Hello everyone, I've searched for this topic on the forum, but haven't found a situation like this one.

I'm about to do a new install with nailed down flooring in 3 rooms above a non-heated garage. My guess is that the floor could be exposed to low temperatures in the 50s in the winter and upper 80s in the summer.

Will this be much of a problem?

If so, should I upgrade to a more insulated underlayment for extra insulation, like cork? This will give me transition problem with my current thinner underlayment. But I can work it out some how.

Im also looking into add some extra insulation in the garage ceiling but that will be
kind of bigger project than I'm looking for.

Thx.

I had a case earlier this year where T+G engineered hardwood was installed over a moving room in a condo that were not heated/climate controlled. Even though this was high rise and the slab was dry, the H/O still had problems with creaking and noise due to changes in the humidity/MC of the floor over this uncontrolled space. It took a lot to figure out the problem but the solution (since we couldn't address the climate in the room below) was to switch materials - ended up installing some nice click vinyl throughout and there were no more issues.

In your case - you might want to consider tackling the garage insulation project, for many reasons, but also to protect your new flooring investment. All hardwood floors perform better in stable conditions.