Hey Guys, I am in the process of adding insulation in my garage. As you can see, I have done the walls using R-13. For the attic, I bought R-30 and I am not sure where the batts are suppose to be installed. I did some research under Google and found that the insulation for the attic was installed horizontally between the joists. In the images below, you will notice two batts of R-30 insulation that has been tacked on top. One runs along the 2x4's up in an angle (left one) and the other simply between the joists (right). If you can point me to the right direction with some advice, I'd appreciate it! Thanks. Images:
I agree. They go horizontally, as shown above. You'll also need to allow for ventilation (via the soffit vents, don't block them off with the batts). What you want is an air space between the insulation and the underside of the roof.
Right, basically you want a way for air to enter (soffitt vents) and then leave (ridge vents, etc), general circulation. If not, there will be moisture issuses.
Another point on leaving the air space - the Depot carries thin (plastic or foam) U-shaped channels that you can tack up before putting up the insulation. This ***ures that you maintain the air gap which allows the requisite convection airflow for moisture control AND, more importantly I think, to keep the shingles from getting too hot and curling prematurely. Is that boxed out area in one of the pics for a ventilation fan? In my shop I built a box with a lid which was controlled by a motorized lead screw I found in a surplus catalog. I can flip a switch to close the lid and keep all the heat from escaping except when I need to evacuate some air. -Chad
Installation of insulation to the roof rather than the ceiling joists requires the use of the venting panels and careful soffit vent integration that was mentioned. It also means more cubic feet to heat/cool and more complicated fitting. The thickness of the R-30 insulation is not good for 2X4 roof rafters. Aeroman doesn't mention if he is "finishing" the ceiling after installation of the insulation. The weight of the R-30 will sag and drop and more importantly if it's attached to the house probably requires code specific sheetrock or other flamespread rated material which will serve to support the R-30. What's the distance between the ceiling joists?. I'm in the same situation of closing in a 24X36 - 5/12 truss garage. I hate to lose the open space and easy access to storage in the open trusses, but it is much simpler to "close in" the ceiling than insulate the roof and finish it. The 2X4 joists of the trusses if 24" OC poses a problem with spanning 2' with sheetrock suppporting R-30. I am planning on closing the ceiling in with Foamboard type insulation which won't have near the R-30 rating (typical 1" board is @ R-5, 2" is @ R-10[$$ !!]). Foamboard will span 2' without sagging but I am concerned about fire safety issues although the garage is not attached to house. Anybody experienced with the foamboard?. Powerband
You can order R-30 in 24" wide batts. You should use strapping 16" oc for the sheetrock. It's easier to strap the ceiling first so you can lay the insulation on top of the strapping. The foam "U" shaped channels BriggsBodied28 mentioned for the soffit are called Raftermates.
I hope you're going to air condition that garage,some attempt at constant temp. If you don't that insulation is going to retain moisture and you'll be ****in Legionnaires mold..the hot set-up around here(Austin) is just to spray your inside walls with heat barrier paint and not insulate, we have a bad winter around here, for about two days...rixrex
Timely discussion. My garage ceiling is the same - open rafters. There are some boards up there - s**** pieces to support lightweight stuff I store up there (empty boxes, fibergl*** stuff, bulky but light stuff, etc). I don't want to close in my ceiling either. Would it be worthwhile to run something like chicken wire or field wire stapled/nailed across the bottom of the rafters & lay the bat down on top of that? Any benefit to putting anything on the upper angled "A" part of the roof at all? TIA!
Simply adding light firring strips or similar, 90 degrees to the ceiling joists to reduce the space between nailers - 16" OC between standard construction . 24" between support for sheetrock or most sheet goods is too much. Insulation is available to fit either. The light weight and rigidity of light foamboard insulation is able to span 24 joist, might sag eventually. I've used "resilient steel firring" for "strapping" to isolate ceilings acoustically. Kind of like steel firring - tin strips punched to act like piano hinges - screwgun applied. Powerband
do you think that 1/2" thick drywall will be fine for the ceiling? The joists are 23 or 24" apart. Thanks.
I put 1/2 inch drywall on the ceiling of my garage. I blew in 16 -18 inches of insulation on top it. It has held up really well, I did this work two year ago. I also put in a vapor barrier across the ceiling and walls. This keeps moisture from migrating through the walls. I don't know if you would have this problem in California **** here in Alaska if any moisture gets into the wall it will freeze some where in the wall and when it thaws mold can grow. The sheetrock should have no problem holding up the insulation in the ceiling.
Strapping the ceiling is the way to go, especially if you're 24" on center (OC) This will also strengthen the span of the trusses. Which will tend to flex, causing the sheetrock joints to crack.
If your going to use the space in your trusses for storage. and putting a platform up there, use furring strips. You don't want to compress the R_30
Been working on the very same thing the last couple of weeks. Getting ready to rock the lid shortly. Got a nice little gas unit heater. Tired of getting froze out of my garage every winter. Paul
My builder did the same thing (vapor barrier, blown-in) but I had him use some ribbed-steel panels (screw down) instead of sheetrock. These panels are not the same as for outside, look the same, but the paint doesn't have any ultraviolet fade protection.
i used 1" foil faced foam board as did my neighbor. its held up with plasicap nails and the joints are foil taped. it works great if you just want to heat it for the day to work out there. its also way cheaper than sheetrock and batts.
Hey guys just a couple of things to consider: Another benefit to insulating between the joists rather than the rafters is that an access is easily installed to still be able to take advantage of the storage capacity, but the effective ceiling is lowered, allowing for much more efficient heating and significant savings on energy costs, whatever your source. If going with foamboard, it's worth it to spend a little extra dough now on higher R values, rather than practically watching your money dissipate through the ceiling, where the vast majority of heat is lost. Again, the energy savings will add up surprisingly quickly.
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