Dense pack 2×4 walls with cellulose
My question/concern is regarding the best approach to take given the following information. I have a 1950’s era home built with 2×4 walls. I discovered there is no insulation in the walls, but there is what appears to be a radiant barrier made up of two layers of foil with pleated paper between.
My question is two part: Should I dense pack over the radiant barrier and crush it rendering it completely useless, or should I leave the radiant barrier alone, remove the siding and install xps board insulation to the exterior of the skip sheeting, fur out windows and doors, and reinstall siding?
Which method would result in the best energy savings and provide the best solution for the building integrity and longevity?
Thank you for your time and assistance
Cameron
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Where are you? Can you do both the dense packing and the exterior XPS, or is it a "one or the other" deal? Is the radiant barrier on the inside of the stud bays, or the outside?
Q. "Should I dense pack over the radiant barrier and crush it rendering it completely useless, or should I leave the radiant barrier alone, remove the siding and install XPS board insulation to the exterior of the skip sheeting, fur out windows and doors, and reinstall siding?"
A. Either method (or both methods together) will work -- your choice.
Q. "Which method would result in the best energy savings?"
A. The answer depends on the thickness of the XPS. If your studs are planed 2x4s that are 3.5 inches thick, then cellulose will give you an R-value of R-13, minus the thermal bridging through the studs. Two inches of XPS would give you R-10, with the added bonus of stopping the thermal bridging. Thicker XPS would perform much better than the cellulose.
It's also possible to do both.
Q. "Which method would result in the best solution for the building integrity and longevity?"
A. Answering this question is easy: doing nothing will be the best solution for building integrity and longevity. No insulation means dry stud cavities that last forever. Your energy bills are high, but your wall stays dry.
Cameron, based on your description of the product currently in the walls and the age of your house, it sounds like you are likely in the south, possibly Florida. Description is that of a product that is still on the market. One current brand is Fi-Foil, although there were (and likely still are) others as well. These products were commonly used in the southern markets in the 50's and beyond. Depending on how it was installed, it may or may not collapse fully when dense-packing your sidewalls, potentially leaving some voids right next to the studs. Google Fi-Foil to see product description and application diagram. If you are indeed in the far south you obviously are more concerned about the cooling season as compared to the heating season. That could have a bearing on your best choice, specifically from an ROI standpoint. Every job and every house is unique. However, most would tell you that correcting air leakage and insulation values in your attic would be the first line of defense. Assume you have already made those upgrades and are now looking to "finish the job".