Worthwhile to insulate/enclose underbelly without heating?

DiskDoctr wrote:

I believe you have that backwards....

XPS (blue/green/pink at big box stores) is considered non-absorbing and EPS (white) is water absorbing.

Owens Corning XPS vs EPS water absorbing foam

I believe you might be correct... (Memory isn't what it used to be.)

Every time I think about the foam they use in the walls, I just can't believe they use something that absorbs moisture. Not good when cold weather camping.

The first and BIGGEST difference insulating can make is 1) Stop the flow of air.

Enclosing the underbelly in a fairly airtight manner is the first and most important step. If air flows through it, the insulation is of much less benefit (especially fiberglass, which relies on trapped air for insulating)

Air is a pretty good insulation, if you can trap it. Just remember to think about moisture in trapped air spaces. Another benefit to furnace heated basements, the airflow helps remove the moisture (can add it too, not perfect)

If you use XPS foam and seal it tight with little or no air spaces, less opportunity for moisture to form and creates a good thermal break.

Good luck ;)

myredracer wrote:

agesilaus wrote:
Styrofoam absorbs water?

It will depending on type. The open cell rigid expanded polystyrene XPS type absorbs moisture and moisture migrates through it. It's the white stuff disposable coffee cups are made from. It's the type that is used in exterior walls of RVs and is a really bad choice because of moisture migrating through exterior walls to a cold exterior skin and condensing.

Closed cell rigid extruded polystyrene EPS type does not absorb moisture and cannot migrate through it and acts as a vapor barrier. It's the pink or blue or sometimes green stuff you see in building supply places. It is denser and has a much higher R-value but is more expensive and is why it's not used in RVs.

Both types come in spray or rigid sheet versions. A better rigid or spray foam is icynene which has a higher R-value but costs even more. It's not fun to work with and makes a nasty dust when cut.

I believe you have that backwards....

XPS (blue/green/pink at big box stores) is considered non-absorbing and EPS (white) is water absorbing.

Owens Corning XPS vs EPS water absorbing foam

rexlion wrote:
Icynene is a type of urethane foam, but not dense so it could absorb water. Application of sprayed urethane is a pro job for someone with the proper sprayer and equipment, not really geared toward DIY, but it (the dense variety) is very good insulation.

EPS will work well too.

I assume you will attach the coroplast with hardware? Those sheets are tough to get glue to adhere... even the specially etched sheets.

Spray foam polyurethane is pretty much do it yourself these days. It might not be cheap depending upon how much area you need to cover but you can buy the kits at Home Depot and DIY.
DIY Spray Foam

rexlion, yes -- I will use hardware for the coroplast. I am leaning toward beam clamps -- they screw onto the flange of the I beams of the chassis.

Icynene is a type of urethane foam, but not dense so it could absorb water. Application of sprayed urethane is a pro job for someone with the proper sprayer and equipment, not really geared toward DIY, but it (the dense variety) is very good insulation.

EPS (edit--oops, should have said xps) will work well too.

I assume you will attach the coroplast with hardware? Those sheets are tough to get glue to adhere... even the specially etched sheets.

agesilaus wrote:
Styrofoam absorbs water?

It will depending on type. The open cell rigid expanded polystyrene XPS type absorbs moisture and moisture migrates through it. It's the white stuff disposable coffee cups are made from. It's the type that is used in exterior walls of RVs and is a really bad choice because of moisture migrating through exterior walls to a cold exterior skin and condensing.

Closed cell rigid extruded polystyrene EPS type does not absorb moisture and cannot migrate through it and acts as a vapor barrier. It's the pink or blue or sometimes green stuff you see in building supply places. It is denser and has a much higher R-value but is more expensive and is why it's not used in RVs.

Both types come in spray or rigid sheet versions. A better rigid or spray foam is icynene which has a higher R-value but costs even more. It's not fun to work with and makes a nasty dust when cut.

We've had both enclosed and open underbellies. I installed 100% electric heating in our current TT and we no longer use the furnace and therefore no warm is blown into the underbelly. We camp down into the 30s but never in freezing temps. When the underbelly isn't insulated or enclosed/warmed, the floor will feel quite cold on your feet and your legs will also feel cold. Uncomfortably so to us and we're not even in sub-freezing temps. We use slippers or heavy socks and when watching TV use a blanket on our legs.

Insulation will definitely help and will reduce stratification, the temp. difference between floor & ceiling and improve interior comfort. I'd also through the trailer and seal up all cracks and gaps you can find in the floor. But you'll still need to vent the interior to remove moisture laden air - a dehumidifier could be an alternative but not without power of course. Resist the temptation to insulate and seal the heck out of it and not vent it otherwise you may end with rot, mold & delamination.

Use a closed cell rigid foam blanket around the tanks and everywhere else you can fit it in and then spray foam in a can to fill cracks 'n gaps. You may want to relocate piping to the underside of the floor as needed so it is on the warm side of the insulation. Note that batt insulation absorbs moisture and when it does, the R-value can drop significantly. It's also not a good choice in RVs but is simply cheaper to install.

We do not winter camp, so take this advice with a grain of salt. Our old trailer did not have an enclosed underbelly nor tank heaters. When I was going to have tank heaters installed to winter camp (which we never did), I was told that I only needed a tank heater for the fresh water and to use salt in the black and grey tanks to prevent freezing.

I do not know if this was work though. Seems like the salt would cause some damage but maybe I am wrong. Other people seem to do it I guess.

kerrlake, we use almost no heat (except at shower-time, when we use the furnace). The rest of the time, even in ten degree weather, we do what the Eskimos do -- dress warmly! It works for us.

And Steve, thanks again for that tip on Blue Board -- I had never heard of that .

Good point, agesilaus, about keeping the trailer cooler in summer -- there are times when we are camped in the mountains in the summer, and it will still get up into the 80s during the day. Without air conditioning (no hookups!), it would be great to reduce the heat gain inside the trailer.

OK -- I think I know what to do -- install heat tape on a just-in-case basis, then insulate, then button up the underbelly.