If it's perceptible, then it's more than likely a real defect. Easiest way to confirm is to bring a round marble. Drop it gently on the floor, and see what happens/where it lands. Take a short video, especially if it lands in the "dip" and goes no further.

Sorry that you're having headaches with your GC. Some will fight everything, knowing that many homeowners will just give up. But I assume you have a contract that guarantees "new" materials and workmanship, not "like new". You should also have a clause that details what to do with disputes. Surprise! Emails, calls don't count- too much plausible denial. Write the GC a letter calmly stating the issue. Let him/her know that you expect a meeting within (3 days max) and a workable solution at that time. "Everything has. been going so well, but this is very problematic as I'm sure you agree". Send it registered mail, return receipt requested.

EDIT: If you are paying cash, yes, as millworkman says, make further payments part of this. If you have a bank- your own- make sure they get a copy of the dispute letter.

And - you are smart to get on it now and get it fixed. 1) it won't get any better and more flooring goes in / on and it will only get magnified and 2) the more that happens, the less likely the GC is to want to fix it / want to make it painful for you to ask!

Like the marble video idea. Document, document, document.

Marble idea is good. You could also buy a 4' or 6' level to check as well. Level might come in handy for checking walls too.

If it bothers you now, it will bother you 100-fold a year from now. On our first custom build, our carpenter assured us that his method of installing subfloor was "the best" and that we'd never have issues (nails and glue versus screws and glue). Less than a year later, we had squeaks galore in our living room and we went through lots of packages of shims trying to eliminate them from the basement level. Moral of the story, fix it now, not later. Don't get railroaded by someone you are paying.

What is the structure of your sub floor and finish flooring? Do you remember if the sub floor flexed as well or is it just the finished floor? Is the floor open below so that you can see the bottom of the sub floor and see if it's flexing (and so not properly adhered to the floor trusses)?

You mention that it flexes and I assume it flexes down. If so then the marble won't work as without weight on it there is likely no dip and quite possibly a bit of a rise. As mentioned above get a good accurate 6' level and use that to show imperfections with and without weight.

And yes, this should not happen, even in a production tract home.

Your issue may be with the designer of your home and not with the builder.

The stiffness of a floor can be affected by a number of variables including the type, size, spacing, span, and span continuity of joists; bridging--if any; the properties of the subfloor, and how the joists and subfloor are fastened. Your floor may meet code requirements, but still exhibit an objectionable bounce (there's a difference between safety and performance.)

If your builder was responsible for construction-- and not both design and construction-- then a quick inspection can determine if it has been built according to the plans. If it has, you should discuss the design criteria with the designer and discuss options to improve the performance of the floor.

What does the 'inspector' say?

Charles, can you explain the dif. between safety and performance?? What is the code???

Regardless of who is to blame, it sounds like it needs to be fixed. Make the next payment with a very perceptible dip in it and see how they react.

I get what Charles is saying but if there is a dip where the floor flexes it doesn't matter who is at fault between the design aandf the builder it needs to be repaired. Period.

Residential building codes encompass building, mechanical, electrical, and plumbing requirements. They are intended to protect public safety, health, and welfare. While the structural requirements specified in the building code for floor systems may protect life safety, they do not guarantee that every homeowner will find the performance of the floor (which is subjective) to be acceptable. Nobody likes the dishes rattling in the hutch when they walk by, but that could be the case even with a floor that fully complies with the building code.

Like many things in residential construction, designing floor systems involves balancing compliance, performance, and cost.

As previously stated, if the builder didn't design the home, he/she is responsible to construct the home according to the plans provided to them. If they've built it according to the plans, then please don't make them to be the "bad guy" for what is a design issue.

Please describe the type of foundation; is it a crawl space, basement or raised etc. what are room span/dimensions? Is this a tract or custom home; do you have access to engineering. drawings? I know these are lots of questions but very basic ones.

I would hope the builder has the integrity to solve any problem the owner perceives. This being said, there is a need to determine if the solution to the problem falls within the scope of the builders contractural responsibilities and expressed so that the home owner understands. There may be some fuzzy areas in this, but I think they only occur on my projects.

Forget the “code” crap/discussion. A dip is a dip is a dip. It may fall within “code” but certainly not within the “Code of Acceptable Building Practice, Good Business Practice, Stellar Workmanship and Customer Service.” I’m perplexed as to why the GC can’t/won’t diagnose the problem and remedy it. Period. Is it a faulty piece of subfloor, sagging floor joists, improper spacing of joists, misalignment of joists, warping of some material, etc.? He needs to figure it out and fix it.

All structural members will deflect or flex under load. That's just basic physics, not an attempt by your builder to cheat you or cause you harm or which demands remediation. The amount of deflection or flex depends on the load applied, the span, and the properties of the structural member(s).

The building code specifies the maximum allowable deflection for a structural member (e.g., rafter, steel lintel, header, floor joist, ceiling joist, etc.) The amount of code-allowable deflection varies depending on the application. For example, a steel lintel supporting a masonry wall would not be allowed to deflect as much as a framed wall with a flexible cladding like vinyl siding. That should square with the "common sense" test or what engineers like to say is "intuitively obvious."

For simply supported spans, the maximum deflection is in the center of the span. A ceiling joist with drywall applied is allowed to deflect l/240 where l is the length of the span. A floor is only allowed to deflect l/360, so a floor with a 12 ft. span would have a maximum allowable deflection of 0.4" That's easy to measure for a static situation.

When you walk on a particular floor, you can induce a dynamic response (e.g., a bounce) which you may find objectionable and others may or may not. It's subjective. At least one manufacturer of wood I-joists conducted empirical studies of various floor assemblies and recorded whether people walking on them found them to be acceptable or not. Interestingly, there were no floor assemblies tested where 100% of people said they were acceptable. Based on their studies, their design software is able to design engineered floor systems which will be deemed acceptable at various levels.

While we don't know if the OP's floor is comprised of dimensional lumber, wood I-joists or lightweight steel joists, the designer's task is the same: to meet the code requirements while balancing performance and cost. Take a look at floor structure and see if it's built as designed. If it is and the performance of the floor system is objectionable, go back to the designer and explore options to stiffen the floor.

This is one of those postings where there's simply not enough information for a thoughtful and experienced response.

Is this a custom home, a semi-custom home or a tract home?

Is this a remodel or new construction?

Is the problem on the basement, first or upper floor?

What is the construction of the problem floor--slab on grade, crawl space, supported by floor joists, supported by trusses, or something else?

Why doesn't the builder think that remedial efforts are appropriate?

So many folks post here with just one or a few sentences of information, thinking that everyone here is clarivoyent...or at least omniprescient...or simply past participle.

Come on folks! If you really want experienced help you have to post enough information to get it.

Thank you everyone for all of your input. After much standing around with arms crossed staring at the floor, our GC decided it would be prudent to head to the basement to check the location of the joists in relationship to the "dip". It turns out that there is a joist and right next to it is a wall dividing the basement into two separate rooms. The "dip" is located above the other side of the wall. The wall is pushing the subfloor up creating a rise and then a dip on the main level. Options include tearing the wall down and starting from scratch or using a leveling agent upstairs and then re installing the hardwood. (I am no builder so please excuse the rudimentary explanation.) As of today, nothing has been done to start the correction as the floor installer says that it's not his fault so he will not correct it, the GC says that the floor installer should have seen the problem before laying the floor, so the blame game has begun....

Sorry about that Virgil, you are absolutely correct. This is a new construction, custom home. First floor over a full walkout basement. Subfloor is durastrand. Supported by floor joists. I think they are 19" on center - definitely not 16" on center.

This is a 'dip' in the middle of the great room floor. There is a bit of bounce across the entire great room, but the dip is pretty significant and when the hardwood was installed, if a person walks across the floor, you can feel and see the hardwood flex downwards.

Well...in addition to the dip issue, if you can see and feel the first floor moving and "flexing downward", you have other problems. From what you describe, including floor joists spaced greater than 16" OC, it sounds like the stiffness or deflection of the floor framing is L/360 or more. While L/360 is a general code standard for many spans, it is not particularly stiff, especially for floor spans greater than 15-feet or so. You don't mention the floor span for the great room, but if it's in the range of 15-feet or more, you probably need a deflection of less than L/360, i.e., L/720 for example. To achieve this means adding additional supporting floor joists or trusses. Good luck on your project.

If the movement in the floor is between the wide spaced joists you can add blocking to support the flooring wherever you are likely to walk. If the movement is from undersized joists you have the problem Virgil Carter describes. Unfortunately, a bouncy floor may meet the minimum requirements of the building code.

Is the flooring being installed parallel or perpendicular to the direction of the joists? Our friend, who is a hardwood floor installer, always recommends perpendicular. I’d see how much it would cost to have more joists installed because a bouncy floor will aggravate you to no end. It’s better to fix that now than later.