Cannot answer your question, but it would be best to deliver the base unit to your builder so they can have the cabinet on site. That way there is no mistaking the clearances. Custom cabinetry is done to the 1/16" of an inch in better lines.

I have Sektion with 2 five inch drawers at the top. It is 10” from the top of the cabinet to the bottom of the second drawer front.

@AquaLove, is there any space between where the top of the drawer frame is to the edge of the tops of the drawer fronts?

Don’t totally understand what you’re trying to achieve but the drawer is like 3-1/8” high. Is this an interior drawer behind a narrow upper drawer front or two narrow drawers stacked on top. I build custom doors for Ikea and have done all kinds of modifications. Again it depends on exactly what you want.

They have some drawers that have a small drawer inside another. I'm wondering what the smallest drawer front measurement is that would fit two small drawers behind one front. Not the premade Ikea fronts, just the measurement of the smallest height a panel could be and cover two.

You really have to have the drawers and inner fronts to play around with to get an exact measurement. You are really covering three drawers because the drawer front that covers the two inner drawers needs to be attached to a drawer below those. Then there’s the space between to consider to get your hand in to open them and lining up with the Ikea predrilled holes. I would do this without having the actual drawers to test first.

I meant one inner drawer, not two. Yes it is looking like I'll just have to order an extra and return it if it doesn't work. Thanks for trying to help.