re: Post Tension Slab

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I know there are many drawbacks but I feel like I have the time and project management skills to pull it off.

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Famous last words.

There have been good responses in this thread, and some terrible responses in this thread. If you are seriously concerned with your foundation strength, then hire a CE firm to come perform soils tests on your lot. They can tell you if the soils conditions present any issues that would require a specialized foundation design.

Truth be told for 90% of residential homes, proper fill and compaction of the subgrade is much more important to the integrity of your foundation than post tensioning. Can't tell you how many homebuilders I see scrape the lot, throw some dirt on it, grade it out, then start digging grade beams.

But for crying out loud, if you even consider placing a post tensioned foundation and then go an place your driveway without putting some damn reinforcing in it, I'm going to laugh my arse off at you. Wire mesh is so freaking cheap, yet no one ever uses it. Had my idiot builder put it in my driveway, I probably wouldn't have to be worried about busting out and replacing the apron right now.

Sub it out. I didnt and regret it. Of course i am a Civil Eng. And have been around house building most of my life and do concrete for a living. I ended up doing most of the gc work along with all flooring, electric and painting.

Next house i will build i will do plumbing and gas also and sub everything else out.

As far as slabs go, dig to good clay, go back with a good mix and let it sit. If you are really worried, do the plumbing and electric and pour the slab then let it sit.

Another thing you can doninstead of post tensioning is drilling out and pouring shafts under the load bearing walls every so many feet.

Wife and I built a house in 2003. We did it ourselves, no GC. Spoke with a few companies that did post tension slabs and the only thing I remember was the answer to a question I asked. I asked if this was being used for commercial slabs and he said no. We went with re-bar and wire mesh. Re-bar and wire mesh has been working for a long time, why change now. Also re-bar and wire mesh slabs use bigger footings which I think is a good thing.

I don't see the advantage of them in residential construction. The only time I have ever seen it done is on mulit-floor commerical buildings, but it was mainly to conserve concrete. I don't see any static building adding that much tension to a pad. Maybe in earthquake areas. You would need a lot of bending stress, or have a need to reduce concrete. For your needs, proper conditioning of your soils should reduce settlement of your house. You can hire a CMT/geotech guy (Civil firm) to test, and evaluate your site.

Everywhere.

Foam, applied correctly, is awesome. It also makes your attic suitable for storage.

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Not sure the added benefit of closed.

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Closed cell = denser= less thickness per R Value. In your walls, you only have so much room to work with. Roofline doesn't matter, plus you want open cell for the previously mentioned roof leak issue.

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Supposedly your attic will only be 10 degrees hotter / cooler than your conditioned home when using spray foam

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This is 100% legit. I did a medical clinic using spray foam, big attic with a mechanical deck. It was incredible how cool it was in late August walking around up there.

I used open cell everywhere.

Correct, you can use a mechanical vent if you must, but I didn't. No combustibles (gas water heater) in attic.

One of our attics is probably only 4-5 degrees warmer than the conditioned space.

The other one, over the garages, is only 10-12 degree warmer than the conditioned space. I've checked this with a spot display thermometer.

AC equipment is obviously far more effeicent

Correct.

You still can't really undersize the units, but they will be way more effiecent.

How much living on each floor?

Do you have an area on the first floor that is open to the scond floor (tall ceilings)?

Assuming 10' down and 9' up?