condensation or moisture from inside

[eggbuilder]

dear fellow dome builders ,
had a question before about salt corrosion and rebars thanks for reply about basalt rebars that should do the trick, thanks.

now about condensation . where i live (by the sea , in north of scotland)there is a high humidity level it is not usually warm here even in the summer (10 to 15 degrees average!) so we cannot rely on the sun to dry things
how do you cope with a) the condensation or water given off at the build stage by the concrete shell,during what is called the curing stage, how does the water given off it escape - down or up? Up from the curing concrete seems blocked by the foam and the airform membrane.traditionally buldings in uk breathe through concrete blocks or brick exterior up here often harled or rendered, and in roof through wood sarking (flat boards)then breathable membrane , then tiles/slates.additionally the roof space is vented above the insulation layer do you use a gortex breathable membrane for the airform? Once built and humans introduced to dome, how do you control interior humidity? the concrete shell is a large cold surface likely to act to condense the warm air.
does issue have to be solved by an active system or can a passive solution be sought? eg by active i mean does this have to be by air to air conditioning/heating which has become very popular here, as well as ground source to underfloor and airsource to underfloor.This does of course leave you reliant on electric power? what solutions have people got for these issues.
regards to all other eggs already up and running and a happy easter
eggbuilder

[Mcfish]

You pose a good question, and I can offer a resource and an answer. Resource first.

http://www.greenbuildingadvisor.com/green-basics offers great information on generalized building science. What i don't know about is the vapor permeability of the urethane foam or the MD membrane. Keep in mind vapor permeability is different from water, as in your Goretex example. As you noted, a mechanical system is one option, and ERV or HRV to dry the air and exchange the heat/cool that it contains.

The reason for the exterior insulation is to keep the concrete shell warm. The warm surface does not condense the vapor. Otherwise any interior surface would condense the humidity inside a house. There are many MD's built in Texas and throughout the midwest that have high humidity, so dealing with that is solveable. The mass in the house will make it easier to heat, and retain that heat. The excess humidity can be vented out (especially with a heat exchanger) with less energy loss, assuming that the air you replace it with is not as humid as what you vented.

I too would like to know more about passive measures that would work. I know that vapor has to pass either inwards or outwards to dry, so you really don't want it trapped in the foam layer. If the airform is vapor permeable, but waterproof, then the issue is solved. Maybe MD can offer more information?

[eggbuilder]

thanks Mcfish

i thought the foam on the outside was (apart from a smart way to hang the rebars) not keep the dome warm but to prevent either excessive cooling of the dome in cold weather or excessive heating in hot weather,in other words to keep the fluctuatutions in temp of dome shell within a small range, and to prevent damage to the dome surface itself
that said the dome, as a mass of concrete, is not easy to temp regulate and will tend to be a cold mass in winter and a warm mass in summer ,
this means that some other system other than the foam alone will be needed for temp regulation ;it also means that condensation will be a problem in cold weather with high humidity.
i would still like answers to the permeability of the airform while the concrete cures and answers on dealing with condensation as the dome is occupied, also some suggestions as to passive methods of dealing with the problem.
is one ( expensive) solution to have an inner dome of a lighter permeable material similar to foil backed plaster?
hoping for more suggestions,
kind regards
eggbuilder

[Mcfish]

It does take a while to bring the mass up to temp; that is a problem if you use the house sporadically like a vacation home. Once at temp, it takes no more energy to keep at temp than any other house, and it takes longer to overheat or cool off. There is anecdotal evidence here; see the Alaskan house that ran out of heating oil for 2 weeks before it got cold. Assuming suitable passive heat source and some active heating (stove, radiant or Forced air) the concrete will stay within a small range, well above temps that cause condensation.

This site has articles about the permeability of the airform; I would think that by simply venting the house occasionally during the curing process one could readily remove excess humidity.

[gearweasle]

Sorry eggbuilder, but that two weeks time frame is just a big McFish story. No link to an html file on the Monolithic website, but here's a pdf link to the Snyder dome he's talking about.

http://static.monolithic.com/pdfs/home-energy-final-article.pdf

Still, two DAYS with no heat in -30F/-35C weather, with lots of windows, and they still don't notice it. They notice that they have run out of hot water from the tap/shower! Then they figure out they've run out of fuel oil to heat the house (same shared boiler for radiant floor heat system).

I live in Minnesota. I'll take that.

--gearweasle

[Mcfish]

Thanks for the correction; i indeed misremembered the correct data. And such a clever use of my nom de plume! But the correct data does support the point I was making.

[royc]

In such climate the best would be a dehumidifier to keep humidity at below the 60% level, it would also add a small amount of heat to the structure.
Of course you still need ventilation along with that.

Roy

[mkrepel]

I don't think you will see as much condensation from curing concrete as you think you will. First of all, concrete does not dry, it hydrates which means that it actually uses the free liquid to cure. Second, at this point in the project, the doors and windows will probably be open to the atmosphere. Any extra water will leave the structure via evaporation. In the event that humidity is 100%, this will not occur, but you should see some evaporation at any relative humidity less than 100%. It may be very slow, however. Finally, when the concrete is finished curing or if you are building at temps below freezing, you will add heat inside the dome which will tend to lower the relative humidity in most cases. Once the dome is complete, you will keep heat inside the dome which will tend to keep the dome shell temperature at the same temperature as the air inside. In the event that the shell temperature is lower than the air temperature and the relative humidity (RH) of the air is 100%, you will see condensation on the shell. If you see these conditions occur very often, you will want to run a dehumidifier as suggested in other posts. I really think that, as long as your inside temp is higher than the outside ambient temp, you will not have a problem with condensation unless you have a heat source that dumps moisture into the air or your normal living conditions add a lot of water to the air.

I hope I did not ramble too much. Relative Humidity is a tough subject that is rarely understood completely. If you can avoid cold spots in your dome (uniform and complete insulation envelope) and maintain the moisture barrier (airform and coating), I think this building system is the best one you could use in your environment. Your biggest exposure for condensation is probably the windows in very cold weather.

Mike