Insulating a Garage Roof
 

I have an attached garage that I just built this past summer. Now that winter is here, I am finding out that it gets COLD! The garage is an unheated space, but I thought that adding some R-19 insulation directly to the roof sheathing would help to take the chill off. The roof trusses are all exposed, so there is no ceiling to insulate.

My question is concerning the soffit and ventilation systems. I understand that I should use some sort of soffit insulation baffle. But to ensure that I still get airflow from the soffit to the ridge vent, do I need to use something else in addition? Since I will be stapling the faced insulation directly to the 2x6 top chord of the roof trusses, I am concerned that once the insulation is installed, I'll still be restricting airflow to the ridge vent. Am I thinking about this correctly?

Thanks!

You should apply Raft-R-Mate or comparable baffles to the underside of the roof sheathing. They will prevent the batts of insulation from pressing tightly to the sheathing and leave a continuous air space from the soffits to the ridge vent

Ventilation is not required in an unheated space. If you plan on finishing and heating it in the future then be proactive and install insulation baffles prior to insulating. They are available at any bigbox store. Also I would recommend using spring wires to install your insulation as staples will not always hold by themselves against gravity.

Just an opinion, but going back to the reason that you are doing this, keep in mind that insulation will reduce, minimize, or, perhaps even eliminate heat transfer in some cases, but it does not generate heat. Point being that if in fact insulation were to keep your garage warmer, it seems to my simple mind that you have a situation where you are currently either loosing heat from your house to your garage, or your garage is receiving some radiant heat, whether through the windows or doors, or through the roof, which you may reduce by insulating the roof. Not saying that it's a bad idea, but just saying that without a heat source, your ROI may be extremely minimal. I have noticed, as an example, that my insulated barn, without a heater running, is often colder inside than outside, particulalry on a cold but sunny day.

Point well taken. I do realize this, and for this reason, I have been somewhat hesitant to do this. However, for times when I am working all day in the garage, I plan to use either a portable heater or even a small wood burning stove to supply some moderate heat. With the insulation in place, I should be able to take some of the load off whatever heat source I use.

Also, while there is nothing above the garage, one side is directly against the house, so the garage will receive some radiant heat, though not nearly enough to keep the garage warm. I figure with the radiant heat from the house, lights, and excess heat from a warm car or truck, the insulation will at least help to keep the garage a few degrees warmer than the outside temperature. And with the addition of a space heater or some other heat supply, I can at least work comfortably in the space when it's only 14 degrees outside.

It's somewhat of a gamble, but if the price is right for the material, it's a gamble I'm willing to take. I just want to make sure I do it right.

This is perfect. I think my local insulation warehouse stocks these.

I doubt the space will ever be finished since we utilize the space between the trusses, but we will heat the space during the winter when we are using the garage for a few hours in a day. Thanks for the advice on the spring wires. That's a good idea.

I hope the house wall and gable wall above have fire-slowing Type X drywall installed per minimum safety Code as it's an attached garage. Fiberglass insulation will slow the cold some but why in the rafters? Drywall the ceiling to keep the stratus of heated air closer to you rather than in the peak of the roof with colder air at your feet and waist. You will wait a long time to get even that. R-19 will allow the air the travel through it easily compared to a High Density batt; http://www.diychatroom.com/f98/how-b...ulation-90438/
The price seems right, interesting marketing ploy for almost worthless low density insulation.

Gary

Yes, we have an approved fire separation between the garage and house. We went through all the proper channels and got all of the inspections we needed.

Drywalling the ceiling isn't really an option sine we utilize the space between the trusses for things like wood storage and other miscellaneous things. So it's either insulate the rafters, or do nothing.

Thanks for the link, by the way, regarding the HD vs. LD insulation.