I've been reading a lot about voids and gravelling, and I'm wondering if I should be considering Pre-Cast instead of ICF.

I'm planning a 36x36x36 3-level house in Vermont that will need as little energy to heat it as possible. I have a fair amount of light construction experience, but little with concrete. I want to plan and build as much of it myself as possible. I work as a programmer, no kids yet, so I can spend my daylight hours working on the house.

There's a Pre-Cast plant in our county. I'm thinking I could have them build me a 6" thick 36'x36'x36'cube, with 4 floors - pad, 1st, 2nd, flat roof. Set it on some solid footings, partially into a hillside if I get the right site. There won't be any doubt as to the integrity of the structure, no voids, no gravelling, just well engineered pre-cast concrete. I'll put 4 inches of foam around it, put a sloped metal roof filled with cellulose on top, detail it out nice.

So what can I get from going with ICFs that I can't get from Pre-Cast? I haven't gotten any bids yet, but general research is showing me very similar price.

Not so fast my friend (sorry college football is almost over and I couldn't help it). First I would be surprised if you are able to get Pre-Cast construction with both the inside and outside insulation (eps) for the same price as ICF, but I could obviously be wrong. I don't believe you are thinking Superior Walls, because they can't go up that high or if so, I wouldn't want to live in it!

I would think for a "box" MIGHT be competitive, but once you start putting in windows and doors and other openings the price will probably increase substantially (please let me know if I'm wrong). As for the consolidation concerns, I think it is more inexperienced installers or really bad concrete that is brought to the job. You can use also the plasticisers (self leveling self consolidating) which the article in this forum mentions and recommends. The article also states that the increase cost of the plasticiser will be offset by reduced labor. I simply believe that ICF dominates Pre-Cast in many ways, but at the end of the day its your house and you should do what you think is best for you. Again, I think that when you get the pricing for double insulated Pre-Cast it will be more expensive than ICF construction and will probably take more time, especially if you are doing multiple levels.

I would like to see which direction you go!

renangle

installing foam to the entire house would be very labor intensive i would think and every door and window would have to be furred out . sounds like a lot of work . i hope everything goes well

Agree with the above, and would add that the whole interior would have to be firred-out as well.

I think your major concerns about voiding and 'graveling' come from that consolidation article. But remember that the walls used there were 4" core, to exaggerate the problems for instructive purposes. In real life 6" and 8" are used, and have far fewer problems since concrete can get past the rebar easier.

Vermonter,

maybe I'm reading your terminoligy incorrectly, but Precast companies make precast panels. You would be in charge of having the panels assembled on site. This requires a crane and a crew. Down sides to precast walls on lower levels it is not monolithic pour. Many joints under ground. Second issie is precast floors do not have open web joists for easy mechanical runs. Then as stated above , insulation must be attached..some how. Interior insulation on the ICF has a buffering effect and makes electrical installation easy. Finally, you say you want to do as much as you can yourself. ICF is much more DIY than precast.

ICF was not my first pick when I began my search. After visiting the World of concrete and this site, we have gone with ICF and Hambro steel/concrete floor system. Good luck

Patrick T

The 4" walls were flat-panel ICFs with extruded polystyrene.  When you read RD134 you see on page 3 that where expanded polystyrene was used it was 6" not 4".  RD134 is not new information to those of us who have been around for a while in the real world, building real buildings.

icfgal

I think people are missing the point. RD 134 concludes that if you are using any type of external vibration tactics, you are like wasting your effort. The only way they got consistant and quality concrete consolidation was to use internal vibration. Something that myself and many others on this forum have been preaching for years.

ICF Contractor

Hm, this is interesting: icfcontractor and icfgal are posting from the same IP address.

Just a thought, what would the cost be to fasten the foam to the house? ICF's have that covered. With ICF's you will not have air leaks that you may encounter with all of the seams in pre-cast. The recent posting on pouring techniques should calm anyones fears as to how to do a successful pour with ICF's.

i would have to agree with all above! I couldn't even begin to explain all the reasons why you shouldn't go with precast so I'll talk about why your fears are convincing you of another method and why ICF is better.

(1) Graveling doesn't excist, its called honeycombing and it happens every day with poured wall foundations. They use heavier slumps i.e. 4-5 inch and not much vibration. They also use 3/4 aggregate due to its cost, and there competitive non ICF market. It consist of the outer 1/4 to 1/2 inch of concrete being non existent in certain places causing the look referred to as honeycombing. It has no structural affect and shouldn't be considered as an issue. If you where to address this issue "honeycombing" in the IRC or prescriptive all the charts on flat ICF walls are based on a nominal thickness off 5.5" or 7.5" inches. SO ITS IRRELEVANT ANYWAYS!

(2) This thread "Graveling" started as a general scare tactic to force the uneducated to hire a "professional " comes from a lack of business knowledge and apparent lack of business! As you can see from the other post stated pouring techniques that an appropriate mix design flows 99% efficient and back then external vibration wasn't efficient as it is today so find a experienced ICF professional with either a proper mix design or proper vibration techniques is imperative.

(3) Structurally precast is inferior due to hinge joints, external and internal fastening points, thermal mass and all the other reasons why. Besides that I'm sure we can find you a good ICF dealer there in Vermont.

Dave

There is always the option of CIC with precast. Concrete on both sides and insulation inside. Thermomass is one company to look at.

Also several of the ICF companies have products that can be Tilt-up on site.

Ah yes icfgal, thanks. I'd read the article quickly and missed that some of the forms were 6". This puts a new cast on their results.