I'm contemplating building an energy-efficient home in the western suburbs of Chicago, Illinois.

I'm trying to get in touch with some green builders to answer my questions, but I figured I might as well hit up this forum while I'm at it. One particular question I have: when it comes to sealing the home, what are the relative merits of ICF versus stick construction? Is one easier to seal (and keep sealed) versus the other?

My (admittedly naive) intuition says that ICF, being a single uniform structure, would be easier to seal. Whereas stick construction, with all the lumber junctions, has a lot of opportunities for leaks. But on the flipside, what happens 10, 20, 30 years down the road for either style? I would assume that the concrete in ICF will inevitably get some cracks such that the home is still structurally sound but the seal is compromised. (E.g., ground settling, temperature/humidity fluctuations, etc.)

No doubt that ICF is inherently easier and more air tight than wood stick frame. If you built a square ICF home with no windows and doors with an airtight roof and then built a stick frame home with no windows and doors and an airtight roof. The ICF house would be completely air tight while the stick frame would have air leakage.

The weak points to any structure are windows, doors and roof to wall connections.

Wood frame has tons of gaps and pieces that create air leaks. It takes time, strategy and extensive labor to properly seal a stick frame home. With ICF, it comes "naturally" in that you have 6" of poured reinforced concrete in the middle with 2.5" of EPS on each side. That naturally creates a very strong and very air tight structure. The weak points would be windows, doors and roof area.

There are stick frame homes that are very air tight but it requires someone knowing that they are doing and the labor involved in making it airtight. Most builders don't know how to air seal a home properly.

if it's your 'forever' home, consider ICF. The attention to detail that's required to do a proper stick build is not prevalent (in my opinion) throughout the industry. Whereas with ICF, anyone who's done one and at least has had some training, can create an air-tight home. Like Lbear mentioned though, the window/door detailing (and the roof) is going to be your weak point. I'm going through my window and door detailing now trying to get it all right.

Even if the stick build is done properly, if you live there another 50 yrs, what are the odds that there won't be expansion/contraction of areas that will then leak? biggest thing with ICF (imo) is any cracks that will occur within the wall, which can be minimized depending on the mix used.

disclaimer: i'm not a builder

Edit: I'm also in process of having my ICF home built, so I may be a bit biased.

IMO ICF has some distinct advantages. All CC cracks, but full depth cracks that would be able to pass any significant air at the pressure differential found in a typical home would be VERY rare. On top of that the CC is covered both sides with 2.5+ inches of foam that the CC is bonded to. I am thinking long term, the air transfer rate in an ICF wall will remain consistently very very low... the CC mass in the wall also helps provide some thermal stability inside the sealed envelope. With good quality windows/doors and good attention to the sealing details around the openings, that leaves you with roof and floor.

IF it is a slab-on-grade, that makes for an easy sealed floor. If it is a conventional floor, well a little more detailing there to seal, but if you use ICF for the stem or basement walls, and consider pouring a basement or crawlspace slab over a vapor barrier, that will seal up the low road. This also makes for a much nicer and dryer crawl space or basement.

That leaves the ceiling. Large open spaces, few penetrations, it is a little easier to seal during construction. If you use a dense insulation layer on top, that also helps with any air leakage. Probably the biggest "leaker" in a ceiling are recessed light cans. A little sealing detail here, or putting sealed boxes over the cans will make the ceiling very tight....

Good luck on whichever path you choose.

We build very tight double wall "stick" houses. So far we've avoided ICF due to the cost premium, but I would agree that for an inexperienced builder, ICF's might help with air sealing. Structural SIPS would do the same thing. Wood houses are not all that difficult to air seal - the first time we paid attention to the number, we achieved less that 1 ACH50 - but they do require attention to detail and an awareness of the issue, and many builders are simply not "tuned in". But with that type of builder, they can lose it in the areas beyond the walls, so ICF is not a "one stop" solution.

The best solution is to find a builder - and they exist in your area - who are tuned into the problem and work with them. Trying to train an uncaring builder on one house is a recipe for failure.

Posted By ronmar on 18 Aug 2016 09:48 AM
That leaves the ceiling. Large open spaces, few penetrations, it is a little easier to seal during construction. If you use a dense insulation layer on top, that also helps with any air leakage. Probably the biggest "leaker" in a ceiling are recessed light cans. A little sealing detail here, or putting sealed boxes over the cans will make the ceiling very tight....

I'm not a builder, but when it comes to ceilings: I've often read about the recessed can lights being problematic in terms of sealing and possibly acting as thermal bridges.

Why can't the ceiling for the light fixtures be a "false" ceiling, and then have a "real" ceiling that can have an unbroken seal, and then be loaded up with cellulose or similar? Of course you either have to make the building taller, and/or give up interior ceiling height. But it seems to solve the problem of worrying about breaks in the ceiling seal/insulation. Also that gap between the false and real ceilings makes for a nice service area if you want to run more wires, service light fixtures, install speakers, etc...

with a flat attic ceiling (such as a ranch or colonial) we install and tape a fabric air barrier under the trusses (Majpelll by SIGA), then strap the ceiling. that gives us 1-1/4" between the Majpell and the face of drywall which is sufficient depth for the thinner LED surface mounted lights that look and work like the old fashioned recessed lights. Also gives us a wire chase. Result - a tight house with no ceiling penetrations. Caution: your electrician MUST be on board with this method. Any penetrations - plumbing or electrical are well taped with SIGA or other good tapes. When that's done, and before insulation, we blower-door test the house, fix what needs to be fixed and move ahead. You can't tell if you don't test, and testing after the insulation is in is too late to address issues.

Bob I, do you happen to have a pic of what you're talking about? specifically the 'strap the ceiling' part and a manufacturer/model of these lights you're referencing?

no pictures that I can find. You can usually find the lights at HD (although it pains me to actually recommend that store). The brands and styles change frequently, but they seem to be available faster there than at commercial lighting stores. They stick down below the ceiling by an inch or so, but there is very little space needed above.

As far as strapping the ceiling - that's a New England tradition and somewhat uncommon in some parts of the country & used to flatten out the ceiling. We use 1x3 spruce strapping, nailed 16" OC to the trusses through the Majpell. (don't worry about nail holes) Also has the benefit of helping to hold the R60 cellulose in the attic, so your not relying on the strength of the drywall.

For cans in attics try the insulite boxes or tenmat covers. Probably takes 15 minutes per can to fit it and seal it with 1 part foam.