Hi there, I’m new here but have been lurking in the background for a few weeks. I know this has been discussed in many threads but I need some help building my raised hearth and could use any advice out there. I have been building my home for four years now. Unfortunately, I fell off of the roof during construction and found that I don’t bounce like I used to. After a year of surgeries and recovery, I’m getting close. I designed and built my home from the ground up, doing everything myself with the exception of the electrical and mechanical. With that being said, I didn’t do enough planning and made some changes mid stream that I shouldn’t have. One of those changes was moving my fireplace insert forward by 16”, effectively moving the hearth area forward of the CMU piers that were meant to support it and the mantle.
I have a heatilator el42 that sits 8” above the subfloor. The raised hearth will finish at about 13” high, 20” deep and 72” wide. I’m finishing it with old Texas brick and a thick mortar sack smear. The mantle will be a solid sinker cypress beam that i milled to 7”x10”x 6’. When dry it will weigh a good 200 lbs. ( I hope) I’ve already kilned out 5 gal of water since I drug it out of the swamp. My joists are 2x12 @ 16 oc spanning 11’, giving me a live load of plus 70lbs sq. The subfloor is three-quarter inch tongue and groove advantech, glued, nailed then screwed. I am considering removing the closed cell spray foam insulation on one side of each joist under the hearth area and sistering on another joist to help with deflection and to bear load. I also thought about adding a 2 x 4 under each joist to help with deflection. I could add another set of peers at mid span and add an I-beam under the joists but I am worried about shear. I’m not sure if this is necessary and would appreciate any input here.
As far as the hearth, heater later requires a layer of micore300 or a minimum of 1.03r under the non combustible framing. I would think that it would be better served under the top sheathing of the hearth but I’m going to follow the manufacturers instructions. I’ve looked for the Micore and simply cannot acquire it in this area. I decided to use a mineral fiber fire rated ceiling tile sandwiched in between two pieces of non-combustible cement board. On top of that I will use metal framing, two layers of Durock and then brick. Common sense tells me I need to attach the base to the subfloor, and not the floor joists. I would like for someone to verify this for me though. Also, is it recommended to put a layer of thin set down before screwing down the insulated panel? I will attach a few photos here. I appreciate any advice or words of wisdom. Thank you in advance
I have a heatilator el42 that sits 8” above the subfloor. The raised hearth will finish at about 13” high, 20” deep and 72” wide. I’m finishing it with old Texas brick and a thick mortar sack smear. The mantle will be a solid sinker cypress beam that i milled to 7”x10”x 6’. When dry it will weigh a good 200 lbs. ( I hope) I’ve already kilned out 5 gal of water since I drug it out of the swamp. My joists are 2x12 @ 16 oc spanning 11’, giving me a live load of plus 70lbs sq. The subfloor is three-quarter inch tongue and groove advantech, glued, nailed then screwed. I am considering removing the closed cell spray foam insulation on one side of each joist under the hearth area and sistering on another joist to help with deflection and to bear load. I also thought about adding a 2 x 4 under each joist to help with deflection. I could add another set of peers at mid span and add an I-beam under the joists but I am worried about shear. I’m not sure if this is necessary and would appreciate any input here.
As far as the hearth, heater later requires a layer of micore300 or a minimum of 1.03r under the non combustible framing. I would think that it would be better served under the top sheathing of the hearth but I’m going to follow the manufacturers instructions. I’ve looked for the Micore and simply cannot acquire it in this area. I decided to use a mineral fiber fire rated ceiling tile sandwiched in between two pieces of non-combustible cement board. On top of that I will use metal framing, two layers of Durock and then brick. Common sense tells me I need to attach the base to the subfloor, and not the floor joists. I would like for someone to verify this for me though. Also, is it recommended to put a layer of thin set down before screwing down the insulated panel? I will attach a few photos here. I appreciate any advice or words of wisdom. Thank you in advance
