Fiberglass insulation questions

[pfettig77]

I'm finishing up my 24x30 cape style garage with bonus room above. I will be heating with a mini split - one 18k head in the garage and one 12k head in the bonus room. I'm in northern Wisconsin. I've already started putting some R13 batts in the garage part. Keep in mind this is just a garage and I'm not looking to keep both floors at 72 degrees all winter. I just want to make it usable.

Question 1: how important is the ceiling/floor insulation above the garage part? Any lost heat will just go into the bonus room, but that still seems bad. If I did insulate the ceiling/floor, what R value should I use? How crucial is that? The I-joists are 16" tall and 16" on center (which makes it hard to use 15" batts because it's like 15.5 between the OSB part).

Question 2: In the bonus room I have 10" rafters with 24" spacing and collar ties at about 8' up (see top pic). Being that I need to allow 1.5" for the air chutes, that leaves me with about 8" for insulation. I figured I could do R19 for the rafters up to the collar ties and I can put some R30 on the collar ties (that can be as thick as I want/need). Is that probably the best way to do it? Might it be kind of annoying to switch from one kind of insulation to another? I might have to cut the ends where they meet at a 45 degree angle to avoid cold spots.

Question 3: I'm going to be installing these chutes in the rafters. I was wondering if it's important to use these chutes with baffles at the end or if I should just use the regular ones. Not worried about the 75 cents, just don't want to mess with it if it's unnecessary.

 

[jack stand]

Look at it this way, if you insulate "better" as in R values you just might knock off 3-4 weeks of heating on each side of winter especially with some air sealing.
Then when you are heating, it'll be more effective with less input from your m/s.
This will happen year after year.

 

[dcg9381]

I'm finishing up my 24x30 cape style garage with bonus room above. I will be heating with a mini split - one 18k head in the garage and one 12k head in the bonus room. I'm in northern Wisconsin. I've already started putting some R13 batts in the garage part. Keep in mind this is just a garage and I'm not looking to keep both floors at 72 degrees all winter. I just want to make it usable.

Question 1: how important is the ceiling/floor insulation above the garage part? Any lost heat will just go into the bonus room, but that still seems bad. If I did insulate the ceiling/floor, what R value should I use? How crucial is that? The I-joists are 16" tall and 16" on center (which makes it hard to use 15" batts because it's like 15.5 between the OSB part).

It's important if you're going to be heating the garage with your 18k mini-split. Substantially important. Otherwise, you're really heating the space above it in the bonus room from below... Every building I've done like this (garage below / living above) we insulated that ceiling/floor. As it's just part time use, I'd say that you don't have to go nuts on insulation - but that insulation is making up the difference from heating just the garage versus the garage+room above....

 

[pfettig77]

Look at it this way, if you insulate "better" as in R values you just might knock off 3-4 weeks of heating on each side of winter especially with some air sealing.
Then when you are heating, it'll be more effective with less input from your m/s.
This will happen year after year.

That's true, but at what point are you actually saving money? Case in point: I got a quote to spray foam the garage for about $7,000. I'll be dead way before that extra $6,000 is ever paid for in slightly lower electric bills. It's hard to calculate what kind of a real world difference R15 vs. R13 or R30 vs. R38 makes.

 

[pfettig77]

It's important if you're going to be heating the garage with your 18k mini-split. Substantially important. Otherwise, you're really heating the space above it in the bonus room from below... Every building I've done like this (garage below / living above) we insulated that ceiling/floor. As it's just part time use, I'd say that you don't have to go nuts on insulation - but that insulation is making up the difference from heating just the garage versus the garage+room above....

Perfect. Thanks. So do you think R19 would be good enough for the garage ceiling?
R38 would be $1.10 per sq. foot
R30 would be 93¢ per sq. foot
R19 would be 52¢ per sq. foot
R13 would be 49¢ per sq. foot

 

[dcg9381]

Perfect. Thanks. So do you think R19 would be good enough for the garage ceiling?

For "my" use case which would be "sometimes" heating of that garage, yes. The more you approach full time use, the more you go with recommended specs for insulation in your climate zone.... (I'm aware that you've got better insulation in the actual roof)

 

[billconner]

What climate zone?

If you're going to keep both spaces heated, I wouldn't bother insulating between them. I would try to get more insulation in rafters of attic room to than r19. You could put in 6" of rigid foam - r30 - and skip chutes.

I would insulate at rafters to main floor walls. I think it's silly to insulate attic knee walls and floor - more area and many gaps.

 

[Notgrownup]

I would concentrate more on the roof and outer walls. Keep the bottom part running at like 62 , get some ceiling fans. When you need a bump in heat, get it warm fast then back it off to where it’s reasonable. I do it in reverse here in eastern NC.I the summer, I keep it on 82, if I’m gonna work in there I put it on 74 on turbo mode for 25 minutes or so. Then bump it up to like 77.

 

[drmarkr]

I live in southern Arizona and i used R25 (ceiling and walls because it fit the purlins/girts). For cooling, not heat. And the cooling is Evap, not A/C.

I'd spend the money for at least that r-value in a cold climate?

 

[Bert_]

R13 would be a good middle ground vs nothing at all.

I didn't insulate the upper floor joist in my house. I don't use the upstairs and do not heat it. The upstairs isn't particularly well insulated and stays 40-something degrees most of the winter. It works fine and honestly my heating bill is less than others with similar square feet but I'm only heating to ~62*.

If I was doing it again I would put some insulation in the floor joists. It's almost too cheap not to do it

 

[rancherbill]

Question 1 Insulate the floor to the max. It will be cold in the bonus room and no one will use it in the winter.

Question 3 spend the money on the better baffles.

In this kind of project more insulation is the answer - it pays not costs.

 

[pfettig77]

What climate zone?

If you're going to keep both spaces heated, I wouldn't bother insulating between them. I would try to get more insulation in rafters of attic room to than r19. You could put in 6" of rigid foam - r30 - and skip chutes.

I would insulate at rafters to main floor walls. I think it's silly to insulate attic knee walls and floor - more area and many gaps.

I'm in climate zone 6.

I've never heard of R30 rigid foam insulation. The highest I see it R10 and even that is violently expensive. For my rafters, the best I can find that's 8" or less is R19. I don't know exactly how it works, but the rafters are at a 45 degree angle - so not quite walls and not quite ceiling in terms of heat loss. I sort of figured most of the heat will travel up that 45 degree angle and want to escape out of the vertical ceiling which is where I'll have my R30.

I can't quite tell what you're saying about the knee wall storage area. We're going to insulate that little triangle just because it's a lot easier. We're using it as storage with short curtains hanging down and I can't imagine how that would work if we insulated the knee walls (or is that what you're saying?)

 

[pfettig77]

I would concentrate more on the roof and outer walls. Keep the bottom part running at like 62 , get some ceiling fans. When you need a bump in heat, get it warm fast then back it off to where it’s reasonable. I do it in reverse here in eastern NC.I the summer, I keep it on 82, if I’m gonna work in there I put it on 74 on turbo mode for 25 minutes or so. Then bump it up to like 77.

That's sort of my plan, but I was thinking of keeping it on vacation mode (46 degrees I think) and then bump it up when I'm working on a project. Where I am, 46 degrees is like a tropical heat wave in January and February. I may just let the heat ooze up to the 2nd floor to keep it reasonable up there. We'll see.

 

[billconner]

I've never heard of R30 rigid foam insulation

3 layers of 2".

I can't quite tell what you're saying about the knee wall storage area.

Yes - what you are doing. Insulate the roof to top plate, NOT down knee wall and across main floor ceiling (attic floor).

At 45 degrees, it's roof. Should be R49 in zone 6 IMHO.

 

[69gp]

I'm finishing up my 24x30 cape style garage with bonus room above. I will be heating with a mini split - one 18k head in the garage and one 12k head in the bonus room. I'm in northern Wisconsin. I've already started putting some R13 batts in the garage part. Keep in mind this is just a garage and I'm not looking to keep both floors at 72 degrees all winter. I just want to make it usable.

Question 1: how important is the ceiling/floor insulation above the garage part? Any lost heat will just go into the bonus room, but that still seems bad. If I did insulate the ceiling/floor, what R value should I use? How crucial is that? The I-joists are 16" tall and 16" on center (which makes it hard to use 15" batts because it's like 15.5 between the OSB part).

Question 2: In the bonus room I have 10" rafters with 24" spacing and collar ties at about 8' up (see top pic). Being that I need to allow 1.5" for the air chutes, that leaves me with about 8" for insulation. I figured I could do R19 for the rafters up to the collar ties and I can put some R30 on the collar ties (that can be as thick as I want/need). Is that probably the best way to do it? Might it be kind of annoying to switch from one kind of insulation to another? I might have to cut the ends where they meet at a 45 degree angle to avoid cold spots.

Question 3: I'm going to be installing these chutes in the rafters. I was wondering if it's important to use these chutes with baffles at the end or if I should just use the regular ones. Not worried about the 75 cents, just don't want to mess with it if it's unnecessary.

They do make 16" wide fiberglass Batts insulation. I would go with 10" between floors and before finishing it off with rock I would add 4"x16 rockwool for added fire protection.

 

[acer66]

Question 1 Insulate the floor to the max. It will be cold in the bonus room and no one will use it in the winter.

Question 3 spend the money on the better baffles.

In this kind of project more insulation is the answer - it pays not costs.

This is what I would do and make sure that you close all gaps, cracks etc before doing so.

Personally I would use mineral wool over fiberglass.