Windows to keep you comfortable inside
Whether you want to keep the heat in or out, RV windows can be be the achilles heel. In a small space, having plenty windows brings in light, which will create a relaxing and enjoyable space. However, windows are not known for their insulation value, and in traditional RVs, can be especially problematic.
Lets first make it simple. RV windows are often single pane, having an R-value of 1. A double pane window could increase that to R-2. While constructed with an air gap and sometimes even gas filled, their seals are most often not able to withstand the rigor of road travel, resulting in drafty windows, sometimes with condensation build up. Compare that to a high performance residential window that achieves R-values of 3 and 4 in a double pane configuration. These numbers can have a staggering effect on the overall R-value of the RV. Consider the statement "a chain is only as strong as its weakest link" and you get the picture. When it comes to making RVs four season ready, or simply keeping them comfortable inside in any season, there is a balance between insulation capacity achieved through R-values, and the structural integrity and weight. Add to that the desire to introduce natural light through the use of windows, and therein lies the dilemma.
The above may be enough to convince you there is a better way, but if you are stickler for numbers, lets dig in deeper. As mentioned above, a single pane window has a typical R-factor of 1. Consider that in relation to a traditional insulated RV wall that may have an R-value of 10. Some four season RVs even claim as high as R-16. A typical RV double pane window may get you a R-2 value. As you consider the true R-value of the wall, you need to combine the values of the walls and the windows.
Just to illustrate, we found this infographic from a european window manufacturer. Now it shows wall insulation of R-50 and windows with R-values of 3 to 8. Nevertheless, you can see the drastic impact windows have on the overall wall R-value.
No wonder most RVs don't offer much natural light. You must also not forget the R-values in the floor and ceiling, the airtightness of all corners, around all windows, and if you have slides, the seals that surround them. We are not going calculate using all of that, but let's dig a little deeper.
To make the basic calculations, we first convert R-value to a U-value, which is 1/R. So a highly insulated traditional RV with R-16 walls would achieve (1/16=0.0625). Now add the windows at R-2 (1/2 = 0.5). Using the same percentages as in the infographic above (85% wall and 15% window) we get (0.85 * 0.0625) + (0.15 * 0.5) = 0.128. Converting that back to an R-value get us (1/0.128=7.8). Not a great number.
If you compare these value with a regular home, there is no comparison. That is why we chose to construct using residential high performance products and techniques. Full 3.5" walls with closed cell insulation (rated at R 6-7 per inch, so say R-24), a light weight insulated sheathing (R-2), high energy efficient double and triple pane residential windows (R-4 to 6) and doors, all wrapped and taped to ensure the best possible results. Using the same calculations as above, we would achieve (1/24=0.041) for the walls and (1/4=0.25) for the windows, resulting in (0.85 * 0.041) + (0.15 * 0.25) = 0.0723. Converting that back to an R-value (1/0.0723=13.8). Almost double.
How important is your comfort, whether trying to keep it cool or warm? Living in an RV, traveling across the country is all about experiencing the outdoors. However, when we do go inside, we sure want it to be comfortable.
Let us know your experiences and how you think your windows are performing. Do you put reflective panels in the windows or have you found other solutions to keep the inside the right temperature? Leave us a comment below.