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Old 12-08-2010, 03:18 AM   #1
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home-made ThermoMass concrete poured wall?


Is anyone familiar with ThermoMass Poured in Place walls? (http://www.thermomass.com/constructi...redinplace.htm) I am in need of what they have, but have not heard back from them on whether or not they deal directly with consumers. I am not aware of anyone up here who installs their products. I need to build a foundation wall for a house that has two, 4" or 5" concrete walls running parallel to each other, and 3" to 4" apart. (In another thread, I asked about a different design, and I think I mentioned this as an option.) So, DIY, here we come, if I can not buy their designed system; it looks just great for what I need. So my question is: If I can't buy it, why not make a reasonable facsimile thereof? Why could one not pour a concrete foundation wall into a 12" wide by 4' high form, in the middle of which is a 4" thick by 4' high piece of XPS? The XPS would have 1' long pieces of galvanized rebar stuck through it, 12" OC in both directions. I don't do much concrete work, but it SEEMS like this would hold the two walls relatively stable, creating an insulated foundation system similar to the ThermoMass PIP wall. I have already figured out (I think) how to lock the rebar to the XPS and how to hold the XPS from moving during the pour, but I have no real feel for whether or not this would be structurally sound. It seems at least similar to the TMass, so why not? Any experience w/ this type of system? Gut feelings? Thanks. john

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Old 12-08-2010, 08:33 AM   #2
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home-made ThermoMass concrete poured wall?


The problem would be keeping the XPS in the center. No matter how you fill it the xps is going to be shifting around. You could build it out of block and fill the block cores solid with concrete and rebar.
You could use those stackable concrete forms made of styrofoam.

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Old 12-08-2010, 02:07 PM   #3
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home-made ThermoMass concrete poured wall?


joe; thanks for the reply. yes, the xps moving is a concern, but thermomass does this, so apparently it is doable. i need to talk to them more; maybe some plywood spacers perpendicular to the xps will hold it, then pull the wood at the end. concrete blocks are not an option for me; way too dang much work, and by the time i do all that work and spend a ton on xps on the outside, the price is a wash w/ icf's, and icf's are a lot simpler/easier. icf's are an option up high on the list. getting them wide enough will take some tinkering, but doable. all designs considered so far, i would rather build the "thermomass"-type wall if i can make it structurally sound. j
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Old 12-08-2010, 02:36 PM   #4
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I have been thinking some more about this. you could put some 2x material to hold the xps in postion. Do not fsaten it in place. Then as the wall is filled pull them out and let the concrete fill the void. The XPS should be held in postion by the concrete when you pull the 2x.
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Old 12-08-2010, 03:05 PM   #5
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Is this basement wall going to be back filled then useable on the inside? If so and if it were my project I would save my money and use PolySteel ICF. http://www.polysteel.com/index.html
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Old 12-08-2010, 03:07 PM   #6
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joe; yes, something like that is what i had in mind. my drawings have 1x2 L's every 2', with the rebar locked to the 1x2s. they would just stay put forever. then i thought that maybe some plywood bracing, as i said above, could be set in place, and raised as the mud is pumped in. i think that once the bottom foot or so of mud goes in, the xps will be pretty much locked in place and won't shear as more mud is pumped in. this requires, or course, a pump operator who is careful. i am going to try to chat w/ thermomass, as i bet that they rely on all their "rebar" connectors holding the xps in place. come spring, i am going to make an 8' section and dump in wet pit run (sand and gravel) on one side only, just to see how things go in a worst-case scenario. j
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Old 12-08-2010, 03:28 PM   #7
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home-made ThermoMass concrete poured wall?


Quote:
Originally Posted by Nucon View Post
Is this basement wall going to be back filled then useable on the inside? If so and if it were my project I would save my money and use PolySteel ICF. http://www.polysteel.com/index.html
Yes, polysteel/arxx blocks are being considered. I could get the 10" (inside measurement, I believe) and taper them out to 12" at the top w/ my own form. I don't want to build a 10" thick wall all the way up, though, but that may prove to be the easiest and cheapest. No doubt about the structural integrity, either! Oh. This is for a foundation wall, 4' high; floating slab on grade, 12" double-wall above, w/ dpc for insulation.

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Old 12-08-2010, 03:43 PM   #8
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home-made ThermoMass concrete poured wall?


Before I get too involved in an answer, did you have certain forming system in mind??
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Old 12-08-2010, 03:46 PM   #9
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Not sure of your project details but, have you considered tilting up the wall? Might be an option.
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Old 12-08-2010, 03:58 PM   #10
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home-made ThermoMass concrete poured wall?


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Originally Posted by jomama45 View Post
Before I get too involved in an answer, did you have certain forming system in mind??
If you mean forms to hold all the mud, I have no details yet, but imagine I would build plywood/2x4 mini walls, 4' x 8', and brace them. In the back of my mind, this speaks to just using 10" arxx blocks w/ plywood on the sides and bracing them; that may prove to be much less hassle. I've only used arxx blocks once, and they were not too bad to brace. Either way, there will be some form building/bracing to do. As for tip-up walls, I have no machine big enough to do that, but if I did, I think tip-up would be the slickest. Thanks for the suggestions. j
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Old 12-08-2010, 04:07 PM   #11
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home-made ThermoMass concrete poured wall?


Yes, that's what I meant is the outside foundation forms.

In your case, I'd reconsider using concrete block on both sides, and tieing the two wythes together with the correct size "Durawall". I,m a mason by trade first, but I also have access to my brother's poured wall forms, and I would opt for the block in a scenario like this. It will save you alot of time, labor, & money IMO. As for block size, I'd suggest 6", as they're easier to lay, have a decent cavity to fill/re-enforce, and are still fairly lightweight. Use the extra width to carry the concrete slab inside.
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Old 12-08-2010, 04:56 PM   #12
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home-made ThermoMass concrete poured wall?


Chitina! In a effort to be expedient, I did not post all the "details", and that was likely a mistake. I will have two, 2x4, load-bearing walls on top of my foundation wall. The width of this double wall system will be 12", which is why I need support 12" wide. I also need lots of insulation in, or outside of, the foundation wall. (Global warming has not turned Frbnks into Miami, yet.) The ThermoMass wall gives me all that, as do a couple of variations of ARXX block walls. Too, the slab will be fully floating, so that I can thermally decouple it from the foundation wall and the earth. The slab will be poured inside the foundation wall, separated by 2" of XPS, and 4" under the slab (6" ??). Thus, I need to determine if I can build a ThermoMass-type wall that is structurally sound, (unless I can buy their materials), AND do it cheaper/easier than a slightly modified ARXX block wall. The TMass walls have a couple of advantages over the ARXX blocks, but the erection will not be quite as easy. (No ED comments, please....) c ya. john
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Old 12-09-2010, 12:03 PM   #13
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home-made ThermoMass concrete poured wall?


John, I understand that you're looking for alternative ways to build this foundation that will be super-insulated, and I can respect that.

BUT, I really think you're compromising some strength of the foundation on this one. I'd simply suggest interior or exterior foam here against a 12" wall, whether it be block or poured. Run the foam from the footing to top of wall, o even continue the foam up the wood walls if you like.

On the exterior app., you could also foam outward on the footing horizontally if it makes you feel better. If you want to terminate the foam at the first floor, you should have no problem cantilevering the treated sill plate out over the foam, especially if you use a wider one piece plate instead of two separate plates. The fact that Your outer wall is non-load bearing will help here as well.

On the interior, the foam is an even easier proposition. No worries of cantilever and no need to protect the foam from damage.

I'm sorry to tell you, but when you get too far away from conventional systems here, it's gets far more costly, risky, laborious, and cumbersome. I'd keep it simple as a foundation like yours is far from being the biggest heat loss element of a living space like this.
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Old 12-09-2010, 03:10 PM   #14
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BUT, I really think you're compromising some strength of the foundation on this one. That, I can't argue, as I don't know fer shur. However, TMass walls are used all over the world, and I know a very competent builder who uses them just because he gets the support for his 12" walls. Too, his houses all bear on the inner 4" wall.

On the exterior app., you could also foam outward on the footing horizontally if it makes you feel better. That is what is typically done here, unless ICFs are used. You then flash over the rigid foam. Horizontal 2" XPS, either 2' or 4' wide is typical, if the builder is not taking short-cuts.

The fact that Your outer wall is non-load bearing will help here as well. Actually, both walls will likely bear significant weight; roof on outer, floors on inner. The Riversong Truss has the bulk of the weight bearing on the inner wall.

On the interior... Roger that, which is one of the advantages of the TMass wall, if you live where bugs get into rigid foam.

... but when you get too far away from conventional systems here... One sure does not want to try to re-invent the wheel too often; been there 1,000 times.

Thanks for the ideas/opinions.
c after bullets. thanks. j
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Old 12-09-2010, 05:57 PM   #15
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As a structural engineer, I would have very serious questions about the real strength of the wall proposed.

The vertical load on a foundation wall is not great and a 6" hollow block would easily be enough for just a vertical load. I have seen 20 story load bearing buildings (no steel or concrete columns) built out of 6" block. These meet all American building codes and standards and they are just engineered better.

The problem with a basement wall is the lateral pressure and stress distribution. A 10" or 12" block (hollow and ungrouted/unreinforced) is more than adequate because there are cross webs to transfer or distribute the stresses to the entire structural wall and make it resistant to lateral loads that cause flexure and not just lateral shear. The shear strength of the muti-layer wall is very questionable and you could be stuck with a single layer resisting the lateral load unless there is structural continuity between the two wythes/layers.

Dick

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