Building a "Hobbit Home" input helpfull .

well guys and gals, I need some input on those of you who have experience with concrete walls.

I have submitted my drawings too the local building department, too see if they will even let me build my "hobbit home" on the existing site . . .
Here is the plan. Pour the concrete wall, paint on a damp proofing layer too seal the outside of the concrete - insulate with about 8 inches of Styrofoam - directly against the wall - then on the outside of the foam - apply the necessary waterproofing layers - the idea being, that the concrete will be a thermal flywheel - stabilizing the temp inside the home, while the insulation (all the way around the house - top and bottom) will keep the place warm.
The now retired building inspector tells me that when the concrete is poured, they can set in 2x4 studs - so when they remove the forms, you have a ready made stud work to fasten dry wall and stuff.

Now - the question is, should I let the guys put the studs right into the concrete ? Or - should I pour the concrete wall first, then lag bolt the studs too the concrete myself - leaving a 1.5 inch ventilation gap in between the drywall and the wall for ventilation- wiring - water pipes etc. . - this method would probably cost alot less to finish - since I can do this myself instead of paying someone too fasten them too the forms - and I kinda like the idea of having a ventilation gap - for circulation. .

This is not about what I want. It's about what is better too prevent mold - mildew - and any other nasty stuff.

Opinions wanted and appreciated.

Update for ya.

I have been looking into how too insulate and water proof this type of home, and have found some conflict with "eps" foam and "xps" foam. eps foam is cheaper too buy and is more environmentally friendly, but is said too absorb water - but then if I install proper water drainage with the proper tiles, will it get wet ? If it does get wet and absorbs water, it losses R value. - - the R value is lower than I thought - so I may have too go with 12 inches of foam instead of the planned 6 or 8 . . . .
While at the same time, xps will not absorb water (or very little) but, it is more expensive. If it does get wet, it will still hold it's R value.

Still investigating this one, but one good thing about this investigation, is I have found people who have built their house footings ON TOP of xps foam - no thermal bridging - which is what I was worried about causing moisture and mold in the corners . . . .

I have found lots of articles that agree with my way of construction - that is pour the concrete wall, and insulate the heck out of the outside wall - there is even information on insulating the inside of the wall, but I would rather have all the insulation on the outside. I have now had it suggested that I go with a "natural" look - mixed with a "industrial" look - in other words, pour the concrete - putting all the insulation on the outside of the wall - with conduit for the electrical. Nothing else - no drywall - no insulation - just concrete walls. Now, up here in Canada, we have too run humidifiers all winter - or else we get cracked and bleeding lips and other nasty things associated with dry air. . add to that, that most of the people up here live in their basements, with no problems at all . . I think I am on the right path. . .. so no 2x4's in the wall . .

As for the HRV - heat recovery ventilator, I may have too look into an "ERV" or energy recovery ventilator. . more about that later. .

I have not given up on installing a rocket stove underneath the slab - the entire 50 foot length of the house . . . we will see . . .

Again, anybody wants too jump in here, and give their 2 cents, by all means - what you may know, I may not have even thought of yet - and I would rather have my eyes opened now, while I can still draw the lines on paper - instead of trying to move a wall . .

later !

Regarding the foam options, I think you have answered your own question there. It may be tough financially but if there is any way to go the extra money i would lean toward using the better grade of foam if at all possible. Either way, make double sure you have overbuilt the drainage and you will never have to revisit that area again. Good luck with the project.

Ells Dunn wrote:Regarding the foam options, I think you have answered your own question there..

Not really . .

If I have a question that I want answered, I usually go onto the internet, and look it up. As an example, EVERY other time I look something up, I get 10 or 20 posts that say - YES do it. . . while on the other hand, I get only 5 or 10 that say - NO bad idea. . . This is the very first time that I have run into an even balance between the two options . . . half say yes, one is as good as the other, while half say no one is better than the other. . ..

Still working on this one . .

there are many types of foam insulation.

white styrofoam, for walls above grade. Lets water and vapor go right thru it, unless it traps the water inside the cells. Not for below grade at all.

pink styrofoam, for low density below grad, less than 150 pound per square foot loading. Water proof

blue or gray styrofoam, for medium density below grade, 250 punds per square foot loading. Water proof

polyisocyanurate foam, closed cell, non water permiable, but pricey and poisonous. Water proof

styrofoam about R3.3 per inch

poly, crunchy foam, about R7.5 per inch

You will pay by the R factor, because the industry knows you need "X" R values to pass code, and prices accordingly.

When building below grade, think submarine, if you don't weld the seams your basment will leak.
The only way to not be a submaine, is to make sure there is a waterfall between your insulation/wall and the soil.
Air gap, between your wall and the soul, and a drain that is below your floor level, all the way around your foundation.
From out side to inside, in cross section, soil - drain fabric - pea gravel - insulation - concrete - basement.
So any water going sideways from the soil, falls, thru the air gap, down into the drain, and has no pressure to make the wall leak.
Because pressurized water wins that battle, every time.
Use as much insulation as you can afford, you only gotta buy it once, if you keep it dry.

Update for you guys on the "hobbit home" . .

I have hit the jackpot ! A friend of mine loaned me an underground home book called "The Complete Book Of Underground Homes" . . .

All my theory's - thoughts and guesses are almost right on ! The only thing that I made a mistake on was too put the foam on top of the roof, and then add the water proofing . . . should be the other way round . . . so any moisture in there won't hit the cold rubber and condense . .

Here are some pics for ya.

I may even start thinking of adding a few sky lights to this thing . .

Now I have too see what the building inspector will say about having a wood frame post and beam and a wood frame plank and beam roof . .

Ya know, it's not that easy trying to design your own home . . .
How big of bedrooms - how big a kitchen - where is the bathroom - can you come inside and wash your hands without crossing the whole house - plumbing runs ? - etc. etc.

So after reading the aforementioned book, I fired up the drawing program I have here, and went too work . . I started with the 40 x 40 layout in the book, and narrowed it down too 40 x 35 . . . here is some pics

I just realized , that I have no front door on this thing . .. ooops . . bottom right corner . .