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Old 04-04-2017, 07:32 PM   #1
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Spray foam is in, now how to deal with thermal bridge of bus ribs....

How did you guys deal with the thermal bridge from the bus ribs before you attached your interior roofing material?

I'd prefer to go with tongue and groove pine on the inside. Should line each rib with a foam or thin wood layer first before affixing the tongue and groove to it?

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Old 04-04-2017, 07:42 PM   #2
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I didn't want my wood interior to touch the ribs so I covered the ceiling with 1/2" styrofoam panels first. The styrofoam panels compressed as I screwed my interior panels to the ceiling making a nice tight fit against the ribs.
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Old 04-04-2017, 07:55 PM   #3
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What type fof screws did you end up using to get through the metal ribs?
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Old 04-04-2017, 08:13 PM   #4
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I first bought self tapping screws but it was taking three screws to get into the ribs because the tips of the screws kept breaking off.
I switched to GRK R4 Multi-Purpose Screws 9x2". Probably not the right screw for this but seemed to work good. What I ended up doing was breaking out two electric hand drills, one with the drill bit and the other with the T-25 driver head.
Yeah, I know. Nobody wants to drill each hole then set the screw, but it goes much faster than the self tapping screws did.
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Old 04-04-2017, 08:30 PM   #5
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yes a foam board between the two is what I did also, well worth the effort.
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Old 04-05-2017, 08:14 AM   #6
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My thought was to attach furring strips to each rib. I've taped off the ribs with duct tape to fit the rib exactly (I learned from your experience Robin97396). Right now, HD has duct tape which is about 1 inch wide. It comes in a package of about 6 rolls. I love it because I don't have to cut down regular duct tape to fit the rib perfectly.
Now I'm ready to spray the foam.

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Old 04-05-2017, 08:42 AM   #7
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The wood will still transfer the heat without something in between. Foam board then furring strips. Then t&g. This also puts a air gap between the t&g and the foam board. Not the only way but it sure stayed cool in Florida. The wood on the ceiling never got above 75. The white roof got in the 105 and the black rib between the windows got to 138.
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Old 04-05-2017, 09:04 AM   #8
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The wood will still transfer the heat without something in between. Foam board then furring strips. Then t&g. This also puts a air gap between the t&g and the foam board. Not the only way but it sure stayed cool in Florida. The wood on the ceiling never got above 75. The white roof got in the 105 and the black rib between the windows got to 138.
Thank you.

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Old 04-05-2017, 10:28 AM   #9
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Last year I stripped out the interior panels and insulation from my bus. Right about that time we got that real hot couple weeks of mid-summer weather. The top of my head was turning red from being in the bus because the roof was so hot. I didn't have a majic ray gun temperature sensor so I don't know how hot the metal was, but I couldn't stand to touch the metal roof with my hand.

The moral of the story is obvious. Don't have bad timing.
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Old 04-05-2017, 11:03 AM   #10
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Foam is good.

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Originally Posted by tobeamiss View Post
My thought was to attach furring strips to each rib. I've taped off the ribs with duct tape to fit the rib exactly (I learned from your experience Robin97396). Right now, HD has duct tape which is about 1 inch wide. It comes in a package of about 6 rolls. I love it because I don't have to cut down regular duct tape to fit the rib perfectly.
Now I'm ready to spray the foam.

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I duct taped the interior of my bus the hard way. I used regular duct tape then went back and trimmed the excess 1/4" stips off the sides of each rib with a razor blade. What a pain. It took me four days just to tape the bus. That's a lot of tape.
As it turns out taping for spray foam doesn't need to be very carefully done. The apparent purpose is simply to have a flat and clean rib surface without a bunch of foam making the rib lumpy. My foam guy sprayed 1 1/2" to 2" deep over the ribs. I had to chisel my way down to the ribs to expose the duct tape on the entire ceiling and walls, then level all the foam between the ribs. That took another eight days of sawing and carving foam. After all the sweating and cussing during the heat of the summer it was well worth all the effort this winter.

Yesterday I finally finished hanging my interior plywood ceiling panels. I still need to box in the wiring bundles that run along the top of the side windows, then finish up around the driver's window. I love the look of the tongue and groove, but I went with plywood as part of keeping this vehicle as the van stated on the title.

Foam is good, and by now all my skinned knuckles have healed up.
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Old 04-05-2017, 12:38 PM   #11
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How about 3M foam tape? Will it work ?
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Old 04-05-2017, 01:34 PM   #12
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I thought of using something like using weather stripping tape.

I chose the styrofoam panels because it also creates a vapor barrior. By vapor barrior I mean it stops the humid air from cooking, bathing, etc. from getting to the cold steel ribs. Also if there are ever leaks in the roof the rigid insulation will cause any water from leaks or condensation to shed to the sides of the bus rather than dripping everywhere.

If you live in a bus while it's interior is all stripped out you learn a lot about how the condensation works. Honestly I was guessing about using the rigid insulation on the ceilings and walls under my plywood interior. I knew I needed a thermal break, but the foam guy I used put way to much spray insulation on the walls and ceilings. Having all the cavities completely filled with foam changed my plans because I knew there would be no airspace for the thermal break. Also watching the small area of exposed rib gather condensation I figured it would be best to have those exposed steel ribs covered as much as possible. The styrofoam sheets would press tight against the ribs, avoiding condensation by covering the still exposed face of the steel ribs.

After all that, I do have five hundred screws that are in direct contact with the ribs likely conducting heat. I can't feel any cold spots and can't see any signs of condensation from the screws. My plywood interior seems to have a very even temperature. I still have a cold floor, but one step at a time.

My claims of a reduced heating bill this winter are true, but that wouldn't have been possible if I hadn't cut rigid insulation to fit snugly into each window. I'm the guy that wanted to keep all my windows so I have a 360* view when I'm out in the puckerbrush, but you can't see out at night anyway. The panels only take a minute to remove or reinstall, and they give privacy at night. The weather is much warmer now but I still use the panels kind of like curtains. From the outside the tinted windows look a bit darker with the shiny side of the insulation panels facing out.
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Old 07-02-2021, 11:47 AM   #13
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Other materials to prevent thermal bridge on ribs

I understand the majority of folks that want to prevent thermal bridging between the ribs of the bus and wood furring strips install insulation board between the furring strips and the ribs. Is there other materials that would be efficient at preventing the thermal bridging? Could you coat the ribs with a rubbery paint such as flex seal or other type of tape to serve the same purpose? Any insight to this would be helpful.

Additionally, screwing in the furring strips, will still cause direct metal to metal contact from the screw to the rib. Would it make sense to counter sink the screws 1/4" and fill the holes in with spray foam?

I am ripping 2x4's in half and using them as my furring strips so that I will be able to have 3" of insulation on the walls and ceiling.
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Old 07-02-2021, 01:06 PM   #14
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Wood itself is a decent thermal break. It has a thermal conductivity roughly 5X higher than foam insulation (so you still want to minimize your use of it), but steel conducts heat 300X better than wood so that's the stuff you really don't want penetrating all the way through the insulation to your interior space.

Quote:
Could you coat the ribs with a rubbery paint such as flex seal or other type of tape to serve the same purpose?
There's no magical substance that can block heat transfer significantly when it's only as thick as paint or tape. R-value is the thickness of a material divided by its thermal conductivity, and when the thickness is 1/30" (at best) the resulting value is necessarily going to be tiny.

Quote:
screwing in the furring strips, will still cause direct metal to metal contact from the screw to the rib. Would it make sense to counter sink the screws 1/4" and fill the holes in with spray foam?
Sure - not for the insulation value which would be pretty minimal, but to prevent potential condensation problems on the screw heads. I did this with my furring strips (sometimes, when I remembered to do it) although I just stuck little bits of XPS scrap in the holes. Wood filler would do the trick as well.
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Old 07-02-2021, 01:10 PM   #15
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Great video on insulation. Guy claims EHP rollboard made a huge difference in his bus that was already spray foamed.

https://youtu.be/hw1UpnSjLV0
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Old 07-02-2021, 01:20 PM   #16
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Originally Posted by 84chevyguyid View Post
Great video on insulation. Guy claims EHP rollboard made a huge difference in his bus that was already spray foamed.

https://youtu.be/hw1UpnSjLV0
Yvan is a stand-up guy who does tons of research. We've also been really impressed with the same kind of product under the Ceratex brand. We first found it in a generator bay, in an ambulance we bought 7 or 8 years ago, and it was amazing how well it blocked heat transfer. We use it as a thermal break.
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Old 07-02-2021, 02:22 PM   #17
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Originally Posted by rossvtaylor View Post
Yvan is a stand-up guy who does tons of research. We've also been really impressed with the same kind of product under the Ceratex brand. We first found it in a generator bay, in an ambulance we bought 7 or 8 years ago, and it was amazing how well it blocked heat transfer. We use it as a thermal break.

Thank you both! That is very helpful.
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