G2G Insulation Twin Falls
Home Improvement

Rigid Foam Insulation

Without a doubt, the best time to insulate your home is during the initial construction. Most people will insulate their homes to the minimum legal requirement for the zoning in their area, but I personally think this is a mistake. The time is right (everything is exposed) so why not get a bit crazy and push the R factor up by 50%? Rigid foam insulation is perfect for this task.

We don’t all have the luxury of building our own custom home, but because of rigid foam insulation we all have the ability to upgrade our home insulation as our budget permits.

Upgrading your home insulation as the budget permits, how can that be?

Since the 1950’s, most homes have been built with trusses. These trusses are very well engineered and built from 2 X 4 components that make up both the roof and ceiling of your home while also creating the attic space. In many cases the strength and cost of having trusses professionally engineered and built produce a stronger and lower cost product, especially when you take into account how many man hours it would take to make your own trusses to be placed 18 inches apart.

Now we understand the trusses in our attic and we know they are normally placed on 18 inch centers, so now we need to go up there and do a physical inspection. The two things we are doing is to verify what type of insulation our home has currently installed (normally it will be the lose stuff) and to take a physical measurement of the space between the trusses. I can sit here on the other side of a keyboard and tell you it is 16 ¼ inches between trusses, but what if your home was made from “rough cut” lumber or the zoning in your area at the time required 24 inch spacing (many homes in the South that do not have a snow load had 24 inch spacing up until the mid 70’s).

This is an insulation upgrade that you will be doing as your personal finances permit, so getting the exact spacing between trusses will keep you from wasting money.

Before we go any further, lets get the concept of what we are doing out in the open. Attic insulation is the most important factor in both hot and cold weather applications. Just like your momma told you that you need to wear a hat in the winter because all the heat goes out your head, attic insulation is the same.

That stupid white rigid foam boards that they make coolers out of has an R factor / value / rating (say it any way you want) of at least 5 per one inch. Let me say this again, at least 5 R rating per inch.  That is higher than both loose and roll fiberglass.

The current recommendation for attic insulation is R-30, which is 6 inches of Styrofoam.

Now we are going to implement our insulation upgrade project using rigid foam insulation on a seriously restricted budget to insulate our attic and get the R Factor up to unnatural levels.

We already know what our spacing is between the trusses, so now you have a couple of options for sourcing your insulation.

This is the most expensive, but sheets of Styrofoam are commercially available. Just buy them and cut them down to size to fit between your trusses.

The second option is much more economical and that is to find a company that is making something out of Styrofoam and ask for their scraps. They send it to a recycling facility and only get a few dollars per ton. A ton of Styrofoam will probably insulate 3 or 4 homes to R – 100.

How many times are you driving down the street and see off cuts of Styrofoam sticking out of a dumpster? I am not advocating dumpster diving, but this is the least expensive source of insulation and if you take the time to find out who threw it out you may end up with a free source of insulation.

Now that we have a source of insulation, it is time to put it in the attic. This sounds simple, but there really is an art to this. First calculate the amount of insulation it will take to fill the space between one set of trusses from end to end (exterior wall to exterior wall) with 4 inches of Styrofoam. When you have acquired enough insulation to complete the run in a single application then you are ready.

Sweep back the lose insulation (or pull back rolled insulation) and lay your thinnest layer of Styrofoam first on the exposed ceiling. Using any type of sealant you choose (I like expanding foam), seal the Styrofoam to the trusses after it is installed. Do Not put any sealant down on the ceiling material first and put the Styrofoam on top. If you do this you will pull down your insulation if you need to make an interior ceiling repair. If you lay the Styrofoam first and then seal it to the trusses on top you will be able to remove your interior ceiling material and your insulation will be “glued” in place and air tight.

After you have laid your first layer of “sealed” Styrofoam then simply add the amount needed to bring it level with the studs used to make the trusses (normally 4 inches, but sometimes 6 inches).

Do as many truss gaps as you have insulation material for at a time but remember to totally complete each gap to the truss thickness and stagger the seams between pieces and parts of the Styrofoam scraps you are using.

Use your brain here, but if you feel the Styrofoam is providing more insulation than the loose or roll insulation, spread the insulation you moved out to another location to improve the R Factor until the next time you go up in the attic.

The final goal of this exercise is to get all the truss gaps filled with Styrofoam and then lay another 2 inches of Styrofoam the opposite way across your trusses for a total of at least 6 inches of Styrofoam (R-30) with your existing loose insulation evenly spread on top for another R-30 of insulation.

The end result is a stocking cap for your home that has a rating of at least R – 60 which is more than most American homes built in Alaska.

The best part is that this can be almost free, minus your time of course, but if it is a hobby then it is fun.



Rigid Foam Insulation