Spray Foam Insulation: Sealing an Old House Against Weather

benefits, cost, and installation of spray foam insulation in old houses

It appears we’ve reached the stage of this rebuild in which one big project will be completed every week. It’s Week Four of the Spring 2020 One Room Challenge™ and today, I’m showing you how we are sealing our historic home from the inside to prevent moisture and weather intrusion and provide a sturdy reinforcement to our old wood siding. Not all progress is pretty but this is my favorite new feature of our house so far.

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Comparing Types of Home Insulation: Pros and Cons when it comes to efficiency, upfront cost, and longevity of fiberglass, spray foam, and blown-in insulation.


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Fiberglass insulation is probably what comes to your mind when you first think of insulation. It’s the pink stuff that will make you itch like crazy if you touch it, right? Well, actually, fiberglass insulation has come a long way in the past ten years.

In 1938, fiberglass insulation hit the American home market and it’s been at the top of the game ever since. As the first easily-applied insulation, fiberglass batting has a relatively high R-value (the measurement of thermal resistance), ranging from R-2.9 (the least thermally resistant) to R-3.8 (the most thermally resistant) per inch of thickness.

Part of the reason for its popularity over time, however, has nothing to do with its effectiveness. The home building industry is somewhat slower to adopt new methods. Tradespeople spend a lot of time honing their skills. Once those skillsets are developed, it can be challenging to convince them to change their processes. For that reason, among others, fiberglass insulation remains a builder favorite to this day.

If you’re worried about going green and think that fiberglass is a less eco-conscious choice, you’re not entirely right. These days, fiberglass insulation is made with up to 55% recycled consumer glass. That means your home might be insulated today with yesterday’s wine bottles!

As for longevity, there are two things to consider here: Proper application and exposure to the elements. Your fiberglass insulation will instantly lose R-value if not installed properly. Think you’ll benefit from having a thicker batt and simple squishing it into a crevice? Think again. By compressing the insulation, you could be downgrading the R-value as much as 20%.

Fiberglass insulation also shouldn’t get wet. If it gets wet, the R-value will drop. So I don’t recommend it for a home with visible gaps in the exterior cladding. If you still want to use fiberglass insulation, I would recommend sealing all exterior gaps with a consumer fill, such as foam, before application.

That said, if all conditions are perfect and fiberglass insulation remains properly installed, it can last up to 100 years, which is impressive! I’ve installed fiberglass insulation in my homes before. It’s relatively simple to get it in place BUT now that I know how much improper installation could change its effectiveness, I would definitely want to call in a professional next time.


cellulose home insulation


The lesser known, but just as prevalent, cellulose insulation has taken a very green turn over the past decade. It’s now made with recycles newspaper and can we talk about how cool that is?!

Most commonly seen in blown-in applications, cellulose insulation is perfect for those who are looking to add additional R-value to their homes without completely renovating. Homeowners can find a professional to remove a line of drywall at the top of their walls, where it meets the ceiling, and have cellulose insulation blown into the wall cavities without removing all the drywall. It’s pretty cool.

The blown-in feature also makes for a quick application in those hard-to-reach areas like attics and crawl spaces and allows for application over existing insulation. With an R-value of 3.2 to 3.8 per inch, depending on depth and density of installation, I definitely recommend this product to beef up your R-value in your old, breezy attic.

But every great product comes at a cost. Installing blown-in insulation can be tricky and requires the use of a blower (think of a vacuum running backwards). You can rent one at a local home improvement store or you could call in the professionals to make sure the job is done right. I’ve actually done both before (DIY and hired out) and have learned that the cost of hiring someone for the job isn’t that much more expensive than the cost of renting the blower.

The other drawback to cellulose insulation is that it won’t last you 100 years, even in ideal conditions. The longevity of the product is only 20-30 years, by far the lowest product. The trade-off is that you’re getting a more green, eco-conscious product that has no dangerous off-gassing or byproducts. But, just like fiberglass, you’ll have to replace any insulation that comes into contact with water. Win some, lose some.

COST: $$

diy spray foam insulation kit


Spray foam insulation has gotten so much press lately, and for good reason. Boasting an R-value of 3.7 to 6.5 per inch, spray foam insulation can be much more effective at containing heat than its competitors. The EPA guidelines provide reporting that indicates a home’s energy efficiency can be increased up to 20% with proper sealing and insulation. AND SPRAY FOAM DOES BOTH!

During installation, the foam starts out as a thin layer of viscous material and it expands quickly to fill in every nook and cranny. This means it’s actually completely sealing off air gaps, working as a vapor barrier and an insulator.

The biggest drawback to spray foam insulation is that you need to have access to your entire exterior wall framing. This isn’t a product you can apply after drywall is already in place. You’ll need to either remove the existing drywall and replace or you can use this product in attic applications that aren’t finished. It basically only exists for people who are building from scratch or completely renovating. That’s a real bummer because the benefits of spray foam insulation could be very useful for old homes that lack proper vapor barriers and have more air gaps than modern construction.

While there are new DIY spray foam installation kits available, I haven’t ever used one. So I can’t speak to the ease of use of those products. Definitely check reviews and watch all the YouTube tutorials you can get your hands on if you’re going to attempt to install spray foam insulation yourself. Because the process requires specialized equipment, I still might recommend finding a professional to give you a quote and weighing the cost/time benefit of going pro with this job.

COST: $$$


Why We Chose Spray Foam Insulation | When we had to rebuild our historic house after a tornado, we opted to go with spray foam insulation. Here's why -

Spray foam insulation is more expensive than any other product on the market. There I said it. You already knew it. But just how much more expensive? It’s probably cheaper than you thought.

When we were choosing a product, we got a quote from the same company to install fiberglass and spray foam. The difference between the two was only $1,000! With a quick calculation of the 20 years we plan to spend in this home, that added up to only $50 a year in cost difference. Since we knew we had an old house with a lot of air leaks, the $50 seemed like pennies compared to our cost savings on heating and cooling. Keeping it real, we paid $3,000 for spray foam insulation of our (now) 2,000 square foot house.

Then we spoke to a neighbor about her storm damage. She had a similar tree incident on her roof but her roof didn’t collapse like ours did. The house is the same age, same style, and she had an asphalt shingle roof like ours. The difference? She had spray foam insulation added to her attic a few years ago. Her contractor told her he believes the foam held the structure in place. It acts like more than just an insulator. It has an additional structural advantage. Having been through this storm damage/insurance process once, we don’t ever want to have to rebuild again.

Adding the additional vapor barrier effect (since we can’t remove the old siding to add a true vapor barrier to the exterior), I was sold. This product would do three things; insulate our house, secure it structurally, and keep moisture out of our walls. HECK YES. Sign me up.

spray foam installation on exterior wall

We had a pretty clear head about our decision but definitely felt a little anxious on the day of installation. As we headed to the house to check on progress, our minds were instantly put at ease when we saw the back of the house:

spray foam insulation for an old house

Haha. Just kidding. We freaked out.

See all that foam expanding out through the gaps in the wood siding? Yeah. We did too! And we panicked at first.

spray foam insulation in an old house - sealing all the cracks from the inside

There’s my general contractor, trying to figure out if we’d just made a huge mistake, after we noticed the spray foam was coming out between the wood. 😆

spray foam insulation seeping out between wood paneling on an old house

Luckily, the whole crew banded together and we quickly determined the excess foam could be easily cut away from the wood paneling, using our fingertips or a scraper. Since we already plan to have the exterior sandblasted to remove the old paint from the original wood siding, we knew this would be an easy fix. It also gave us peace of mind to know that all those tiny air gaps are now sealed and our HVAC system will be able to run effectively.

installing spray foam insulation

After that, we got to sit back for a few minutes and watch the crew at work. The process was actually really neat to see. The installation crew sealed off all the windows and doors with plastic sheathing and then applied the foam. Once it cured, a crew member came back over the walls with an electric foam knife to cut away the excess foam and allow drywall to sit flush upon the studs.

spray foam insulation installed between studs on exterior walls

As we watched, the foam expanded to fill in the little holes and gaps left behind from the plumbing and electrical tradespeople’s work.

spray foam insulation around electrical

The whole house already feels … different. Of course, it’s still a construction zone but the foam has added an acoustic barrier that creates a feeling of coziness throughout.

I genuinely can’t wait to live here again. I know there will be approximately 50% less arguing over the volume of the television or music between our family members. What you’re doing downstairs won’t even be a problem for someone upstairs to hear! As a mom, I’m all 🙌 hallelujah 🙌.


You’ve seen the foam filling in the gaps around the rest of the house. Here’s where we hope to see the biggest benefits: Our bedroom.

Since Christine has allergies, I’m excited to get back into a house that doesn’t allow for penetration of exterior allergens like dust and pollen all the time. Does this mean I can cut back on dusting? I hope so.

Here’s the bedroom, as viewed from the hallway:

bedroom update with spray foam insulation

Since we have vaulted ceilings throughout the upstairs, I’m really stoked to know that the insulation is going to cut down on the amount of echo in our home, especially in our bedroom. A girl needs her beauty rest, of course.

Here’s the bedroom, as viewed from the bathroom:

old house renovation with spray foam addition

You can see that the spray foam is only applied to the exterior walls. This allows heat and air conditioning to remain within the home but to move freely in order to best condition the spaces.

Here’s the same view from the doorway of the bathroom:

bedroom insulation with spray foam

And one last view of our bedroom, from the far left corner wall, opposite the bathroom:

master bedroom update with spray foam insulation

You can see we’ve taken the closet studs down again because I just can’t seem to make up my mind about this configuration. Hopefully, we’ll have the new framing in place this week because DRYWALL WAS DELIVERED YESTERDAY!! That means we can start drywall TODAY!

Here’s the deal: we need two months from the date of completion of the drywall before we can have the house finished to move back in. So I’m hanging onto that date for dear life. I really, really want to go home.


I’ll be back next week with (fingers crossed) a drywalled space to show you! In the meantime, head over the the ORC blog to see the rest of the rooms as they get transformed: One Room Challenge Blog



Stay safe and sane, my loves. I’ll be back soon.


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