Help with insulation please UPDATED!

[tome14]

I know this topic has been discussed many times. I just can’t seem to find out what I’m looking for. I’m hoping to turn in half of my garage into a golf simulator. There is no insulation currently, but I plan on insulating with bats on the walls. My confusion is coming from how to insulate above.. I have a cathedral ceiling with 2x4 rafters. Below that the ceiling joists are 2 x 6. I was thinking of laying down plywood or foam board on top of the joists to create a “floor”. I would then use fiberglass bats, and roll them out on top of it, therefore closing off the top, in essence, creating a flat ceiling in the garage. Is this permissible? I don’t really need it for storage so I was thinking the phone board would be easy. I could do it with a ladder by myself. Where is plywood sheets would be difficult for me to do alone. I am in Western New York, where it’s very cold in the winter and I feel like I would be heating much less space it would only be heated when I am out in there using the simulator. I will attach a picture. Thank you.

 

[u2slow]

I have my shop ceiling to do also.

Foam board is pricey. What you propose will create an awkward junction where the wall meets ceiling and preserving roof/eave venting.

I plan to do R30-40 batts, poly vapour-barrier, and white or galvanized steel liner panels (lighter and no painting req'd).

 

[tome14]

Thanks for responding..Where do I get those panels? So in essence the panels become the attic “floor” and the insu goes on top?

 

[billconner]

Foam or ply would require more ceiling joists. At least some liner panel will span the exiating 6' with insulation on it. I'd prefer cellulose blown in but batts will work.

You'll want attic vent baffles - prevent and propavent are 2 brands - stapled in each rafter bay - before installing insulation (and much easier to install before ceiling).

 

[tome14]

Foam or ply would require more ceiling joists. At least some liner panel will span the exiating 6' with insulation on it. I'd prefer cellulose blown in but batts will work.

You'll want attic vent baffles - prevent and propavent are 2 brands - stapled in each rafter bay - before installing insulation (and much easier to install before ceiling).

ok, so I still but in the baffles even though I’m not doing any insulation in the rafters? Thanks for replying!

 

[dcg9381]

ok, so I still but in the baffles even though I’m not doing any insulation in the rafters? Thanks for replying!

You're building an "attic". Attics are vented.

Cheap: Throw insulation up between the rafters, stapled down. I wouldn't vent it.

Quickest: They can spray foam that structure in under an hour. As the roof isn't vented, you're setup for it already. This is also by far the most expensive option but also likely the best.

 

[u2slow]

ok, so I still but in the baffles even though I’m not doing any insulation in the rafters? Thanks for replying!

Yes. The baffles (vents) go in to keep an airway open from the eave, up into to the attic space.

Even without liner panels, the poly VB and some strapping will keep the batt insulation up.

 

[tome14]

How do I tell if my ceiling is vented.. I have these cutouts in the top of the roof..See picture. Also my joists are 48” apart, that seems to be perfect for a 4x8 sheet. the steel panels are more per square foot than the foam panels. I’m planning on doing this alone and figured the foam board ceiling would give me extra insulation and I could easily lift these on a ladder and secure to the top of the joists, then just lay the bats on top going in the opposite direction. sorry I’m a total newbie and this is the fist step in my build and am stuck.

 

[dcg9381]

How do I tell if my ceiling is vented.. I have these cutouts in the top of the roof..See picture.

Yes, you have a vent. Just not a "ridge vent". What do your soffits look like?

I’m planning on doing this alone and figured the foam board ceiling would give me extra insulation and I could easily lift these on a ladder and secure to the top of the joists, then just lay the bats on top going in the opposite direction. sorry I’m a total newbie and this is the fist step in my build and am stuck.

Foam board is expensive (per R value) and it's not structural. It won't hold up much of anything. If you want to do a foam board "structural" panel look at Zip-R.

I mean you can either insulate the roof or you can build an "attic" - that's your first level of choice...

 

[tome14]

Yes, you have a vent. Just not a "ridge vent". What do your soffits look like?

Foam board is expensive (per R value) and it's not structural. It won't hold up much of anything. If you want to do a foam board "structural" panel look at Zip-R.

I mean you can either insulate the roof or you can build an "attic" - that's your first level of choice...

So do you think insulating the roof is better? I figured if I “made” an attic there would be less room to heat as the peak is much higher? I will look at the zip-r. I don’t need to attic floor to be structural. But if I did, I guess it would be play wood and batts.

 

[dcg9381]

So do you think insulating the roof is better?

I didn't say that. But standard insulation between rafters pretty easy. You have a vent up there, putting insulation on the roof, heat can escape out that vent.

I figured if I “made” an attic there would be less room to heat as the peak is much higher?

That's absolutely true. Less area to heat. All about the pain-in-the-*** factor.

I will look at the zip-r. I don’t need to attic floor to be structural. But if I did, I guess it would be play wood and batts.

There is minimal room up there for you to crawl around and place insulation. Foam board (4x8), I wouldn't trust it even with standard roll insulation. It'll sag.

 

[tome14]

I didn't say that. But standard insulation between rafters pretty easy. You have a vent up there, putting insulation on the roof, heat can escape out that vent.


That's absolutely true. Less area to heat. All about the pain-in-the-*** factor.


There is minimal room up there for you to crawl around and place insulation. Foam board (4x8), I wouldn't trust it even with standard roll insulation. It'll sag.

Thanks for the insight!

 

[billconner]

Rafters 4' on center will not support ply, or not play less than 7/8 or 1 1/8 inches. Maybe just sag a lot or maybe fail. I suggested the liner panels to avoid having to add framing on 16 or 24" centers.

I said baffles because you said it was vented and I assumed soffit and high vents. I would push the batts right against the baffles for best performance. As I said I'd rather blow cellulose onto ceiling but batts are ok.

My guess is the vents you have will be adequate to minimize condensation on the roof, but without dimensions can't be sure.

 

[tome14]

Rafters 4' on center will not support ply, or not play less than 7/8 or 1 1/8 inches. Maybe just sag a lot or maybe fail. I suggested the liner panels to avoid having to add framing on 16 or 24" centers.

I said baffles because you said it was vented and I assumed soffit and high vents. I would push the batts right against the baffles for best performance. As I said I'd rather blow cellulose onto ceiling but batts are ok.

My guess is the vents you have will be adequate to minimize condensation on the roof, but without dimensions can't be sure.

That was my next question, will the rafters support plywood. The previous home owner has 3 or 4 sheets up there just laying on the joists, not secured.

 

[billconner]

Probably not by accepted practice, but don't know without knowing span.. Why we suggested liner panel - lighter and will span between existing rafter ties. Most ply will not.

 

[racecougar]

What is the span on the 2x6's? Are they continuous wall-to-wall, or spliced? No posts, right?

 

[billconner]

I don't know what span of 2x6 is at 48" on center but from 2024 IRC for ceiling joists with no attic, assuming SPF no. 2:
12" o.c. - 18'-8"
16" o c. - 16'-11"
24" o.c. - 14'-9"

Just for an idea of what it will support.

 

[tome14]

What is the span on the 2x6's? Are they continuous wall-to-wall, or spliced? No posts, right?

The span is 20 feet and no posts .. house built in 1983

 

[billconner]

20' 2x6s 48" on center shouldn't be counted on to support a ceiling and insulation. 2x8 216" o.c. or 2x10 24" o.c. is how I read the code.

Not really per code but add 2x6s so they're on 24" centers and add a vertical hanger from ridge to each rafter.

 

[tome14]

Ok so I messed up.. the rafters are 2x 6 NOT 2x4… looks like its best to just get the bats in there under the roof deck

 

[billconner]

So, just trying to help, but are you abandoning an attempt at venting to prevent/reduce condensation on the roof deck?

I think your best bet would be undaced 6 inch batts and a 10 mil poly vapor barrier meticulously sealed. There are flame retardant faced batts that you could leave exposed. I haven't used them but those with taping the seams could be ok. Not having to supplement ceiling framing is a big plus.

 

[tome14]

So, just trying to help, but are you abandoning an attempt at venting to prevent/reduce condensation on the roof deck?

I think your best bet would be undaced 6 inch batts and a 10 mil poly vapor barrier meticulously sealed. There are flame retardant faced batts that you could leave exposed. I haven't used them but those with taping the seams could be ok. Not having to supplement ceiling framing is a big plus.

No, I believe I still need the baffles?? Then I was going to use faced fiberglass bats stapled to the rafters. i believe I can only get r19 to fit in the 2x6 rafters.

 

[billconner]

No, I believe I still need the baffles?? Then I was going to use faced fiberglass bats stapled to the rafters. i believe I can only get r19 to fit in the 2x6 rafters.

That will work. The baffles will compress the batts some and reduce the R value - maybe to R14 or R15.

Get a good scaffold system. Between the baffles and batt's, you're going to be up in tight space a lot. Maybe a temporary center beam and some planks you can slide around on the rafter ties would work.

 

[tome14]

That will work. The baffles will compress the batts some and reduce the R value - maybe to R14 or R15.

Get a good scaffold system. Between the baffles and batt's, you're going to be up in tight space a lot. Maybe a temporary center beam and some planks you can slide around on the rafter ties would work.

Thank you.. maybe I will hire it out! If the r 19 will compress to r14 or 15 should I get r30 and compress that? What would that work out to?

 

[racecougar]

If the r 19 will compress to r14 or 15 should I get r30 and compress that? What would that work out to?

No, that won't improve matters.

I don't see how baffles are going to work with your current roof vents. Only the bays that have the vents will get air flow. It would be different if you had a ridge vent.

 

[tome14]

Sorry for all the questions but am new to this. so does that mean I shouldn’t use baffles and just cut a hole in the insulation where I have the three vents? Would using Roxul help since it’s a little more resistant to mold etc?

 

[racecougar]

No. That would open the climate controlled space to the outdoors.

I don't see a good way to insulate the roof deck with the venting present. If you had a ridge vent, I could see installing baffles all the way from the soffits to the ridge with insulation directly beneath, but that doesn't work with your roof vents.

 

[tome14]

No. That would open the climate controlled space to the outdoors.

I don't see a good way to insulate the roof deck with the venting present. If you had a ridge vent, I could see installing baffles all the way from the soffits to the ridge with insulation directly beneath, but that doesn't work with your roof vents.

That makes sense… so I’m back to creating an attic I guess?? Or spray foam?

 

[billconner]

I go back to 6" untaxed batt's and a very good poly vapor barrier. Unvented. (flame retardant poly)

What are you going to do in garage? Constantly heated or sporadic? Or is this primarily a cooling climate? Much moisture in slab? (tape a piece of poly to it overnight and look for condensation.)

 

[tome14]

I’m in upstate ny and it gets cold… I am trying to make a golf simulator in there..I will heat it only when I’m in there with some kind of electric heat. not sure about moisture in the slab

 

[hobie18]

Do you have enough height?

 

[billconner]

I’m in upstate ny and it gets cold… I am trying to make a golf simulator in there..I will heat it only when I’m in there with some kind of electric heat. not sure about moisture in the slab

Me too. In NYS. On St Lawrence Seaway. I understand cold.

For what you say you're planning for doing on garage, I'm more satisfied the batts between the rafters and a very meticulous vapor barrier - as good as possible - will be fine. Vapor barrier should come down wall. Electric resistance heat will be fine. No fuel burning.

Dose something metal on the floor rust?

 

[tome14]

Do you have enough height?

Yes the bottom of the joists are 10 feet off the floor

 

[hobie18]

Is that tall enough for a swing?

 

[tome14]

Me too. In NYS. On St Lawrence Seaway. I understand cold.

For what you say you're planning for doing on garage, I'm more satisfied the batts between the rafters and a very meticulous vapor barrier - as good as possible - will be fine. Vapor barrier should come down wall. Electric resistance heat will be fine. No fuel burning.

Dose something metal on the floor rust?

I’m in Rochester.. not quite as cold as where you are. So if I use a vapor barrier does that mean unfaced bats, what if I use roxul? Can I use roxul on ceiling and faced fiberglass on walls, or should I keep it the same?

 

[tome14]

Is that tall enough for a swing?

Plenty… 9 feet is the minimum

 

[tome14]

Ok I’m going to kinda start this again now that I have a little more information on my garage. Hoping to turn 1/2 into a golf simulator during the winter months in upstate NY..Garage is roughly 29x21, NO soffit or ridge vents. I have 3 box vents near the top of the ceiling and an 4th under a 4 ft. Drywalled area nearest thehouse that is not exposed to the open garage. Rafters are 2x6 and joists are 2x6 that span about 21.5 feet. I’m trying to do this job by myself to save on the cost. The joists are about 10 ft off the floor, plenty of room. I am going in insulate the walls with fiberglass batts , but the roof deck is the issue, with no soffit or ridge vents. I will only heat this space before I go into the garage to use the simulator. Can I ”create” a ceiling on top of the joists by stapling Reflectix to them? I know this isn’t “insulation “ but wouldn’t it keep the heat down in the area I’m using for the times I’m in the garage? Joists are 48” OC so drywall or plywood is not an option.

 

[racecougar]

Are you able to install soffit vents? If you use that "double bubble" insulation, are you taping the seams?

 

[billconner]

Buy on PC of 2" XPS, lay it across 3 rafters, and see if the sag bothers you. Seams taped, it would make a big difference. Honestly, just poly would make a difference, so I guess reflectix would too, but 2" of XPS a lot more. Don't use anything with a flame inside garage. An electric resistance heater might cost several bucks to run each session, but may be worth it. (I wince that my fitness center only costs me 75¢ a day, but the gas for car is over a gallon for a round trip.)

After a year if sag bothers you add a ceiling joist between each pair. BTW are the jousts supported at all from roof rafters?

 

[tome14]

Are you able to install soffit vents? If you use that "double bubble" insulation, are you taping the seams?

I would tape the seams yes.. there are soffits but there aren’t any holes for insulation… there also appears to be wood on the inside of them