Thickness of slab, driveway, ...

[David]

What are the standard thinknesses for the following?

- Slab for a 1 story home, a/c unit in attick, shingled roof (= intended load)
- Slab for a 2 story home, a/c unit in attick, shingled roof (= intended load)
- Slab for the garage and shop w/ no rooms above garage (same as house? can it be thinner?)
- driveway
- walkway between the driveway and front porch
- front porch

Is there a good reference website for me to look all these things up?
I've been reading this one: http://www.concretenetwork.com/

How are minimum thicknesses determined? Is it purely by the load calcs for each type of concrete, or do localities have their own load factors?

Is it common for slabs to have control joints? I didn't see any in my house when it was built (near Houston).

Thanks!

- Dave

[David]

no replies? I'm trying to learn as much of this stuff as I can.

[Rich]

Slab for any basement - 4"
Slab for standard garage - no dump trucks :) - 5" (4" would probably be alright too with rebar @ 18" o.c. each way) with 8" depth across the entry.

Typically control joints are on a 10' grid - at least that's what I like to do.

These are not standards (although if there are standards I'm pretty sure these would be close) - just what I do.

[David]

Thanks Rich!

So no real load calculations are necessary? And 4" - that's all! Even for a 2 story house!? Wow, I would have expected more like 8". I once worked in a concrete test facility for the state gov't. I remember testing those interstate highway cores - some were 18" thick! But that was in the midwest if it matters.

Seems like 5" would be easier than 4" with all that rebar. Setup time could take a while. When using rebar for foundations, do you need to use those cleats (whatever they are called) to hold up the rebar? Do you need to tie every intersection or everyother one?

Who supplies the tension cables? Is it typically a company different than the concrete supplier?

[CThomp]

Slab post-tensioning is done by the company doing the slab. The tension cables are laid, the slab is poured, and then sometime during the drying process the cables are tensioned using a heavy duty hydraulic tensioner.

I'm no expert but aren't isn't the exterior of a slab usually 8" thick as well as in place in the floor plan where a stud wall will be?

[CThomp]

aren't isn't. double redneck negative. Thats awesome.

[David]

Yeah, I believe someone mentioned (or was on the hgtvpro video) the perimeter is thicker than the normal 4", mimicing a footer. I just expected the 4" depth to be more like 8".

I would have expected there to be other thicker parts where walls would be placed, until I saw the way our foundation was poured! They leveled the ground, placed the forms around the perimeter, placed the plumbing, and poured.

[David]

aren't isn't. double redneck negative. Thats awesome.
:shock: :shock:

[CThomp]

Floating slabs are exceptable as well. Especially in parts of the country that don't freeze/thaw on a regular basis. Not sure how thick your average floating slab is though.

[David]

That is what we have here. Floating slabs with tension cables.

When people quote (like on another post ealier here) that local concrete rates were 85 to 110 (or so) per cubic foot, do such quotes typically include labor and setup, or is that strictly for the material w/ labor being extra?

[David]

And how much is reasonable for tension cables? Are they priced per linear foot, are there varying degrees of quality, do they have varying degrees on tension amounts, .... ?

- Dave

[VALENT]

the 85 to 110 quotes were per cubic yard of concrete delivered to the jobsite by the ready mix company. I think down here in Houston you will probably get by for less, though.

[David]

Duh, sorry, I meant cubic yard.
- Does that include labor to pour it and smooth it?
- Around here, do they typically install anchor bolts (name?) for the exterrior walls?

[VALENT]

nope. Well actually I guess it does include pouring it(out of the truck) but the smoothing is handled by your foundation crew. Anchor bolts are very standard.

[David]

What spacing is best for anchor bolts? Are they used only in exterrior walls, or are there cases where it's good to use them for interrior walls?

I've seen a few foundations poured (6 or so) in my neighborhood, and I didn't see any anchor bolts installed. Just a flat (definitely not smooth) surface. Are they cheapening the product, or is there a newer method they may be using? Are they just using concrete nails thru the sill plate?

[CThomp]

Your local code or texas building code will tell you what is required for anchoring the exterior walls to the slab. Much of it is based on what kind of wind zone you're in. I live in a 130mph wind zone. So anchoring and strapping is usually just over killed for good measure.

[David]

We live near Houston, and a hurricane is likely to come ripping thru sometime in the next 30 years, I'd like to make a house that will withstand hurricane winds - as much as possible. I'm inclined to overkill on the anchorbolts. Does strapping play a role if one has a layer of OSB sheathing?

There is a bare foundation up just down the block from me. I'm gonna go check it out tonight and see if they used any anchors. Maybe I should take pictures.

[Cole]

I've seen a few foundations poured (6 or so) in my neighborhood, and I didn't see any anchor bolts installed. Just a flat (definitely not smooth) surface. Are they cheapening the product, or is there a newer method they may be using? Are they just using concrete nails thru the sill plate?

Please dont use them on interior walls. No need too.

Yes they are just trying to save money by not using bolts. I know numerous builders that like them or dislike them. I use them but some builders think it is a waste of time here in Tejas.

Yep concrete nails through the sill plate is the norm.

[CThomp]

If you are wanting the ultimate in hurricane building, look into Florida's 150mph building code. For platform construction on a slab look into Simpson Stron-Tie's Strong Rod Anchoring system. It attaches you top plate all the way down into the slab. It uses anchors that are imbedded in the slab during the pouring process. There are diagrams on SST's web page about this. Its basically a super long hot-dipped galvanized all-thread. I'm sure Texas has its own 150mph building code that may be similiar to Floridas. Have your draftsman/architect draw this into the plans. It will of course add more cost but you'll have piece of mind. Homes built to this standard that were in the path of hurricane Charley survived with only blown out windows. And now all windows in this wind zone are required to be impact windows. These are very very expensive windows

[David]

Please dont use them on interior walls. No need too.

Yes they are just trying to save money by not using bolts. I know numerous builders that like them or dislike them. I use them but some builders think it is a waste of time here in Tejas.

Yep concrete nails through the sill plate is the norm.

Why would it be a waste of time? Because they have never seen a flood or high winds carry a home off of its foundation? Or because they feel that if such event happened, that insurance will foot the bill anyway?

I expect to use them in my next house(s). I don't think concrete nails will hold a house down if a hurricane comes thru. Katrina, Rita, ... should be warning signs to all of us on the west side of the Gulf Coast. I think the rest of the Gulf Coast has been learning for the past few years!

Anchor bolts would at least help keep the house from lifting off in the event of a flood. Granted, the house would be destroyed by flood waters, but I'd rather keep it on the foundation as much as possible, than have it float into other things like homes, trees, etc.

Cole, would you agree that Texas has some of the easiest residential building stardards in the US?

[Cole]

Cole, would you agree that Texas has some of the easiest residential building stardards in the US?


Dave, I agree with that 100%.

You know I have never thought about requiring anchor bolts on interior walls but it doesnt sound like a bad deal, it could be a new selling point for me.

Just make sure you have a good concrete man that knows how to read a tape measure.

[David]

If you are wanting the ultimate in hurricane building, look into Florida's 150mph building code.

I plan researching their building codes for hurricane resistance. I did some research about a year ago. I've had a hard time finding some good summary info, but I haven't looked around recently.

The impact resistant windows would be nice to have, but I'm not sure I can get them in the sizes I want. And the cost would be outrageous to get large, low-e, impact resistant windows!

I'm trying to think of a better way. One idea that I'm toying with is to install some form of nut/bolt system installed during construction, so that in hcane prep, one could bolt plywood over the large windows that are just under 4'x8' in size. Granted, the plywood wouldn't be as strong as the special impact windows, but the cost of doing such windows will probably put them out of consideration.

[David]

You know I have never thought about requiring anchor bolts on interior walls but it doesnt sound like a bad deal, it could be a new selling point for me.It may become more hassle than it's worth, though. I would think that it would slow down the pouring process quite a bit. Anchor bolts are installed during the pour, not during prep/setup, right? Maybe you could swing it, but will it provide a real service to the client?

Just make sure you have a good concrete man that knows how to read a tape measure.
:shock: :shock:
I don't trust too many other people as it is!

[Cole]

It may become more hassle than it's worth, though. I would think that it would slow down the pouring process quite a bit. Anchor bolts are installed during the pour, not during prep/setup, right? Maybe you could swing it, but will it provide a real service to the client?


:shock: :shock:
I don't trust too many other people as it is!

Yeah I think it would be a hassle for interior walls.

[Rich]

A 2 story house does not place anymore weight onto the slab than what is encountered on a patio... until you place a weight bearing column or wall onto it. When that occurs then you will want to thicken that area.
If you are pouring a monolithic slab (slab on grade) then you will thicken the edges (where the weight bearing walls are) to a minimum of 12" IMO.

For anchor bolts - I place them at 32" o.c. during the pour. I figure it takes a guy about 20 seconds to place one at this time... and if they do it afterwards it takes about 5 minutes to hammer drill the hole and then the pull out capacity of the anchor is contingent upon getting the anchor set correctly.

[David]

All we get here is slab on grade, which sucks IMO. Nonetheless, isn't it common for some of the interrior walls be load bearing?

[David]

Rich, I forgot to mention: 32" oc? Holy cow!! And to think many around here use none at all. Quite a difference. I would not have expected to use that many.

For those of you who do use them, what spacing do you use?

[Cole]

32" is the normal, I have seen 48" and 24"

[Rich]

Interior walls do not need to be load bearing at all. I've done homes with 50' rooms and no load bearing walls except at thickened edges.

[David]

Sounds like a whole new thread to me!

[Cole]

Interior walls do not need to be load bearing at all. I've done homes with 50' rooms and no load bearing walls except at thickened edges.

Dave,
Its not like you are going to build a 50 story building.:)

[David]

so no matter how wide and long the house is, only the exterrior walls will bear loads?

[Rich]

I didn't say that either :)
The point I'm trying to make is that you don't have to make a slab thicker just because you make the house taller or bigger. You only need to thicken areas that will bear weight.. i.e. load bearing columns and/or load bearing walls.

[Dragon]

Interior walls do not need to be load bearing at all. I've done homes with 50' rooms and no load bearing walls except at thickened edges.

This is not always the case.

I have done homes that specifically required interior load-bearing foundation points.

Its all in how the house is designed. If the plans call for it, put it in.

[David]

Let's say I design the house with some middle-end software ($500 software), which I plan to do. From there, I go to an architect with those files.

Assuming the house isn't too far out of the norm, can I specify that load bearing walls should be on the outside?

It sounds like it is normal (most commom) for the interrior to have no load bearing walls. Is that fair to say?

[David]

I didn't say that either :)
The point I'm trying to make is that you don't have to make a slab thicker just because you make the house taller or bigger. You only need to thicken areas that will bear weight.. i.e. load bearing columns and/or load bearing walls.

OK. So my original question that was intended to ask more about load calculations.... In essence, load calcs aren't performed for the foundation's sake. Rather, the foundation's thickness is determined by type of foundation, and where the load-bearing walls are placed - usually on the exterrior. And where a load-bearing wall does exist, the foundation should be about 12" thick by rule of thumb.

Do I understand it ok?

[Rich]

This is not always the case.

I have done homes that specifically required interior load-bearing foundation points.

Its all in how the house is designed. If the plans call for it, put it in.

Absolutely Dragon.. that's why this comment was posted


...thicken areas that will bear weight.. i.e. load bearing columns and/or load bearing walls.

[Rich]

d2frette.. foundation wall and footing (pad and strip) sizes are based on actual weight of the structures.. along with the weight bearing capacity of the soil. In general - yes your comments above will get you to the initial design phase with the architect... they can figure it from there.

[David]

OK. Thank you. I'll have more questions later.