internal external drainage?
Frank D Malczewski
Seems the 'independent' engineer used by my builder has a
seemingly unusual way of running external foundation drainage.
Rather than running it around the exterior of the foundation,
it is being run around the interior of the foundation (along
the foundation walls), above which will be the basement
floor. [The adjacent crawlspace will have no drainage either
internally or externally.] It is highly stressed here in
Colorado that soils can be a problem, and the story we get
(awaiting the arrival of the engineering report at this
point) is that we have wonderful soils, so shouldn't have the
worse(r) case scenarios to deal with. What is typical of
houses in our neighborhood is to not have any vegetation
near the foundation (including grass) -- usually bark(?) or
rocks seem to be used -- and fairly good slopes (and gutter
drains that dump the excess water into a little valley
between adjacent houses) to help draw the moisture away
from the house.
The builder does its best whenever possible to stress that
all foundation considerations are not their responsibility,
and are determined by the engineer after soil analysis for
the lot is done (which raises a red flag for me), but for
the most part it seems somewhat reasonable given the over-
all picture above to think that maybe it is a reasonable
approach. Has anyone ever had any problems with such an
approach? Is this a Colorado thing, or would a different
Colorado soil engineer (out of my pocket) tell me that
this just won't work, and what are those guys trying to
pull? All opinions welcome...
M
As a Building inspector I see this poor attempt frequently. The correct
place for foundation drainage is the exterior of the walls. To get into
the inside drain it must travel thru the wall or under the footing which
washes out the bearing of the wall. The exterior drain can be stone only
all the way around at least a foot thick leading to a pipe under the
footing, leading to a sump pump pit or on a sloping site, a pipe
draining to daylight down the hill. Over the stone you need a silt
screen or here thet sometimes use burlap or a thick layer of straw to
prevent the dirt from clogging the stone and drain.
Don't settle for less! It's cheap now, even if it's extra.
Jim Irvine
M wrote:
>
> As a Building inspector I see this poor attempt frequently. The correct
> place for foundation drainage is the exterior of the walls. To get into
> the inside drain it must travel thru the wall or under the footing which
> washes out the bearing of the wall. The exterior drain can be stone only
> all the way around at least a foot thick leading to a pipe under the
> footing, leading to a sump pump pit or on a sloping site, a pipe
> draining to daylight down the hill. Over the stone you need a silt
> screen or here thet sometimes use burlap or a thick layer of straw to
> prevent the dirt from clogging the stone and drain.
This is not necessarily true. We have been installing interior drains for
many years depending upon the soil conditions that work flawlessly. Two
techniques are used for homes without a gravity fall to daylight situation.
1- Run the interior drain tile under 4-6" of stone to the sump pit. Every
8' run a 2" pvc pipe over the top of the footing to the exterior with about
2' of stone surrounding the inlet on the exterior. (one technique is to
fill burlap bags with 3/4' stone and lay them over the pipe ends to act as
the dirt filter) This system requires that about 2 to 3 inches of stone be
placed on top of the footing to prevent the poured slab from clogging the
pipes, which are actually weep holes.
2- Use the above system, however, if the foundation is a block wall,
include notch type weep holes in each block on the interior only, to allow
any water that may reach to cores to drain under the slab to the drain
tile.
An interior drainage system must allow for the build up of hydrostatic
pressure that can develop on the exterior of the foundation and this is
precisely what the engineer is retained for when designing such systems.
> >
> > Seems the 'independent' engineer used by my builder has a
> > seemingly unusual way of running external foundation drainage.
> > Rather than running it around the exterior of the foundation,
> > it is being run around the interior of the foundation (along
> > the foundation walls), above which will be the basement
> > floor. [The adjacent crawlspace will have no drainage either
> > internally or externally.] It is highly stressed here in
> > Colorado that soils can be a problem, and the story we get
> > (awaiting the arrival of the engineering report at this
> > point) is that we have wonderful soils, so shouldn't have the
> > worse(r) case scenarios to deal with. What is typical of
> > houses in our neighborhood is to not have any vegetation
> > near the foundation (including grass) -- usually bark(?) or
> > rocks seem to be used -- and fairly good slopes (and gutter
> > drains that dump the excess water into a little valley
> > between adjacent houses) to help draw the moisture away
> > from the house.
--
____________________________________________________________________
Jim Irvine |
James R. Irvine Construction Inc|
jrir...@fred.net |
http://www.fred.net/jrirvine |
hi...@millcomm.com
Common practice around here is to run an exterior loop and an interior one
and connect them every 8-16 feet. This is apparently what the inspectors
like to see here.
Dan Hicks
Hey!! My advice is free -- take it for what it's worth!
http://www.millcomm.com/~danhicks
Frank D Malczewski
No so grandiose approaches here. Basically to summarize the
state of our foundation, for those who tuned in late:
The foundation was dug in error with the expectation of a full
basement going to be built. Well, no, it was supposed to only
be a standard basement, with a crawlspace area. So, the
builder went ahead and made all the foundation walls, including
the crawlspace, of equal height. They were rather in a hurry
to do this, so really didn't get a chance to work something
(realistic) out with them to get the full basement (and we
really didn't want to pay much more than we are already paying
for at this point).
Part 2 is the detailing: the black sealant was sprayed all
around the foundation (external walls only). Water was brought
through the foundation, as was a sewer run. The window
well was put into place (no drainage for it). The foundation
was backfilled all around. A sump pump pit has been added,
and the internal drainage system (pipe run along the four
walls of the foundation) put into place in the basement (no
drainage put into place in the crawlspace), leading into the
sump pit. This drainage is surrounded by largish rocks and
a black plastic cover place on top of that. Also, normal
drainage to the sewer has been put into place. Finally,
additional dirt has been put into place to level the floor,
and the basement floor is about to be poured (it appears).
Remaining to be done is for them to fill the crawlspace back
up (at least that was the early plan -- kind of surprised
that this has not been done yet). The goal tomorrow is
to either convince them to not fill in the crawlspace or
to at least put the black sealant onto all four of the
crawlspace walls before they do put the dirt back in.
And, the soil report should be ready pretty soon now.
Everything else looks pretty hunky-dory, but then they haven't
gone much beyond the foundation at this point (got a nice
garage floor and driveway...)