We're in the middle of constructing a new home that will have a masonry fireplace.

Although we were very explicit with our builder in wanting an arched fireplace, the mason our builder hired built a standard rectangular box with an straight/horizontal lintel.

We are planning on making the surround out of granite, and our builder is telling us that it is both "too difficult" to redo the front of the firebox with an arch and that it would be perfectly fine for us to create an arched opening by having the granite cover the upper corners of the rectangular firebox.

This seems suspicious to us... it would expose the back of the granite directly to the heat from the fire.

We're unsure if that would lead to risks, such as transmitting heat directly to the surround (without it being obvious that the granite is directly exposed to heat).

This is a 42" masonry fireplace built to "standard" dimensions (so we've been told).

Do we need to have the mason redo the work and build in an actual arch in front of the firebox?

Or are we overly sensitive to the impact of having the surround partially cover the firebox, meaning it is perfectly ok to go with the builder's recommendation?

Been lurking here getting other information to use in our build (thank you, Garden Web Forum!)... hoping to get some insight on this fireplace issue, as there doesn't appear to be much information about this that we could find on the web.

Thanks in advance for your help!