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I have an unfinished bonus room above the garage and I am looking to finish it. The room is approximately 12'x12' with 3' knee walls and the roof/ceiling slanting up to around 8'-9'. The roof/ceiling is made of 2x8s and currently is filled with unfaced batts (with the styrofoam things to allow for proper air circulation under the roof decking). Think of the space above a two car garage that sticks out in front of the house.
I had this type of room in a previous house and it was always colder/hotter than other rooms in the house. So, I have a few questions I am guessing someone will know the answer to.
1. The knee walls are 2x6 with unfaced batts. do I need any sort of vapor barrier on them? There is unfinished space behind them.
2. Do I need vapor barrier on the roof/ceiling section?
3. Is there anything I can do short of making the room smaller (and using the other space for more batts) to keep the room a decent temperature?
4. is spray foam insulation an option for the roof/celing? Or does not that work because it needs the air circulation?
The room is going to be used for storage so it does not need to be great but since it will have HVAC running, I would prefer to insulate it right the first time.
Kneewalls are to have R-30 (craft paper to the conditioned side in all scenarios)
Vaulted ceilings are to have R-19 (in order to get the proper space you have to add a 2X rip to any rafter that is less than 2X8)
Vaulted ceilings that are common with attic space are to have R-30.
Flat ceilings are to have a minimum of R-30. Go more if space allows.
The only exception is on kneewalls- you can use R-13 in conjunction with 1" rigid foam board.
When we renovated a bathroom, we opened the ceiling to the roof. We installed vinyl channels against the underside of the roof, with the bottom end of the channel open toward the soffit vents and the top end open to the ridge vent. (The channels fit between the rafters and were about 1" deep to allow the air directly beneath the roof to move. Purchased at Home Depot.) We then used the pink stuff, paper side towards the bathroom (cannot recall the R value now), and then put up plain sheet rock.
This renovation was up in New England, and we didn't notice a problem with extreme heat and cold in the bathroom after completion.
One of the biggest contributors to the inside temperature differential in bonus rooms is the common error of trying to heat/cool a room with poorly sized and poorly routed ductwork.
Too many bonus rooms have poor conditioned air delivery, and this exacerbates the tendency of a room with a large outside exposure to be difficult to heat/cool.
Get the equipment properly sized with properly installed ductwork, and it will somewhat reduce the problem.
Fiberglass batts lose efficiency when the unfaced side is exposed to ambient air currents.
Consider sheathing, or wrapping with Tyvek®, the backside of the kneewalls. Take the air currents off the fiberglass, and let it trap conductive heat as intended.
If you want to have spray foam installed, it is a fine product. Spray foam will typically not need ventilation between the insulation and the roof deck, unless there is something in your local code. But, if it is a storage area, I would consider tightening up the envelope and assuring delivery of sufficient conditioned air before I spent spray foam bucks.
I'm not sure exactly what you're asking, but I'll try to answer some questions as well as I can.
Quote:
Originally Posted by AtlDad
I have an unfinished bonus room above the garage and I am looking to finish it. The room is approximately 12'x12' with 3' knee walls and the roof/ceiling slanting up to around 8'-9'. The roof/ceiling is made of 2x8s and currently is filled with unfaced batts (with the styrofoam things to allow for proper air circulation under the roof decking). Think of the space above a two car garage that sticks out in front of the house.
I had this type of room in a previous house and it was always colder/hotter than other rooms in the house. So, I have a few questions I am guessing someone will know the answer to.
1. The knee walls are 2x6 with unfaced batts. do I need any sort of vapor barrier on them? There is unfinished space behind them. When you say "knee walls" I assume you're talking about the vertical walls of the room, before they meet the roofline?
Kraft-faced insulation is often used in this application, mostly for the purpose of being able to staple it to the studs and keep it in place.
Yes, you'll want to put a vapor barrier over the top of the insulation.
2. Do I need vapor barrier on the roof/ceiling section? Yes, you'll want to put a plastic vapor barrier
3. Is there anything I can do short of making the room smaller (and using the other space for more batts) to keep the room a decent temperature? I once added a family room - with a vaulted ceiling - onto a house we lived in in Minnesota. Because I wanted a higher R-value than I could get by putting batts between the rafters, I used 1" thick pink polystyrene sheets of insulation. The vapor barrier. Then drywall. I had to use extra-long drywall screws, but considered it well worth the effort.
4. is spray foam insulation an option for the roof/celing? Or does not that work because it needs the air circulation? I cannot answer this for sure, but I believe you'd have to be sure of airflow, regardless of the insulation used.
The room is going to be used for storage so it does not need to be great but since it will have HVAC running, I would prefer to insulate it right the first time.
Thanks.
You might want to check out the Owens-Corning Website. It has some good information and ideas in it.
K'ledge Builder - that is extremely useful information. Thank you. The floor is insulated with batts in the floor joists. I spot checked several sections by cutting holes in the subfloor and they all appear to have R-19 unfaced batts and fill the width of the cavity (but leave a lot of space in the hieght, as would be expcted).
It sounds like my vaulted ceiling is going to be ok but I should add vapor barrier and that I will need to add more insulation to the knee walls.
For the vapor barrier, people have mentioned craft paper. Since I already have unfaced batts, is there any problem with me essentially wrapping the interior of the room with 6 mil plastic as a barrier (basically wrap the plastic everywhere i am going to put dry wall). It seems like that would provide both air and moisture resistence? I have a roll of 100'x10' plastic lying around that was left over from a previous project and this seems like it would be a good use for it.
As for the A/C, I have aleady had an HVAC company come out and run an extra line (through the attic) so hopefully they knew what they were doing. It is zone with the room right next to it (this was planned for when the house was built so it shoud not canabalize air from the other room).
K'ledge Builder - that is extremely useful information. Thank you. The floor is insulated with batts in the floor joists. I spot checked several sections by cutting holes in the subfloor and they all appear to have R-19 unfaced batts and fill the width of the cavity (but leave a lot of space in the hieght, as would be expcted).
It sounds like my vaulted ceiling is going to be ok but I should add vapor barrier and that I will need to add more insulation to the knee walls.
For the vapor barrier, people have mentioned craft paper. Since I already have unfaced batts, is there any problem with me essentially wrapping the interior of the room with 6 mil plastic as a barrier (basically wrap the plastic everywhere i am going to put dry wall). It seems like that would provide both air and moisture resistence? I have a roll of 100'x10' plastic lying around that was left over from a previous project and this seems like it would be a good use for it.
As for the A/C, I have aleady had an HVAC company come out and run an extra line (through the attic) so hopefully they knew what they were doing. It is zone with the room right next to it (this was planned for when the house was built so it shoud not canabalize air from the other room).
Just some thoughts, in line with your concern about bonus rooms being difficult to heat/cool:
Did the HVAC company also do the original installation?
Have they committed to you that "running an extra line" will adequately service the bonus room? I.e., committed with a guarantee?
Is the return air collection grill located so that the return air from the bonus room has direct path to it, or a torturous path that will reduce efficiency?
Is the extra line run directly, or looped around trusses or other framing, so it will not deliver supply efficiently?
If you need a vapor barrier for air flow resistance, you have already confirmed that your fiberglass batts efficiency will be compromised by air infiltration.
Stop the air infiltration before it hits the fiberglass, either with sheathing or tyvek on the outside of the batts.
K'ledge Builder - that is extremely useful information. Thank you. The floor is insulated with batts in the floor joists. I spot checked several sections by cutting holes in the subfloor and they all appear to have R-19 unfaced batts and fill the width of the cavity (but leave a lot of space in the hieght, as would be expcted).
Number one boo-boo (although theres nothing you can do now). A proper install of batt insulation will have little or no space between itself and the conditioned space.
It sounds like my vaulted ceiling is going to be ok but I should add vapor barrier and that I will need to add more insulation to the knee walls.
The plastic is fine for vapor barrier- you just don't want both (craftpaper & plastic) together. Remember to caulk all of the plates and use fire-rated foam for all of the plate penetrations (wire, pipe, etc.).
Be sure all pieces of plastic overlap at least one foot and tape all seams.
For the vapor barrier, people have mentioned craft paper. Since I already have unfaced batts, is there any problem with me essentially wrapping the interior of the room with 6 mil plastic as a barrier (basically wrap the plastic everywhere i am going to put dry wall). It seems like that would provide both air and moisture resistence? I have a roll of 100'x10' plastic lying around that was left over from a previous project and this seems like it would be a good use for it.
As for the A/C, I have aleady had an HVAC company come out and run an extra line (through the attic) so hopefully they knew what they were doing. It is zone with the room right next to it (this was planned for when the house was built so it shoud not canabalize air from the other room).
Depending on the depth of the dead space behind the kneewalls you may be required to have access doors (fire code). You can get insulated, weatherstripped versions from building supply companies (not big boxes).
Measuring from the plate of the kneewall to the wall that the rafters are sitting on, if it measures greater than 60" you may need the access doors.
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