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Old 06-07-2019, 05:43 PM   #1
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How much insulation is too much?

Apologies if this has been discussed earlier and my searches didn't find it.

I'm working on a full-size bus conversion. I'm still in the demo phase and the plans are wide open. This will be an extensive conversion with the intent of going full-time eventually.

My question regards insulation. Specifically how much is too much? I've been researching various kinds and am down to foam board (easier to deal with, replaceable) and spray foam (better coverage, R-value). Assuming I've planned out my layout, and all other things being equal, how much insulation should I put in? Where is the point of diminishing returns when it comes to insulation?

I'd like to be able to stay in all kinds of weather and go all over North America. I've never been to Canada or Florida but would like to go to both at some point without freezing solid or melting into a puddle. So I'm planning on doing extra insulation in any event, but I'd also like to minimize the overkill.

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Old 06-07-2019, 05:48 PM   #2
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It's too much when it starts eating up floor/wall/ceiling space.
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Old 06-07-2019, 06:30 PM   #3
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What are your plans for heating and cooling? Reason I ask is that (IMO, anyway) if you don't plan on having some sort of AC system then you best have plenty of windows to get a crossbreeze and a ceiling fan or 2 to exhaust the hot air. I've been in buses that are very well insulated but are like dark caverns because they've been skinned and insulated and had maybe 10 sq. ft. of window opening. Add to that the garage in the back and it leaves for very little ventilation. Takes forever to cool down.

We've been baking in the Badlands sunshine for the past few days and the indoor temp is the same as the outdoor temp. when our windows are open. When we were gone for the heat of the day and the bus was closed up and the insulated shades drawn, it was maybe 10deg warmer inside but it cooled down to ambient temp in like 20 minutes when we opened it up.

Insulating the ceiling made a huge difference. We also put 3" in the walls, below the windows. We kept all of our windows and installed screens. Kept the back door opening and installed a screen as well.

I'd rather have to heat a bus up than have to cool it down.
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Old 06-07-2019, 06:53 PM   #4
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Too much depends on how much living space you're willing to give up.

Of course tight vapor barrier, stopping drafts leakage, thermal bridging, radiative losses, etc is every bit as important as R-value.

Sitting running aircon off a gennie in the AZ desert, or camping in high altitude ski country all winter, is where mote diligence is required.
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Old 06-07-2019, 07:05 PM   #5
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2 closed cell foam is good. More is fantastic but you have to do In a second application. But your windows are still a problem. If you delete a lot of windows or replace with good RV windows it will make a big difference.

Also consider ways to section off sleeping spaces so you can climate control a smaller area at night.
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Old 06-09-2019, 10:41 PM   #6
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Quote:
Originally Posted by o1marc View Post
It's too much when it starts eating up floor/wall/ceiling space.
That was my initial idea as well, but elsewhere I've read comments like "more than two inches is a waste." So I thought I'd ask.

Quote:
Originally Posted by Drew Bru View Post
What are your plans for heating and cooling? Reason I ask is that (IMO, anyway) if you don't plan on having some sort of AC system then you best have plenty of windows to get a crossbreeze and a ceiling fan or 2 to exhaust the hot air. I've been in buses that are very well insulated but are like dark caverns because they've been skinned and insulated and had maybe 10 sq. ft. of window opening. Add to that the garage in the back and it leaves for very little ventilation. Takes forever to cool down.

We've been baking in the Badlands sunshine for the past few days and the indoor temp is the same as the outdoor temp. when our windows are open. When we were gone for the heat of the day and the bus was closed up and the insulated shades drawn, it was maybe 10deg warmer inside but it cooled down to ambient temp in like 20 minutes when we opened it up.

Insulating the ceiling made a huge difference. We also put 3" in the walls, below the windows. We kept all of our windows and installed screens. Kept the back door opening and installed a screen as well.

I'd rather have to heat a bus up than have to cool it down.
I have plans for both. I'm planning on a mini-split, but not sure if I can get away with just one. I'm looking into a ducting setup so the air can be pushed around the bus. I'm also looking for something like I've seen a buddy of mine use. It's a large box fan with an integrated evaporative cooler. He fills up a tray from a quart jar every couple of hours and a little pump keeps the mat wet. Finally I'm planning on 3 roof vents with fans (kitchen, bathroom, and bedroom) so I can open windows and get a cross breeze.

For heat, I'm deciding between a propane furnace, a diesel heater, and a wood stove (with one of the previous two).

We've already had to bungie a box fan in an open roof hatch and open other windows to get some relief from the heat (bus is not a white-top yet, we live in the desert).

Oh, also I'm planning on deleting all the existing windows (minus windshield and rear escape window) and putting in insulated RV windows with screens were appropriate. In extremes, we'll be using window insulation.

Quote:
Originally Posted by john61ct View Post
Too much depends on how much living space you're willing to give up.

Of course tight vapor barrier, stopping drafts leakage, thermal bridging, radiative losses, etc is every bit as important as R-value.

Sitting running aircon off a gennie in the AZ desert, or camping in high altitude ski country all winter, is where mote diligence is required.
I'm designing for two, with temp accommodation for two or three more (fold down couch, convertible dinette). I'm doing a roof raise (8-12", depending) with insulated furring strips, so I've got some room. I am also planning a very tight vapor barrier, trying to keep as much moisture out of the insulation (and inside metal skin) as possible. I'm aiming to make the bus liveable in extremes for several days to a week (for say a snowmobile or ski trip, or a rally, or a freak blizzard).

Quote:
Originally Posted by david.dgeorge07 View Post
2 closed cell foam is good. More is fantastic but you have to do In a second application. But your windows are still a problem. If you delete a lot of windows or replace with good RV windows it will make a big difference.

Also consider ways to section off sleeping spaces so you can climate control a smaller area at night.
I've heard about problems with closed-cell foam curing correctly if you go too thick, so I was planning on multiple layers to get my desired thickness (If I DIY, I'm hopeful a professional would know that) under an interior vapor barrier under plywood walls. I'm planning on deleting nearly all the windows, mainly because old bus widows suck and I'm not nearly as attached to them as a lot of people.

I will be working on ways to section off the bus. Thanks for the idea.

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Old 06-09-2019, 11:52 PM   #7
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Formular 250 Rigid Pink insulation in a 2" thickness gives it an R10 factor, double it to 4 and it doubles the R factor to R20. If you're spraying it, you can spray up to 2-1" layers before needing to let it cool before more layers can be added. So you can get what you need in a single application.
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Old 06-10-2019, 10:59 AM   #8
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From reefer box testing, the maximum R-value is polyiso sheet foam, shielded by a 1/2" of XPS on the outside.

Get all that fixed in place inside an external vapor barrier

not just for moisture, means perfecting the envelope against convection / infiltration, e.g. HD dropcloth

then use a good 2-part spray to fill all the gaps, seal it all up as a locked-in monolithic shell - more vapor barrier envelope perfecting

and maybe add a bit more thickness to the inside if you have leftover.

For the spray part, try to find a local contractor who's friendly, work around their schedule maybe drive all prepped to an existing construction job site they already have booked, might end up cheaper than DIY.

A big challenge is scraping any uneven protrusions interfering with your innermost finish paneling, really just tedious but a pro job should help minimize that.

I've also seen that inside layer used as a "mold", add tongue and groove from the bottom up filling in the between space as you go. DIY with a pourable 2-part is another option with that approach.

But anything strong enough to resist the (very strong!) expansion force will be heavy, you don't want to deform the inside surface any more than the vehicle skin.

Warm temperatures and humidity specs are critical to proper curing, read the datasheets!
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