R25 vs r30 insulation

[zio]

Hey guys I am planning on building a new garage in the spring. The ceiling joist will be 2x10s. Everyone seems to reccomend r30 and I understand why, but would dropping down to R25 be a huge difference. I am asking because Menards has R25 on sale for 1/3 of the cost of r30. If it is not a big difference I am going to ****** it up while the price is right.

Thanks
Tom

 

[larry_g]

Kinda depends on where in the country you are, the number of days you will heat/cool the space.

lg
no neat sig line

 

[Smoky14]

Get twice as much and go R50

 

[zio]

I will be unable to double it up because I will be using the attic for storage so I will have plywood down for flooring. I live in Chicago so it is definately cold in the winter. If I do decide to heat it all winter I will keep it about 45.

 

[GS-Louie]

Go with the R-30. Heating costs aren't going down any.

Lou

 

[StingRay]

I have about R52 with a combination of batts and blown cellulose. Around here its about the minimum you'd want to have if you are heating full time. There are diminishing returns on insulation but in a climate like I live in R60 is preferred. Most heat loss is upward so invest in as much R value as you can fit into the space you have. You can always blow some cellulose on top as well.

Glass is fairly low density and blown cellulose will be more energy efficient for an equivalent R value. Denser products minimize heat loss via convection loops in the insulation. The less air can move inside the insulation the less of a convective loop you will have.

 

[NUTTSGT]

I'd almost always want more insulation but sometimes you have to make choices based what you can do at the time. If you're building in the Spring, why not buy the R30, a bit at a time so you're not shelling out all your dollars at once ?

Possibly buy some every time Menard's has an 11% sale. When you get the rebate, hold onto it till the next 11% sale and buy more. Just do it in a cycle.

 

[RossABQ]

You really can't justify the thicker insulation for your situation. R-25 gets you the biggest bang for the buck at the kind of prices you are seeing. Unless it were a constantly heated space and at comfort levels (68+), the savings is so minimal it will never pay back.

 

[MAKinForest]

RossABQ has an unbeatable argument but, if you want the max insulation and are saving 2/3 then doubling the thickness is still a 1/3 savings and more "comfort". The truss co. can add an extra board to the bottom cord or if stick-building the same for the ceiling/floor joists. There are some concerns with this doubling but it's mostly about head space near the sides. We're planning a queen roof truss for our house and this was the combined recommendation of the HVAC engineer and our architect.

 

[Big Bad Dad]

What does the building code require in your area? That is probably why the R25 is on sale for cheap, nobody can use it.......

 

[theoldwizard1]

When building new or adding insulation in a place that will be heated/cooled YOU WANT AS MUCH INSULATION AS YOU CAN POSSIBLY AFFORD OR PROPERLY INSTALL !

Remember, you pay for insulation once but pay to heat and cool everyday that your own/use that building !

If you can properly install R50, do it, especially in the ceiling !

 

[Lassen Forge]

Even if you lost some of the insulating value by packing it down and putting plywood over it, the idea of going double R-25 might be cheaper...

We had the same kind of deal on R-19 a couple years ago... tired of my office in my shop (with exposed metal roofing) alternating between refrigerator and sauna, so I put a first layer of insulation, and it helped... then put up a second and held it into the ceiling joists with wires crisscrossing... still up there, and the office is cool in the summer, warm in the winter.

The biggest questions are (1) where do you live, (2) what are your climate variables, and (3) What does your local building code specify as minimums. There's a difference between the moderate weather of central coastal California and someplace of Extremes, like the Mojave Desert or North Dakota, and what you need to hold the heat/cool in.

 

[woodrail]

If your like me and money is tight when doing big projects, I would go with the 25. Sacrifices and decisions need to be made. Sometime "short term" wins out. Are we talking $400 versus $1,200?

 

[NUTTSGT]

You really can't justify the thicker insulation for your situation. R-25 gets you the biggest bang for the buck at the kind of prices you are seeing. Unless it were a constantly heated space and at comfort levels (68+), the savings is so minimal it will never pay back.

I don't think that chart is quite accurate for this scenario. It's showing some huge added costs, $16K plus for R26 over R19. You would literally have to buy a **** ton of insulation to reach a $16,000 difference. Building a garage or even a new home, there will not be that much of a price difference in insulation.

The OP stated that the R25 is on sale for a third off the cost of R30, not for a third of the cost of R30. It won't take years to see a return on investment if the OP decides to use his garage and heat it more often. The biggest item will be getting and keeping the concrete slab warm. The R30 will help hold that heat in the garage, which in turn helps the slab hold it's heat.

If the OP can swing the more expensive insulation, by all means go for more R value. There is no chart that can accurately show you a return on investment when it comes to insulation. The heating cost will vary year to year (whether it be electric, fuel oil, wood, NG or LP), Winters vary every year with types of weather and the amount you use the garage will all take effect in the scenario.

 

[MagKarl]

I'd go R25 if it were me. The difference is small, and either is better than your walls/windows/doors will be.

 

[zio]

Thank you everyone for the input. Nuttsgt I meant 1/3rd of the cost of r30. Sorry about the typo. I will more than likely go with the R25 for now. I was originally not going to be able to afford to finish the inside of the garage right away. But if I can keep finding some decent deals like this I might be able to pull it off.

 

[NUTTSGT]

Thank you everyone for the input. Nuttsgt I meant 1/3rd of the cost of r30. Sorry about the typo. I will more than likely go with the R25 for now. I was originally not going to be able to afford to finish the inside of the garage right away. But if I can keep finding some decent deals like this I might be able to pull it off.

Well, that does make a difference.

When you want to find the deals, you have to keep your eyes open. As you know most of us couldn't do our garages all at once either. Take your time, do it right and the way you want, snap several pictures and start a build thread when you get the project off the ground.

Don't forget, most of the big box stores offer some kind of deal if you spend a certain amount on their in store credit card like $300 for 6 months interest free. Menard's also gives you a 2% rebate annually on what you buy with your card. Not a bad deal if you are smart about using it and paying it off monthly or in the alloted time frame.


BTW, you may want to edit your profile to include a general location (like Chicago area). It'll help you get more accurate answers to your questions.

 

[RossABQ]

I don't think that chart is quite accurate for this scenario. It's showing some huge added costs, $16K plus for R26 over R19. You would literally have to buy a **** ton of insulation to reach a $16,000 difference. Building a garage or even a new home, there will not be that much of a price difference in insulation.
....

I posted that for the curve, not the costs. The costs are the incremental cost of insulating a whole house's roof of a certain size to the various R-values.

Those crying for "more - more- more" are being pretty free with the OP's money. Instead of paying for a small amount of extra fuel for heating his garage occassionally to ~50 deg with R-25, he'd be paying off the cost of added insulation, which is up-front and substantial. His money would be better spent adding insulation in his house where there is a bigger temperature difference between inside and outside, and 24/7.