Is it OK to install hardwood over 12" spaced sleepers? I have heard both Yes and No from different experts. If it's a qualified Yes, what needs to be done to improve the chances of a good outcome? Thanks very much. Army

yes you can..only up to 3" is recommended..

Planks need subfloor by guideline.

prepare by proper fastening and vapor barriers underneath..
I assume you are going over concrete of some sort.

What are the sleepers on?

Heated concrete?

Of what type (wood species) and size (thickness and width) of the sleepers?

Here, the homes built at the turn of the 1900's don't have subfloor and have strip or plank flooring nailed directly to the floor joists. I was just in an old historic mansion, in West Austin that had 8" wide mahogany floors, from 1921. They were awesome and had only been sanded once in their service life.

Alot of things were done on the past that are different today..What I listed was guideline.

under 4 inches only directly to sleepers joist etc.

just like only up to 4" over radiant.

many things have been done and worked and failed. thus guidelines.

Anyone is free to approach anything the way they choose.

I would venture to say that those floors you saw were pine of some sort and usually full to long length.

Not T& G oak plank.

with proper moisture barriers I suppose you can pull it off

I'm sure you have seen a 250-300 year old floor in NJ, some things never change.
The deal is, it is more feasible to put down a subfloor than 2x4's on 8" centers, to maintain the proper nailing schedule. Most screed systems are 12" centers, not close enough to maintain the required 8" schedule.

Ladybird Johnsons(President LBJ wife) old homestead house has 5" 33/32 Pecan on 12" sleepers, over concrete poured in 1911 and no moisture barrier what so ever. The floor is cupped looking at a cross section, but flat on top and been that way for 100 years. I got called in, because they added wood to match it in the dining and kitchen and it cupped immediately. They had resanded and stained/ finished it all and only the new cupped. The new section had moisture barrier, but they allowed the non moisture barrier area to vent over to the new section. They didn't know or realize how the old section was originally done.