Building solid foundations

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Old 02-12-19, 07:59 PM
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Question Building solid foundations

A simple question, perhaps sort of dumb to others: How is the proper way to build a solid foundation for a decent room-size addition, with a 36" crawl space...all the way to the first lumber that is laid in, and exactly how IS the first couple of courses of lumber added. I know there is hardware involved, i. e., lag bolts or similar. I want to build on to a mobile home's master bedroom, including a very nice master bath...NO tub, only a very nice walk in shower w/ smoked glass, but for now, I only want details concerning the foundation, please. Thank you.

P.S. There will have to be a step-down from new addition to old part. Old has about 16" of crawl. That's a REAL BEAR to slide around in for a 60+ year old with a bad back! LOL! Thanks again for any advice or expertise at all.
 
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Old 02-12-19, 08:13 PM
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Here is a brief overview:

It starts with getting permits and submitting a plan. You need to know your frost depth. Then you dig a trench about 36" wide and pour a concrete footing that is about 16" wide and 10" deep with rebar in it, and rebar protruding vertically out of it.... to about 36" above grade. For the foundation walls you can lay 8x8x16 concrete blocks or set up ICF (insulated concrete forms) and pour the foundation walls. If you used cement blocks, you slug the cores that have rebar with concrete... every 4 feet or so vertically. Then place j-bolts in that wet concrete, allowing the threads to stick up about 2 1/2" or so.

After that you can place a sill plate over the bolts and bolt it down... place your floor joists and rim joists... and lay subfloor. Then you are ready to waterproof the foundation add perimeter drainage tile and backfill. Then you are ready to build your walls.

Depending on where you live, you may need ventilation in your crawl space walls. Or it might need to be encapsulated and conditioned. And you will likely want an exterior accesss hole/door.
 
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Old 02-13-19, 06:51 AM
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Thank you very much, XSleeper. This detailed description will be a great start. There are a few terms that I'll have to Google, but that's no problem, and I'll get it right. This is a future plan anyway, so I'll have plenty of time to study concepts, procedures, etc.

One question: How do you support the horizontal rebar that goes into the concrete foundation pour, and do you just stick the vertical rebar in the ground , and level and plumb it? Okay, two questions: Do you take measurements along the foundation perimeter to assure that the vertical rebar goes into the holes of the cinder blocks after all of the rebar is set in the concrete, and are the cement blocks laid in the wet foundation pour, or do you allow that to dry and cure, then just mud the bottom of the cinder blocks, and start leveling/ plumbing then, as the foundation walls are being laid? Thank you very much once again, for the reply. Your expertise and instructions are much appreciated, and will be printed and in my hands when this project has begun.
 
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Old 02-13-19, 07:43 AM
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My inspectors want to see the horizontal rebar wired to rebar holding it in the correct position. That way it can't be forgotten during the pour and the inspectors and inspect the rebar and it's position within the footing.

It is best to measure so your vertical rebar are located to hit the voids of your cmu blocks. The blocks are set in mortar on top of the footer after the footer has cured. When wet the concrete doesn't have the strength to support blocks above so it needs at least a day or more to cure before setting the block. This also allows you more time to insure the blocks are straight and square since you're not working with the short time window when concrete is still wet.
 
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Old 02-13-19, 07:43 AM
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You use rebar chairs. They come in a variety of heights. So for the footing you might use 5" rebar chairs if you needed 3 pieces of rebar centered in a 10" thick footing. More rebar is tied on top of that, perpendicular. Tie wire is used at intersections to fasten it together so it doesn't move. (You generally first need to have a "foundation plan" that has been drawn up by a structural engineer, then you build the foundation to his specifications.)

Rather than trying to describe it all, you might find YouTube helpful. Go there and type in "how to tie rebar" and look for a video that says episode 12. It gives a very nice overview.

Yes, if the vertical rebar is specified in the foundation plan, you would have to measure very carefully and temporarily anchor that rebar (bent 90 degrees and tied to the rest) to a temporary form (to hold it vertical and to prevent it from moving)... then pour the footing first, then remove all the forms, then build the walls. Some inspectors will allow you to drill into the footing after it is poured to place vertical rebar, which simplifies things tremendously.

If you will have any underground utilities... electrical, water, sewer... these need to be run before the footing goes in. (I assume you might be doing that afterward- in your crawl space- since you are tying into an existing home) Footings need to be placed on compacted soil as well so you don't want to overdig the area because then you would be putting the footings on disturbed soil. It's always good to rent a compactor and run it around the excavation prior to building your footing forms.
 
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Old 02-13-19, 08:24 PM
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Thumbs up Re: Foundations

A hundred Thanks to the both of you XSleeper and Pilot Dane for the quick replies, and nicely detailed expert advice. Exactly what I wanted, and was sure I would find it here @ DIY Forums...the BEST forum site on the Web!

BTW, XSleeper, Great Avatar!

 
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