Waterproofing and Insulation of Monolithic Dome

You would probably save yourself a lot of headaches and just hire a monolithic dome specialist construction contractor....or at least take guidance from those who have already faced these challenges....

http://www.monolithic.com/topics/domes

Thanks solarEagle, I have all the schematics, have been studying it for 16 years. Just looking for comments on NEW methods/materials for waterproofing, alternatives to shotcrete, etc., materials that may now have other uses not considered for the design above.

Well I think most stuff that I would consider new, like nano materials, or recycled materials, will either be too expensive or untested for this purpose....For any materials to be added to housing construction takes years of testing, and is not unilaterally accepted generally speaking....If you plan to adhere to local codes, your materials have probably already been chosen....

How interesting...this uses the air form on the OUTSIDE of the dome. Cool.

Northern Ontario. Hmmm. Cordwood, built like a hugemoungous Igloo. Parge w. concrete if desired.

Insulation would be difficult. You can't use poly-urethane foam inside because of outgassing (its against code) but there are some spray foams which have been found to be safe. The blue stuff is VERY expensive, but its a lot safer. Personally, I don't trust it...but it WOULD meet code. And besides, its made from oil...and is not "green" You can't just use fiberglass because you have to install an impermeable membrane between the fiberglass and the air in the room or else you get crystals of glass in your lungs for eternity. Loose cellulose has to be held in place somehow, and mice like it. OTOH, if you are working with cordwood, you have a solid third of a metre to act as insulation, so why bother. Just put in a wood stove. Make use of the re-newable energy in the trees around you.

Use R2000 grade air exchangers, and make yourself a home that uses no questionable foam. Most materials will be found close to where you are building.

Well, you asked for alternatives. I personally would not call a foam-fiberglass-shotcrete dome eco-friendly since it violates several principles of "green building".

You could discover/invent/design a rammed-earth igloo.

4" of urathane foam would work really well, I think. I saw this done on a flat roof hear in california and they threw the stone on it while it was setting and it bonded to the stone. The R value was very high and the residents no longer needed to use their air conditioning during the summer and their heating bill went down considerably in the winter. The stuff was sprayed on and it expanded to about 2" with each pass. They did two layers and got four inches. It was hard enough to walk on in only one hour and I got to walk on it myself before the installers left and I was impressed with how tough it was in that short time. It did take special equipment to apply, but the end result was fantastic.

Check <www.csidomes.com>

Vince

Ecogeek,

I have an architect friend who started building these about 25+ years ago and I worked on three (and have been inside a fourth).

• An air-inflated exterior form on which the shotcrete is blown will sag some--not a structural problem, but if you don't have enough headroom on an upper area this could bite you badly--so design it with at least a foot more height than you expect to need.
• He used a lot of steel fiber reinforced concrete. Problem with this is that you don't always know the thickness of shotcrete as you apply it, so in places the final concrete was as much as 4-6 inches thicker than I expected when I laid out the embedded PVC conduit for the wiring. Although he added extension rings to the boxes as the concrete was sprayed, you try to go 8" back in a stack of extensions to get to the original box and conduits when pulling wire!
• Go over subcontractor needs very carefully for such things as penetrations, placement of fixtures, and how to get electrical or water to the required places. You will have many isolated sections of framed walls that need to be connected to electricity or water; if the needed path is not in the concrete this can be a real problem after the shell is in.
• Consider white EPDM (roofing type) as your waterproofing membrane. It has some stretch and can be glued in strips to conform to the shell. I believe it is OK for direct contact with potable water.
• An alternative you have not mentioned is the sandwich type of concrete shell dome. This is a ferrocement type layer of concrete with foam insulation inside it and then a second layer of shotcrete inside this. The first (outer) layer is applied without an air-filled form, to a rebar dome shell with the expanded metal lath in a couple layers attached to the rebar (include stirrups for the inner rebar to attach to this later). The shotcrete is blown against the metal lath at an angle so it has very little penetration. The foam is sprayed inside this, and then the inner rebar is attached to the stirrups with more metal lath, and the interior side concrete is blown on.

Have you considered the use of straw bales as the main structure, laid into a dome shape, with exterior and interior facing with ferrocement? This certainly would be ecological and may prove to be the least expensive construction method available to you. I don't know if anyone has done a dome with straw bales, but they certainly have a good track record and may now be in the IRC (international residential code).
Good luck--John M.

One other thing--one I worked on was an entry to an underground library at a university. After the dome was built most of it had earth cover, to many feet of depth, so it is strong!

Straw bales would be great as they have an R value of almost 100- but you would need a flexible waterproof membrane to cover- I did a normal UG house and we used rigid foam, a membrane and 6 feet of earth then graas and trees (not straw)- good luck- I am in Mid ontario

The last bullet you mentioned was actually the closest design that was considered. Almost to a T. But, the idea is to stop the cold from penetrating the shell before it hits the core of the building, hence the inner shell/metal framework/outer shell then waterproofing followed by insulation and finally earth. Sounds about right? Your comments? Note: trying to avoid polyurethane foam. Would straw bales decompose if laid on top of the waterproofing, creating a thick Matt of duff layer? then covered with sand/gravel/soil layers and planted with short-rooting shade plants. It would obviously compress over time... Well, quite quickly I assume.

Ecogeek,

Oh, yes, straw bales would decompose, if on top of the waterproofing.

One waterproofing material you have not mentioned is a layer of bentonite clay. It comes in a wide variety of products, but probably the best is a layer of it in its pure form (often sold in farm supply stores under the generic name of "pond sealer"), followed by layers of backfill as needed.

It sounds like you are looking at an earth-sheltered type of structure. A dome shape is very strong in compression so you won't have any serious structural problems. However, one overlooked problem is slow settling of the footings. The shell is supporting a huge amount of weight, which is being carried down to the footings. Frequently they will settle some, which will cause the floor inside to appear to rise. This is a real problem if the floor is pinned to the walls because it will then crack with portions tilting some. So, if you are going earth-sheltered, be very careful about the subsoil and the type of footings you use.

--John M.

The foam I used on my underground house was derived from vegetable oil and once cured there was no gassing off. I remembered the old foam from the 70's and it gassed off isocyanate which was very nasty stuff especially during the spraying. The foam has to be covered in our area not due to gas but due to possible fire hazard which I might add is very insignificant. In industrial buildings they use a spray concrete product but in some applications we sprayed on a coating that was a water based plastic membrane specified for the intended use. There are several dome houses that were made by same technique you are discussing using the foam as part of the structure. Very good insulation and rodent proof for same reason, if they try to nest they dehydrate due to over heating.

I am very interested in what you have said, specifically the sprayed waterproofing, and also the foam as part of the done. Do you have any links to view this info? Rory

I think there are any number of Youtube links on dome building, my house was a concrete pour with special dome forms. They poured the walls, roof, skylight wells and parapet wall in a single pour. I have seen the internal bag system, light screen with plastic and foam then the spray on concrete. The spray on foam is water tight and contrary to some comments will not absorb water as it is a closed cell product with according to data about one million closed cells per cu. in. It does need to be protected from sunlight with earth or a coating. Personally I am a very big fan of spray foam especially now that there is little or no isocyanate. I had a very bad reaction to that stuff and wish never to see it again.

Here's some idea's that seem effective....

Earthbag construction...

Plastic earthbag....

This has loads of natural lighting....

http://www.inspirationgreen.com/earthbag-construction.html

Yeah, I've seen this form of building before... What are the bags made of? Plastic, I assume? I don't like that just as I wouldn't want tires filled with sand. Maybe if they were made of burlap or whatnot. Trying to be as sustainable as possible. Does the clearinghouse the bags make it waterproof completely? And how about snow load, window overhangs etc? It seems better suited for arid climates, not the flood and snow zones of Ontario. Just a thought.

The bag is temporary and can be used on many projects. It is just there to get the shape stabilized. I have seen several methods but the bag will stabilize the rebar as it is formed and connected into a sustainable grid. Sometimes they spray the foam onto the bag and it is treated with a release agent and after the inside is coated with code approved material the outside usually gets the sprayed on concrete then some form of coating. If the foam is on the out side it also has to be protected from the sun and other possible hazards. Snow load calculations are up to the engineer. I had to hire an engineer to translate the drawings from the US format into an acceptable Canadian format for the building inspector and to adjust the rebar matrix to suit him as the building inspector passed all responsibility on to the engineer. All in all it was a great project and as comfortable as I was led to believe.

Right on. Great reply. But, how does the bag get removed, if it's wrapped around in a coil? Is it not just earth in those tubes?

You know, you really should try some experiments. We don't know your weather types , snow loads and budget. Though we, here in Southern Ontario have an idea. A shotcrete dome is a big expensive undertaking. I would never build one...I would hire somebody who has done it before to do it.

But some experiments with alternative building materials will help you to determine the cost versus labour ratio which defines something as "efficient" or not. Rammed Earth is cheapest for certain values of "cheap". Labour would have to be cheap. Churches built by volunteers can provide cheap labour to get their church up, just as a for instance. You can get dome bricks for cinva rams...the all time cheapest method which would still be light enough to make a dome and provide some insulation. Straw bales are not used AS straw bales under Ontario code, you have to compress them in a special machine. How much straw do you have around your area? Could you use straw bales to make arches, which would become a dome

... sure you could. What does the code say? Bales over head may not be covered by code. Cordwood is a wonderful material. Code covers cordwood walls, and there are plenty of them in our area. I have never seen them brought up into a dome though. But seriously, I can't see why not. You would have to build it the way the parthenon was built though....laid up as arches on removable forms. Cheap, and reasonably quick, uses local material, not nearly as labour extensive as rammed earth. What does the code say about that? I have not found any ICF domes on the internet...usually it is a shotcretted dome that some have erroneouly called ICF. Too bad because I could see an icf igloo in a heartbeat! But then, have you built an igloo....\

I saw a dome (for an oil tank) built out of concrete...they built the circular wall. Then filled it with sawdust. Poured the concrete on the sawdust, and dug out the sawdust a week later, to use for the next dome in the string. I have no idea where I saw that! But that would work pretty well, if you have a pile of sawdust lying about. Or corn. Or wood chips. No shotcrete. And look at all the wood chips you get to use for insulation afterwards. Keep the chips from blowing away, or becomig mouldy with a good tarp over it and more wood chips. And wasn't Dennis Weavers tire house covered with a dome?

Found the reference...it wasn't an oil tank...it was concrete granaries. (I had to ask my uncle, who was happy to hear from me. Call your uncles today...they won't be around next year!) He remembered them, they looked like short stacked silos! Big sauce pans. In Saskatchewan. They made a lot of them, looked like this, and they were not so big. They were made to expand storage space for grain during bumper years and provided a nice dry place for it to reside after being dried. They use steel nowadays apparently for the same thing. Some twenty five feet I think. But thats how they did them. I was young at the time, and have no freakin' idea how they kept the concrete from sliding off the admittedly shallow dome. As far as I could see, they just poured it from a pipe, a couple of guys pushed it out with concrete rakes, and walked away. The roof wasn't very vertical, but it was a dome. And it was concrete. And a team of four men made one a day. Not counting wiring up the rebar I guess. I noted the rebar was laid circularly and radially. But I was about fifteen at the time, and as interesting at that was, I didn't get much out of it. Now you have me interested....see if I can find some pictures. I bet those domes were made by general labourers...with a sweating engineer in the background looking like he was loosing sleep...grin!