"Robert Allison" wrote in message
news:nZAhi.258$bO2.83@trnddc05...
headware wrote:
On Jun 25, 7:18 pm, "aemeijers" wrote:

"headware" wrote in message

groups.com... I'm
planning on pouring a concrete patio up against my house in the

back yard. A friend of mine has suggested that I drill holes into the
side of the house foundation and plug rebar into them so when the
patio is poured it will be "attached" to the house slab via the rebar.
He says this is necessary to prevent the patio slab from sliding away
from the house after it begins settling. I'm a total novice, but none
of the books I've seen have mentioned this issue. Is he making up
problems or is this something I should take seriously?

Oh, hell no. If the patio frost heaves, it'll crack the foundation.
Horizontal movement isn't the problem- up and down movement is. 2nd big
problem, especially if patio does frost heave, is water on patio ponding
near house, draining in the crack where it meets foundation, and flooding
basement. (I have a small dose of that here, with an abandoned patio
buried
under a 18" tall deck. No way to fix without tearing out deck.)

So, you want patio to have the classic 1/4" per foot slope away from
house,
you want yard past that to keep sloping, you want good flashing on house
side where it meets the patio (and never pour concrete so it buries the
siding), and maybe just for laughs a drain tile on house side of patio,
going to daylight or a collector box. A good roof overhang or awning
helps,
too. Patio itself needs footings, either traditional or a monolithic pour
based on shape of the hole and the fabric and rebar. Any good concrete
flatwork company will understand, and do what is appropriate for local
climate and soil conditions.

aem sends....


So it sounds like this might be a really bad thing to do. I live in
Austin, TX where we do occasionally have pretty serious (but brief)
freezes, but I don't know how much they affect the soil.

My yard is on a slight slope with the back (where the patio is going)
being higher than the front. I am planning on sloping the patio away
from the house with the end running into a dry creek bed that will
serve as drainage.

I guess I'll just have to see what the building inspector has to say
about it.

Thanks for all the help.

Dave


Hey, if you are here in Central Texas, you should pay attention to this.
I have only done 50 or so new slabs against old slabs, but they have all
been engineered. In every instance, the engineer specified dowels into
existing concrete, spacing, etc. I always do this here as I have had to
remove 3 slabs (not mine) that have move away from the old foundation
enough that it caused problems.

I know that many of the people in here are against dowels and some are
against rebar at all. I have been working in this area for about 30 years
and I have never seen anything but 2nd story patio slabs (lightweight
concrete, 2" thick) poured without rebar. And I have never seen a slab
connection that did not have dowels.

I have never had an engineer that is familiar with the soils in this area
spec anything but dowels and rebar for new against existing. The soils in
this area demand it.

Okay, backpedal time for me- I slid right over where OP said 'slab' in his
original post, nor did I know he was in Texas with their notorious funny
soils and moisture control problems. What I said is true for 'up north'
basement/crawl construction with block or poured walls, and frostlines that
are actually below ground leverl. Slabs on clay, especially pretensioned
ones, are pretty much outside my realm of experience. If the house is built
on an itty-bitty runway, as it were, that is probably a whole different
section of the how-to book, and one I haven't read.

aem sends...