How To Insulate RV Underbelly?

Moving in a recreational vehicle (RV) is one of the most fun things to do. However, things can go south quickly during extreme weather conditions. For instance, if it is hot outside and you have your air conditioner running but the insides are still hot. Or, it is cold outside and you have the warmer on but it is still cold inside. This is most likely happening because air is leaking in or out of the RV through its underbelly.

To put an end to this problem, you need to insulate the underbelly of your RV. But, the question is; “how do you do that?” Never to worry, we will be teaching you how to insulate RV underbelly in this article.

Types Of Insulation

There are different types of materials that you can use for insulating the underbelly of an RV. Each type of material has its advantages and the location or weather condition they are suited for. You will be learning about all of them below.


If you will be using your RV mostly in a place with low humidity, then the fibreglass is a great choice. Besides, the fibreglass is easily the cheapest option for insulating the underbelly of your RV. It is also known for handling hot weather conditions and this is because it has an excellent R-value. R-value simply means how well an insulation material can resist the flow of heat.

Furthermore, fibreglass helps to slow down the spread of heat, cold and sound in any material. This makes it an ideal option for insulating the underbelly of an RV. However, note that fibreglass doesn't do well against water or moisture. Because of this, you might need to change the insulation after some years.

Spray Foam

Another option for insulating the underbelly of an RV is using spray foam. Spray foam is ideal for moist weather conditions as it is impervious to humidity. However, spray foam doesn't do well against extreme heat. This means you should avoid using this in hot areas. Besides, spray foam is the lightest out of all types of insulations for RV underbelly. Not to mention, insulating an RV’s underbelly with spray foam is very technical. And, it is advisable to employ a professional to do it for you.

Also, we like the fact that spray foam is good for the climate as it releases no harmful substances to the air. Not only that, it can reduce the potency of different odour or pollutants. Again, it also does not attract insects and rodents which in turn make it last longer.

Rigid Foam

Lastly, you can always opt for rigid foam. Rigid foam has the longest lifespan on this list and it is the easiest to get. You can always find this foam in any hardware store around. Besides, you have a choice to choose how thick you want the foam to be as they come in different sizes and thickness. Also, rigid foam is resistant to moisture and heat which makes it ideal for all weather conditions. However, it is not easy to install rigid foam. This is because the foam can break if you apply too much pressure on it.

Besides, you can use multiple foams to get the level of insulation you desire. Note that there are 3 types of rigid foam and they are; Extruded Polystyrene (XPS), Polyisocyanurate (ISO) and Expanded Polystyrene (EPS). Whilst the three types of rigid foam are good installation materials, the Extruded Polystyrene (XPS) is the least recommended. This is because it has the least heat retention rating. This means it doesn’t do well in hot weather conditions.

Also, it tends to absorb moisture at a pace higher than the other types of rigid foam. However, regardless of all its shortcomings, we like the fact that the Extruded Polystyrene (XPS) is recyclable.

Steps On How To Insulate RV Underbelly?

Steps On How To Insulate RV Underbelly

Now, let’s get to the main reason we are writing this article which is how to insulate an RV underbelly. Below are the steps to follow.

Step 1: Examine And Measure The RV’s Underbelly

First thing you need to do is to examine the RV’s underbelly carefully for any damages. Take note of the places with holes as those are the places you will be insulating. The reason is that; it is through these holes that air goes in and out from the RV. After inspecting the RV’s underbelly, the next thing to do is to measure the underbelly. The reason for this is to determine the exact size and thickness of the insulation material you will use for insulating the RV’s underbelly.

Note that it is advisable to do the inspection and measuring during the day. This is to ensure that the underbelly is very visible and to make sure you miss no holes.

Step 2: Detach The Underbelly

The next step is to detach the underbelly of the RV. However, note that some RVs have a material called coroplast under them. The coroplast is plastic like and it can look like a cardboard box. The work of the coroplast is to protect everything under the RV. So, before anything, you need to remove the coroplast with screws to unveil the undersides of the RV. Besides, you should also check the condition of the coroplast to determine if you should change it or not.

After removing the coroplast, remove or disconnect all the wires and pumps that might disturb your insulation work. However, make sure you take note of how each wire or pipe is connected to make reconnection easier. You can do this by using markers to make marks on the wires and pipes. You can also use cameras to take images of the wires and pipes.

Step 3: Installation Of The Insulation Material

This is where you will take the measurement taken in step one into use. Here, you will use the measurement to determine the size of the insulation material you want to use. After getting the right size, you will have to install the insulation between the joists. You will start the insulation from the front of the RV, and end it at the rear. Also, make sure that each space around the joints is well insulated to prevent air from leaking in or out of the RV.

Furthermore, if you are using rigid foam or fibreglass, you can use wires or screws to hold the insulation in place. The reason for this is to prevent it from falling off. Finally, if you will be using these foams, you need to put fire-resistant sheets between them. This is to reduce the risk of the insulation burning.

Step 4: Put Everything Back

Now, it is time to reconnect all the wires and pipes you disconnected. Make sure you check the markings and the picture you took to ensure that everything is in the right place. This will be an easy task as long as you follow the markings and the pictures you took. Also, remember to tape the wires well or use connectors to avoid partial contact. Not only that, ensure that the pipes are not leaking too.

Step 5: Sealing Up

Now, you need to put the coroplast back in place. Remember to replace the coroplast with a new one if it is not in good shape. Also, you can add Dupont Tyvek for extra protection against moisture or water. Note that you can get the Tyvek from most hardware stores around as it is quite common.

Step 6: Cleaning Up

The last thing to do is to clean up the surroundings of where you did the insulation. Make sure everywhere is tidy and dispose of any dirt, debris or foreign material left over.

Safety Precautions

If you will be using fibreglass, ensure you wear a safety mask. This is to ensure that you do not inhale the fibreglass as it is harmful to the body. Not only that, wear protective gloves to avoid cutting your hands when working on the RV, also important is to use insulated screwdrivers when loosening the screws on the RV. Like we mentioned before; ensure that the wires are connected properly to prevent partial contact. This is because partial contact can lead to a fire.

Furthermore, test the RV to ensure that there are no leakages and if there are; you just have to fix them to perfection.


We have come to the end of this article of how to insulate RV underbelly. You will find that to insulate the underbelly of an RV is quite easy to do. After successfully doing this, we assure you that you won’t witness any unnecessary heat or cold due to your RV leaking. Besides, insulating your RV’s underbelly also comes cheap which is something most potential users can afford. Also, ensure that all the right tools like the protective gear are put in place before starting. Finally, we hope you enjoyed reading this article as much as we enjoyed writing them. We also hope you learnt a lot in the process of reading this article.

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