We have a room with an aggregate concrete floor (pebbles on top). We built our joists and blockers and attached this platform floor to the studs of the existing walls and the footer boards. Once we got done with framing the floor, we planned on shimming up the platform floor before moving on to the plywood on top and vinyl planks.

We are at a standstill now...we have a pretty level platform floor and the aggregate on concrete floor under it is awful! It dips and comes back up...on and on. It is driving us crazy!!! We realize that we should've leveled the concrete prior to building the platform, but we are where we are and stuck!

Any suggestions as to how to support the platform, so that after we install our heavy washer and dryer and walk on this raised floor everyday, that we don't have it unsupported and potentially causing a ton of problems later?

We thought of angle iron brackets dropped to concrete level and then attached to the joists or composite shims screwed into place...please help us!!!!

You need to shim, lots and lots of shims. Also, the shims need to be pressure treated (if you make the shims yourself) or composite (if you are buying them pre-made.

You don't say the dimensional size of your new floor joists but the smaller size they are the closer together you will have to set shims.

You should also somehow get your hands on a laser level as this will make your job 1000% easier. Basically, set up the level so that it can shoot the entire room. The beam can be set at any height but best is between 1" and 6" above the top of your joists. Wherever you set the laser will be your baseline. Then start shimming to bring your joists up to level - take a read off the top of the joists and read against the laser line. Check every couple of feet in all directions and shim until everything is level. Tow-nail a screw or finish nail through the joist and into each shim to hold them in position.

Got a picture of what you have so far.
Trying to figure out why you decide to do it that way.
All I can picture is you now have to step up to get into the room, and also the doorways going to be a big issue.
What's the finished floor going to be?

I too am curious as to what you have done so far. No doubt that the best solution would be to use a leveler compound instead of a raised wood floor, unless you wanted the extra height. If all you've done so far is add a bunch of cut joists that are too small in dimension anyway, could be that starting over will be the easier route.

First of all...thanks for replying to our post!

I will take pics tmrw for y'all to see.

We do have a laser level and plan to try your method this week. We have to get the composite shims and we hope it will work!

We wish we had the time and patience to start over and disconnect the floor from the walls and level the concrete, but we don't. Our 3 year old is tired of all it and we are, too!

Will get pics and let y'all know how it goes...and thank y'all so much for taking the time to respond. If you think of anything else let me know.