Bonus Room Insulation - retrofit options?

[larry4406]

I have a bonus room above the garage of my house. This space is hotter than hades even though we have ac. Located in northern VA. The cooling unit is a 3 ton heat pump unit common with the master bedroom on the first floor. Bonus room is about 14 by 25 and master is about 18x18.

The bonus room has knee walls about 4 feet tall, then a sloped ceiling following the rake of the roof, and then a flat ceiling. The knee walls are 2x4 framed with R-13 insulation, open to the attic space on the back. The sloped ceiling portions are R-30 with an air vent /baffle tray behind it and the flat ceiling is also R-30. Insulation is kraft type fiberglass batts. Inside surface is drywalled, painted, etc. Ventilation system has perforated vinyl soffit and "cobra vent" ridge vent (unobstructed).

Simply, the space is not conditioned well; in the summer the AC can not keep up.

In surfing the net, I read about radiant barriers, foil backed foam sheets which should be on the back of kneewalls, etc.

Practically, what retro-fit options are out there short of taking all of the drywall down and coming back with a spray foam system or putting in the mother of all AC systems? The house gets full sun. I have access to the back side of the knee walls.

 

[trloh]

I had a room like this that I was able to finish off myself. So far it doesn't sound too bad except maybe not enough air flow and return from your ac system.

Having a barrier on the back of the knee wall will help as long as you don't trap moisture there. Also check to be sure that the hot air is not allowed to get between the floor of your room and the ceiling of the room below. This can be sealed off with foam board and caulk.

The roof rafters also transfer some of the heat direct from the roof towards the drywall of the room. To combat this I used a layer of 3/4 foam board before putting up the drywall. You will loose some headroom so be sure to measure carefully. You might be able to add this and then redrywall over it but make sure your ac has a return to **** the hot air off of the ceiling area.

The level of attic ventilation and insulation is not bad for most construction like this.

I used the double foil bubble foil in the rafter spaces before adding fiberglass insulation. I am sure it helped. I was also sure to leave airspace on both sides of the foil - maybe 1/4 inch or so.

 

[kbs2244]

I would agree with trioh that the first thing to check for is air flow.
You can try and pump cold air into the room, but if you don't let the old air out, it will just back up.
You may need a "warn air return."

 

[larry4406]

The room has one 12x12 ceiling mounted return, centered on the short dimension of the room, and on one end of the long dimension of the room. It also has two 8x12 supply registers (one at the middle, and the other at the end opposite the return).

I have wondered about the amount of return air. The air flow through the filter grill seems like its moving very fast (i.e., it will pull a new filter up into the housing with force). We leave the fan in "On" mode so it circulates 24/7.

The floor system insulation is fully sealed off at the knew walls.

The HVAC system is common with the master bedroom on the first floor. The t-stat is located in the master bedroom. The system has a total of three (3) 12x12 returns - one in the bonus room, one in the master bedroom, and one at the base of the stairs heading to the bonus room. I thought about enlarging the return in the bonus room, but was concerned that it might throw of the balance elsewhere.

This is not a new or sudden problem, but one I have put up with for 8 years. When we built the house, the HVAC contractor said the system would have issues and the only solution was to install a split zone system for mucho more $$$.

I have thought about moving the t-stat upstairs to the bonus room.

 

[trloh]

You have most bases covered and will need something like a split system. It will be even more $$$ now since it is built though. Moving the thermostat will cause more issues in that bedroom.

 

[66HertzClone]

We had a similar problem with the bonus room over our three car garage. It was heated and cooled (not very well) by the gas fired forced warm air furnace and A/C unit for the second floor of the rest of the house. The thermostat is located in the hallway of the bedroom section of the house.

We called out an A/C heating contractor, he recommended dampers in the ductwork and a thermostat in the bonus room. This made all the difference in the world, we use this room as a playroom for our young son. We set the thermostat to keep the room not too hot or cool depending on the season and adjust it temporarily when the room is in use.

One funny mistake made during the install, there is a controller that operates the dampers, the contractor's crew connected it to a switch outlet in the basement. Works with the lights on, when you leave the basement and shut the lights off, the system shut off. The install was done during my wife's 7th month of pregnancy, she was not happy when every evening we had no A/C, it took a few service visits before someone figured out what was wrong. The contractor was very apologetic, he gave me 2 extra panels and filters for the April Air filter and humidifier units we added.