Insulating my shop attic---need some advice from a carpenter/contractor

[Jameel Abraham]

I'm remodeling my workshop and currently have insulation between the rafter bays (it's a 1950's garage) right up against the back of the roof. (I've read that this a bad practice and can cause some real problems--it's been this way for about 10 years) Ceiling is already drywalled, and the walls are drywalled and insulated. I'd like to insulate the attic space with blown-in insulation (standard practice around here), but the structure was build without any ventilation of any kind. The soffit is completely solid (no soffit vent)and closed off from the rafter bays by blocking that sits on the top plate between rafters extending up to the roof sheathing. There are no vents at the gable ends, and no ridge vent at all. So how do I insulate this space and allow for ventilation? I need the roof to be cold in the winter at the eave to prevent ice dams. In all the new construction I've done I've blown in insulation, but there was a soffit vent in place and I installed styrofoam channels between the trusses to allow some air flow. But this old building has me stumped.

[Jim Becker]

To put the insulation (unless it's spray foam) in the rafter bays, you need to install baffles that keep the insulation away from the roof deck and vent the space, at least at the soffet. (a hole saw and some simple inserts will deal with that part) The baffles are most often made of Styrofoam as you state and can be stapled up with a staple hammer quickly. The quandary is that you already have the drywall up it seems. Unless you're willing to pull that drywall (or the roof... :eek:), it's going to be nearly impossible to "do it right". Blown-in insulation in rafter bays isn't generally done...batts stapled in or spray foam is the right way to go for that kind of setup. Most blown in/loose fill insulation will settle on sloped areas, leaving no insulation at the top.
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Edit...if I misunderstood you and you're not making the attic conditioned space, the solution is simple...pull out the stuff between the roof rafters, put in gable vents as well as baffles at the bottom of the slopes and get your insulation blown in on top of your ceiling rock...

[David G Baker]

You are going to have to add soffit vents and some way for the attic to vent. I have had a new roof installed and when it was done I had the roofer add peak venting.
I live in Mid Michigan and have a 12-12 pitched roof on most of my house. The previous owner had a new roof installed using 7/16" OSB over 1"X8" boards. He had installed the can vents on one side of the roof and covered the soffit with the perf plastic material. My roofer removed some of the soffit material to find that the soffits were completely enclosed and fiberglass insulation packed hard in the soffit area. The roof was approximately 7 years old. All of the OSB was covered with black mold and the 1"X8" boards were rotted to the point of crumbling. There was no place for air to enter the attic so the moisture could vent out of the vent cans. There was no ice guard around the edges and no roofing felt under the asphalt shingles.
All of the OSB had to be replaced with 5/8" OSB and all of the 1"x8" had to be removed. A $7,000 job ended up costing me around $12,000.

[Ben Grunow]

Sounds like you have some access to the space above the ceiling so you might just try to take a thin board and flatten the existing insulation away from the roof to allow for a little air movement. The foam baffles are 2" but even a 1/2" space is better than none. You could even make wood baffles with lauan (sp?) and thin strips of wood on top and try to push them down the rafter bays.

As for the eaves, I would try to remove the blocks and replace them with a soffit/fascia with vent strip of soome sort if possible or at the very least add midget louvers (http://mooreindhardware.thomasnet.com/viewitems/louvers-ventilators/midget-louvers?&forward=1) in each bay.

A simple solar power vent or gable louver would do for the attic space if no ridge vent exists.

Some is better than none. I have taken apart many houses without any vents and there is no mold or rot to be seen sometimes. Do your best. What else is there?

[Jameel Abraham]

Edit...if I misunderstood you and you're not making the attic conditioned space, the solution is simple...pull out the stuff between the roof rafters, put in gable vents as well as baffles at the bottom of the slopes and get your insulation blown in on top of your ceiling rock...

Yeah, attic is unconditioned. I figured this is what needs to be done, but having no soffit vent is the biggest problem. I will have to do something major here I'm afraid.

Although today I pulled one of the batts from between the rafters and the sheathing looked fine, same as the uninsulated half of the garage. Maybe I don't need any ventilation?

[Jim Becker]

Jameel, if you pull out the existing batts in the angled rafters and put baffles at the bottom of them to keep the new blown-in material away from the roof deck, you don't necessarily "have to" re-do your soffits to add venting as long as you add enough gable venting to properly handle the space. The soffit vents are "desirable" if you can do it, however...and as I state, you may be able to do the hole-saw and round insert vent thing.