I'd probably add insulation; make sure a good vapor barrier is properly installed & infiltration is to a minimum.

The system is probably not delivering enough air to & from the MBR.
Do what ever is necessary to improve the airflow to the MBR.

What does the humidity level run at in the MBR & the other main areas of your home?
What is the temp-drop below the return-air temp?

 

As you note, rooms over garages can be difficult to keep comfortable, and that's mainly due to poor understanding on how to properly air seal and insulate these spaces.

For example, you noted above that the garage ceiling is insulated. However, if the insulation is batt fiberglass, and there is a gap between the top of the insulation and the floor of your bedroom, that can lead to problems. Ideally the insulating material should be in contact with the bottom side of the subfloor for your master bedroom. Otherwise there will be air movement in this gap, and if the band joists (where garage ceiling/bedroom floor joists meet exterior wall) are not insulated and air sealed, convection will occur in the gap (known in building science terms as an "interstitial space" and the floor in summer will be much warmer than it should be. This heat will conduct into the room and make you feel warmer even if the air is cool and dry enough.

That you're having high humidity levels in the bedroom is also indicative of air leakage from outdoors into the bedroom space. Best approach there is to have your entire house blower door tested with an infrared camera included to see where the air leaks are as well as compromises in insulation integrity. Rule for insulation is to have it as uniform as possible, and to keep air from moving through or around it.

 

Read this article written by my friend Allison Bailes about rooms over garages:

http://www.energyvanguard.com/blog-...ding-science-HERS-BPI/bid/38832/Does-Your-Bonus-Room-Need-More-Air-Conditioning

 

Thank you for the follow up.

I don't have a way to measure the humidity in the MBR at the moment. I think the thermostat is only reading the humidity downstairs. Can you explain what you mean by temp-drop below the return-air temp?

 

I appreciate the detailed response. I read the article and understand some of the challenges I'm up against now. Are there ways to identify the issues mentioned between the walls, ceiling of the garage and floor of the MBR without tearing out the drywall that is up? Sorry for my ignorance, but I want to know what to expect when I contact someone locally for assistance.

 

. Are there ways to identify the issues mentioned between the walls, ceiling of the garage and floor of the MBR without tearing out the drywall that is up?

a blower door test, in conjunction with a thermal scan of the room will show you
an excellent visual of the problems of the frog.

great blog post by Alison Bales, just feel like he missed a great opportunity
to address how to solve the issues these rooms cause. thanks for linking Shophound!

my go to for homeowners is this pdf file:
http://www.southface.org/default-interior/Documents/airsealingkeypoints.pdf
page 5 tells you how to seal knee walls manually.
great detail.

The pics in the energy vanguard blob post, with its pics
of different kneewalls than in pdf file, show a good examples
of knewalls. some kneewalls are simply the change in ceiling heights
in the attic.
the blog post also shows what most people miss...the sealing between
floors of these attic spaces.
we solve these frog problems two ways.

diy the foam board sealing shown in southface pdf,
of spray foam insulation.
cost wise the diy material costs, time & labor, plus the skill to
create a total air barrier...breaks out to about what the faster
and costlier spray foam seal.

spray foam has to be continuous from top of wall to between the
joists. usually between the floor joists batt insulation is rolled
and placed into the cavity, then spray foam seals it in place.
foam goes to the roofline to make a complete seal of wall.

this eliminates the extreme attic temps on sides, top and
bottom of these rooms...again...see energy vanguard's pic.

I've looked at two frogs already this month. both opted
for foam. one of those "you know its summer when" things!

what is your location?

best of luck

 

Thanks energy_rater_La. I'm in the western suburbs of Chicago. I know my attic has the loose-fill insulation over the main portion of the home. Would that need to be removed to put in the foam you mentioned?

 

Is the room common to the rest of the house via open stairwell, or is it separated....

 

Some videos that might help shed light on the "FROG" (finished room over garage) problem:

https://www.youtube.com/channel/UC9YtXgkAw5B9djEns9Hibtg

https://www.facebook.com/ElmEnergyGroup/videos/1209941272363908/

Bottom line is that insulation needs to be in contact with the surface that is supposed to keep heat in or out of a room, and there should also be no air movement through this insulation.