I have read other threads in the past about it on here. But my question is not if I NEED to, as we all know you do not. However we are considering furring them out with 2x4 framing. Reasons being- current and future wiring, cabling, (ease of) installing things like cabinets- install blocking as normal or screw to the studs increase the r value of the ICF wall- ICF walls are on the low end of a good value in zone 6. attaching trim around windows and base Routing plumbing or drain lines at exterior walls I realize all of these things can be done with various methods I have read on here. But it all adds up to time and cost, similar to that of furring without the various other benefits. The cost of furring it all out and adding insulation is only about $700 for the entire project. It would boost the r value to the high 30s (forms are r28 average). The boost would allow the use of a mini split hyper heat unit, so large cost savings there on hvac. Any strong thoughts or opinions based on the above train of thought?

If, by chance, you are thinking of putting the 2 x 4s flat against the ICF you may have a problem with wiring. Code requires that wires must be 1 1/4" behind the edge of the furring or framing. With the 2 x 4s flat you probably would not be able to comply with with this requirement unless you put the wires in shallow grooves in the foam.

2 x 4s, especially if placed edgewise, would make it easier to run plumbing at the exterior walls.

The $700 number seems quite low to me.

You're going to lose some square footage, which is probably worth more than the $700 figure by itself.

dmac- no they would be a typical framed wall that is tilted up. yes, we would lose approximately 52 sqft in the house. The other wall assembly we were considering was the double stud wall, so this places the total wall thickness about the same as the double stud. By switching to ICF all the way up, it added sqft, so this takes it back down. 700 is materails price, labor is done by me.

Adding additional insulation to ICF to gain higher "R" values by far exceeds any diminisioning return on the $ spent for materials and labor.

I did this with metal 2x3 studs in my basement (Nudura).   Worked out well,
and just needed the metal studs punch and plastic insulator bushings for the electrical
(smurf tube) 

If I had it to do again for a whole house (might be happening soon),
I might use wood for ease of mounting cabinets, baseboard, crown, etc. despite the
extra work drilling for cross runs.

If using metal studs, investigate the commercial metal boxes that mount between
2 studs.  Would be a lot sturdier.



allan

MY wife and I was thinking of doing the same thing with or ICF project but with out the insulation since that will get in the way of wiring and pluming. I Think it a great Idea why would you want to cut in in the foam or have installer not having a clue on what to do and jack things up!!!
The only draw back is the home is one story 6998 sqft so there a small hit in sq ft;-(

Though I just thought of something.   The studs are not structural.
no need to drill studs, you can notch them twice with a circ saw
and hammer/chisel.   should be quite a bit faster than a hole hawg even.


or gang them up and hit them all simultaneously on a RAS with a dado
blade.


allan

I personally wouldn't do this, defeats the entire purpose of ICF being a one step process of forming, insulation and studs.

But, to look at what you are doing, use 2x3 (wood or steel, doesn't matter) set the plates 1/2 - 3/4" off the ICF wall and you just eliminated 95% of the holes you need to drill into this studding. About the only thing left will be the drains/vents for the plumbing, and possibly the water lines if your still using copper, use Wirsbo and you eliminate drilling for them too

Posted By Chris Johnson on 15 Jul 2012 08:54 AM
I personally wouldn't do this, defeats the entire purpose of ICF being a one step process of forming, insulation and studs.

But, to look at what you are doing, use 2x3 (wood or steel, doesn't matter) set the plates 1/2 - 3/4" off the ICF wall and you just eliminated 95% of the holes you need to drill into this studding. About the only thing left will be the drains/vents for the plumbing, and possibly the water lines if your still using copper, use Wirsbo and you eliminate drilling for them too

good idea.   2x4 plates and 2x3 studs.  1" clearance.


The interior walls will probably be done with conventional, so you're already
doing some light framing.  Marginal cost of the 2x4s is going to be maybe $.10/sf
for 24" centers + a very minor amount of labor.   Give it to the junior guys
as wall raising practice.

We didn't need it, but next house will be in a cold climate @ 6200', and
3-4" of extra spray foam would be nice.   Any thicker and you're going to
be dealing with really big jamb extensions.

We put 1" of polyiso on the outside, but I like the 2x4 idea inside better
since the house will heat up quicker if you're not warming a massive
heat sink.

what about anchoring the wires?
One issue I have with 2x3s are they are not as strong and typcially warp really easily. Placing 1/2" gyp, 24" centers on 2x3s is not something I would want to do, especially being held away from the way. Placing it against the wall would make it more strudy (can not push back on it) plus it could be anchored to the plastic ties.

Referring to payback- only costing around 700-800, that is not much for an r11-ish boost to typically a low r design (do not start that thermal mass enhancement with me! )
However the boost gets it up closer to an r40, allowing the elimination of a central furnace and instead going the mini split route. That 800 cost now translates into 6k savings. I would not feel comfortable going mini splits in a shell under r30 in zone 6.

Posted By allan-sf on 14 Jul 2012 10:20 PM
I did this with metal 2x3 studs in my basement (Nudura).   Worked out well,
and just needed the metal studs punch and plastic insulator bushings for the electrical
(smurf tube) 

If I had it to do again for a whole house (might be happening soon),
I might use wood for ease of mounting cabinets, baseboard, crown, etc. despite the
extra work drilling for cross runs.

If using metal studs, investigate the commercial metal boxes that mount between
2 studs.  Would be a lot sturdier.



allan

Metal studs work fine for building in the clearances for running the power, etc, but take a serious performance-hit when used for adding insulation, since the thermal bridging of a metal stud is several times that of a wood stud.   eg: A 2x4 wall with wooden studs and cellulose fill comes in at around R10 after thermal bridiging, but the same wall with metal studs only noses up on R7.

Since one of the stated goals here is enhanced thermal performance, going with wooden studs would be better from that point of view, even if metal studs would give you a flatter wall, etc..

Posted By lzerarc on 16 Jul 2012 08:52 AM
what about anchoring the wires?
One issue I have with 2x3s are they are not as strong and typcially warp really easily. Placing 1/2" gyp, 24" centers on 2x3s is not something I would want to do, especially being held away from the way. Placing it against the wall would make it more strudy (can not push back on it) plus it could be anchored to the plastic ties.

Referring to payback- only costing around 700-800, that is not much for an r11-ish boost to typically a low r design (do not start that thermal mass enhancement with me! )
However the boost gets it up closer to an r40, allowing the elimination of a central furnace and instead going the mini split route. That 800 cost now translates into 6k savings. I would not feel comfortable going mini splits in a shell under r30 in zone 6.

Finger-jointed 2x3 stock is pretty straight compared to standard mill-run goods.

You would be right to be closer to R40 than to R20 when heating with mini-splits in zone 6.  Even in zones 4 & 5 that would be preferable from a room-to-room temperature balance point of view, even if it works OK at R15 in nearly-ideal floor plans in zone 4.

IMO, someone needs to make an ICF block that has one cavity for concrete and another for dense pack cellulose. Then you can get R40 walls for a reasonable price.

Jon, do you really believe the R value when measuring EPS? if so what is it in relation to? From my perspective, look at fibreglass batts for R value, i.e. R-12, R 20, R 28, etc. but to cross over to EPS which is not a fair comparison. Measure the U value of an ICF wall and it's almost zero.

Like in Dana1 post, comparing a wood stud wall to a steel stud wall by itself I accept, but building it inside an ICF structure and I see don't the value in the difference of R10 vs R7 when you have a almost zero U value right behind it.

R20 of EPS + R20 of cellulose or R40 of EPS or U.025 of either - they are all 1/2 the heat loss of a normal ICF block. Payback is a question, but the first one is likely to be better than the second.