Expansion gap around 60"x20"x3/4" marble hearth

[chipbl]

Great forum.

I'll be installing 3/4" 3" or 4" width BR-111 solid, (good choice?) most likey something like BC over AdvanTech subflooring in a 3 yr-old townhouse (2" staples). I have a gas fireplace in the corner of the room at a 45 degree angle with a black marble hearth. I've never installed hardwood, but I'm very handy with other flooring and DIY in general.

I have pored many entries in this and other forums to get the consensus on whether I need an expansion gap between the frame and the hearth, but most replies tend to address a tile hearth and suggest a gap equal in width to a grout line filled with grout-colored caulk. (I will mitre the corners and either biscuit/glue join or route the boards to join T&G. Thoughts?)

However, a local hardwood dealer says it's ok to butt the frame against the hearth, and pictures I've seen in various forums do this as well. I've also seen such installations firsthand. Note that because the fireplace sits at a 45 degree angle, the field would be end cut at a 45 degree angle against the frame (if that matters).

I really don't think an expansion gap filled with black caulk would look nice, and I'd like to avoid a threshold if at all possble as well. However, either of those solutions looks nicer than a buckled floor, so I'm asking for expert opinion! I have the time, desire, and skill to do this job right, I just need some advice. I live in Northern VA, and RH is generally stable right now at around 50%.

Thanks!

[Chris Mha]

All areas need expansion. Especially parallel to the width and a 45 degree angle is considered parallel.