I started to build a dormer recently, its 235 sq m.
I observed the foundations being poured and about 36-40 metres of
concrete went into it.
The trenches are very wide in places because the foundations were dug
more than once (don't ask!).
I meaured the depth in a few places and which varied from over 3000 mm
in places to 2500 mm in others but worringly as low as 1750 mm on an
external wall corner. Steel mesh has gone in also. The ground is
without doubt solid and excellent and has been inspected by an
engineer. The foundations contain a number of steps.
Should I be concerned? It is obvious that this is well below the
official spec so I was a bit worried on seeing it. Have people seen
houses built to this spec which survived long term? Can mesh and width
compensate for shallowness? BTW there will be concrete slab floors
What was the "official spec"? This is almost 6-ft depth at the minimum
which would be well below frost-line at most any place. If the ground
was undisturbed and solid and seen and the excavation was inspected and
approved by an engineer it would seem adequate.
But, that's just a guess based only on the depth and your description
and a generality about frost depths; it would require far more to make
anything sort of realistic assessment.
Why not ask the architect/engineer/inspector?
Well, one would assume he would have observed the depth and compared to
the spec and that the concrete would then be at the bottom of the
trench. :) Consequently, if he approved the trench for pouring, it
would seem as though the depth was considered adequate.
You quoted a "minimum" of 1750 in your original post which is nearly
three times the depth of the minimum "below grade" spec and over 4X the
actual required concrete. W/O seeing it, surely sounds as though it
well exceeds the design.
You lost me now...if the trench was deep enough relative to the
finished grade level, then unless the grade of the finished pour is
wrong, there should be adequate material in the pour. But if the top
of the foundation isn't the right height, nothing will work in
constructing the structure on top correctly. I can't see a competent
engineer doing an inspection before the pour letting that go by, nor
should have the jurisdiction inspector after the pour.
Can you describe more precisely the geometry of the situation? If
there is really only 6" of foundation at one area, that would seem
quite shallow and I'm having a hard time figuring out how it could meet
the requirement. Seems like it would have to have been dug into a
hillside and the depth measured from the original ground level not the
finished grade. If so, then that would seem to indicate the inspection
wasn't up to par.
I think you need to talk to them about the situation directly and ask
the question straight out and get an explanation of why it is adequate.
Here, if you have an actual spec and can point out a deficiency to the
City Engineer, he has the authority to halt construction until the
defect is remedied or otherwise cleared by reanalysis/review as not a
serious deficiency. If you have a formal contract, it should also
provide you recourse that substandard work be corrected. I don't know
what rules apply in your area, obviously.
The house is built into a hill. The trenches at the front are about 17
inches deep whereas at the back they are much deeper. Like I said the
front trench looks about 7 /8 inches short of the top. There is no
jurisdiction inspector. The only inspection that has been done was of
the trench before the pour. The responsibility for anything going wrong
after that is with the builder.
Makes no sense to me...who/what was the "engineer" that did the
previous inspection and how come he has no responsibility to see that
the resulting pour would be adequate? As noted before, what was he
inspecting if it did not include the height of the finished foundation
in relationship to the bottom of the trench and the finished grade?
Who wrote the "specification" and in what document is it contained?
What are the provisions for ensuring it? If the builder has the
responsibility for "anything going wrong", then it would seem that all
you need to do is point out there is an apparent problem. (But, I
doubt a contract reads that way in actual wording.)
With whom do you have a contract and what does the contract say about
resolving any dispute or question? (Which, of course, raises the
question of did you have any legal counsel for review of the terms of
the contract(s) before you signed them?)
Is there a lending institution involved? Undoubtedly they would be
interested in knowing of any substandard construction and possibly
could be of help in ensuring any defect were corrected before doing so
became any _more_ expensive. Also, you'll need to work out any
arrangements w/ them if you have any intent of using payment to require
resolution before going on.
End the end, I ask again as you haven't responded to the question of --
Have you asked the builder directly the question of your concern? What
does he say? And the engineer/architect/whoever you got the plans
from/whoever else has been involved...
Do you have building permit, if required? Are you trying to do this
avoiding getting one where it may have been optional? Did you not find
out whether one was required and "just go ahead" as someone suggested
in a totally separate thread recently? So many questions, so few
I don't think anybody here (me included) can help any further. You've
got to get busy and take the bit in your teeth and pursue this or just
sit back and let things take their course and hope for the best...
Thanks for your patience. You have some good suggestions.
To respond to some of the questions.
The builder when approached about this denied there was any problem
He also said that if we didn't trust him there was no point in he being
The engineer was also unapproachable on the matter and reiterated his
confidence in the foundations despite not having inspected the pour.
The same engineer wrote the spec and yes we DO have a building permit.
We simply want to get a feeling for how shallow foundations can be as
we really would prefer to take our chances and let things take their
course. The prospect of a redig is truly offputting. Problem is I dont
know if we're being neglifient in ignoring foundations which on some
walls are only 7-8 inches deep. Got any gut feeling on this? Remember
the ground was very good and steel mesh was used
Impossible to say w/o much more information than is available. Would
need basically enough information to do an independent
analysis/evaluation of the design and site. Specifically, amongst a
myriad of other details, is no indication of the loadings expected to
be borne by the foundation and no real data on the ground or climate.
Also you have indicated the depth varies drastically from one location
to another so part of what might an alleviating factor would be if this
particular section is very short in relation to all the rest. Still is
a puzzle to my why, given the amount of excavation that must have gone
on otherwise this is so shallow. I also wonder if the structure is
built into the hillside and thus apparently the foundation is below
grade, is that factored into the design for the rest of the structure?
All in all, my "gut feel" would be that 8" of concrete would be
adequate to support a single-story residence, but would still have some
trepidation on possible frost heave and so on if there were a
significant section above a frost line of the finished elevation.
There's another of those key elements that is unknown here -- if it is
indeed going to be 5-6 ft or so below finished grade, it undoubtedly
will be stable from frost, etc., and the only question is whether it is
strong enough. But again, w/o more information than possible to know
here, can't really even guess for your particular situation.
As for the builder, the "don't trust me?" ploy is a favorite of many to
cow a client. It isn't a question of "trusting" or not, it's whether
the job is up to snuff. Question is, how does he answer the question
to demonstrate the work as performed meets the engineer's
specifications to which he is supposed to be conforming?
As for the engineer, was this a one-time purchase of a set of plans or
is he part of the project on a continuing basis? If the latter, I'd
provide a written letter and photographs w/ measurements of the
questionable areas and ask for written confirmation/approval of
adequacy. Actually, I'd do the same even if not, and see what
happened. I would also strongly consider finding another opinion
before proceding w/ construction if I were concerned. Despite the
unpleasantness of the action and possible ramifications of needing
corrective action, it will certainly be far less of a pita to deal w/
now rather than down the road if a problem does occur because you let
There is no City Engineer or other agency who issued the building
permit that can be consulted? That seems very strange, indeed.
Again, have you discussed this w/ the lender/legal counsel? (That's
rhetorical ??, not necessarily prying).
Bob Morrison, if you're lurking, you got any other suggestions on how
to follow up? I'm just a (non-structural/civil engineer here, spouting
more or less platitudes). :) Obviously, can't tell OP whether his got
an actual problem or not, and that's not my question.
10 in stepdown (3 inches)->
| | 6 in (DUG)
| | 8 in (Dipped)
12 in | | 9 in (Dipped)
There has been further work done on this problem of the shallow
The engineer requested that I dig along the trench in the trouble spots
so he could later inspect. His position will be that if there is less
that 9 inches of concrete then a remedy is required. In the course of
digging two holes I was impressed by one of the depths I saw (15
Above is the diagram of the front projecting wall of the study along
with rough depths. Each vertical tick is 2 feet or less in length
roughly. Where you see the six inches is where I dipped the cement on
the night but also where I have dug a one foot wide square hole
alongside the concrete.
Through this hole I could observe that there was about 6 inches of
concrete on top of a solid square rock about six inches deep itself.
Combined depth of concrete and rock is 12 inches. This was the last bit
of trench filling done on a very slow job (10 hours) and is just below
a 3 inch step. It is quite possible the builder ran out of time.
Now I would like to know the best remedy or if one is even required.
There is talk of building a lean mix concrete bridge over this shallow
corner instead of dead building. I am not familiar with this. Will it
bind well and will it improve the foundations or is it possible it
could make them worse. Is a more drastic remedy required. There was
also talk of cutting and dowelling concrete or drilling in steel. I go
to the internet for help as my engineer still has not come out to
inspect this despite many phone calls.
Was wondering what transpired... :)
Not sure I fully understand again, particularly I don't know what you
mean by "Where you see the six inches is where I dipped the cement on
the night....". Don't know what to say in response since I don't know
what you mean.]
It would seem there's at least a short section around that corner that
is well under the engineer's specification for depth. If the rock is
only a single rock of 6" square and 6" deep, that would not in my mind
count as anything other than soil. If, otoh, it's part of an actual
ledge and that's why the trench was shallow, that's something else
again and might justify there being no concern.
At this point, given that this is only the end of the first week in
January after the holidays, I'd probably give the engineer a little
slack on getting out this past week but request resolution in a timely
fashion. If you have done all the site preparation for his inspection,
I'd use the formal letter to the office notifying them of that and
requesting their response. Usually that will work.
I think unless I couldn't get a response from that after a reasonable
time I would expect them to come up w/ the solution or approval.
Again, you need to be formal in this so he's required put his name on
the line where it's traceable.
I go back again to the question of where's the city or building permit
folks in all this?
To answer your last question, in our jurisdiction their is no concept
of a building inspector of that sort...
On the night of pouring I was able to dip the corner in question while
the cement was still wet and I came up with the readings you see of 6,
8 and 9 inches.
I wouldn't think there is a huge ledge there but certainly the rock is
longer and wider than 12 inches. Put this way it was someting which
didnt come up with the digger which the engineer asked them to dig out
but which it seems they decided to leave in.
I know I'm jumping the gun but I'm worried about it, any thoughts on
I measured the ledge a bit further.
It runs for at least 3 ft along the wall and goes in to at least the
middle of the trench based on having dipped over it.
It is 5 inches deep I was able to measure it at its outside because its
coincides with the edge of the trench. ie coincidentally it ends where
the side of the concrete ends. If it wasnt so smooth it could easily be
mistaken for concrete.
That may make it ok, my first guess would be the engineer will probably
decide so, particularly if he can determine that it is actually tied to
more and not just a single rock, albeit a large one.
Ideally, the builder/excavator should have gotten approval from the
engineer to either pour as he did or for a on-site fix/workaround
before completing the pour, but that, of course, is concrete already in
the dam. :( But, imo, that does put the onus back on him to make any
My recommendation still is to notify the engineer's office officially
of you're having the site ready for the followup inspection and
requesting approval or instructions/plans for whatever rework/additonal
work is required. If you were to want to be passive-agressive about
it, you could always cc: the builder, lending institution and your
counsel on the letter. :)
I'm still a little unsure about the overal depth of this with respect
to frost line and the finished grade, but that would/should be a part
of the engineer's inspection/approval, not just the depth of the
foundation pour itself.
One last point I may have over-belabored...are you absolutely sure
there's no equivalent of the building inspector or are you relying on
word-of-mouth of friends or "they say"? It's very unusual in my
experience for a locality to require permits but to have absolutely no
enforcement whatsoever, so I'm only suggesting you make sure you know
actual ordinances, etc., not just rely on conventional wisdom...
You've been great about this.
Yes I'm sure about building inspections. In fact somebody from a nearby
jurisdiction which does have strict building control inspections
commented on how lax our system here is. I suppose thats why I went
running around trying to do it.
Don't worry about frost line as there will be a lot of dead building at
this spot. It is the lowest part of excavation. Im sure they would have
let the builder pour over it. But he definitely should have moved his
step down to a later point and poured 10 inches over it instead of 6 or
The engineer has been informed and I am disappointed that three days
later he has still not examined this hole. Now the builder may arrive
before he does. I will follow up with an e-mail but am still anxious
until I get a response.
More later hopefully.
While I'm sure you're antsy, three days isn't that long especially when
you take in to account the time of year. I'm sure this must be a small
job in their business and while it's a big job for you, to expect him
to rush out is, while understandable, not surprising he hasn't.
I would try very diligently to communicate to the builder and the
engineer both here so that you don't have the builder show up until you
have approval. If you haven't told the builder you want/have asked for
an approval before continuing, best do so.
I'm still amazed any locality would have requirements for permits
assuming that those permits require design details, etc., and have no
provision for enforcement. If the permit is only a tax with no other
requirement, that I could see. May I ask where this is?
I'm outside nearest city 3-mile jurisdicitional limit where they city
can require compliance and there isn't but a health ordinance in the
county so don't have to file anything other than the septic/sewer
plans. They would like permits to be filed, but can't require it.
Something like that I can see, but the requirement to file the permit
and then have nothing seems bizarre! :)
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