Oven like conditions are a worry in winter, depending on where you live. Imagine that it's heading to 60 degrees on a bright January day; the sun streams through your long bank of south facing windows from sunrise to sunset. There is nothing in the room to absorb all that heat except for drywall, carpet and furniture. This is a sauna in the making.
Granted, that would be an unusual winter day, and winter presents the best geometry for overheating. Warm, bright days will occur more frequently at the tails of the heating season, but properly designed overhangs will also shade more of the window. In the summer there should be no direct sunlight through it.
Thermal mass introduces time shifts, assuming your house occupies the right piece of earth. It takes many hours of sun to warm 10 tons of concrete, which stays warm for many hours more. The trick here is to get enough sun on it to keep the cycle going. That won't happen in many parts of the world, including Pa. To bask here in an 80-degree room on a bright January day heading for 30 degrees, you'd want nothing in the room more substantial than drywall and fabric.
Of course, anything can be fixed, or at least improved. It just takes more futzing and more tolerance in the Northeast than it does in the Southwest. If you live here, as it appears you do, you have some decisions to make. Good blinds, definitely; a way to pull hot air out of the room and circulate it, probably; thermal mass, maybe. Acres of glass? I'd want a very good view.

General rule of thumb is 7 to 1, square footage to absorb solar through glazing. 20 square feet of window equals 140 square feet of thermal mass absorbtion area...concreate floor, wall, etc. This formula allows the heat to be radiated back when the sun goes down (clouds, evening), and prevents overheating when the sun is out. I read this in solarwashington's design page. It makes sense. :)

OK, but solar mass isn't just square footage, it has thickness, too. I know that one of the variables in solar slab design is the thickness of the slab. Are they using a standard thickness in their formula?

http://www.ases.org/ Use these guys to do some research. They have the calculations and experience. You are correct though, and there are other variables that affect the "system". I was just quoting a rule of thumb, not pretending to know all of the variables. The general principle being discussed is similar to a battery with a load on it hooked to a PV panel. Sometimes the load can be greater than the PV panel and sometimes not. Hopefully, if the design is correct, the battery "smoothes" out the load, such that the disired work can be performed. Too much juice and the battery gets fried. If not enough, the "work object" quits working. I think this is the same with solar energy and thermal mass. Balance the load against the work needed and you will be successful. Only you know the "load" and your "checkbook" will determine the work. LOL :)

Jim,

 

I looked at AAC and it looked interesting at first. But I saw a few major down sides;

How do you re-enforce with steel? Can't imagine how a AAC wall would compare to an ICF with 16" grid of 5/8" rebar. So for bacements or multi levels I see trouble

Ele would be a lot more work

Stacking blocks without mortor, thin set, would be alot more work than stacking ICFs

Patrick T

The blocks have vertical cores that you line up on either side of window and door openings, and at corners. You slip rebar into them and fill them. The top course is a U-shaped block, which creates a trough for a concrete/rebar bond beam a la CMU construction. Laying up the blocks would be slower than ICF, but you'd make up time skipping drywall and applying stucco in two steps rather than three. You also have a chance to see your mistakes and fix them before they become catastrophic. Anyone who contemplates doing this once would be far happier filling 3-inch vertical cores than an ICF cavity.
The principal complaint with AAC is friability, which is to say it has to be handled carefully to avoid bunging up corners and edges. You'd want a stucco or brick veneer over it. On the plus side, you can cut with a hand saw.
Remember that the Europeans have been building with it for 60 years. If you have ever been in one, you know that your average German home makes U.S. stick built seem like crackerboxes.

toddm,

I have seen AAC in Europe. I mostly have seen it used as in fill in some sort of post and beam structure. I don't see how it could handle a bacement with lateral loading. Compared to stick building, it's better. I think the skill set required to stack ACC walls is greater than the skill set required to stack and pour ICF walls. The R-value is about R-1 per inch and takes a mighty large wall to get good insulation. Also, long span headers over windows and doors can't be done by AAC alone. With ICF, beams are poured in place. Lastly, what is the material cost for a 12" thick wall, per sq-ft

Patrick

I've been quoted $2.50/sf for 8-inch block; $3.50/sf for 12-inch block. I haven't priced the steel and concrete yet, but it isn't likely to add a great deal to those numbers. Depending on what my engineer says, I expect to use steel beams under the second floor, and 3-inch steel pipe under the beams, set in the walls and bolted to the foundation. Even overbuilt, it should cost less than ICF.
AAC also comes in 2-foot panels. A 6-inch panel spanning about 10 feet costs $3.60/sf. I'll have a flat roof that can't rot over a garage that will shrug off leaks anyway.
I am not using AAC below grade.
Yes, snapping together foam forms takes less skill than setting block with thin set. The trouble with ICF is that you don't realize that your bracing/pouring skills aren't up to the job until it is too late.

What about shot crete against a single ICF panel?

Poured columns and ICF formed floor & beams?

Todd, I appreciate your comments. I too am in PA and thinking about using AAC/ICF to build a home, but I am not nearly as far along in the research process. 2 questions

1) What are you using below grade?

2) Are there other resources you found useful in your research? (like UCLA and builditsolar.com)

Thanks in advance.

Is AAC the same as foamed concrete but with the firing?

Phillysphan: I an using ICF for a slab on grade with perimeter walls of about three feet. Should be easy enough for DIY, but I will defer to my engineer who is an ICF buff. Go here for AAC installation specifications http://www.xella-usa.com/html/us/en/hebel_downloads.php And here for a more accessible how-to http://safecrete.com/aac/building/buildingwithsafecrete_new.cfm . (Note that they don't agree; Xella won't recommend AAC below grade absent engineering and testing while Safecrete does.) I should say that ICF is a better choice in Pa than AAC, except for me and my crew of one (also me). I hope to do this with little or no help and no special equipment.
GBSolutions: A shotcrete rig isn't in the cards.
ICFConstruction: There are several approaches to low-density concrete: AAC is the most popular: You toss powdered aluminum into the slurry, which reacts with lime to it puff it up like a marshmallow. It's then cured under heat and steam. Another approach uses foaming chemicals to achieve the same result. A third mixes concrete and reclaimed EPS. All three are reasonably common in the sunbelt. Not so much in Pa.

I am also in Southeastern PA and getting plans ready for some new work and renovation.
Would you be willing to give me the name of your engineer?
My parents have an ICF home in New Mexico. It is great.
But if ACC can get me to a similar place, why not.
I have talked with 3 arch. none with any real experience with these materials.

I am building near Gettysburg, so that's where my engineer is. I have been working with him by email. His name is Jeff Fertich; his firm is Structural Engineering Resources. His email address is [email protected]. His phone number is (717) 337-1335. Jeff is halfway through his first AAC assignment (my house), but he is a unabashed fan of engineered materials and eager to expand his repertoire. Happily, AAC construction methods are similar to CMU, and the manufacturers are eager to help.

Todd
Thanks for the reply.
I am in Valley Forge.
I may call him any way.
You never know, he may have a friend working near by.