Is there a rule of thumb out there when trying to decide R-13 vs R-15 wall insulation or fiberglass vs Rockwool?
A portion of my remodel required 240sqft of wall insulation.
I figured to upgrade from R-13 batts to R-15 batts would cost 9% more
R-15 fiberglass to R-15 Rockwool is a 31% increase.
R-13 batts to R-15 Rockwool is a 43% increase.
Is there a quick and easy rule of thumb to determine how long to recoup the cost increase with potential energy savings?
Apples to apples, is Rockwool really worth 31% higher cost over R-15 fiberglass?
I love Rockwool, super easy to work with and dense but IDK about the higher cost. Specially these days…
Replies
Hard to answer without knowing climate zone, but there's a very small difference between r13 and r15 batts in a wall which probably is 20-40% windows and framing. The milder your climate, the closer in performance these 2 batts are.
You can calculate the ROI if you know energy cost of your heating / cooling and heating degree days of your area, then it's just some math to convert r value to u values and all of those fun formulas.
Climate zone 5 (northern Illinois).
HDD is 6464 annually and CDD is 809 annually. What those degree days mean, I have no idea
It's a measurement of energy demand to heat a building in a given area. HDD are calculated by subtracting the average daily temperature from 65, so more HDD means a colder climate. Don't need to worry about much else realistically.
From your other post you saw the upgrades don't really pay off in any significant way.
That makes sense.
Thanks for the insight!
I used an online “insulation savings calculator “ and entered the required info.
To upgrade R-13 to R-15, I would potentially save $3 per year at the current natural gas rate.
So it would take me 24 years to recoup the extra cost from R-13 batts to R-15 Rockwool
8 years for R-13 batts to R-15 batts
Not worth it if the above is correct
The differences and benefits of rockwool over fiberglass are not limited to the energy savings per R value.
all that being said, usually the best bang for the buck for energy and insulation upgrades, is to focus on the worst part ( Highest energy loss) of your existing structure.
but there also is the attractiveness of making improvements when the access is available.
Also remember that energy costs are variable, but likely to go up over time, as will the value of any improvements. It can be difficult to project ( I was off a bit with my guess as to the cost of natural gas when I did the analysis 12 years ago before an HVAC replacement. who knew fracking would be a thing and provide significant reduction in the cost of nat gas?)
I'll add any additional expense and effort into excellent air sealing and more insulation in the ceiling / attic.
Best of luck to you.
As was said, there are other benefits to Rockwool beyond its R value. It’s hydrophobic, for one, unlike fiberglass which absorbs water. BTW, the 9% cost going from R13 to R15 gives 13-14% more R value, so that makes economic sense if you want more R value.
If you calculate this out with U value, the marginal change between r13 and r15 comes out to a negligible difference in heat flow. Also since it's a wall, the whole wall doesn't have the insulation, so the effect is even less.
But definitely appreciate the other benefits of rockwool over fiberglass either way beyond thermal performance.
I can’t imagine the thermal performance is big enough to matter. I’d rather work with rockwool and that’s what I’ve chosen for the rehab work I’m doing on my house.
You are agonizing over 4 bales of Rockwool (240 ft). The price difference in the grand scheme is nothing. As mentioned above, Rockwool is hydrophobic, fireproof, a Great sound reducer, doesn't sag over time, is better at filling gaps and therefore makes a better installation with fewer air gaps. The best fiberglass installation is generally terrible, but even a homeowner with some care and a very good knife can do a first-rate rockwool install.
Eric, you just wrote exactly what I was thinking while reading the original post and all of the other replies. Thank you.
Forget the knife and use an electric carving knife (like you use on a turkey). It's faster and easier for Rockwool (Roxul)!
I’m with you on Rockwool. Far superior product and easier to work with. For me personally, I always find myself trying to get the perfect blend of performance and cost savings since someday I will sell this house and have to make all of the effort and time worth it financially.
None of the above. For my whole-house remodel, I’m using closed-cell spray foam in all exterior walls and Rockwool Safe ‘n Sound between most interior walls. And air sealing any ceiling penetrations with canned spray foam.
But as others have said, the benefits of Rockwool go beyond just ROI, including the sound-muffling and fireproof benefits, ease of installation, lack of sagging over time, making it, in my opinion, the winner between the two options.
while the % differences are useful, ultimately what's the actual difference in cost of the installation
$10-$100 - probably better to spend the extra money
$100 -$1000 - need to think about it
$1000-$10000 - probably going with the lesser cost
hopefully I'm not insulting anyone, but my idea has always been I'd rather spend a little more money once than less money twice - the insulation is only going in once and given the added benefits of rock wool over fiberglass , I'd go with the rock wool
other note - I investigated a fire where the property manager used a painting heat gun in an attempt to thaw some frozen pipes in an exterior wall. The Kraft paper ignited and the fire took out the kitchen he was working in and the one on the next floor. I don't know about the wind washing ability of rock wool to keep the waterlines from freezing, but I think it would have been better with the heat gun
sorry about being so long
good luck with your decision
That’s pretty interesting about the fire and a good point about making decisions on a cost bracket system.
I just had to make a cost decision for a boiler at a rental
cast iron boiler, 80+ % efficiency , $5900 installed, cast iron lasts "forever"
Navient hi-efficiency (90+ %, rebate $1200), $10500 - warranty for 10 years
trying to make the house better for the tenants(get better tenants) and resale
house isn't a 90% house, no easy place to do wall mount and vent to exterior - better off spending the $2700 difference in cost on new windows that will improve the house for hopefully more than 10 years
still looking at where the $5900 is actually coming from - credit card for now- 30 day interest fee loan and either 1or 2 % back on the card
good luck on your decision