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Advice sought. Trailer in SoCal. Wood/vinyl flooring.

 
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This is my first build.

I rent single-wide house trailer (circa 1970, with 4” walls, unknown insulation, poorly constructed, 650 sq ft) that currently has no heat. Previous tenant used portable propane heaters. I am in Southern California in the hills above LA. It is noticeably cooler than living in the LA basin, but not as cool as the High Desert. It is about halfway in between the two, climate-wise. Heating Degree days is 2500.

I am going with a 6” RMH. I am using the Walker ceramic fiber core J design. I’ll wind up with something like Wisner’s 6” Annex design by the time I’m done.  Just out & back with a flat bench. 2.5 ft x 9 ft, roughly. Drum & chimney completes an L shape to the straight bench at one end.  I’m conscious of not putting too many turns in because my climate seems not cool enough to allow for great chimney draw.

I have a big pile of free red bricks to use and the local soil is very mineral rich, low clay, virtual no organic matter. I figure to just mix straight soil with fire clay for the cob, and call it done. Does that make sense? Is straw a necessary ingredient?

I am in the middle of reinforcing the suspended wood floor now to take the weight (easily done). It was 2x6 on 2 ft centers with 3/4” OSB and roll vinyl on top. Now it’s plenty hefty for the weight, but protecting the vinyl concerns me.

Plan A: Put greenboard, or masonry board, or something down on the vinyl. Put red bricks down flat on greenboard with plenty of air gaps (two-thirds air, one-third bricks, say). Put another layer of greenboard down. Build a rim of flat red bricks around the circumference. Fill the interior with perlite/clay, 2” (one brick depth) deep. Build up from there with cob.

Plan B: put greenboard down. Rim the circumference with vertical red bricks. Fill the interior with 4” of perlite/clay. Build cob up from there.

I’m not sure how important the air gap layer is for a wood/vinyl floor. Advice welcome.

Offhand, I prefer Plan B if the vinyl is safe that way ... less greenboard to purchase ... goes in faster ... and fewer spiders will move in under my RMH.

Thank you all for the forum and for being a cool community.
 
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Hi Peter,

A few suggestions to consider:
If you were to eliminate the piped bench and go with a bell bench instead, you would eliminate a lot more friction and would be a lot lighter on your floor as well.

Adding straw to the cob is important as it provides tensile strength in those areas especially that are going to experience wear and tear. It also is good if your looking to have a bit more insulation added in key areas instead of mass.

A fellow rocketeer has just recently posted his findings on a raised platform here that may be helpful for you:
ton-RMH-basement-floor
 
Peter Mauk
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Thanks for your reply.

I really want mass to keep the place warm for my dogs while I am away all afternoon/evening (I work the swing shift)... So, I think a flue pipe bench with mass is a better choice than a bell bench in my application.

The link you shared makes me think that an air gap is needed under the burn box (and maybe manifold) area to protect the floor, but not for the bench area. Perlite/clay, say 4”, might be good enough there.  Any thoughts?

My concern isn’t weight, it is keeping my vinyl flooring from melting.
 
Gerry Parent
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No absolutes Peter, as it really depends on how much you burn in a day that will dictate how hot the floor under the bench will get.  

In Stove Chat 31 around the 30 minute mark, Matt Walker talks about foundations under a RMH.
 
Peter Mauk
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Gerry, thanks for your comments. That Stove Chat 31 was right on point - appreciate the link.

My conclusion now is to not worry about it so much - I’m going with perlite, no air gap.

As the Video points out, when you raise up the build to allow an air gap, you also automatically create pressure points under the supports, leading to uneven weight distribution, which is another challenge for the wooden floor that then must also  be addressed. Distributing the weight with cement board seems far wiser in my application.

I won’t ever be running it all day, or anything, i think. A cold spell here is a few weeks in the 30’s at night, but it rarely ever even frosts. So, major heat buildup under the stove will never be an issue.

My burn box is ceramic board. I’ll put a layer of fire brick splits under that, and 4” of perlite in a hardiboard “box” under that. Sound about right?

Best Regards.
 
Gerry Parent
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Glad the video helped. There is a live one today at 11am on Matt's broaudio channel as well if you have any more questions or just want to listen in.

Your recommendation sounds about right for the amount of burning your going to be doing, but being overly cautious in this area can never hurt either. We'll let you decide on that one.
 
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The firebox does not have to be a major mass (it's mostly hollow after all ), so I don't see bricks to raise it and make an air space to be problematic. Even if you lay the bricks flat and leave one brick's worth of gap between them, you would get significant venting capacity, and also be able to verify that it is not getting too hot at the floor.
 
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