cinder block v. poured foundation?


  #1  
Old 11-16-05, 10:50 AM
gaylenb
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Question cinder block v. poured foundation?

I am planning a small (24x32) one story home constructed in a zone that is earthquake prone. The water table is about 7 feet. Foundation depth (footers) at 30 inches. Are there disadvantages in using cinder block for the foundation? Should it be fortified by re-bar or filled?
 
  #2  
Old 11-16-05, 05:32 PM
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cinder block v. poured foundation?

Where are you located.

Cinder block are not made in the U.S. or most countries. That is the name for an old product made from waste materials.

Modern concrete block are well suited to all construction in seismic areas. In general, they may be reinforced and partially grouted or they be left empty depending on the loads.

According to most codes the amount of steel is the same for either block or poured concrete. If you use thicker block walls, steel may be eliminted, reducing the cost. Poured concrete does not have this cost advantage. I would recommend some steel in a basement in a seismic area.

In some areas, all the cores of the block are filled. This is just like having a poured wall without the time and labor of forming the wall, removing the forms and disposing of the forms.

A poured basement is more prone to shrinkage cracks since the concrete shrinks a great deal as it cures. Concrete block are already cured, so this shrinkage does not occur after the wall is up.

With a 7' water table, any basement should have some drain tile to help prevent leakage.

Dick
 
  #3  
Old 11-17-05, 08:19 AM
gaylenb
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I'm in Idaho. My mistake, further reseach informed me "cinder" is a thing of the past. My problem is it will cost $300 per trip delivery charge for about 12 Cu yds of cement to do this project if it is poured. Problably two truck loads travelling 200 miles round trip. If I use blocks I think I can mix the cement on site. If I understand the last response I should put rebar every 16" and fill all holes with concret. Should I use metal lathe horizontally. My biggest concern is cracking. Do I make some sort of expansion joint to prevent cracking? The advantage in using blocks is I dont have to build the forms, or pay the delivery costs. Although I can use the forms for floor sheathing afterward. Also; Any idea how to measure the quantity of cement needed to fill the blocks. There's got to be a forumula out there somewhere?
 
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Old 11-17-05, 07:32 PM
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cinder block v. poured foundation?

I would check with you local building office to determine what thickness of wall and how much reinforcement is required in your area. 16" on center is over-kill. Often, local conditions can over-ride any national standards when seismic factors, wind and snow are concerned - especially in western states.

It is usually not required that all the cores be filled with grout - only those with steel. Normally, there is nothing wrong with filling all cores, but there are a few exceptions.

The "metal lathe" you refered to is joint reinforcement. It is used for crack control in longer masonry walls above grade. It is normally not used in basements. It has some benefits for seismic resistance. As you know, if you have earthquakes, you can have cracks no matter what you do.

Seismic requirements are similar to other disaster realted events, such as flood and fire. First, they are implemented from a "life safety" standpoint to allow people to escape without loss of life. They are not a guarantee that a building will be salvagable after a earthquake of design magnitude.

Dick
 
  #5  
Old 11-18-05, 05:30 PM
B
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What is the cost to have the block delivered?
What is you time worth?

$300/truck sounds like a lot but is only an extra $50/yd.
 
 

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