Insulation, Radiant and Vapor Barriers - Cold Room over Garage

I have an 8 year old home in Ontario. I have a master bedroom with cathedral ceiling directly over the uninsulated, unfinished double garage. The garage ceiling is insulated and drywalled, as per code. The bedroom has one long HVAC run with vent near the large front window. This room becomes 10-15 degrees cooler than the rest of the house in deep winter. The padded, carpeted floor gets cold and almost feels damp. I can use a supplemental room heater, but cold air pours out of this room, down the stairs and into my living room. If I close the bedroom door, it gets even colder. Question: can I use a rigid foam insulation over the existing drywall in the garage ceiling and then drywall over that? If so, what are the materials used and the best procedure. Any help and/or alternatives greatly appreciated. Have done lots of on-line reading...now must ask for help.

I have almost the exact same problem but I got my difference down to 5 degrees difference. Making an additional dropped down ceiling probably isnt going to work cause what you need is effective insulation to be actually touching the subfloor of the room. You say that the garage ceiling is already insulated: is it with fiberglass and how much? Regardless of the R value if they insulated your problem is most likely air infiltration into that area between the ceiling and the subfloor.
I would drill a hole if you dont know the amount of fiberglass already present and measure the amount there as well as the full height from the ceiling to the subfloor above. If its not full of insulation (and it should be) then think about filling the entire space with dense pack cellulose. You can use a long fill tube to snake it in there and crush the existing FG if its not full. If its currently full to the brim them your only option might be to tear down the drywall pull the batts and put back up some drywall; drill holes and fill it then with the blow in. Lots of people do the tear down and then call a contractor to spray closed cell foam all up on the subfloor but its really really expensive.
Also make sure that if you have short kneewalls in the room over the garage that they are properly insulated and sheathed.
How is the cathedral ceiling of the room insulated? Thats a tougher issue to solve but i bet the floor and any kneewalls is the bulk of your problem. Its a shame that builders dont take the time to really make these rooms right seeing how they make so many of them. Essentially every wall in that room is an exterior wall inculding the flloor and any lacking detail renders them way uncomfortable.
Sorry I know this reply is long but just let me say that for my room I started with it being 20 degrees cooler than the rest of the house. A new furnace with a variable speed blower ( i needed the furnace anyways) got me only a 10 degree difference improvement. Last winter I drilled holes in the 5X20 foot kneewall in this room and pumped in cellulose to totally fill the 8 inch gap behind my wall. With that I now have a 5 degree diff and have been able to use the room unlike before all year. In the summer it didnt get super hot like before and wasnt any different than the other rooms but now in the winter I have to use a small oil filled heater for it. What I have done right now is drill 2 inch holes all over the garage ceiling in every joist bay as I get ready to blow in my cellulose. Hopefully I will solve this problem with that and blowing all the other interior walls as well.

Thanks, Doobs. It is terrible that in an 8 yo home with "Modern construction" that a homeowner has to jump through all these hoops. I bought this home so I wouldn't have these problems as with an older home. I am not sure I want to start rebuilding this home because of an inept/uncaring/uneducated builder. Not sure I want to start drilling holes into finished interior knee walls...don't think my wife will appreciate it. I suppose there is no quick fix when you are fixing someone else's mess.:mad: I will think on it some more before I plan a course of action. Thanks again for your input. I appreciate and value your experience.

Actually your problem isn't insulation, it is "Heat Load". The cathedral ceiling and areas exposed to unconditioned spaces for this room require more heating BTU's per hour (BTU/hr.) than the other rooms in your home. Another way of putting it is the "Heat Loss" per hour in this room is greater than the "Heat Loss" than in other room in the house.

The dampness you feel in the carpet is a result of "Relative Humidity" (RH%). The amount of moisture throughout the house is probably equal. However as the temperature drops the RH% in the objects (including a carpet or air) increases. As the temperature approaches "Dew Point" they will feel damp.

Supplemental heating is usually the easiest way for compensating for the Heat Loss for this room. However you can minimize the use of supplemental heating by adjusting your heating distribution system.

I recommend you pose this question in the Heating System Forum.

Two suggestions.

First of all, I don't agree that this is a heat load problem. You want heat consistently at your feet and no amount of heat from forced air can overcome the cold floor.

The key is to make the floor warmer. Heat rises afterall. If the garage is at 0 degrees, the floor won't be much different. You could try to insulate and finish the garage wall to warm up the room. The earth beneath the garage floor is nice and toasty - you can harness this natural energy even if the garage isn't heated. You'd be surprised.

The other idea would be a radiant heat system installed in the bedroom floor taking advantage of the easy access from the garage.

Or do both and really lick this one in the bud. This is a solvable problem. More insulation in the floor won't be enough. Good luck.

More insulation in the floor won't be enough. Good luck.

Read this study done in ohio on dense packing the floor with cellulose. Specifically look at the data for house # 1 and 3 and you will see that if done correctly its enough. http://www.energydesignedhomes.com/Papers/BnsRmFloorTemp2.pdf
Your suggestion of adding radiant heat will work but again is expensive, will waste energy, and really is like the authors say more of a band aid.

Are you POSITIVE that the garage ceiling was insulated? It might be worth checking it first and also making sure they installed the correct R-value(which would be as much as they can get in there).

I know i had a good laugh when i started drilling a hole to check my garage ceiling. Sure it was insulated but with only 2 inch batts. They are laying directly against the garage ceiling. Above that I have 10 more inches of clear space all the way up to the bare subfloor of the room. I felt more wind flowing thru that almost empty joist space than in the garage below it. Even though it must have been done a while ago (52 yr house) How people could do such a piss poor job is baffling. They could have left it empty and saved themselves the time, would have been no difference.

I apologize if I misled you. I am still a little suspicious of the data. There has to be a temperature gradient from the floor to walls and I challenge why none is reflected in the data. I hope they didn't do anything funny like measure the floor temp directly above a heat vent or something.

Regardless, seems like a relatively simple and inexpensive fix to dense pack. Or I guess you could raise the existing insulation to the subfloor? Try to seal air leaks first with foam, etc.

The only problem is if the dense pack is insufficient, then what?

FYI, radiant heat while more expensive to install is more efficient than forced air. Good luck.

Hi guys,

Figured I'd post a reply here b/c I'm just learning about dense pack cellulose now. I had been considering going with a foam-in-place insulation called 'tripolymer' foam, which is water based, very similar to 'Retrofoam' if anyone has heard of it. Does anyone know how this stuff actually performs in the field? It seems like great stuff, a little pricey, but high R-value of 4.6 once installed and isnt' supposed to shrink (although i have some doubts)?

Carl