I'm no pro but in ours they nailed down 1/4 inch plywood.

I would go with 6mm (1/4") cork. You have to either float or glue the wood. No nails. No staples. I have many installers use 6mm cork underlay for a quick, easy, cheap, comfortable floor height raise.

But the thing is: The wood floor MUST be FLOATED or it must be GLUED. Floating is easier. Gluing is superior (superior = more expensive).

So the question becomes...what is the installer going to do about the MOISTURE content in the subfloor???? It is a little weird to have plywood to be so DAMP. I would question the REASON for the DAMP...

Putting ANY wood product over damp plywood = NOT good! So why is everyone ignoring the warning signs...DAMP plywood????

What has happened that is driving the moisture content SOOOOO high in the underlayment? Has anyone REMOVED a layer of underlayment to see what has happened??? Is it worse around the outside wall??? Is it better in the middle of the home?

Before you spend MASSIVE amounts of money on an "improper" installation, I HIGHLY recommend finding the answer to the question: Why is the plywood so DAMP?

And we normally like to see plywood UNDER 10% MC...we prefer to see 9% MC in plywood. The 12.5% is too high...for ANY FLOOR covering. I wouldn't even put carpet over plywood that is that damp.

Start with the basics. Find the REASON behind the wet; fix it; then lay the REALLY expensive floor.

I agree with finding the cause for the high moisture content in the subflooring. It might be as simple as the interior being open to the elements during construction and the subflooring taking on moisture from high humidity or from being rained on before the roof and walls were closed in...very typical on new construction unfortunately. Or, as Cancork suggests, a more serious condition may be causing the somewhat elevated readings. If there is no cause other than exposure to the elements during construction, the readings will revert to a normal range once all the wet trades are finished and the HVAC system is operating.

Cancork Floor Inc.

I could write a book about
the moisture issues we have had to deal with over the last 30 years. Ten years
ago we were in the process of putting in new windows and a deck and we also
knew there was a moisture problem. We called an encapsulation company and they
inspected our crawlspace and found standing water and extensive damage due to
moisture. In addition, we only had 12” under the beams and 18” under the joists
from the soil. Also our crawlspace only had three vents and they were all on
one side with no cross ventilation. So began the 10 year journey to force our
HOA to address storm water drainage in the complex and rebuild our home from
the ground up.

We cribbed our townhouse and
excavated the crawlspace to increase the distance between the joist and beams,
poured all new pads, replaced all beams and joist and installed new 3/4'”
T&G STURD-I-FLOOR. We also installed a 6 mil moisture
barrier. It is very nice now in our crawlspace and I believe the moisture level
is fine. I measured the moisture content of some of the lumber in the
crawlspace and it was 12%. I snipped this from a document on Wood Moisture
Content. 12% - 16% is not considered wet and is healthy for a crawlspace.

http://www.rlcengineering.com/wmc.htm

"12% - 16% - Readings in this range are common to lumber during
construction, air dried lumber and "healthy" residential
substructures (beneath first floor in crawl spaces). These are typical readings
for exterior wood."

BTW, I used a General pin
type moisture meter, Model MMD4E. I understand these are accurate for Doug Fir
and plywood.

Below are before and after photos in one area of our crawlspace.

I put a moisture meter inside the our townhouse, in the crawlspace and outside. I got the following readings.

Inside: 45

Outside: 57

Crawlspace: 58

ifcwood

We were thinking of using ¼”
cork underlayment and floating the floor, but we heard that required a
transition strip between our kitchen and dining/living area. Unfortunately
there is no attractive way to add a partition strip between the two spaces. Is
a partition strip necessary for areas with a floating floor that flows from one to another. The kitchen and dining/living areas are only separated by a peninsula
and walkway.

Perhaps you need to consult with your original installer and have him investigate the moisture levels in both the plywood and the subfloor, as jfcwood says. This ought to give you the difference in readings between your subfloor and the solid wood you want.

Glennsfc

We have given up on
installing solid wood and decided to go with engineered hardwood flooring. We
are trying to decide the best way to raise the ½” engineered hardwood flooring ¼”.
I am thinking we will have to lay down a another layer of ¼” material such as
plywood or laun if we want to nail. We would like to go with a floating floor
with ¼” cork, but a transition strip between the kitchen area and dining/living
area will not work since there is no practical place to put it. We would prefer
to go with the floating floor if we could.

nsfc

Don't use luan. It is WORSE than OSB. If you want to use cork...simply GLUE it in place and GLUE the hardwood (double stick method). That way you can have your floor height raise and your "butting" to the kitchen.

Of course these things add plenty of cost whereas a T-molding is $18 - $20/linear foot and is super easy to work with. You will still need something at the junction between the kitchen and the hardwood.

Now that you hare comfortable with the "why" and plywood, it will be up to your professional flooring installer to ensure the moisture content of the engineered hardwood is within 3% of the moisture content of the plywood.

And if you really want to do without the extra layer of plywood, you can go ahead and find a 3/4" engineered hardwood. Once everything is paid for, it will probably work out to be the "same price" as laying a new layer of underlay (and labour) and then installing a thinner hardwood over top. If you spend a few more $$ per square foot for a 3/4" hardwood, you will "save" the same amount on the LABOUR/material costs of adding new plywood.

I would investigate the price difference between the two jobs. You are looking at TOTAL price per square foot...not just cost of engineered hardwood.

Cancork Floor Inc.

Thank you.

Originally we were going with Brazilian Teak in ¾” solid
wood, but we can’t use that due to moisture issues. We now are looking at
engineered hardwood, but Brazilian Teak is only available in ½” thick planks.
It is not available in ¾” thick planks. We couldn’t find any exotic hardwood
engineered flooring in ¾” thick planks.

NOTE: We are hesitant to glue down a floor should a future repair
to the floor be required.

It appears we only have two options.

1. Float the ½” engineered Brazilian Teak hardwood on ¼”
cork.

2. Nail down ½” engineered Brazilian Teak hardwood on ¼”
plywood or luan.

We want to use the same engineered Brazilian Teak flooring
in the kitchen and the dinning/living area We would prefer to float it
over 1/4" cork, but read that if you have a floating floor you need to
have a transition strip when you move from one room to another. Is there
any reason we can’t run the engineered Brazilian Teak flooring continuously
from the kitchen to the dinning/living area without a transition strip?
Our kitchen doesn't have a doorway, just the entrance between the wall and the
peninsula.

So given the two options above, which would be the best
installation?

Were it mine I'd put down a layer of 6 mil poly (if you don't already have one under your plywood, fit and nail a layer of 1/4" plywood and staple down the engineered Brazilian Teak flooring. Layers of felt paper could be used in areas where you might need to fine tune the height. My preference would be to modify something like a Bostitch M111FS for 1/2" flooring and use a staple that would go through your 1/4" ply into the base layer. I would do this all over and not float the kitchen.

jfcwood,

Thank you.

There is 6 mil poly covering the grade in the
crawlspace and we did plan to put 6 mil poly between the 3/4" subfloor and
the added 1/4' underlayment. I see Cancork does not like 1/4" luan. How do
you feel about luan as opposed to plywood. Is there a better grade of plywood
that does not have voids?

I just called one of our local specialty wood
suppliers and he recommended ¼” solid core maranti plywood which he has in
stock for $17.00 for a 4 x 8 sheet if I take 500 sq ft. I will go over this
afternoon to see what the material looks like.