Tearing down addition.

[CThomp]

It turns out that the addition built on to my 1950 home was pretty poorly built in the 1970's. My father and law and I have decide we're going to tear it down to the slap, bring it up to the level of the rest of the house which is on a crawl space about 18" off of the ground, and rebuild the addition to code. This addition is about 800sqft.

I'm in Florida so I still need to figure out what I can and cannot do because of code. Can I build a crawl space or anchor pilings to the existing slab to achieve the amount of clearance I am looking for?

[Sweep]

The only restriction I can think of is the minimum height in your area for wood joists above a crawl space but if the clearance is 18" and it is over a slab it should be fine. If the slab perimeter is adequate to support the new structure, you can build a short "cripple wall" with a PT sill bolted to the slab and a double top plate and then add the first floor platform with joists and band joist. Build the walls on top of plywood subfloor on the joists. Be sure to brace the cripple wall with diagonal let-in members or plywood sheathing. Provide hurricane ties from the slab to the cripple studs and perhaps even from the studs to the main wall studs depending on the kind of sheathing. Tie everything together to the rafters. Center structural supports are another matter.

[Cole]

Wow, now that is a reply.

[Tom R]

And I believe if you need a beam along the center, - - you can get away with a minimum of 12" clearance under that. Or if you're doing a flush beam, and it's engineered, - - keep it about 3/8" to 1/2" lower than your joists to allow for shrinkage.

[CThomp]

Thanks for the reply!! That was awesome. Most of the time my ideas are shot down. I haven't even started with renovations yet so i'm still tossing around ideas.

What if I use pilings anchored to the slab and run select ones all the way up through the perimeter exterior walls? Is that possible? The cost would go up of course because I would need more 12' 6x6 pilings but the whole structure would be tied in together. I think my piling spacing would be kinda short distances for long term stability. All wiring and plumbing could be run underneath the floor very easily.

The best way I think to describe it would be a beach house on pilings but the pilings wouldn't be sunk into the ground. The pilings would be achored to the slab with L shaped brackets on various sides. And there would be alot more pilings and the first floor would obviously be much closer to the ground.

I'm thinking of this design because I can do it myself without breaking the bank. The slab might need to be resrufaced but for the most part I think it's in good shape.

[CThomp]

I'm answering my own question.

Yes I can do what I want to do. I'd basically be building a tough as hell cripple wall if I do what I want to do.

[CThomp]

Like what Sweep said but more stout. I like stout. I'm a big fan of over kill. I'm still hiring an architect and he/she will probably scale me back a bit.

[Rich]

I don't see an issue with what you've suggested... like you said - maybe a little overkill but I agree - that's ok :)

[CThomp]

Alright but I do have another question. I've been investigating various anchoring devices like simpson strong tie and alot (not all)of those anchors are anchors that are preset into the slab during the pouring process.

Does this mean I should use more posts to compensate for this with anchors that are just bolted to the cement?

I'm trying to avoid the use of cement if at all possible. If I have to jack hammer select spots to repour with anchors thats one thing but cement can get expensive.

[Rich]

Not necessarily - most epoxy products are stronger than the concrete is.. so bolting to the concrete is definately a viable solution. I've used Rockite also - it's a fast setting, non-shrink, grout.. if you do find it locally and use it - don't touch the bolts for a couple hours as it makes some heat :)

[CThomp]

So put the Rockite ovr the bottom of the anchors and then bolt them to the slab? That makes the most sense.

Thanks for the reply. I hope I get to do this my way after talking to the architect. Wood is 10 times easier to deal with than cement or block. But I guess its in who you talk to.

[CThomp]

Wait so Rockite is like a builders grade of the Marine glue 5200? I just went to the website...thats strong stuff.

[Rich]

I don't know if I would call it glue - more like hydraulic mortar or grout. You'll want to bore a hole in the concrete a little larger than your anchor bolt size.. fill it about half way with Rockite and then place your bolts.

[CThomp]

So now that we've decided how to build the raised foundation whats the best thing I can use to seal the pretreated lumber once it is in place? In Florida cement lasts a real long time but even pre-treated lumber can begin to decay in less that 20 years when exposed to the elements.

I was thinking that once the floundation is built up with all anchoring and what not completed and before the platform is built that I would take some time to seal the wood as best I could to make it last as long as possible.

[Rich]

Probably your best bet is an epoxy based primer/paint. Talk to your local paint store - should be able to make recommendations.

[CThomp]

Sounds good. Maybe even something marine grade.

Awesome...thanks for your help Rich.

[CThomp]

Would a concrete pier and beam foundation system be more cost effective than a wooden cripple wall type system? The piers would only be about a foot tall.

Also, if I did use a pier system, how deep should I start the piers and does anyone make a device that would add stability to the pier itself.

My soil type is basically well drained dirt with a limestone substrate some feet down but i'm not sure how far. I'm in FEMA rate code B so i'm not in a flood plain.

[i_am_chris]

I don't know if I would call it glue - more like hydraulic mortar or grout. You'll want to bore a hole in the concrete a little larger than your anchor bolt size.. fill it about half way with Rockite and then place your bolts.

Rich - could you quantify that "little larger" in the above suggestion? I am setting a 1/2" rebar into stone, then pouring a footing around it. I've been using a 9/16" bit and setting the rebar in epoxy, but am going to start using Rockite/Kwixset instead. Is 9/16" hole big enough, will it allow for enough Rockite to do its thing? Should I go with a bigger hole (and go shopping for a bigger bit - which is cool with me but not necessarily with this year's tool budget).

Thanks

[Rich]

I believe the Rockite website states 3/4" minimum diameter hole for 1/2" diameter bolts or posts. You can see the tables for imperial measurements here
http://www.rockite.com/calculations/imperil.htm