Subfloor not flat

[NorthGaMan]

I am putting in engineered flooring in my house and some areas the floor is not flat, I have areas over a 4 foot span I can have a 5/8" dip, rooms had carpet so never noticed before. So now this is nail down flooring being installed over plywood and the plywood is two layers, one 5/8 inch and the other 3/4 inch. Ideas on how to fix? I am thinking ripping luan and 1/2" plywood in to 4 inch and 8 inch strips along with asphalt shingles to fix low areas. Good or bad? 

Thanks for any help.

[joe1086]

Post deleted...misread the OP

[Cooler]

What floor is this on?  Is it a foundation issue or just bad carpentry?

If it is just bad carpentry, then you can lift the subfloor and sister up the low points and then put it back down.  

Poured self-leveling concrete would be fine if you are floating a floor or gluing it down.  I don't think you can nail down over the concrete.

[NorthGaMan]

What floor is this on?  Is it a foundation issue or just bad carpentry?

If it is just bad carpentry, then you can lift the subfloor and sister up the low points and then put it back down.  

Poured self-leveling concrete would be fine if you are floating a floor or gluing it down.  I don't think you can nail down over the concrete.

The floor is on a crawl space. And taking up subfloor is not a option for me, I am doing this myself, with the help of my wife and really just do not want to tackle a job of that size
.

[Bit_Fiddler]

Poured self-leveling concrete would be fine if you are floating a floor or gluing it down.  I don't think you can nail down over the concrete.

self leveling concrete sandwiched between a wooden subfloor and the show floor will likely not hold up to the flexing over time.  Just like laying tile directly over a wooden subfloor, the flexing will crack and fracture it over time making a bigger mess than what you have now.

To do it right, you are looking at having to fix the reasons for the dips - sister them up and then put the subfloor back.  Or try to return the hardwood and go back to carpet....

[NorthGaMan]

self leveling concrete sandwiched between a wooden subfloor and the show floor will likely not hold up to the flexing over time.  Just like laying tile directly over a wooden subfloor, the flexing will crack and fracture it over time making a bigger mess than what you have now.

To do it right, you are looking at having to fix the reasons for the dips - sister them up and then put the subfloor back.  Or try to return the hardwood and go back to carpet....

Sorry but not options, again there is always more than one way to skin a cat gentleman and ladys and that is what I am looking for the other ways to skin this cat.

[Cooler]

Without looking you don't know if it is a foundation issue or not.  

Looking entails unscrewing or cutting the subfloor.  The fix, if it is not a foundation issue, is simple.  You sister up a piece of 2" x 8 lumber to bring the structure up to level.  Then screw a fresh piece of plywood or OSB in place.  You might have to sister up a few boards, but the job itself is not difficult or costly.

But poking around in crawl spaces can reveal unfortunate structural issues and if they show up, then you need to call in a professional.  It becomes a $1,000.00 or a $5,000.00 job to fix.  But putting a wood floor over a sunken subfloor sounds less than ideal.

[AUswimKC]

You gotta get in the crawl space and see what’s up. Then there are several options.

If there are major problems then now is the time to fix it.

Maybe the joists are too long and sagging. Easy to add a support across the center and a screw jack every other joist.

Maybe it’s been way too wet down there and the joists are rotting.

Maybe there’s insect damage.

Maybe your supports are sinking. Or your supports are wood and rotting or insects.

I’ve seen it all throughout Atlanta. Many times you won’t have to remove the subfloor.

Before spending all this time trying made due from above, and before spending all this time on the floors, you gotta find the root of the problem.

If the problem is just long joists that have sagged due to creep, then You might be able to fake it from above. But if it’s one of the other reasons, why have the potential for ripping up what you just put down in two years?

[NorthGaMan]

You gotta get in the crawl space and see what’s up. Then there are several options.

If there are major problems then now is the time to fix it.

Maybe the joists are too long and sagging. Easy to add a support across the center and a screw jack every other joist.

Maybe it’s been way too wet down there and the joists are rotting.

Maybe there’s insect damage.

Maybe your supports are sinking. Or your supports are wood and rotting or insects.

I’ve seen it all throughout Atlanta. Many times you won’t have to remove the subfloor.

Before spending all this time trying made due from above, and before spending all this time on the floors, you gotta find the root of the problem.

If the problem is just long joists that have sagged due to creep, then You might be able to fake it from above. But if it’s one of the other reasons, why have the potential for ripping up what you just put down in two years?

I have been under checking it out, no issues in rot or block giving way or falling apart, what I see is
2x10 12'long on 16 inch centers for floor joist, what I think happened when the house was built 30 years ago, somebody was putting joist crown up and then every so often put one crown down, that created my high spots and my dips. I am going to do some serious sanding on the floor in the high areas which are not that many or that large of a area , then use some shingles laid out under the new flooring to build up a little where needed and see how this works.
God Bless and have a great day

[Robert Adams]

I have been under checking it out, no issues in rot or block giving way or falling apart, what I see is
2x10 12'long on 16 inch centers for floor joist, what I think happened when the house was built 30 years ago, somebody was putting joist crown up and then every so often put one crown down, that created my high spots and my dips. I am going to do some serious sanding on the floor in the high areas which are not that many or that large of a area , then use some shingles laid out under the new flooring to build up a little where needed and see how this works.
God Bless and have a great day

             Shingles wouldn't be my choice of shim but anyway...  Assuming everything it basically sound and just sagging over time due to crown etc then yeah you can fill those areas with thin plywood or thin rips of wood then glue and screw it down to make up the majority of the volume up then floor leveler over it. There is a primer to use on wood before pouring floor leveler. 

       Our house was built in 1960 with recycled lumber from a really old house. Very heavy, hard and lots of growth rings and cut on a circular saw mill and most of it not straight or flat... ( I think it's fir) The floor joists are mostly 2x8 on 7' centers on poured concrete pillars and concrete perimiter wall (the only thing they got right on the house). There are a few spots where they put crowns upside down or the board was a little too narrow and resulted in a dip...  So yeah I have done allot of shimming and filling myself. I hate that old lumber but it sure is extremely strong stuff compared to the balsa wood we have today.