Another Hearth Pad Construction Question

[randjj1]

First of all, I've been reading through posts and am impressed with the wealth of info here. I really just want to double check that I'm thinking correctly regarding building our own hearth pad. We are building a home and will be putting a Quadrafire 3100 step top wood stove in. The instructions state "minimum thickness of 1-1/4 inch or 1/2 inch of k value of .84 thick metal clad millboard or equivalent a minimum of 16 inches in front of glass .....". Can anybody clarify exactly what this means? If it's 1-1/4 inch of noncombustible material is that OK? If it's only 1/2 inch but the k value is .84 - is that OK? I'm honestly not quite sure what it means - I did email Quadrafire and am waiting for a reply. I called the local dealer and they weren't much help - they don't install the hearths, just sell the stoves and actually told me I could just set the stove on a wood floor with a hearth rug in front of it.
We think we want a raised hearth anyway, so here's what we're thinking of doing:
1. 2x4 or 2x6 frame with 3/4 plywood or OSB on top
2. 5 layers of 1/2 inch Durock to get .84 k value - screwed with Durock screws to the plywood base along the perimeter
3. Tile on top using thinset
4. We'll be placing it on top of tongue and groove wide plank pine without anchoring to the the pine floor
A few more questions -
Can the Durock/plywood just be dry stacked with no adhesive between layers?
Do I need to screw/nail it together anywhere besides the perimeter?
Does it matter what tile I use?
Is the Durock really heavy - will this be a heavy hearth pad?
Any other ideas, thoughts would be appreciated.
Thanks!

 

[begreen]

Yes, it would be really heavy. I don't think you need the durock build up. To make it really skookum, after the plywood top, use 1/2" micore, then a sheetmetal layer (can be thin 28 ga.), then 1/2" layer of durock, then tile.

Or you could use metal studs on 12" centers to create an air space and just a couple layers of durock before the tile.

https://www.hearth.com/econtent/index.php/articles/k_values_what_does_it_all_mean

 

[randjj1]

Thanks for the advice. I just heard back from Quadrafire (very quick response) and they said that as long as my noncombustible material is 1-1/4 inch thick, it doesn't matter what the k value is. If it's less than that - it must be at least 1/2 inch and have a k value of .84. That gives me a lot of options!
Thanks for your help!

 

[begreen]

Yep, lots of different ways to skin this cat. I'm glad to hear that Quad was quick to respond.

 

[Maineah]

I had some 10' pieces of hat channel given to me yesterday. So for my pad for a napoleon 1400, I was going to put 2x4 flat on my floor, screw the hat channel to them, 1" air space, screw 2 layers of durarock to the hat channel and then tile. My stove only requires a non combustable approved material. No r value quoted. Will it work??

 

[begreen]

If just a non-combustible shield is required it should be fine.