How to tie Blocks to Footer


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Old 11-12-05, 08:26 AM
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How to tie Blocks to Footer

I plan on laying 2 layers of 6x8x16" hollow block down on my footer, filling the cavities with concrate, and putting a 2x6 pressure treat sill plate on that and building from there. My house is in a 105mph hurricane zone, so I'm going to use simpson hurricane straps to tie the sill to the concrete block (183lbs uplift/16" @ 110mph, slightly less for 105) but I wasn't sure how to tie the blocks to the footer. As the concrete-filled blocks weigh 150plf, they'll more than anchor the uplift, so I don't technically need to transfer any uplift load to the footer, but I'd still think I need more to hold the blocks to the footer than mortar- what do I need to do? Thanks!
 
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Old 11-12-05, 12:01 PM
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How to tie Blocks to Footer

You definitely need to anchor directly to the foundation.

You are grossly over estimating the weight of the block and how much of the weight you can actually count on. Almost all of the block made in the Tidewater area are lightweight units with a maximum density of 105 pcf. When I was in the area the usual density was about 95 pcf, although some were under 90 pcf. The densities are the density of the concrete itself.

The 6" blocks made in Chesapeake have a maximum weight of about 30 pounds and may be as low as 22 pounds. Even filled with concrete you, will come up with less than your numbers. To utilize the weight even then you would have to put the anchors into the block at 16" on center unless you add a bond beam with steel.

The proper way is to anchor directly into the foundation with a anchor bolt and forget about the gimmick hardware. The ties straps are a minimal connection are based on a wall with significantly more mass and rigidity the two courses of 6" block. Remember - the code is a minimum and is not necessariily what you should do.

Anchorage is very easy if you do it when you begin. If you are just getting to it now, I would drill holes and epoxy bolts in.

Since you are now looking at the anchorage to resist uplift, you better look at shear anchorage also. Even the Chesapeake code office would catch this. I always found them very capable.

Make sure you do use the block to keep the wood well above the ground level. Much of Cheapeake is not too dry and the climate can be tough on wood.

Dick
 
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Old 11-12-05, 06:38 PM
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Thanks for the feedback!

Shear was one of my concerns for wanting to tie the blocks down, which is why I asked. I have some real concerns with my shearwalls too I want to run past the code office; I'm more concerned with doing it right than I am skirting the codes! As to the ties, we haven't broken ground yet, so all options are open. What sort of tie bolt is required, 1/2"? Should I size them so it will extend the whole way from the sill plate into the foundation? IRC is pretty clear on the spacing of them- 12" max from the end of sill plates, etc; I was intending to put them every other block or thereabouts, well within code for spacing. It just seemed like a real PITA to have to precisely place the anchors in the footer so that it would fit perfectly through holes in the blocks and miss the studs and all, and I thought there might be an easier way. I mean, 183lbs is not a lot of uplift, that's what, a typical drywall screw? The weakest strap in the simpson catalog was rated for 500+.

Edit: Found the paragraph, R403.1.6, 1/2" bolt sunk at least 7" deep, that answers my question! So, I'll need at least 25" 0.50 L-bolts I suppose, and a lot of 'em! Time to change the 3D model, heh, I'm showing simpson MAB23s everywhere now.
 

Last edited by grover; 11-12-05 at 06:55 PM.
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Old 11-12-05, 07:28 PM
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How to tie Blocks to Footer

I haven't had a chance to look at my IRC, but my gut tells me that a 1/2" anchor bolt carries more load than a Simpson tie. That means you should be able to spread them out quite a bit. I will have to look at the code for the allowable on a 1/2" anchor bolt. Your designer could also give you some help.
I think the Cheaseake code office could also give you some help on the standard practice. You are right - you really do not have much uplift, but you do have shear.

I did not pay particulat attention to the anchor bolts on my Chesapeake house (Riverwalk - west of Battlefield Boulevard) when I was crawling around underneath. They appeared to be about the same as the anchor bolts on a midwestern house (tornados) with a basement (anchor bolts at 6' or so)

I would embed the bolts in the concrete and have them long enough to pass through the block and the plate. If you have a lot of shear, you may have to fill a few block cores at the bolts. Layout is not a problem if you keep them in modules of 16" (same as studs). Just layout the first one to a good location missing the first stud off a corner and the rest will miss the remaining studs. Put the nuts on the top of the bolts, chalk the tops, and set your plate on the bolts tops to mark it. If a bolt is a little low, you can still get a mark by raising the nut or mark with a pencil. Flip over and drill.

Dick
 
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Old 11-13-05, 08:22 AM
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I'm having trouble finding 1/2" anchor bolts- the longest I'm seeing is 18" which is about 7" short, and so would only be embedded inside the block and not extend into the footer. I have seen 3/4" bolts long enough, though. Are larger anchor bolts required because of the block? I assum that 1/2" anchor bolts with the blocks backfilled with concrete would be good. What's standard practice when using two rows of starter blocks? My other option is to do a slab-on-grade which would only need one course of blocks but I'm worried about the contractor's ability to get everything perfect in a single pour. What are the pros-and-cons there?

I'm really only using the start blocks because I need to get 12" above grade to start the wood (for rot and termites) and 2 layers of block seemed the easiest way. I'm open to suggestions- I plan on contracting the slab & footer out so the contractor will hopefully know what they're doing and take care of everything (I fully expect to change my plans completely once I talk to them) but the engineer in me wants to have all the bolt locations, ground pressures and everything else bulls-eyed up front so I don't have to go back and try to retrofit later.

Rendering of my foundation thus far:
http://img453.imageshack.us/my.php?image=foundation2hw.png

Speaking of which, doityourself.com's store has 18" anchor bolts in packs of 50 for for $.14 apiece which seems awfully damned cheap, is that price accurate? That's a third the price of rebar!
 

Last edited by grover; 11-13-05 at 08:34 AM.
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Old 11-13-05, 12:52 PM
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How to tie Blocks to Footer

I was not able to see your foundation posting - I will try again later. Are you concerned with the complete house or just a portion such as a garage or family room?

Do you have a designer or are you trying to do your own design and then trying to modify it to the code, local standards and materials as you go?

You really do not have high enough loads to try to re-engineer what already has been done many times before.

When you are worrying about the .14 price of anchor bolts and the details that others do every day you are not making the most of your time. If you want to build a house yourself, you should have a professional tell you what to do to make it fit the local codes, techniques and materials. Then you can spend your time doing it the best, easiest, fastest and most economical way.

You already recognized you will have to re-do your design after you talk to the contractors.

DIY designers frequently have big problems in the end.

My home in Chesapeake was two story on interior concrete block piers with a continous block and/or brick exterior foundation wall. The garage was built on continous block stem foundation wall with a floating slab. - Very simple and done everywhere in The Tidewater area. The house was high enough above the required water level and I think the garage was 2 or 3 steps down and was below the required elevation. The stick garage walls were 12" above outside grade.

You have many choices and combinations - slab with thickened edges, stem walls with a floating slab, continuous stem walls with interior piers, etc. You could lay a course of block on top of a thickened edge to get the 12" you desire - there are many combinations and choices depending on the site and floor plan.

I wouldn't worry about the contractor's ability to do everything perfect according to your plans - I would worry about getting a good contracor to build to a conventional local design. If you want to reinvent someting, you will pay more in the end and be responsible for things you are not familiar with.

Dick
 
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Old 11-13-05, 04:30 PM
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"The garage was built on continous block stem foundation wall with a floating slab. - Very simple and done everywhere in The Tidewater area."
This is how our house is constructed, how I was recommended, and what I intended. It's just the details I'm a little fuzzy on!

This is a foundation for a 2000 square foot addition to our 1600 square foot house- will be roughly 40x28 and two-stories, with a garage taking up half of the 1st floor, and a kitchen, dining room, bathroom, 3 bedrooms and a balcony rounding it out. I'm doing 100% of the design myself and with the exception of the excavation and concrete work, my wife and I indended to do everything ourselves. I'm an electromechanical engineer (should have my PE within a year, too, if all goes well) so in theory I'm qualified to, if not stamp the design yet, at least recognize my limitations and regurgitate code. But I'm really just enjoying the whole process! People might call me crazy, but I read through the IRC cover-to-cover and annotated it, and actually *enjoyed* it! I'm looking forward to the work, too, I really do enjoy a challenge Well, except for the drywalling but that's my wife's forget- my wife and I complement each other very well in our talents which has turned out many an excellent project over the year.

Plus, this gives me an excuse to buy new tools, like am impact hammer, better table saw and laser-guided chop saw

As to the 14 cent thing, we're way over budget as it is- what was supposed to be a $20k addition has snowballed into a $70k addition and I'll need 85 of them, which is not much at 14 cents but a lot at $2 apiece, and $40 saved is $40 saved regardless of where it came from.
 
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Old 11-13-05, 07:17 PM
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How to tie Blocks to Footer

I would ask for a recommendation from the local code office on the preferred method of anchorage. Since the big box sells only 18", they probably are the most common used size and do comply with local requirements.

You are completely correct that you are qualified to regurgitate the code requirements. Unfortunately, if and when you become a P.E., you still will not be permitted to properly sign an engineering document outside your area of expertise, which is dictated by your education and experience. That is what I learned from the stanards of practice as I went through the registration process and for 30 years after.

We write codes and standards keeping in mind they are frequently regurgitated. This makes the codes appear to be an overly complicated document for a minimum standard of construction. The situation is one of the reasons that people must be qualified to interpret and apply the codes and to approve applications.

You are not wrong strictly following the code, but you may not be right.

Dick
 
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Old 11-14-05, 02:09 PM
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Well, I've got approved health dept and zoning plans now, that's a start!

I talked to the city today about the structural design and they dropped a bomb on me- A new FEMA regulation prohibits finished floors below 9'-6" above sea level. My house was built to the old 8'-5" code and the existing slab is 8'-9", 9" short! On top of that, the adjacent room to the addition only has 7'-4" cielings, so I'm screwed. I'm going to have a measly 6'-7" opening unless I do significant structural rework on our existing house to raise the ceiling...

Footers in my area only have to be 12" down to the bottom and 8" thick, which matches the existing house. Which is simpler than I expected, I thought they had to be 24" deep! As to tying the blocks into the footer, he recommended #4 rebar bent in an L every 48" OC , with 10" of L sitting 3" from the bottom of the footer. Then I can just grout those cavities and sink a standard 18" anchor bolt (coinciding with the rebar) in the block. And that suffices for the standard walls. For the shear walls, we both pored through the codes trying to come up with a solution- He recommended to me a reinforced stem wall where I have a solid concrete cap on top with #4 rebar Ls (Cs?) tying the concrete cap directly to the footer, and I could sink 5/8" anchors in that, secured with 2" washers, and 7/16" ply both sides of the shear walls. (Will be fun to rough in the light switch, lol...) And this is for 100mph; he was telling me about some of the codes in florida and it's unreal what they have to do down there!

He identified some gable problems related to my vaulted scissor-truss ceiling I hadn't even considered that caught me offguard that I'll have to address, too. So now I gotta find a source for 24' 2X6s!
 

Last edited by grover; 11-14-05 at 02:25 PM.
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Old 11-14-05, 08:18 PM
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How to tie Blocks to Footer

Glad to see you are getting some building department help on the local applications of the code.

If he makes suggestions to help you, he certainly won't reject anything and an inspector wouldn't go against him.

On your shear wall, you mentioned "L"s or "C"s. Usually it is easier to use 2 "L"s and lap the vertical portions to make it easier to build the wall. You just insert the top "L" after you have laid the wall. Then lay the #4 in a bond beam block. Frequently, a bond beam block is uesed on the top for an easier and more positive method attachment in place of a poured concrete cap. It eliminates forming and gives a uniform appearance if exposed. The old Florida method of using a poured concrete bond beam on the top of a wall instead of a block bond beam is archaic and not used anywhere else in the world to my knowledge.

If you were in the critical areas of Florida, you probably would not have wood exterior walls because of the newer hurricane standards for projectiles. It seems a wood wall will not resist a 12' 2x4 fired out of an air cannon at 120 mph. Zero penetration is permitted. Lesser caliber of projectile for windows. The guys in the southern tornado belt think they have the best lab job in the world shooting their air cannons at walls and windows.

Good luck

Dick
 
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Old 11-15-05, 02:31 AM
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It seems I misunderstood him; he did specify "bond beam" (a term I wasn't familiar with) and talked about pouring concrete and the # of bars I needed, and I assumed that was just the technical term for a concrete cap which is why I called it a cap in my post- I see from a google image search that there are other methods too. What exactly makes it a bond beam, the steel reinforcements? He wanted me to grout all cavities in the shear walls beneat the bond beam.

I had joked with the city guy that I thought wood construction .period. was illegal in Florida after Andrew! According to him, southern florida (140-150mph zones) requires all wood construction to meet the same impact tests that solid masonry concrete block walls do. And that to design the criteria for those tests, they started shooting 2x4s at block walls to see at what speed they started penetrating, and it was about 32-35mph. And so, that's what the design is for- it's required to be sheathed in 3/4" ply covered in metal lathe and stucco and even the little cripple studs under windows have to have hurricane straps, as simple 2x16d installed studs blow out when hit with a 2x4. Sheesh, and I thought *I* have wind loading problems!
 
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Old 11-15-05, 01:01 PM
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How to tie Blocks to Footer

A bond beam makes more sense than a lot of extra pieces that you have to hold together later. Build the little shear wall from normal concrete block.

For the top course, use what is called an "open bottom" or "pour through" bond beam block - It looks like a regular block with the cross webs reduced in height to permit laying a piece of horizontal steel (usually #4) to tie the entire wall together and provide a solid bearing surface for the wood walls that may blow away. An alternate is to knock out the top of the cross webs down a couple of inches. You may have to do this since the Tidewater area does not offer the variety of block available in othe areas. From a structural standpoint, it is not necessary to fill all the cores, but it is easier, not detrimental and usually cheaper and stronger.

The hurricane situation is more severe for structures than the U.S. construction industry recognizes. Unfortunately, mis-directed traditions lead to disasters in housing like the recent hurricanes and the demolition/rebuilding problems. Some areas rebound quicker from disaters than other because of material usage. That is just a reflection of the use of wood for residential constuction in the U.S. compared to the rest of the advanced world. Internationally, usually wood is thought of low quality construction.

Dick
 
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Old 11-18-05, 12:54 PM
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Oh, this is good..

You guys are killin' me. I'm a couple of hundred yards west of the Intracoastal Waterway in the heart of S. FL. Here is how my 2 car attached garage is being built. Drive 5 4" pin piles down to resistance to support 20Ton load each. One of these went to 40 feet. Compacted and termite treated soil to 95+%. 8" by 24" below grade footers with 4 horiz. #5's around the perimeter, also one of these grade beams down the center (interior) of the garage. Vertical #5 every 4'. #5 rebar crossed and tied at 10" centers for the slab. 400 sq ft of that. What you here seem to be calling the cap contained 4 more #5 horiz rebars with hoops every couple of feet. Formed and poured. The slab ended up at 8" thick. It took three truck loads of concrete for my 20 by 20 garage.

Did I read correctly; you build a decent foundation up there, and then expect the house of sticks to blow off in a big wind??
 
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Old 11-18-05, 01:20 PM
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How to tie Blocks to Footer

I am trying to help someone build aa addition according to the code standards for his area. The code is a minimum, not necessarily the right way to do.

Virginia is not Florida and the requirements are different because of the conditions. Your requirements are more severe because of the proximity to the coast and the history of storms. If you take a look at a map, you would understand why the requirements in Virginia are different.

His foundation is lighter than yours because of the requirements. His footings are about the same as yours. You have hoops(properly called stirrups), while his code official suggested L or C shapes rebar, which makes more sense for masonry. Your need for the piles is due to the soil conditions, since they are not very effective in wet sand during a hurricane. With so few piles widely spaced it is not surprising you have a beefier foundation to distribute the loads. Don't let anybody fool you about 95% compaction (even if it the Modified Proctor) since that is quite easy to obtain with any reasonable soil in Florida.

I agree with the comment about a stick built house, but that is personal preference for a different climate. I hope you had enough sense to build out of masonry in your area. Even though Florida has low-tech masonry, the value of permanent construction is valued more than in other disaster areas such a the Gulf coast.

Dick
 
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Old 11-18-05, 02:48 PM
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point taken

OK, my garage MIGHT be overbuilt, albeit low tech. But then, we are due for a cat 3 to 5 hurricane some day. We are all a bit shell shocked down here. I just noticed that we are in the path of a tropical storm this weekend, unbelievable.
Yes, all CBS. It's the bugs, also...Boring ants, termites, even nesting ants making a mess in wood construction. Nothing dies in the winter.

cheers.
 
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Old 11-24-05, 06:52 AM
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Ya know, at first I was cursing some of these wind load requirements, but after hearing about all the ridiculous stresses in the 140/150mph zones in southern florida, it makes me SO glad I live in Virginia!
 
 

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