I was contacted by a builder who said he can build a wall with 3" foam + 8" concrete + 3" foam for about 50% from the price of the equivalent ICF wall. I have a couple of questions here:
1. Is this a good alternative to ICF?
2. Is there a posibility to build a wall that has 8" concrete + 6" foam (exterior only) and achieve a high interior thermal mass?

My concerns regarding this alternative are eventual gaps or spaces between consecutive foam boards and how well will be connected the foam boards to the concrete (so air will not enter in eventual gaps).

Many thanks,
Beno

Beno,

After I was done laughing I relized you were serious.

First off what kind of foam is he talking about using. Expanded polystyrene is the typical choice for ICF due to its thermal and non-absorbing features. Not all foam is alike and things like extruded polystyrene don't have the same properties and are usually not used. So I would first be careful that he is comparing apples to apples. EPS of the same density is about the same in cost if you form it into a block or a sheet. Around here EPS sells for about $1.00 a sqft in 3 inches thick. The cost of 8" of concrete is the same, the cost of the foam is a little less, the labor to install it has to be more than a conventional concrete wall, then all the labor to attach the foam. So now I already question the 50% price. The old adage is still true, If it looks or sounds to go to be true it probably is.

Secondly how are you going to attach your sheetrock siding ect. This will take another fastener and more time and more cost.

This has disaster written all over it. I would ask the contractor how many of these buildings he has done. Tell him you would like to tour several homes done by this method. If you are satified with his work and the homeowners are happy with their homes and you decide to use this method, go get 3 ICF bids, pick the middle price, cut it by 50%, draw up a contract and have him sign it. I will guarantee you there is no way he could do it for 50% less and stay in business. Hell 50% to 60% is in the materials anyway.

I would run, but that is just me.

Good luck and let us know how it turns out. Please post pictures and copies of the details of all of the attachments.

ICF Contractor

OK, let's say that the price of this alternative is the same. And also, on the interior walls I apply stucco and paint. Would you consider this alternative in order to have a high thermall mass?

The benefit of more or less foam on one side of the wall or the other would depend upon what part of the continent you are from. 

Ottawa, Canada. Cold winters, hot summers.

I was looking very closely at T-mass, Concrete/foam/concrete, for many of the reasons you have brought up. In the end of my research, I am going with ICF.

I agree with ICFcontractor. First off, a poured 8" wall will cost about $7.50 (usd) a sq-ft. ICF, about $10/sq-ft. By the time you add an equal amount of foam....you'd be prety close to the same. And as stated, no ability to attach siding, drywall or much of anything. 

The other option you mentioned, 6" foam on the outside and 8" concrete on the inside. 
   1 Where would you put your electrical?
   2 Thermal mass only has a benifit where daily temps are above and below inside temp in short periods. This has the most appeal in high plains desert conditions. There they can have 90 deg daytime temps and night time temps in the high 30's. Hence adobe earth homes.
   3 Attaching 6" of foam, enought said before

For me, the ideal system is a standard 8" core ICF block with an additional 2" attached to the outside (some what like EFIS). By doing this you have about 7.5" of foam mostly on the outside. Easy electrical install due to the  2 5/8" on the inside. Also, the inner foam will act as a buffer, some where in between a concrete box (cave effect) and a total insulated inside envelope.

If you are really set on thermal mass, go with a Hambro/speed floor concrete floor system. This will give you the op to have very effective radient heating.

Patrick T

Patrick,

Why did you decide against T-Mass?

Orono,

Mainly I walked from T-mass due to the complexity with out much benifit. Believe me, I really wanted soild concrete walls both inside and out. No denting the stucco with a missed baceball on the out side and traditional plastered walls inside. To use the T-mass system where it is poured as a monolithic wall, removable forms were required. I could get no intrest from my local poured wall guys to set the forms so far apart and wait for ele to be installed. These guys are busy all Summer doing easy to quote work. Also the cost for a 6" foam center core was quoted a $5.85 a sq-ft, foam and majic connectors only. On top of that you would still have at least a $10 sq-ft forming and pouring cost not considering the T-mass added extra effort cost. I'd bet you'd be pushing $20 sq-ft. The thermal mass benifit is small in my Indiana location. Our home will incoperate alot of porches and patios. These will also be of the Hambro floor system. With the T-mass system, the wall has two concrete walls. with the use of porches, you'd need to have the outer 'skin' as structural as well. So before you know it, you would have two 6" concrete walls seprated by 6" of foam. With 12" of total concrete wall you have a lot of cost. Some folks use 6" core ICF blocks for bacements. We will have 4500 sq-ft of Hambro floor system under roof, all concrete. I think I will have all the thermal mass I will need!

I just placed my order with Fox blocks yesterday. Between the Fox blocks and the Hambro guys, I'm a 100% confident I have made the correct choice. In a few phone calls I found a contractor who has built 4-5 ICF projects.  We will have the bacement dug in a few days.

 

Will you use Hambro also in the basement? How does Hambro compare in costs with regular wooden floors (wooden joists and plywood)?
I also planned to use Hambro at the beginning but I heard of higher costs, so I changed my mind.

Beno,

Basement will be a slab on grade. The floor, porch/patio and roof area is 10,368 sq-ft of Hambro.
I'm looking at the total cost for the floor system. The Hambro system joists  was quoted at about $4 + sq-ft. With labor and material, I estimate less than $10 a sq-ft installed floor. Since we will go with stained concrete floors done ourself, the end cost is quite low. A wood material floor system starts cheap but ends up expensive if you go with $5.00 per sq-ft hardwood flooring. The added benifit is the radient heating. Also, running your mechanicals is a pc of cake with an open web steel joists 16" tall.

How does hambro compare with speedfloor? I am in minnesota and also looked at using Tmass but will prob go with ICF. The vertical TF icf looks interesting.

slenzen,

Hambro is an open web design. And I believe the Speed floor is rolled sheet with 'punch outs'. Hambro has a longer span capability, 35'? I think I remember seeing Speed floor as having 28'. Not positive so check out both web sites. The big diff is the ability to run large mechanicals. With the open web truss, you can just about run in any direction.

 

Patrick T

Hi, Posters

This is my first post , so be gentle......
I also am seeking the holy grail and know enough to confuse and 
send  some into many different directions if the so choose.

Basically I like to be comfortable at home and favor building systems
that have lots of insulation, and are well designed and simple to construct.
Again be....... gentle.

I feel so strongly about the way we build, I started several Blogs on
Future Building Systems that are available today. There are a few, well maybe
more than a few but importantly the are departures from what we know as
common ways of building.

ICF's, SIP's, are not always favored buy myself because they have been
around awhile and have run into a stagnant rut, they cost a lot and make the
average structure way more expensive than necessary, there are better ways.

The StyroHome Designer

http://ergodesk.blogspot.com/

http://ergodesk.wordpress.com/

http://ergodesk.vox.com/

SpeedFloor can be stretched to 38" but requires interim bracing when poured.