Addition to CMU residence.

[ChiefInspectorJeff]

How do you verify existing footings and wall specs when designing an addition that will bear on existing wall?
Do you allow the existing trusses to carry the loads of the rafters and sheathing?
As an inspector I assumed someone had looked at all this but in retrospect I doubt the plans examiners were concerned.

 

[Ron]

Was there an engineer involved in the design of the addition?

 

[ChiefInspectorJeff]

Not yet, but how would they determine these things without an existing plan?
Has to be just common practice. I know trusses have a live load that is only called upon during things like wind or snow events and this extra capacity and the factor of safety must be the reasons that the extra loads don't cause deflection problems.
I have also seen many truss engineering that does not add in the extra dead load of overframing.
And for that matter I have never seen a truss web designed for loads perpendicular to the plate for applications such as gable bracing. Another can of worms::sorry.

Inspector Jeff

 

[KootK]

My understanding is that the existing structure is, and ought to be, considered by the renovation design team. This can be accomplished via:

1) existing documentation.
2) testing.
3) reasonable assumptions.
4) demonstration of negligible impact.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[concretemasonry]

Jeff -

Is it actually masonry structure or a wood frame structure with a masonry veneer? How tall is the structure.

Depending on the location and date of construction, there may have not been a need plans to get a permit to build.-I built a 1650 sf lake home (8" very lightweight block with a cavity and a 4" brick veneer) in northern MN and had all the necessary drawings (just my opinion, being a PE and SE - ret.). Before I got the drawings out, the license clerk said it was in an unincorporated area and the was no model state code an since it was 100' set-back from the lake the fee for a permit was $25.00. - She added that there were no inspections except the electrical and septic systems and they would follow within a year after construction.

For your situation, if the structural walls are are supported by buried strip footings, you can do a quick survey by driving rebar down a few inches from the surface at several places around the home parallel to determine the minimum footing width.

It extremely rare to have a vertical bearing problem with hollow masonry walls unless the walls are high or if there some hefty long span beams.

Your home may be considered unreinforced masonry with only the necessary reinforcement (amount can be determined by scanning). In that case the only reinforcement could be the minimal vertical amounts for continuity around openings or in a bond beam/lintel that is also minimal. My annual snow depth was about 150".

If you can find a tag on the trusses, you can possibly determine the roof capacity for addition loads. With some sketches and photo or two, a truss manufacturer could determine if it is a common truss with a known capacity and the ability to take loads added later since they may be supplying the trusses for the addition.

Good luck with the research on the home.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[ChiefInspectorJeff]

We were concerned with the additional uplift of 320 PLF. Not knowing if there are rebar in filled cells anchoring the bond beam I can only assume the bond beam weight for resistance. I could run a threaded rod from truss anchorage to epoxy into existing footing and put it between the existing interior furring strips.Or a coil strap on the face of enough blocks to provide the dead load.
Cheaper than forensics.

Inspector Jeff

 

[Ron]

Jeff...what you are proposing should be engineered. Also, if there is no engineer involved, how was the 320 plf uplift determined? Just because it is a residence doesn't mean that engineering is not required. Presciptive measures in the code do not have universal application.

 

[ChiefInspectorJeff]

Ron,
In Florida the statutes allow non licensed design professionals to produce plans for one and two family residences and certain commercial buildings.They can also do the wind design on the structure using the Florida residential code and the AFPA high wind load prescriptive manual.
As a plans examiner I have accepted hundreds of plans not sealed.Also a contractor who takes a wind design course can certify these plans.

Inspector Jeff