Residential concrete roof - mortar this problem??

[Surfpath]

Greetings folks,
I have a somewhat pressing concrete roof and foundations dilemma. Since I am located in the Caribbean it's a little difficult to get quick advice. Here's what I have:

A 2000 sq ft (49' x 43') concrete roofed structure set on a pitched slope with a 10' x 49' "apartment" below. The construction is at the point where the slab for the bottom apartment is about to be poured. But a few days ago I noticed that the contractor may have cut a few corners.

Due to a draughtsman's error he overbuilt a retaining wall. This wall is a part of a passage that runs the length of the "apartment" below (#3 on attached plan). In now constructing the larger load bearing wall that runs all the way to the roof (#4), he neglected to install the footer and the two 'inside' reinforced columns/posts (I'll post the aerial view which show these - again on the wrong wall). He did, however, install the two external columns. I called him out on all of the above. Here's his solution.

Please can you help me make sure this will work, because I have a lot at stake...my family will be beneath this roof.

He says that he will now create a reinforced footer for wall #4 by digging a 7" x 32" x 49' trench into the already compacted dirt below where the 5" apartment floor slab is to be poured. He said that the concrete for this footer would be poured at the same time as the apartment floor slab (he says it'll also be tied into the rebar for the slab). His logic is that, with the slab, this would now add up to a 12" x 32" footer. #4's wall going up from there would be like the rest of the house, ie reinforced concrete filled 8" block. #4 would also be tied into the reinforced ring beam that circles the ceiling on this floor.

I am generally happy with the rest of his build (other footers are 14" to 18" deep and 22" to 25" wide), with rebar tying in foundations together - again aerial view soon).

The main issue as I see it (disclaimer: not a structural engineer!) is that wall/foundation #4 plays an important role in supporting our 6" concrete roof over spans of 15 feet (the kitchen/living room) and 10 feet (the porch). Installing a sort of footer that ties into the ground floor slab is better than no footer at all. However, this footer is not sunk down like the other footers, and there is no real 'foundation wall' to speak of. In his solution, wall #4 will be technically anchored to a footer but only sunk in 7".

I have hear that the weight of a concrete roof alone helps to resist uplift forces (we are located on the edge of the hurricane belt - one big storm every 40 years). Although we are not in an earthquake prone area, the mass of that roof above my family is important to consider.

The house plan was not verified by a engineer. However it is very closely based on my parents larger house which was engineered.

Any help is truly appreciated,
PJ

 

[Surfpath]

Aerial view attached...

 

[ishvaaag]

Sou seem to have moderate spans, and the builder seems to be proposing a reasonable solution for the standing condition. Ensure that

-rebar of the slab is solidary to that of the new footing and this to whatever other concrete work adjacent through drilled connections

-there is atop of wall 4 support anywhere in the design there was; if some embedded column cannot be made without destruction of some work, ensure there is at least a running beam atop the wall 40 cm or more deep, or better, reconstruct it.

For what I know caribbean soils can be very problematic in many aspects and I see no good in not having the house engineered with a proper soil report. You must understand that dear that it may be, the more certain way to an ensured standard of safety for your home is to engage some qualified Architectural-Engineering team working in the zone.

 

[ishvaaag]

So you... should have been the starting words.

 

[Ron]

Where is your engineer in all this? These are not assessments that can or should be made by other engineers in a forum based on very limited information. Get a local structural engineer involved. If you have to slow things down to make that happen, then so be it.

 

[csd72]

surfpath,

There is potentially much more to this than could ever be transferred in the form of drawings.

You need to get a qualified, experienced structural engineer on site to verify that the proposed changes are compatible with the actual site conditions.

Most construction collapses happen during construction when a change has been made without being checked.

Do not take the risk.

 

[Surfpath]

Thank you for your replies. Yes, we are trying to contact the engineer who assisted my parents. He is located on another island and hard to reach. Anybody interested in popping down to the Caribbean on very short notice?

I realize that more specific advice is difficult to obtain, especially without all of the relevant tests and data. However I was hoping for general information concerning the construction of footings/foundations in relation to concrete roofs. Ideally the latter will help me to better understand the principles of this issue.
Thanks again.

 

[a2mfk]

What island? I'm in Florida and may be able to help. But the problem is as the others have stated, and you have stated, is that essentially someone took your parent's house design and tweaked it. But that means no structural engineer has designed THIS house, and nobody knows what may have been changed. So your best bet is to get the other engineer involved, since he is familiar with the original design and can most easily assess this current design, though he may not want to since it sounds like you reused his original design without his permission?

Plan B- Hire another structural engineer. Most SEs will hopefully want to look at the original design and check EVERYTHING, and see what has been constructed to date. This person may give you lots of bad news- columns, beams, footings, etc. may not meet code requirements. If there is no specific code for the island, then I'd want to use another one that is close- FBC/IBC with ASCE wind for that region. Some things may have to be strengthened or worse case, demolished and rebuilt.

I am sorry we are the bearers of bad news, but from where we stand this situation is mostly your own fault. You should have spent the extra money up front to rehire this engineer to tweak his design of your parents' house, OR hire a new engineer for a new design. And have a contract in place so that the engineer is on board for the construction, we call this phase Construction Administration, and it is obviously a very important one.... Especially when things don't go according to plan, pun intended.

 

[Surfpath]

A quick update: We managed to contact our man and are working on rectifying the issue before construction in that area continues. Thanks again for your assistance.

 

[a2mfk]

That's good news, you are doing it the right way now...