Insulation

What it is

Insulation is the thermal barrier inside walls, ceilings, and floors that slows heat transfer. Three types show up on flips: fiberglass batts in wall cavities, blown-in cellulose or fiberglass in attics, and spray foam where air sealing matters more than just thermal resistance. It’s graded by R-value — resistance to heat flow. Higher R, more resistance.

In older houses, you’ll find houses that don’t even have insulation inside the walls, or not enough in the attic, or none in the crawl space. Back in the day, there were no energy codes. So they just didn’t put it in.

Two products often get confused: vapor barriers and air barriers. Plastic sheeting stops everything. House wraps like Tyvek stop bulk air and water but let vapor pass. Getting them layered in the right order is the difference between a healthy wall assembly and a mold sandwich.

Why it matters

Insulation is code-required, inspected, and one of the failure modes that compounds. On the Larossa system, insulation sits between framing and drywall in the inspection chain — miss it and the schedule stalls. But the bigger issue is what happens when there’s not enough of it and you don’t catch it: water lines aren’t protected, and you get breakage from freezing. That’s not a cosmetic problem showing up at listing. That’s a winter emergency on a house you’re holding.

Also, and this is real: if you have to open up walls to do any work, and those walls are exposed, you’re now required to bring the insulation up to current code. Once it’s been touched, grandfathering goes away. So what was going to be a cosmetic flip suddenly has an insulation roughing requirement, which means a framing and insulation inspection, which means drywall can’t go up until that passes. You see how a cosmetic flip turns into a full renovation just because you opened the walls.

How it shows up

Failure modes are consistent. Subs install batts upside down with the paper facing the wrong side. Blown-in contractors skimp on depth because nobody’s pulling a ruler up into the attic. Any penetration between floors, attic, and basement needs orange fire-blocking foam — different product than regular expanding foam, and it gets called out on inspection.

Cathedral ceilings are their own trap. Never hang drywall directly against the rafters in a vaulted space. You need a vent gap between the insulation and the roof deck so condensation has somewhere to go. Get that wrong and you cook the roof sheathing from below. Your framer needs to know this before drywall goes up, not after. I’ve bought houses where they did it wrong and I didn’t catch it until I was paranoid about seeing signs of the professional DIY. That’s why I start asking questions whenever I see a vaulted ceiling on an older house — somebody thought they knew what they were doing.

Related

drywall, framing, inspections, permitting, hvac, code enforcement