Garage roof insulation and heating?

[IROCZ]

Hi, I'm still a newbie here as I finally got my first real garage. I live in the soon to be frozen north of Pa. I want to use my garage/shop all winter. The walls have 4 inches of fiberglass insulation. The roof is not insulated at all. I need some idea about the roof insulation, I've been told that I need to leave an air gap between any insulation ang the actual roof. I was thinking of cellotex type insulation boards held up with furring strips leaving 3 inches of air space above it. Should I leave the ridge open? What about the eaves? Leave them open? Any thoughts on heat? Gas or electric? How many BTU's? Oh, the garage is a 24x24 frame construction detached. Thanks in advance!

 

[IROCZ]

No replies, Come on guys, I know theres an insulation Guru here somewhere! My main problem is the garage can't be a financial burden to heat in the winter. The very understanding wife would not be happy. But I want to use my shop 12 months out of the year. No one wants to tear down a hot rod in the summer! Thanks!

 

[porschedude996TT]

You don't say if the ceiling is finished or drywalled. I would insulate with R30 and then drywall the ceiling. Make sure that you have proper ventilation flow through the attic space. Eve vents and gable end vents at a minimum. As far as heater, go with a 75K btu. They don't cost that much more than a 45K. Again, if the ceiling is unfinished you can easily place the ductwork before the insulation and drywall.

If the ceiling is finished, then you may consider the blown in insulation and make sure that you have the eve vents and the gable or ridge line vent before the insulation is blown in. To prevent the blown in insulation from blocking the airflow, there are staple in Styrofoam baffels to prevent the blockage at the interior of the eve. Mr. Heater makes a nice ceiling hung heater in either 45k or 75K. It all depends on how hot and how short a period of time you want the area to heat up.

 

[Dragster Racer]

Let's hear about the ceiling. Best is to insulate above the ceiling and have good ventalation above.

 

[IROCZ]

The ceiling is just open joists now. I don't want to sheet rock in a ceiling as I want to use the rafters as storage shelf space. I have already built some shevling and a tire rack up there! First I added another 2x4 onto the top of the center beam and glued and lagged it into place for reinforcement. I do have a thermo controlled gable vent in one end installed with louvers. Thanks for the replies!

 

[timgr]

The air gap is known as a "cold roof." The main concern is condensation on the underside of the cold roof sheathing. The air gap keeps the underside of the roof cold, and the air circulation (from gable to ridge vent) removes any water vapor that gets through the insulation.

There are also "warm roofs" and "hot roofs." The warm roof requires an excellent vapor barrier between the heated space and the insulation placed on the underside of the roof. If the vapor barrier fails, water vapor will get into the insulation, condense on the sheathing and the roof will rot. I have a warm roof in my stick-built garage. I used bubble insulation for a vapor barrier, and sealed all the edges with silicone and aluminum tape.

The "hot roof" is also known as an arctic roof, and has rigid insulation on the outside of the sheathing, with roofing on top of the insulation. The insulation forms a vapor barrier between the sheathing and the roof.

Those are your options in a nutshell - cold, warm or hot.

 

[Shocker]

A 45k BTU Mr. Heater would be more than enough for your shop. Anything larger will short cycle and wear out rapidly and cost more to run.

 

[Falcon67]

Redesign your joist storage. Lay some 4x8 OSB up there in places for a floor and leave yourself access by skipping a joist gap between the storage areas. Insulate below and use chicken wire to hold it up, thin OSB, drywall, sticks, whatever. If you insulate below the rafters, I would install a ridge vent and soffit vents to make sure you had air moving up and out to carry out condensation. If you don't have moving air up there, you will have issues. 45K heater with insulated ceiling, probably a 75K with the rof area open.

 

[IROCZ]

Thanks for the ideas! I think I'll go with the cold roof idea. Now still looking for heat ideas. Thanks again guys!

 

[dipper]

check northerntool.com for deals on mr. heater. I have the 45k btu in my 20x22.
You could get away with that or bump to the 75kbtu. They are available in natural
gas or propane. Very nice heaters, many members here have them.