Planning on building a very energy efficient ICF home around 3800 square feet.

Wife and I went and toured one this weekend which was gorgeous - but had steel joists.  The guy who built it had a background in commercial construction so I guess he is used to doing it this way.

My question is - Will the thermal bridging mess up my energy efficient plan?  He said that the joists only run a few inches into the concrete and so do not break the outer foam. But they do breach the inner foam -

He also put in concrete floors.

Any thoughts would be helpful. I live in northern Ohio if that helps.  I may use EIFS as well to add a few R value points.

Todd

There are multiple ways to incorporate steel framing, including Sipson steel ledger hangars similar to the ones for wood frame.

Personally, I think thermal bridging is measureable, but not a negative when you are building with so much thermal mass!

Steel joists are nice to install, especially when embeded into the concrete core, makes for a faster install then wood, where it becomes slow is installing the sub-floor, either screw it down with drill point screws (which is really slow in 12 and 14g steel) or ET&F makes a nailer, cost $ 2500.00 system, it's a real kicker. I have 'borrowed' the ET&F nailer from my rep and purchased the nails to do this, still fasteners are pricey but increases productivity. Don't worry about thermal loss, joists are not penetrating the exterior of the foam.

Todd, any photos or a link to his project? I am designing a similar structure.

Todd, are going to pour concrete floors? This is the big question that leads to whether you need steel or some other system capable of handling the weight. As far as eifs goes this will not add any r-value in your case. On your house it would be efs
(exterior finish system) hence the ICF foam (insulated)is already there.

Be careful as to the brand of ICF because some are not EFS compatible.

Which steel floor system was it?

Thanks Always Dave

Thank you all for your helpful comments. I'll reply line by line -

- the joist system is TradeReady by Dietrich

- I am unsure if I will be going with concrete floors. I think it sounds like a very nice feature but I will need to compare the pricing. I like to use a whole house fan in the summer so i think the thermal mass will be good for storing nighttime coolness.

- I don't have any pictures but if you want I could email you the builders email.

- I think the ICF system that we will go with is Nudura which I believe if EFS compatible.

Thanks Todd

walltech - could you tell us which ICF's are not EFS compatible, or maybe tell us what criteria make them incompatible? I'm guessing it's if they have the plastic webs showing through the exterior foam layer?

Todd
I'm not sure where you are building but if you sustain high temps, say 80+ for a period, once the building starts to warm up from the daytime temps, a whole house fan CANNOT cool it down during the nite. It will feel cooler because of the air moving, but the cooling factor isn't there, because the thermal mass slowly changes temperature, and its not easy to reverse it.

I have a 1000cfm wholehouse fan which we use in the spring and the fall, during the summer the air is on. I won't let my clients build with AC for the very reason above.

Jim - I live in Cleveland - so we don't stay above mid 80's for more than 5-7 days at a time (at least not yet)- plus my wife and I tend to be happy if it's about 79 or below inside (as long as humidity is not too high) and we will have geothermal heat and cooling.

You said "won't let me clients build WITH AC"? - did you mean won't let them build without AC for this reason?

Also my original question was about whether thermal bridging from the steel joists is a big deal and most of you seem to think it is not - and I mentioned that I was going to put EIFS (i.e. another inch of insulation) on the outside of the ICF but Walltech said this would not add any R-value? Why not? ICF wall is around R-value 24 - why not put on the EIFS and take it up to R value of 30? I understand some SIPs panels are as high as 40.

I know the "effective" r-value of ICF is like 40 - but thermal mass don't mean much if it is never gets warm outside to add the heat back to the walls. I.E. the thermal mass helps a lot in spring and fall in Cleveland when we are getting big temp swings but when we get into one of those long cold spells here on the north coast it would seem to me that then you are dependent on your "true" R-value.

I looked into it and the extra layer of insulation (i.e. enough EPS to cover a house) only costs like 2000 bucks. I expect to live here for life and I expect energy prices to go up so I think I'll make most if not all of it up.

That's just how I'm approaching it - want to know what you all think if that sounds like a reasonable approach.


Thanks Todd

Nobody has had time to respond to the above post - but I have one more question on this project.

The builder whose ICF house I looked at said he does NOT vibrate - i.e. he does not do internal consolidation with a wand. He said the reason he doesn't do it is that he doesn't use rebar. At this point I'm getting real scared and am ready to bolt and go to another builder because I've read here so much about how consolidation is key. Anyway - he says that he uses a product called "Forta-Fiber" instead which is a copolymer fiber that is added to the concrete to make is reinforced and stronger. I went to their website and looked good but I'm not a construction person....

So my questions are 2--

1. Is Forta Ferro or similar thing as good as rebar?

2. Can you get away from consolidation when you don't use rebar?

Thanks a million - Todd

Here we go again.  The best way to consolidate concrete internally is with a vibrator.  Even with fiber you need rebar around window and door openings.  It seems everyone would like to forget the internal vibrator, including me.  My experience shows me the  the internal vibrator is still the best way to insure consolidation.  Look at some of the old posts regarding consolidation.  Not much has changed in the last 6 months to change any of the processes.  There may be a "magic bullet" that will allow the elimination of the vibrator, I just haven't seen it yet!

Todd, of course adding foam will increase R. However this will make your firring-strips that much deeper. May not matter though if you glue on the boards and use EIFS. With EIFS it is CRITICAL to waterproof around windows and doors. Better yet, use cementious stucco not EIFS, because the latter has developed a terrible reputation. Might be hard to resell the house.

And although fiber is the poor cousin to rebar, it is nowhere as good, particularly in seismic areas. And consolidation MUST be done. Fire that builder. He cuts corners here, he cuts corners elsewhere .

For interfloor deck I recommend post-tensioned concrete. Why put in a flammable floor, when concrete can cost less? Ither noncombustible alternatives if your builder cannot do post-tensioned are the Hambro system, or Metwood's. Metwood's beams let you clear-span 40', with 18" inter-floor space.

Quantum or anyone else,

Why post tensioned concrete? Why not just pour concrete for the floors? I know pretensioned concrete has greater tensile strength but do we really need the extra strength? Todd

Todd,

 

You need the extra strength if you want long spans or short depth of joists. The top of any joist system is in compression and the botom is in tensile. middle is Zero (good place to drill holes:) ) Concrete has very high compression but much lower tensile strength. As a tensioning rod is added to the lowest point of the joist, smaller joists or longer spans can be achived.

Patrick T

Right. Longer clear-spans, more economically. But special methods must be used with PT+ICF. The floor must be allowed to flex.

So if I don't have any real long spans in my design then I save money by not having to use pretensioned concrete? That would be helpful to know when we sit down with the architect.

Todd

So is there much post-tensioned concrete being used in single family residences?

Quantum, any chance you could name a ballpark cost per linear foot of those Metwood beams?

Todd, if the builder you are interested in using does not typically use rebar and consolidation then you really should consider finding another builder. Even if he agrees to use it for your job, it is something he is not use to doing and in the hurry of getting the job done he might just "forget" or do an inadequate job since he doesn't really think that it's necessary.

I'm a DIYer and I used an internal vibrator with absolutely no problem on my ICF pour. There is no reason to not do it (the cost is minimal) and many reasons to do it.

Todd, I have no idea how much engineered-wood joists with concrete overlay cost, but it might be cheaper than PT for shorter spans. My whole orientation is non-combustible construction though, and I would never consider engineered wood for many reasons, not least being outgassing of formaldehyde. It may be that a composite floor system by Metwood or Dietrich is as cheap. But for commercial projects PT is used more often than not for many reasons, most being economic.

Jelly, I know of only about 10 residential projects in the US which used post-tensioned. It is not done because it is not possible with stick-built. It is possible with ICF.

And gregj, +1.