perhaps true in a Bedroom where egress is required. Every where else I would say no.

Generally, no, there is not a code that regulates the split of a window opening. That said, the best thing that you can do here is contact your local building inspector. States may differ as far as code goes, and even individual municipalities can as well. There are a few things off the top of my head that could be coming into play here, primarily as it pertains to the need for tempered glass, but again, a local inspector assessing the situation based on the protocols that they enforce would be best.

70/30 would most likely be a custom size. 60/40 is a standard proportion for the window manufacturer I use the most. Your builder's "not up to code" is most likely accurate. If you were to get a price quote for windows with a 70/30 proportion, you would most likely find the 60/40 proportion just fine regardless of what the code says.

What was in the contract or the blueprints concerning window specs?

The blueprints show a 50/50 window. The builder showed us a new build with 7' windows that were 70/30. I fell in love with the view and requested them when we initially signed the contract.

Since there was a change in spec and in price did this get updated and specify a 70/30 window?Ask them for the specific code they are referring to.

Assuming these are double-hung windows and the building code is derived from the International Residential Code, if the upper sash is 30% of the height of the window, the clear opening height when the lower sash is fully raised will not meet the 24" minimum required for emergency escape and rescue from a bedroom. This is in section R310 Emergency Escape and Rescue Openings which is independent of section R311 Means of Egress. This section is sometimes amended by a state.

Changing the sash proportions from 70/30 to 60/40 made the bedroom windows code compliant and I assume it was desirable for the other windows to match but you haven't shown us the elevations of the house.

If the windows had been 7 ft tall with a 30/70 sash ratio, they would have complied.

Its likely the window openings meet the 4% of floor area natural ventilation requirement for each room but you haven't shown us a plan of the house.

Whether or not the builder is obligated to inform you of changes would be contained in your contract. It's obviously not a good practice.

The other variable is the sill height. Perhaps this problem could have been avoided if the window sills had been higher but we don't know that dimension or the ceiling height. You might investigate raising the windows. This is like trying to solve a visual puzzle without a picture.

And if you want building code advice you should say where the project is located.

The choice of windows should be made in the design phase and specified on the plans. Changes to the approved (contract) plans--particularly verbal changes--are opportunities for mistakes.

Mistakes = disappointed clients or disappointed builder + additional costs for either or both + potential bad reviews = less future business for builder.

The solution to the above equation is intentionally left as an exercise for the student.

I designed a home with bedrooms where the sill height could not meet the sill height requirement off the floor for an egress window, so I provided a window seat below the windows to meet the code. Without my knowledge the home owner and builder eliminated the window seats during construction. It passed inspection and sleeping dogs are left to lie.

It might be that the non-compliant windows passed based on an inspector's judgement or it might be that it was simply not picked up during final inspection. Code compliance inspections are a sampling--not a comprehensive inspection.

I was not about to look the gift horse in the mouth.