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Temperature variation in bonus room over garage

Scott Razzino | Posted in Energy Efficiency and Durability on

Two-story home is located in Atlanta, Ga, and built in 1984. The house faces west. The bonus room over the garage has a separated roof from the main section of the house which make up most of the angle portion of the ceiling in the room. The roof has ridge venting.

The issue is continually battling temperature variations as I have tightened up the house with air-sealing.

The room has one left front (over garage) attic kneewall with a door opening into the room itself. The rear of the room has a vertical short wall which makes up the back of another long attic kneewall which is accessed via the back the closet in the master bedroom located next to the bonus room. The third attic kneewall is on the right front side over the garage with access door in the other closet in the master bedroom.

There is a rear stairwell which is an access point to the bonus room from the 1st floor laundry room which sit directly over the crawlspace. A garage storage closet is below this stairwell.

I have an 8 degree temperature difference with heat not running and 5 degrees when heat is running.

There is a door between the bonus room and the short hallway where both master bedroom closets reside. We have to keep this door closed in the winter.

What I have done to attempt to remedy the situation in the last 5 years:

(1) Replaced windows with Low E Argon filled double pane vinyl windows

(2) Sealed all lighting/electric/hvac penetrations

(3) Added batt insulation to the small section of flat ceiling which makes up the top of the ceiling

(4) Added 2″ of Polyiso all around interior of kneewalls/taped and sprayfoamed all joints

(5) Removed all garage drywall sealed and insulated walls with ridge foam and caulked edges.

(6) Added cellulose insulation to ceiling of garage and blocked front open joists to interior section of home.

(7) Added rigid foam and caulked and sealed both walls of closet under back stairwell (Did not remove ceiling drywall on bottom of steps)

(8) Left and rear outside walls were air sealed reinsulated and resheathed with polyiso prior to cement siding added.

(9) Caulked and air sealed all plumbing/electrical penetrations from crawlspace underneath.

(10) caulked seams of lower three steps where large air leakage was present.

Question: Is the cold air coming from the crawlspace up the interior wall of the steps?

Three Options:

a) Remove drywall ceiling under steps in closet air seal and insulate.

b) Go from 8″ to 10″ HVAC air return

c) remove all angled drywall which makes up ceiling and insulate. Add 2 ” of polyiso over stud then add drywall.

Any suggestions on why room is still cold with all I have done are appreciated. Last blower door test for whole house was 2865 CFM50.

Thanks,
Scott

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Scott,
    To determine any remaining air leaks, you need to use a blower door, several window fans, or a theatrical fog machine. Here's more information on blower-door-directed air sealing:

    Blower Door Basics

    Pinpointing Leaks With a Fog Machine

    Of course, it's always possible that you don't have an air leakage problem. One other possible problem is that your HVAC contractor never performed a room-by-room heat loss calculation, and that your forced-air supply ducts are undersized.

  2. Doug McEvers | | #2

    I tend to side with Martin on his second statement, It's a HVAC problem. You have heat loss on 5 sides and the remote location means air flow volumes will be scant.

  3. Kris Knutson | | #3

    Scott,

    I would recommend calculating the load using manual-J and measuring the air flow into the room. It is quite common for bonus rooms to receive far less conditioned air than they need. You may have brought the load down substantially, but not knowing the actual load and how much air you are getting will leave you without vital information. Another problem with the bonus room is that although it might receive the right volume of air, the air may have undergone significant convective losses in the duct to a cold in winter attic or hot in summer attic. You could have 1000cfm supply air to that room, but if it does not move the temperature far enough in the right direction, you'll never get there. By way of example, I lived in an apartment in Atlanta with a loft bedroom. The room was bitter cold in winter and unbearable in summer. Measured air flow was ~70 cfm. Calculated need was nearly 200cfm.

    Also, look for ways to give the air a return pathway - jump duct, transfer grille, etc.

    Sometimes, depending on orientation, exposures, etc the only way to have the bonus room optimally comfortable in all day in summer and winter is a ductless mini-split.

    Here is a short article I wrote in 2008 about bonus rooms:
    http://georgiamagazine.com/archives_view.asp?mon=11&yr=2008&ID=2040

    Good luck!

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