of the house shown in this thread. And thin-shell dome owners have a nationwide open house once a year in October. Huge range of designs and.....what to call it......attention to detail. Some look like survival shelters (at best) while others (I'm thinking of one on Sullivan's Island, SC that pre-dates any of my involvement) are sculptural masterpieces (IMHO). The builder of this one has a great eye for them, and a great attitude....I think any of you would love working with him....class act.
This is likely the last in the series. Today I helped my friends finish stuccoing the exterior, clean the site, and pack up the truck for the trip back to Colorado. Unless the owner invites me back for the house-warming, likely won't get over there again too much. First photo is the method used to apply the synthetic...a simple hopper gun. For larger areas, there are better means, but this fit the scale of the house.
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This is my favorite angle on the house. The wall was sheet foam with rebar on each side, then shotcreted and troweled. The building in the back is a storage shed built as a 10'D dome. It's very spacious inside and took very little material to create something with a bit of distinctiveness and a ton of strength.
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We'll finish off with pix showing the final color (owner specified, with some simplifications proposed by the builder and me) from some of the same angles as in earlier shots so the progression is more obvious.
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Thanks for following along...
Starting to shape up very nicely, you ever feel like your living with the Jetsons?
How much longer do you have until complete?Never be afraid to try something new. Remember, amateurs built the ark, Professionals build the Titanic.
Wow, if I win the lottery, will you travel to San Diego? I have wanted a dome home since I heard of them back in the Whole Earth Catalog/Mother Earth News days. Really nice job, Jim. They are quite energy efficient, eh?
The owner is very close to moving in. I'm done...just did some simple design mods at the request of the guy who did the dome shell and kept them company now and then. He's all done and paid and headed home, so the guy who did the interior can finish out his punch list, they can get a driveway in, and that's that.
On energy efficiency, rule of thumb is that the heating/cooling loads require equipment on average less than half of an equivalently-sized, conventionally-built structure. And most noticable is that there are fewer drafts because there is no air infiltration possible except at doors and windows.
>Wow, if I win the lottery, will you travel to San Diego?
I'm married kai. <G> Beyond a few drawings to correct mistakes in the original prints, and some exterior concepts, my contribution was mostly limited to clicking the camera shutter. Builder's a friend, so I just documented the job for him. He get's the credit for the smooth work. Building my own convinced me that compared to construction, designing hurts less the next day. (Though it was kinda fun to get out like today and do something useful on the jobsite, even if it's mostly picking up the trash--not in the job description of most designers, huh?!)
Building my own convinced me that compared to construction, designing hurts less the next day
OK, well, if I win the lottery will you make sure I get a good designer/builder? Didn't you design/build yours?
How do you hang art? With the slope or perp to the floor?
I wish dome domiciles had caught on more due to the energy conservation alone. Do you have solar panels or anything like that? I forget where the link is to the show you were on, or for more info.
Oh, and I know you're married, and if I were that sort of woman, I would travel to you LOL, but I'm not :-) I'm here for the knowledge! You, DW & DD are living a life I once dreamed of (dome house, adopted non-Caucasian daughter, loving spouse), so I like to follow your family's successes. Wish I knew why the dome thing is so important to me. Oh well, it wont fit on this place, uh, except down the canyon. It's nice to daydream.
:) You win the lottery, I'll design and help find you a builder! And then we'll all congregate there for a BT Fest! We tend to hang art on the interior frame walls. We've liked the shapes of the curved walls so much that we haven't wanted to put anything on them. But if you want to, a hammer-drill's all you need.
Are there any domes open in the Arvada, CO are (or say 75 mile radius, NW corner of Denver)
hey CH;
oct 19 is coming up soon, got any places to view in roanoke va area?
have you done any really thin wall stuff like ferro cement? 1/2"-3/4" thick, double wall with poly in the middle?
great work!!! info like this is hard to come by, thanks for the effort.
dennis.