We totally replaced the exterior wall insulation in the Fixer Upper Main House here at One Hundred Acres Home. This post will show you how we upgraded the wall insulation R value with the 2×4 wall insulation, what we did with the old insulation, and how we addressed the lack of vapor barrier. This is a DIY exterior wall insulation replacement done over a few weekends to make our home more comfortable and save some money while we’re at it.
This post is part of a series showing the DIY home renovation of the Main House. You can check out how my husband and I decided to buy this Fixer Upper here. Then we got to work removing the siding and replacing rotten framing.
Right, so we’ve removed the old siding. It was T1-11 plywood panel siding that acts as the structural siding as well, so there is not plywood wall sheathing under the siding. It was just exposed insulation as you can see in the siding demolition photo.
Exterior Wall Insulation R Value
The old pink fiberglass insulation from around 1980 was R-11. That does not meet today’s code standards, and there are options to improve it. However, the exterior walls are made with 2×4 studs so we are limited on wall thickness. The good news is that you can now buy 2×4 wall insulation for 2×4 studs with higher values.
Spray foam insulation would give us the highest R-value increase – I believe something like R-24.5 when using closed cell foam with an R-value of 7 per inch thickness. That’s really awesome, but the spray foam has a lot of hazardous chemicals and is trickier to DIY.
Another option is to use typical fiberglass batt insulation that now comes in R-15 for 2×4 studs. That’s still an increase over the old R-11. However, fiberglass insulation offers no fire protection. Some argue the paper vapor barrier liner contributes as a fire hazard.
Rockwool Insulation:
In weighing all the options, I found an alternative batt insulation product called Rockwool that is a mineral wool made from volcanic rock and recycled slag – a byproduct of steel production. Rockwool not only provides an R-15 value in 2×4 walls, but it is also very fire resistant, mold and moisture resistant, will not deteriorate when exposed to moisture as standard fiberglass will, AND it provides a nice sound dampening to outside noises. Moreover, it is a natural material that is way less hazardous to install compared to the other options listed above.
Here is our order of rockwool delivered to the driveway. Thankfully this stuff is lightweight an easy to move.
If you want more details on that large white fence, you can check that out here. In the delivery photo above, you can see that I ordered Rockwool on the left and the pink stuff on the right. Overall, Rockwool seemed like the best option for our home. BUT, there is one thing missing: the Rockwool does not come faced with a vapor barrier. Hmmm…so I did some research and found a way to add a vapor barrier. But I ordered the pink stuff as a back-up in case my plan didn’t pan out. Don’t worry, it did work! I later returned the pink stuff.
Vapor Barrier with Unfaced Rockwool Insulation:
The general rule of thumb is that in cold climates (where we are), a vapor barrier is needed on the interior face of the wall insulation. You know we want to use Rockwool for the exterior wall insulation replacement, but it does not come faced with it’s own vapor barrier like the fiberglass pink stuff typically does.
So. What are the requirements of a vapor barrier? Well, our local building code provides some guidance on that. This is from the California Residential Building Code, but it is based off of the International Residential Building Code (IRBC) – of which most US State and many other country building codes are based.
The requirements for vapor barriers are covered in Chapter 7 Wall Covering of the IRBC. The code gets fairly technical with various classes and zones. In the end, I decided that I wanted to install a vapor barrier with effectively the same permeability rating (perm rating) as the faced insulation that we are replacing. Per the code ,the perm rating for faced insulation should be greater than 0.1 and less than or equal to 1.0.
After some internet digging, I found a brush-on (paint-on) vapor barrier membrane called HydroHault. This stuff has a perm rating of 0.17 which meets the requirements perfectly. The plan is to paint it on to the exposed gyp board from the outside. It is rated as low VOC but it is an asphalt-based product so I was a little concerned about bleed through and smell.
I painted a test patch and waited a few days. Thankfully, there was no bleed-through to the interior face of the wall gyp board. The HydroHault is smelly at first but that faded away shortly. After that small test, we decided HydroHault and Rockwool would be our path forward.
Here is the painted on HydroHault at the front wall. It is a bit striking in black!
This is full-view look at the applied vapor barrier in preparation for the wall insulation replace. I’m sure our neighbors through we were crazy at this point. It looks kind of cool through, yeah?
Install Replacement Wall Insulation:
Rockwool is super super easy to install! And thankfully it is not nearly as itchy as the fiberglass stuff. But it is still a good idea to wear a long sleeve shirt, pants, gloves, and a mask.
If you’re going to install Rockwool, get yourself a bread knife to use to cut the insulation around electric boxes, electric wire, and misc framing.
Here I am getting ready to help my husband with the Rockwool.
Do you see the orange foam around the electric box in the wall behind me? We used a can of foam insulation around all the boxes for a little added insulation.
Here is the replaced wall insulation! If you’ve been following these posts, you know we placed some rotten framing where the old decks were. We painted mold-resistant primer at the rim to prevent mold this time around. The siding joint will also be along the rim joist, so this add some peace of mind.
Now the insulation is complete! Feels good to be making progress.
You can see I’ve started adding house wrap and foundation crawlspace vents in preparation for the full house wrap. More on that in the next post! Stay tuned…
What to do with the Old Insulation:
Oh I almost forgot. So what did we do with the old insulation? Well, did you know that you can pull off the paper facing from the fiberglass batt pretty easily? Yep. So I did just that, tossed the paper facing, and threw the leftover fiberglass into the attic! An extra R-11 from the old wall insulation really helps keep the home comfortable with no extra cost. It was still useful, and it’s great to keep that stuff out of the landfill….
