If you are on slab, I'm not sure what you would be nailing TO. Adding in a sleeper subfloor would be very expensive and will still require a vapour barrier underneath. *Technically a glue down SOLID hardwood can be done on slab - but it isn't recommended unless your HIGH END flooring installer has done it successfully in the past. A glue down engineered floor is technically "more stable" in the widths they are suggesting, but I would question a comparison to a 2.25" solid hardwood. Especially if the solid NARROW strip hardwoods are rift or quarter sawn. The same adhesive would be used regardless of plank structure (solid vs. engineered). The RIGHT adhesive (aka. EXPENSIVE glue) MUST be used over slab in TX. And then the proper SPREAD RATE must be used (lots and lots of the expensive glue will be required) as well as the PROPER TROWEL profile/depth will be required. These expensive adhesives ($100/gallon is common) will achieve 30-50sf per gallon. These adhesives will be the vapour barrier. The most expensive ones will have "limitless" moisture content as one of their key features. Even with the TOP adhesives, the installation will still be cheaper than a sleeper subfloor + nail down installation. The sleeper subfloor would mean a lower priced flooring professional can be hired to achieve the nail-down installation. The glue down method will require the higher skilled professional with all the knowledge required to install a glue down wood floor PROPERLY. And the next issue is the HVAC system. Regardless of the installation method, your HVAC will have to have the ability to maintain a CONSISTANT level of humidity. Sometimes A/C isn't enough in high-humidity environments. Sometimes a whole-home dehumidifier is required in extreme humid areas. Please review your HVAC system's abilities to TIGHTLY control humidity (somewhere around 40% is PERFECT...and it must be maintained 24/7 for the next 25-60 years). Start there. Spend more money for the upgrade on the HVAC system so you can have the wood floors - regardless of width/composition.

As above. The wide plank (anything 5" or wider is considered 'wide' by the industry) must have a 'glue assist' if you use nails/cleats/staples. That is an added expense...that's why wide plank wood floors are a serious upgrade. If you are going to use a glue-assist, then a full spread glue WITHOUT the nails is just the next step. And as G & S points out, the nailing down of thin planks (3/4" is the industry 'gold standard') could lead to more problems. And of course, being in SC you will want to make sure you have the HVAC system updated (it it needs it) to include a whole home humidistat (includes humidifier or dehumidifier or both depending on your local year round climate). Before you do anything, make sure your HVAC system has the RIGHT attachments to handle a home full of wood flooring. Traditionally that requires an upgrade....but not always (we've seen some homes that already come with the top of the line HVAC systems that have all the bells and whistles already attached).

I like 1/4" (6mm) cork underlayment as a double stick install in a home. Of course a double-glue down install makes for a large jump for installation costs. Instead of the usual $3/sf install for a normal glue down (labour costs) this jumps to $5 - $6/sf. The upstairs would benefit from the double stick...the downstairs needs to be evaluated. What is your substrate for the lower level? Is it wood-joist construction (such as over a basement) or is it on a concrete slab. If it is on slab, you will need to have the slab assessed for moisture. If there is ANY suggestion that a glue down should NOT be attempted, I would float both the cork and the floor and be done with it. A floating hardwood floor over top of floating cork (nothing is glued to anything else) is one of the cheaper ways to get cork underneath engineered hardwood. And be aware your material costs go UP when you glue cork underneath a glue down hardwood. The amount of glue you MUST order goes UP! Way up! Look at your budget and decide what you can afford. And if you are on concrete, remember that you MUST spend money on the preparation. A poorly prepared substrate will create a poorly installed floor - regardless of the method of install.

Does the install include subfloor prep? Or just the labour for a glue down application? Is the glue included? Is the wood included? Right now you are looking at $8/sf. That could be right on (as in the labour + glue + substrate prep = $8/sf) or it could be too low, or it could be too high. We won't know until we know what is INCLUDED in the $1200 install for 150 sf of flooring.