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diamand 09-02-2009 02:34 PM

Insulating bonus room above garage
We have a bonus room over the garage that is very cold in the winter/hot in summer. It has duct work for HVAC, but needs to be hooked up to the furnace. I plan on finishing this space and want to insulate it.
My plan was to insulate it using rigid insulation and put a 1" spacer against the roof and the rigid insulation so there would be air flow to the roof vent. After the rigid insulation is in place, I would insulate the remainder with regular pink fiberglass insulation with the kraft towards the warm side. The rafter space is about 6". I live in PA. Please see crude picture drawing of what I had in mind:

Additional pictures of the space for reference (please excuse the mess)
Since this space can get so cold or hot, I want to insulate it as best as possible. Do you think what I have in mind would be a good idea? If not any other suggestions?

Scuba_Dave 09-02-2009 05:16 PM

Are you sure this was designed as living space?
Those look like trusses
What size are the top lumber pieces that support the roof sheathing?
What size are the lower pieces that are supporting the ceiling below?
Do you have a bigger pic of the area?

Plumbvoltage 09-02-2009 06:52 PM

When they did my addition, they used short pieces of a corrugated type of plastic material between each edge of the truss betwen trusses near the soffit so the insulation wouldn't block the venting. The pieces are about 1" to 1.5" thick. I would consider using this all the way to the peek and just put fiberglass insulation against it. That way the roof breathes and your room is insulated.

Gary in WA 09-02-2009 09:58 PM

You have continuous ridge vent, which is good. And the trusses were built for the level ceiling. But, you need to furr out the truss space for insulation equal to your area. 6" of insulation may not be enough. Are you trying to save headroom space with the foam? Baffles as Plumb is talking about are good, but expensive compared to buying the insulation with an air gap figured in already.

Be safe, G

diamand 09-03-2009 07:41 AM

Can you explain how to fur out the trusses so I can have more room for insulation? What are the baffles that Plumb is talking about. Do you have a link with a picture, I have never seen anything like that. Here is another picture of the space. Please excuss mess.

Ininkus 09-03-2009 10:09 AM

Personally I think you are on the right track.

If it were me, considering this is a bonus room, I wouldn't over complicate it much. I would buy the foam baffles they sell at all the big box stores, staple those all the way up with run for the air flow that you are trying to acheive, and then use fiberglass batt insulation on top of that, followed by drywall.

By using that thick foam, you are greatly minimizing how much fiberglass insulation you can put in there. Granted, the foam is also a great insulator, but for me it would be one or the other....

1) all foam, leaving the gap for air as you show in your rendering.

or 2) thin baffles for air flow and insulation as I said above.

Reason I would go with option 2 is simply because of ease, and it will be as effective as most walls constructed in new homes today.

Good luck!

Scuba_Dave 09-03-2009 01:41 PM

This is the rafter vent - they come in styrofoam & plastic
They have ribs to keep them away from the sheathing
Much easier to put up, staple them in place

Insul;ation required by zone - where you live
You are loooking at around R30-R38 - cathedral ceiling
The more insulation, the better

Gary in WA 09-03-2009 06:20 PM

Furring out a ceiling or wall is adding framing material to create a greater thickness or depth. Install 2x4's, on edge to the bottoms of your 2x6's on the slope. Because they installed the access door off-center, you are limited for interference. (Where the ceiling lowering would hit the top corner of the door).
Here is some background on foam, the price may be the deciding factor:
Enter any questions on fiberglass insulation here: http://saveenergy.owenscorningblog.c...questions.html

Hint: run a string line (tightened) 1-1/2" away from the first and last wall studs to check the in-out of the middle studs. Do the same on the level ceiling framing. Rarely have installed bonus room trusses where they did not need tweaking somewhere for a straight drywall application. May need to add cardboard shims from H.D. or Lowes.
Be safe, G

diamand 09-04-2009 09:45 AM

Thank you for all everyone's input. I have decided to go with all foam. I plan on adding a 1x1 to the existing trusses. This will make the space 7" and gives me space for 6" of foam with a 1" air space. I checked out the big box stores for the foam and the thickest they have is 2" which is going to yield a R-value of 10. I'm going to sandwich 3 pieces together in each wall cavity so it should give me a R-value of 30. Do you think this will be enough R-value for central Pennsylvania? Also, when I sandwich the foam together, should I use caulk as the adhesive or liquid nails?
Thanks again for all your advice.

Scuba_Dave 09-04-2009 10:17 AM

Make sure that foam is tight to the edges of each side of the rafter bays
If there are gaps it will decrease the Rvalue quite a bit

Gary in WA 09-04-2009 03:42 PM

I would install it using canned foam as glue on the sides (gap filler) and between layers. Or caulk as a gap filler, a lot cheaper. A few well-placed nails will support it temporarily. Here on sizing, cutting and installing, same principles:
With only a 1x1, that may be hard to break drywall joints on.....

Before you start, seal the space under the floor/wall joint with foam pieces, not glass batts, which do nothing to stop cold air to the rooms floor interior:

Be safe, G

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