24" is fine. 20" would probably be ok, too.

I thought 40x was for splices / areas of tension.  Since the dowels are for sheer (not tension), the foundation company engineer said 40x diameter is not required.

I found a Nudura manual that seemed to indicate 8" was minimum, the foundation company brought out 24" dowels (12" sticking up, 12" in the foundation), others have suggested 40x.  I think 12" will work, but I would like some other input since I'm getting conflicting info.

Thanks

My engineer suggested that the dowels must match basement walls vertical rebar.
My basement walls had 15m of 12" o.c. So I used the same as dowels. And he said that they must be min 4' such as 2' in footings , 2' in walls.

When my son doesn't like the answer he gets to a question, he keeps asking in hopes he'll get one more suited to his expectations. Good luck.

How deep are your footings?

12" should be sufficient for a footing that is for a slab on grade design. If these footings were holding a below grade wall that was pushing against a lot of earth, then 24" of rebar above the footing would be minimum with at least 24" in the footing itself.

In a seismic zone the 12" would be a no-no as the home wall would literally want to slide off the footing during an earthquake. Rebar steel is what adds the strength in tension to concrete. Ever see the rebar schedule in a seismic zone concrete wall footing? It gets pretty insane at times but it is required.

I remember a thread on here that the guy had NO rebar dowels installed in his footings. The contractor just stacked the ICF wall onto a footer and was hoping that the weight of the wall would plant & keep the wall on the footer. Needless to say the poor homeowner had to go back and modify the footing to wall attachment by running rebar from the slab to the wall to help tie in the wall.

What did the engineer say about the 12"?

Yes, it is a slab on grade design.  There is no dirt pushing in on the walls.

It is the foundation engineer that says the 24" (12" each way) is plenty.  The ICF sub (non-engineer) is the one recommending using more.  I agree that more is probably better, but since it is the day before the pour, I'm thinking this is probably not a big enough issue to delay the pour.  Especially since it is the licensed engineer that made the dowel decision.

The foundation company did bring 100 or so longer (36") #4 this afternoon.  I'll probably use the longer ones for corners and both sides of any doors/openings.  The pour starts at 4am, so there is no easy place to pick up a couple hundred more longer sticks at this time.

Yes, I saw the no dowels thread.  Definitely a bad deal!  I'm just glad they got it to work out in the end.

Make sure they put caps on the dowels for safety.

My walls were 12' long below grade.

Here are a few pre-pour pics:



Front corner of the house.  You can see the large beam that crosses the storm shelter.




I have a couple 1500 ft geothermal pond loops (black HDPE) that enter a utility room here (as well as the main water supply (copper).  My backup water tank I mentoned earlier is a seperate system (not an inline / flow through tank).



After they put up chairs.

A better picture of the big transfer beam. It basically keeps all the weight of the house off of the shelter below. It is 20" wide, 36" deep, and about 48 ft long.  It has 12 strands of post tension in the middle, 7 sticks of #6 rebar on top, and 7 sticks of #8 on bottom.  The engineer says even if all the post tension strands fail, there is enough rebar to keep it intact.  Both ends of the beam sit on 30" diameter piers.

Is that a raft slab foundation?

Did you add any drainage rock to the soil or is that raw compacted natural soil?

Posted By nd96 on 04 Feb 2013 09:59 PM
Yes, it is a slab on grade design.  There is no dirt pushing in on the walls.

It is the foundation engineer that says the 24" (12" each way) is plenty.  The ICF sub (non-engineer) is the one recommending using more.  I agree that more is probably better, but since it is the day before the pour, I'm thinking this is probably not a big enough issue to delay the pour.  Especially since it is the licensed engineer that made the dowel decision.

The foundation company did bring 100 or so longer (36") #4 this afternoon.  I'll probably use the longer ones for corners and both sides of any doors/openings.  The pour starts at 4am, so there is no easy place to pick up a couple hundred more longer sticks at this time.

Yes, I saw the no dowels thread.  Definitely a bad deal!  I'm just glad they got it to work out in the end.

More is usually better but I wouldn't be too concerned about it. Remember with engineering they always over-engineer things by at least 20%. If you were in an earthquake zone C or D, that would be a different story but the engineer would have designed for that. With the weight of an ICF home sitting on the footings with rebar dowels at 16" oc, it ain't going anywhere, especially in a non-seismic zone area.

As always, keep good drainage on the home site so that water doesn't collect at the base of the home. Use geotextile if needed and keep the water flowing away.

My backup water tank I mentoned earlier is a seperate system (not an inline / flow through tank).

What's the source of that water for the backup system?

Lbear - The house/yard should have very good drainage. The ground there was built up for the house pad a few years ago. There is about 16 ft of 1:8 slope, then a drop off (4 ft retaining walls) around 3 of the 4 sides of the house. No place for water to back up (unless you count my pond). The 4th side has the driveway, but still a decent 1:12 slope after the drive.

Soil testing was done down to 25f ft. In the soil report, the company stated that the soil on site was basically fully saturated/swollen (a benefit to being fill dirt from the pond and retaining wall work), and therefore had little or no potential for further swelling. Due to this, no soil conditioning was required. The foundation company was able to use the native soil, add a few inches of sand on top, then the plastic/moisture barrier. That saved a little bit of work. Since the foundation/house rests on the piers and not on the soil, the usual cycle of shrinkage and re-expansion of the soil around here shouldn't cause any problems - even if we did flood the foundation with standing water (in theory anyways).

I'm not familiar with the term "raft slab" foundation, so I'm not sure.

The backup water tank (1200 gallon) is just filled with regular potable water and capped off. Nothing special. It is just there in case we loose the regular co-op (city) water supply. It is just gravity fed, so it drains down to the storm shelter plumbing system with a turn of a valve. I'll probably want to refresh the water in the tank every 12 months or so, otherwise I hope to never need it.

We used about 500 foundation dowels total - half 24" (buried 8" deep, 16" exposed), the other half 36" (12" deep, 24" exposed). I'll be surprised if anything happens to lift the 2 million pounds of walls/floors above, off of the foundation - even if all the dowels didn't end up being the ideal length.

We have orange safety caps on about half of the dowels right now, but need to pick up some more to finish off the job.

I'll post a pour update and pictures later.

The foundation pour went well.  It started with a pump truck and about a dozen workers showing up at 3:30am.  The actual pour started at 4am and was done by 8.  They spent the rest of the day working the concrete.  When I left for work at 6pm, there were still 5 guys and a couple of power trowels putting the final touches on the finish.  Overall, I'm very happy with the job the foundation company did and feel I have a good start on the house.















Now it is time for the ICF sub to take over. They expect to be starting next week. Hopefully the ICF portion will go as smoothly as the foundation.

Posted By nd96 on 08 Feb 2013 12:45 AM
The foundation pour went well.  It started with a pump truck and about a dozen workers showing up at 3:30am.  The actual pour started at 4am and was done by 8.  They spent the rest of the day working the concrete.  When I left for work at 6pm, there were still 5 guys and a couple of power trowels putting the final touches on the finish.  Overall, I'm very happy with the job the foundation company did and feel I have a good start on the house.

Now it is time for the ICF sub to take over. They expect to be starting next week. Hopefully the ICF portion will go as smoothly as the foundation.

Things are looking good. That is one big slab. Do you know what type of mix they used (how much psi?) Do they vibrate the slab pour? Why did they start so early at 3AM?

Do they have to keep the slab wet with a spray hose for a couple of days?

We did not talk about the watering and covering the slab. This was the important point. My guys sprayed "seal and cure" for basement and first floor (it was 32mpa). But I had lots of cracks. I poured the second floor myself. I did not use "seal and cure". I watered everyday and I coverd the floor with things what ever I found (wood parts, unused forms, nylon packaging leftovers). As a result no cracking.

Good points about the slab.  If it were summertime here in Texas, the watering would be an absolute must.  The foundation company did not spray or water the slab.  That was something I thought about, but felt comfortable without doing for a couple reasons.  First, it was poured on a foggy / humid day, and it stayed that way for about 36 hours.  It was the following afternoon that the slab first started to have surface drying.  Second, since it is a post-tension slab, the post-tension helps to put the concrete into compression and reduce/minimize cracking.  2 days after the pour, they tensioned the cables to 50%.  They will come back at 7 days and tension to 100%.

I will probably have some surface cracking, but nothing structural.  The only area that I will not have a flooring covering the concrete is in the garage.  Everything else will be covered with tile (about 50%), rug (25%) or wood (25%).  If I was doing stained concrete or something with large amounts of exposed concrete, then I probably would have done the watering.

They used 3000psi concrete.  I think they started that early in the morning just to have the entire day to work the concrete to a nice finish.  As far as vibrating, they did vibrate the large beam that goes over the storm shelter really well, but I don't think they did other areas of the foundation. 

One thing that I found interesting was how the engineer planned the post-tension in the large beam.  All of the slab will be fully tensioned by 1 week, but the beam is done differently.  There are 12 post-tension cables in the beam.  The way the engineer explained it, is that they intentionally let the cables sag in the middle of the beam.  When they tension the cables, the sag provides uplift to the the center of the beam.  After the initial foundation pour, they tensioned just 1/3 of the cables in the beam.  He says when we pour the 1st floor wall and floor above, they will tension the next 1/3.  When the 2nd floor walls and floor above are poured, they will tension the last 1/3.  The uplift in the beam from the cables is designed to match the weight of the floors above, so that there is no net deflection in the beam itself.

I'm just showing off here, but if anyone likes stained glass, the link below is what I'm putting in the tower:

http://www.ebay.com/itm/Fine-100-Ye...3f109c4407

I didn't pay that much, but I did buy it.  It is sitting in my garage just waiting for a house to put it in.

Posted By nd96 on 09 Feb 2013 12:45 AM
Good points about the slab.  If it were summertime here in Texas, the watering would be an absolute must.  The foundation company did not spray or water the slab.  That was something I thought about, but felt comfortable without doing for a couple reasons.  First, it was poured on a foggy / humid day, and it stayed that way for about 36 hours.  It was the following afternoon that the slab first started to have surface drying.  Second, since it is a post-tension slab, the post-tension helps to put the concrete into compression and reduce/minimize cracking.  2 days after the pour, they tensioned the cables to 50%.  They will come back at 7 days and tension to 100%.


I'm just showing off here, but if anyone likes stained glass, the link below is what I'm putting in the tower:

http://www.ebay.com/itm/Fine-100-Ye...3f109c4407

I didn't pay that much, but I did buy it.  It is sitting in my garage just waiting for a house to put it in.

Post tension slabs are really bullet-proof when it comes to preventing structural cracks. The one downside is that you can't drill or cut the slab down the road. So no anchoring safes into the slab or you could end up busting the steel cable which would prove disastrous and/or deadly.

Is that stained glass window going on top or the side of the tower?

Thanks for the pics and keep them coming, especially during the ICF stack and pour.

What is the rebar schedule like for the ICF walls? What psi mix are you going with?

I agree that a pre-stressed or post-tensioned cable should not be damaged.  However, the engineering company can usually advise as to where the cables are located.  Small holes and cutouts are allowed in a slab provided the cables are not damaged.  Beams can contain so many closely spaced cables that it is best to avoid cutting or boring into beams.