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Old 01-05-2022, 10:10 PM   #1
Mini-Skoolie
 
Join Date: Oct 2021
Location: Southern California
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Is 3/4” of insulation enough for winter?

Hello! My bus was 6’4 before I took out the plywood. I am 6’1 and trying to save some head space. HOWEVER, I plan on taking my bus in winter climates to ski. If I do 3/4 on the floor, ceiling, walls, and re seal the windows, should I be okay? Thanks in advance!

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Old 01-06-2022, 09:21 AM   #2
Skoolie
 
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From what I have read here, 3/4 on the floor with subfloor and any ceiling finishing will take 2" off the in socks available headroom. I think you'll need to shuffle carefully to not hit your head and have to be prepared to keep your heat cranked and have fans to push the heat around rapidly. Effectively you'll have maybe R6 if you really, really pay attention to blocking infiltration, more likely R4~5 effective -- less with anything but the most effective sort of foam board.


With walls/floor/ceiling that cool, you'll have to have vapor barriers of 100% continuity, and likely want to look at heat sparing air exchangers/dehumidifiers.
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Old 01-06-2022, 09:40 AM   #3
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You can probably wedge 1.5” between the ribs on the ceiling if you take the ceiling down, which I definitely would do, then maybe .5” over all of that so you have a barrier between the ribs and your finished ceiling.

If you strip the floor down most people tend to add 1.5” to the floor, then 3/4” subfloor and finish flooring, usually totaling about 2.25”

If you do that you’ll just about be out of room but you’ll still have cold feet. I would do at least 1” on the floor and the 1.5 between the ribs and you’ll be able to walk around okay but bring slippers.

Walls you can and I think should get 3.5” easily if you frame out with 2x4s, and I would very strongly consider removing as many windows as you can because they suck worse than you think. Depending on how much sun you have and your location keeping one side with more windows that you can face south when parked is advantageous but the cold nights around 0 degrees (f) challenge my 5k diesel heater in my 35’ bus and less windows would help a lot.

That being said, if I had two 5k heaters in my bus I’d be fine probably to -10 but on days like that I’m sure I would be burning through at least 2-3 gallons a day of diesel, something like $300/mo in heating.

All this is my experience with 1.5” ceiling insulation, 1.5” floors, 3.5” walls and about half of the windows gone in a 35’ FE flat nose in the Santa Fe area at about 6000 feet. Blankets over windows and a big ass comforter blocking the front drivers area for the most part.

Hope that helps!
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Old 01-06-2022, 10:20 AM   #4
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There's no real way to answer that question. Insulation is all about heat movement. In the winter you hope to slow the movement of heat out of the structure, in the summer you hope to slow the movement of heat into the structure. Why? So whatever methods you use for heat/cooling can move heat in the opposite direction faster than nature. If you have a bizillion-BTU heater, maybe a 1/4" of cardboard is enough. If you have a few birthday candles for heat, you might need to measure insulation thickenss in feet. Somewhere in-between is where you'll lie, but that depends on how much energy you're planning to provide as input to the system. And honestly, that's probably an under-estimation.

Also, insulation is a net sum game. You can insulate your stud (hat channel) cavities to R30, but if the metal studs themselves, windows, and other direct conductive/convective paths for heat to flow (effectively bypassing your insulationg) aren't addressed, you're not going to get the performance you hoped for.

I was going to link to a great online tool I used to create a rough guideline of our anticipated heating requirements (with some creativity to adapt it to a bus build), but apparently the author pulled it (link is dead). One thing I found enlightening when playing with this calculator was the impact of windows. On our 6-window short bus, the calculated difference between insulating all the side windows (R6), vs leaving them as is, with all other variables being the same, was a 20-degree delta. Meaning, with the same heat source, we could increase the temperature of the bus an additional 20-degrees simply by insulating / walling over all the side windows.

Windows are the worst. Many people delete or replace all/some. In our case, we wanted to keep the side windows for aesthetic purposes, but our insulation plan includes methods of insulating them (insulated cushions cut to fit window voids) in environments where necessary.
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Old 01-06-2022, 08:06 PM   #5
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I'm 6'1" and started with a 6'4" height.

We pulled everything off the floor down to bare metal and will be installing 1" Owens pink foam board, with 1/2" ply and then the finish layer,.

For the ceiling we pulled the metal (screwed in) ceiling and want to put that back up AFTER spraying foam to the level of the ribs (about 1.5")
The walls will be getting 2.5 to 3.5" inches of spray foam after being furred out with either wood lath or cut strips of plywood.
We have coach type windows and will be leaving two in the read bedroom, 4 in the front (living room). All others will be removed, framing installed as needed, and closed with 16ga cold rolled steel with the spray foam.
UNDER the bus we plan to have near 100% closed up with a combination of storage down the sides, closing panels across the center section (this is intended to provide both aerodynamic smoothing under way AND reduce heat transfer by providing an area of much more still air than if not closed.

We don't plan to do extreme cold weather but do plan on at redundant heat methods and are exploring:

A single mid body coolant style heater for when driving (along with the dash heat/defrost).
Two diesel fired 5kw heaters
Small wood stove for scavenged wood heat
110VAC electric blanket
Propane Mr Buddy backup
110VAC portable backup


I would consider 3/4" insulation insufficient for any build but if you're willing to spend more on heating energy every month you can probably usurvive.
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Old 01-06-2022, 11:20 PM   #6
Mini-Skoolie
 
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Quote:
Originally Posted by HamSkoolie View Post
I'm 6'1" and started with a 6'4" height.

We pulled everything off the floor down to bare metal and will be installing 1" Owens pink foam board, with 1/2" ply and then the finish layer,.

For the ceiling we pulled the metal (screwed in) ceiling and want to put that back up AFTER spraying foam to the level of the ribs (about 1.5")
The walls will be getting 2.5 to 3.5" inches of spray foam after being furred out with either wood lath or cut strips of plywood.
We have coach type windows and will be leaving two in the read bedroom, 4 in the front (living room). All others will be removed, framing installed as needed, and closed with 16ga cold rolled steel with the spray foam.
UNDER the bus we plan to have near 100% closed up with a combination of storage down the sides, closing panels across the center section (this is intended to provide both aerodynamic smoothing under way AND reduce heat transfer by providing an area of much more still air than if not closed.

We don't plan to do extreme cold weather but do plan on at redundant heat methods and are exploring:

A single mid body coolant style heater for when driving (along with the dash heat/defrost).
Two diesel fired 5kw heaters
Small wood stove for scavenged wood heat
110VAC electric blanket
Propane Mr Buddy backup
110VAC portable backup


I would consider 3/4" insulation insufficient for any build but if you're willing to spend more on heating energy every month you can probably usurvive.
Thank you!
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Old 01-07-2022, 10:48 PM   #7
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Just to be sure you understand..... our plan to put the metal ceiling back up will save head room BUT will allow thermal bridging from the outer skin of the roof to the inside metal ceiling.
We're hoping that, since heat travels upward, it will not be an issue in our normal operations. If it is, we will have to put up another layer on the ceiling which will lower headroom.
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Old 01-08-2022, 09:05 AM   #8
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Quote:
Originally Posted by HamSkoolie View Post
We're hoping that, since heat travels upward, it will not be an issue in our normal operations.
As has been mentioned in this thread, heat does not travel upward. It travels from hot to cold. Everything that is cold will take heat from the space your are trying to heat. The colder they are, the more heat they'll take away.
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Old 01-09-2022, 06:00 PM   #9
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Quote:
Originally Posted by ennonne View Post
As has been mentioned in this thread, heat does not travel upward. It travels from hot to cold. Everything that is cold will take heat from the space your are trying to heat. The colder they are, the more heat they'll take away.
The laws of thermo dynamics are in play but it's not so simple as stating that heat travels to cold. That's just a simple lay statement that leaves out information that is important for systems planning and development.
ENERGY does indeed transfer from warmer materials into colder ones but cold does not "take heat from...". The mechanics are that the higher energy (faster moving) molecules in the heated media transfer energy into the slower moving cooler media thus speeding up the molecules in the cooler media. But there is far more at play than JUST that.
Warmer materials also expand thus reducing their mass per given volume (aka density). Warmer air, with less density than cooler air, does indeed rise as the cold air also sinks due to its greater relative density.
My prior statement that "since heat travels upward..." was simply refering to the amount of warm air at the ceiling height preventing uncomfortable "cold spots" on the ceiling.

We know there will be heat transfer to the exterior through the metal thermal bridge of metal ceiling to metal rib to metal out skin. We're just hoping that in daily operations it won't be an issue but have the backup plan to mitigate should it be an issue.
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ONLY YOU can ensure your safety! . . . . . We've done so much, for so long, with so little, we now do the impossible, overnight, with nothing. US Marines -- 6531, 3521. . . .Ret ASE brakes & elect. Ret (auto/aviation). Extra Class HAM, NAUI/PADI OpenWater diver
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