Question about attic insulation

[JAred]

I have a 500sqft uninsulated garage that shares an attic with the 400sqft main floor in my house. the attic only has insulation over the main room. If I insulate the rest of the attic will it help insulate the main floor? Or should I instead insulate the the crawlspace thats underneth the main floor better? I was thinking of adding those plastic bats that are designed for foundations ect. Some of the bats stuffed in and around the sill plate are missing or falling down. not to mention my gas furnace is loacted in the crawl space with all the forced air ducts. Would should I do first that will be the most effective?

 

[PAJerry]

Since heat rises, do the attic first. If the crawlspace is cold, it would pay to insulate at least the heating ducts. You can never have too much insulation. I have done an awful lot of it in our 1941-built cape cod style house and it has been money well spent. Just be sure to wear a good respirator when working with any insulation - it is nasty stuff to breathe.

 

[djamwolfe]

Go ahead and insulate the whole attic- just be sure the attic is vented well to the outside or youll have hell to pay in the summer months. I wouldnt worry so much about the crawlspace right now but some of that foam core stuff on the walls would probly work great.

 

[Marcus]

I would think you would be better off putting $ into insulating the area over the house better, rather than insulating over the garage. If you live in a cold climate like I do, my roofer and insulation people have told me not to insulate over the unheated garage. This allows more cold air to get into the attic and will help to prevent icing and ice damns. Like djamwolfe said, you definitely need good ventilation into the attic if you are going to insulate it.

 

[Corey]

If I understand correctly, you are wanting to insulate over an unheated garage that shares an attic with your house or insulate the crawl space under the heated house?

Insulating over an unheated garage won't get you very much in the way of energy conservation. Insulating the crawl space under the heated house would be better (assuming that the attic above the heated house is already up to standard) Basically, you want to create a "blanket" around the heated house space - most importantly in the ceiling, secondary in the walls, and finally the floor.

Corey

 

[JAred]

yes that would be correct.

I found it odd the first time I poked my head up there and noticed just the living space had insulation over it. The blanket theory is in place there so I think i'm ok. Also all of the attics are vented properly. I think my best bet is to spend the money on the crawl space and possibly insulating the ductwork under there.

Another question now that were on venting I have two large 36''x36'' vents on the uppermost attic above the living quarters that are in place for our whole house fan. Should I be blocking these off in the winter time? the attic is about 600 sqft and has a total of 6 eave vents and two peak vents in addition to the two large vents for the whole house fan.

 

[Corey]

With any modern house, the purpose of the attic is mainly to shed water and keep the elements out. That is to say the space serves no direct insulation purpose - it is designed to be ventilated. So it shouldn't matter how many (or size of) vents -unless you have issues with wind, rain, or elements entering the vents - but that is a different problem all together. All of the insulation properties should be in the layer immediately above the ceiling.

In the old days - heck, even to this day - you can still see people putting trashbags over the "turbine vents" and sealing off the other roof vents in a misguided effort to stop cold air getting in the attic. All it really does is stop moisture from getting out which causes other problems.

Insulating over you garage attic may make it slightly more tolerable in the summer by helping keep heat in the attic (depending how hot your summers are, but won't save any energy unless you start to heat/cool the garage.

Corey

 

[elkimmeg]

I would be more worried about protecting the living space from the garage area. Code requires one hour separation wall between garages and living space, Usually achieved by installing floor to roof line 5/8" fire code sheetrock

 

[tutu_sue]

If snow on the garage roof melts before the snow over the main part, insulate the garage attic space as well. I found a great site for insulation and energy efficiency info.: (broken link removed)