Tim,
I'm adding a 9x13 foot extension to my home built in 1950 on a concrete
block foundation in Atlanta, GA. I plan to use the same style foundation
for the addition. Must the concrete blocks lay on top of a poured cement
footing? If not, how should the blocks be connected horizontally?
Mali
Residential Foundations Tips
Summary: If you want a strong residential
foundation, make sure you follow the tips below. Use reinforcing steel, don't
backfill too soon and leave poured concrete forms in place a couple days after
pouring concrete.
Related Articles: Illustrated Concrete & Concrete Block Publications, Poured Concrete & Concrete Block Walls, Poured Concrete Walls vs. Concrete Block
Tips on Residential Foundations
Give serious consideration to installing vertical reinforcing rods in your foundations. Most building codes insist that you install horizontal steel bars near the top and bottom of your walls. However, virtually no code (except earthquake areas) requires the placement of vertical steel. In the event that your foundation cracks, I guarantee that it will cost you many times more money to repair the crack than to have installed the steel in the first place.
NEVER backfill a foundation until both the basement slab and the first floor subfloor assembly are in place. These two elements are critical. They are the top and bottom of the "box."
Wait as long as possible to backfill. Concrete or concrete blocks develop strength over time. In fact,under ideal conditions, they often achieve only 75% of their design strength after 28 days!
Negotiate with your builder or foundation contractor to leave forms in place for three to four days if possible. Removing forms the day after the pour subjects the fresh concrete to rapid moisture loss. The concrete needs water for it to gain its maximum strength. During hot or windy weather, consider applying a curing compound to the walls immediately as the forms are removed.
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Comments:
Mali 22 Feb 2008, 23:07
AsktheBuilder 01 Mar 2008, 07:30
Mali,
Yes, you need a footing. Yo install 3/8-inch steel dowels into the old foundation at the top of every other course. Arrange for a call if you need more help.
Dale Alsum 20 Jun 2008, 10:57
Where can I learn more about a reverse brick ledge foundation design?
Raki 25 Jul 2008, 14:56
I have a 4 year old two storey home in New Jersey. It has a basement. It
has hollow concrete blocks for foundation wall. Builder did not provide an
exterior perimeter drain. Water is entering basement during heavy rains.
Builder has been asked by Code officials to install an internal perimeter
drain by cutting the basement slab around and providing drain pipe and sump
pits. Question is as to whether it is safe to cut open the floor slab all
around? What is the proper way of doing the job? Can this be done in stages
so that the slab is not cut open all around all at one time?
Raki
Santa Fe, NM 01 Mar 2009, 18:45
Our current structure's foundation is pier and beam; must/should we stay
with that if we add on?
Martin 25 Aug 2009, 13:34
Hi Tim,
My property was recently excavated and since the day after it was excavated it has rained every week since. I live in north east PA. The soil is mostly clay and I have the foundation already set up with drain tile so very little water is left in the foundation area however, the clay soil in areas at the corners are wet and a bit mushy. When it finally dries it will be rock hard and I when I finally backfill I won't worry about it getting wet again. My question to you is I want to start the footer forms, pour the concrete and then start the block foundation but with some areas mushy how do I go about pouring the footers to make sure that the foundation will be strong. I have looked at every article on your site and can not find anything close. I had one person tell me that I can add clean stone and compact that and then install the forms and concrete over that. I have been told however that you must put the footers on undisturbed soil. If you can help me I would greatly appreciate it. Thank you for your time and all of the great information on your web site View all comments |
