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Insulation Installation

Insulation installation | You need to read the written instructions. This is a modern vapor retarder, but some contractors don’t believe in them for a host of reasons. (C) Copyright 2019 Tim Carter

"The same exact thing can happen inside a wall cavity in a home in a frigid climate if you don't block and stop the water vapor from getting into the wall cavity."

Insulation Installation - Simple If You Read Instructions

The inspiration for this column happened just two days ago while I was working on my daughter and son-in-law’s new home up in Downeast Maine. It’s important to realize I’m not the builder but act as their primary advisor, the plumber, electrician, and radiant heat installer.

My son-in-law and I arrived at the house to work about 7:00 AM and at 8:30 AM a medium size box truck pulled onto the lot along with a pickup truck. Five workers tumbled out of both vehicles and they started to put in fiberglass insulation up under all the floors in the house.

With the help of my son-in-law, a month or so ago we had installed 900 Uponor heat transfer plates and 6,000 feet of Uponor hePEX tubing that will keep my daughter, son-in-law and new granddaughter warm as bugs in a rug.

Uponor hepex

This is the Uponor hePEX that we installed under the floor of the future office/guest bedroom suite above the garage. It's not easy to install it three rows of heat transfer plates per truss bay. CLICK or TAP HERE to watch a video showing how it's done.

Uponor happens to be one of the leaders in radiant heat products and technology. Read the beginning pages of their installation manual about the simple science behind radiant heat and you’ll be amazed.

The middle-aged leader of the insulating crew, let’s imagine his name is Sebastian (it’s not), and I got into a friendly discussion about exactly how the insulation batts should be installed. Sebastian asked me, “Do you want a 1 or 2-inch airspace between the insulation and your PEX tubing?

I don’t want any airspace. The Uponor installation manual says to put the insulation in direct contact with the tubing.” I replied. “Well, my entire career we’ve always installed the insulation with an airspace. That’s the way to do it.” Sebastian countered.

That’s very interesting, Sebastian. Since heat travels directly to cold, you want the insulation to be in contact with the heat pipes. This forces the heat upwards into the floor. If what you suggest is the right way to do it, why are you filling the wall cavities all the way with your fluffy insulation? Why not leave an airspace between the back of the drywall and the batt?

I said the above as respectfully as possible because most older people don’t like to be challenged or have their intelligence questioned. I could tell the gears up in his head were spinning. We then had a quick discussion about the new high-performance vapor retarder my son-in-law and I were installing over his insulation. Once again, his lack of scientific critical thinking soon bubbled to the surface.

Downeast Maine can get darn cold in the winter. This past winter I was working in the house installing cast iron drain pipes and it was 2 F in the house. Sebastian had never thought about the condensation that forms on the outside of his cold can of beer while sitting on his deck after work.

The same exact thing can happen inside a wall cavity in a home in a frigid climate if you don't block and stop the water vapor from getting into the wall cavity.

The water vapor that’s in the warm air inside a house can easily travel through drywall and fiberglass on its way to the outdoors. When this vapor contacts the cold exterior wall sheathing, it transforms to liquid water just as the droplets of water form on your soda can, beer can, or glass of iced tea on a humid day.

When Sebastian first arrived he introduced himself to my son-in-law. At lunch that day, my son-in-law said to me, “Tim, guess what? Sebastian came up to me a couple of hours after talking with you and out of the blue said, ‘I just discovered I’ve been doing things wrong for my entire career.’ "

I’ve had similar conversations with other contractors and sub-contractors for years, but Sebastian was the first one that admitted he was wrong. You should realize that a strong ego is highly recommended if you want to survive in the residential construction industry. But you can temper it with an open mind and the desire to apply simple science to the building process.

One of my biggest complaints about the construction industry, as a whole, is there’s no formal education required to get into the game. Think about it. You can go to a big box store just after reading this column of mine and buy a ladder, a tool belt, a hammer, tape measure, and razor knife and be a roofer by noon. Yet, you’ve never been trained on how to install a roof. You’ve never read the written instructions that are out there. However, my guess is you can get a customer or two to hire you to re-roof their home.

What does this have to do with you and your hard-earned money? You need to stop trusting all contractors. You need to STOP assuming they’re always doing things the right way. You need to stop assuming they’re always thinking of your best interests.

You need to start doing one simple thing to protect your home and your investment. You need to select the products you want to use for your next project, your next remodeling adventure or your next new home. Then you must take the time to READ the written installation manuals or watch the manufacturer’s installation videos online.

You need to do this before you hire a contractor not after when things go wrong. Ask her/him exactly how they intend to do the job. See if they’ve been doing it wrong their entire career.

Yes, this is work. Yes, this conversation with the contractor is not comfortable. But what the heck, it’s only your money so what’s the big deal, right?

Column 1305


14 Responses to Insulation Installation

  1. I agree with a moisture barrier on the inside of a dwelling, just like I believe houses in all climates need to be insulated, not just ones in the north. The backing on fiberglass insulation is suppose to be a vapor barrier, if it is installed properly but the overlaps of the backing and the staple holes to attach it give innumerable openings for moisture to move around and get into wall and floor cavities.

  2. Many years ago when I completed the contractor-provided shell of our home, I worked with the local utility to make it a 'super good sense' home. They had me apply a vapor barrier inside all of the exterior walls, and tape all of the seams. The electrical penetrations (i.e. outlets, switches, etc.) were all sealed and the vapor barrier secured to the boxes. We had to, of course, install an air-to-air heat exchanger.

    • It's not my house. Talk to my daughter and son-in-law. Closed-cell spray foam was used around the house where all the ends of the floor trusses are as that would have been impossible to put a high-performance vapor barrier. Have you ever stopped to do the math as to the ROI of spray foam over fiberglass? If not, you should. It's all about ROI when it comes to insulation. How many years does it take to BREAK EVEN on your investment?

  3. As I finished a bedroom in the basement, put up insulation between the studs with the insulation vapor barrier facing the inside of the room and then covered that with 6 mil plastic sheeting. Not only did it stop moisture but had a sound deadening effect.

    • Mike, I hate to say this, but you should not have been sick the day conduction was discussed in your high school physics class. Or if you were in the classroom, you probably shouldn't have been drawing illustrations of ligers. INSERT SMILEY FACE emoticon Put an aluminum spoon or implement in a pot of boiling water and tell me how long you can hold onto it with your bare hand.

  4. From Duke Energy, a very large electric company:
    install insulation over subfloor underfloor radiant heat system

    • Duke Energy is in the business of SELLING energy. If you want to know the correct way of insulating a floor that has a radiant system, look to the manufacturer of the radiant system and consult with their engineers.

  5. Maybe Sebastian inferred that since you normally leave a 1 or 2 inch gap between insulation and roof decking for ventilation (which is needed because any moisture getting through the insulation will condense on the cold roof), the same should be done under flooring.

    • Maybe Sebastian should stop and read the instructions provided by every radiant flooring manufacturer. One shouldn't infer or assume anything. One should also apply critical thinking skills with respect to simple science when it comes to things. Maybe I'm expecting too much.

  6. Oh, so Sebastian knew he was insulating under radiant heating? I just assumed, (you know what happens when you assume), that the crew was just hired to do the job, not necessarily knowing about the radiant heat. And that leaving an air gap was just standard installation procedure for any and all joist bays regardless of what was in it. But you're right, basic science should tell you that leaving an air gap between the insulation and floor is just going to provide an open channel for any cold seeping in from the rim joist to flow under the entire floor as if there was no insulation at all.

  7. I live in South Texas where in the summer it is hot and humid and the winter it's cool and dry. If i put the vapor barrier between the insulation and interior of wall, I'll have a moisture problem in the summer. If i put the vapor barrier between insulation and exterior wall, then I'll have moisture on the insulation in the winter. What would you suggest?

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