Floor insulation

[BuswithJason&Angie]

We are converting a coach and looking for advice on floor insulation. Our coach is quite vintage (1948! ) so we are limited in height and really don't want to loose too much clearance. We will have to put down a plywood subfloor to stick our marmoleum tiles onto. Is it worthwhile to add a layer of thermal underlay beneath the plywood? That stuff is so thin I am skeptical it will do much.

[dzl_]

Originally Posted by BuswithJason&Angie

We are converting a coach and looking for advice on floor insulation. Our coach is quite vintage (1948! ) so we are limited in height and really don't want to loose too much clearance. We will have to put down a plywood subfloor to stick our marmoleum tiles onto. Is it worthwhile to add a layer of thermal underlay beneath the plywood? That stuff is so thin I am skeptical it will do much.

If you don't insulate the floor you are leaving ~20% of your bus uninsulated (plywood does provide some minimal amount of insulation but not much).



I would think an uninsulated floor would be unideal in any climate but much more of an issue in cold weather or when actively heating or cooling the bus.


Even 1/2" (or maybe even 1/4" if its available) could have a big impact on the overall insulation of your floor. (1/2" Polyiso is upto R 3.2)
However, if you live in temperate climate and/or if you will not be insulating the walls or ceilings, maybe its not adding insulation but losing standing room. I've lived in a home with an uninsulated floor and ceiling my entire life, costs more to heat in the winter, but I live in a very temperate region where "hot" is above 80 and "cold" is overnight lows in the 40s.

[BeNimble]

You could put insulation under the floor. It won't be nearly as effective, but much better than nothing. As I was using old fridges for insulation, I was going to leave one side with the steel and have it be the bottom side to keep the foam from getting torn up. I raised my roof, so no reason to do this now. What flooring? Maybe skip the plywood and use foam instead.

Heat rises, so the roof is more important for heating, your cold a/c sinks, so the floor more important for cooling, but it all matters.

[dzl_]

Originally Posted by BeNimble

What flooring? Maybe skip the plywood and use foam instead.

Cork is another option. R3.6 per inch, used for both thermal and acoustic insulation and is commonly used as sublayer beneath hardwood, cork, or vinyl floating floors. A thin layer of that would be better than nothing and kind of purpose built for the application. I would look into how moisture resistant/tolerant it is before selecting it though.

Heat rises, so the roof is more important for heating, your cold a/c sinks, so the floor more important for cooling, but it all matters.

I agree with the first part but not necessarily the second. Most of the heat gain will be coming from the roof and south facing wall, while I agree with you that cold air sinks and thus to minimize the loss of cold air insulating the floor makes sense, I suspect that particularly in temperate or desert climates (low to medium humidity) ceiling and wall insulation may have a bigger impact in keeping interior temperatures lower. I could well be wrong though, just sharing my thinking.

[john61ct]

The best R-value per thickness is polyiso slabs, but a tight envelope aka vapor barrier is important - boards + spray foaming the underside might be best.

But of course your relative need depends on the temp difference between inside and out, and how efficient/costly your heating / cooling measures.

Lots of **floor** insulation would only be "needed" using aircon off grid in very hot temperatures.

For snow conditions, if your heating isn't costing too much even just carpeting + underlay may be enough.

[musigenesis]

Heat doesn't rise, hot air rises because it's less dense than colder air. Heat moves from hot objects to colder ones irrespective of gravity.

[BeNimble]

Originally Posted by musigenesis

Heat doesn't rise, hot air rises because it's less dense than colder air. Heat moves from hot objects to colder ones irrespective of gravity.

Indeed if your hot metal roof is radiating heat into the space, air conditioning is not going to keep up no matter how much insulation is in the floor.

[BuswithJason&Angie]

We are going to use commercial grade floor tiles to get the checkered pattern we are after, so they need something solid and smooth to stick to. Maybe I can give up 1/2 for foam underneath that.

Has anyone tried any of those flexible thermal underlays?

[musigenesis]

Originally Posted by BuswithJason&Angie

Has anyone tried any of those flexible thermal underlays?

I'm assuming you mean this stuff: https://www.homedepot.com/p/SilentSi...0B35/204399267. It's probably slightly better than nothing, but even 1" XPS foam board would dwarf whatever tiny insulating benefits it would provide.

an integrated radiant foil middle layer that promotes heat retention within the conditioned space

Reflective foil bottom layer reflects heat back into the room in winter

These particular product claims are essentially bunk, for two reasons: 1) a reflective layer requires an air gap of at least 1" to have any effect at all, otherwise the radiant energy that it reflects is absorbed by the adjacent solid material and it ends up in your living space anyway; and 2) the amount of radiant heat given off by an object is basically miniscule within the range of temperatures that people normally occupy; it only becomes slightly relevant at the high temperatures a roof out in sunlight will get to, and a bit more relevant with the temperatures an oven or wood stove will get to (which incidentally is why a reflector behind a wood stove is so important). On your floor, that foil layer (or is it two foil layers?) is useless, so all you have is a 1/8" thick layer of foam for a generous R1 (about the same insulating value as your plywood layer, which is what makes this better than nothing).

[dzl_]

Originally Posted by BuswithJason&Angie

Has anyone tried any of those flexible thermal underlays?

You should provide a link to what you are referring to, there are about a million and a half different underlays and insulation types, its hard to guess exactly what you are referring to.

[BuswithJason&Angie]

Originally Posted by dzl_

You should provide a link to what you are referring to, there are about a million and a half different underlays and insulation types, its hard to guess exactly what you are referring to.

I did not have a specific product in mind, but have seen some listed online.

[CHEESE_WAGON]

If operating primarily in colder climates, you might consider re-working the floor to include a subfloor with radiant heat using pipe encased in foam insulation, plumbed into the engine's cooling system. You also might consider incorporating this idea with an automatic power unit (APU) sourced from a semi tractor. If you go APU, stick with ThermoKing -- ComfortCool units SUCK!

Besides saving fuel, an APU can also provide electric power and be plumbed into the chassis engine's cooling system to help keep it warm for easier cold starts -- something I imagine to be a huge plus with a vintage coach, as most were 2-stroke Detroits, which are not known for their cold-weather eagerness.

[dzl_]

Originally Posted by BuswithJason&Angie

I did not have a specific product in mind, but have seen some listed online.

Whatever, products you look at, I would (1) look for products that state the R-value for a given thickness prominently and without wierd caveats, (2) stick with products that are at least somewhat known and trusted in the trades (this doesn't have to be just construction, automotive, marine, rv), (3) don't trust unsupported company claims (there are a ton of snake oil products in the insulation space), and don't trust consumer opinions alone (most consumers--including many youtubers--don't really understand insulation, hence the popularity of reflectix and similarly ineffective products).

[john61ct]

^^^ +1 ^^^

[Rock-N-Ruth]

Originally Posted by BuswithJason&Angie

We are converting a coach and looking for advice on floor insulation. Our coach is quite vintage (1948! ) so we are limited in height and really don't want to loose too much clearance. We will have to put down a plywood subfloor to stick our marmoleum tiles onto. Is it worthwhile to add a layer of thermal underlay beneath the plywood? That stuff is so thin I am skeptical it will do much.

Since you really don't have a lot of room put insulation on the floor you might consider spray foaming underneath the floor. We live in New Mexico where it doesn't get very cold very often so we put a couple of layers of those puzzle piece phone block floors down and it keeps the floor comfortable to bare feet. We didn't put any kind of flooring on top of it and it is getting a little marked up with pitbull claw marks. I guess we could trim his claws or teach him how to walk little more lightly.

[joeblack5]

Wow..that "walking more lightly" would be impressive.... Cbd oil?

[Bon Voyage]

I put 1.5” of ridgid type foam (R 7.5 I think, can’t remember) followed by 1/2” plywood with laminate and underlay. We also had about 1/3 of the bottom outside part of the floor spray foamed. The floor still feels cool on the feet if it’s cool outside. If you’re going to be in places that get below 40 or above 80 I would definitely have at least 1/2” insulation in there. Any thin flooring underlay will do next to nothing for insulation. And a big thing is to spray foam any gaps you have, it can make a huge difference.