Insulating Shop roof

[decibel]

I'm working to get the insulation finished and have finished the walls and I'm ready to move to the ceiling. I have no real "ceiling" as it's just open and I can see the rafters. It's a 12X24 barn style. Seems from what I can gather I should fill the 2X4 rafter because to allow for air to circulate above the insulation. Seen some roof "baffles" or channels that keeps the fiberglass from touching the roof skin. However it looks as those systems go from soffit vents and I don't have those. I do have 2 gable vents and 1 16' long ridge vent. So would I put the channels in and run the insulation/drywall up to the ridge vent?

Also I'm doing R13 in the walls any reason to move up to R15 in the roof or stick with R13?

I'll added some pics later.

 

[cskipper]

I'm clueless, but am sure someone will have some input in the morning.

 

[TominZebulon]

I'm not sure how close you are trying to follow code, but it requires R-30 in the ceiling/roof. Here is a link to the state building code if you want to look at it: http://ecodes.iccsafe.org/nxt/gatew...=templates$fn=main-nf.htm$3.0#JD_TableN1102.1

Just for reference, Mecklenberg Count is in Zone 7 on the chart. And it is my understanding that the baffles are required to keep the insulation from contacting the roof decking. This allows air circulation so the wood does not rot. You will need to decide how closely you are going to follow code. I built a shop at my old house without getting a permit and got caught. Luckily, I had followed code closely enough that I did not have to tear the building down. So, I will not be doing that again. Its a pain and hassle to pull the permit and get the inspections, but it is worth it in the long run, especially if you go to sell your house. Most real estae agents will not even list your house if you have un-permitted work done like a building.

 

[McRabbet]

Patrick,

It is best practice to add the styrofoam channel pieces against the roof sheathing from the soffit to the roof vent to insure that there is good air flow to reduce moisture buildup between your insulation and the roofing. In a house attic, the insulation is normally R-30 to reduce heat loss during the winter and heat gain during summer. From your post and the dimensions given, it sounds like this roof is not in your house per se, but is in a small utility building, right? Because your rafters are only 2 x 4's, R-13 is all you can add to fill the space. After the channels are stapled in place, the insulation will fill the rafter space and the paper face will be to the inside. You should then cover that with sheet rock or OSB and you will have fairly good insulation (most attic roofs have much deeper rafter space to accomodate thicker insulation).

 

[PChristy]

Patrick if you have the room and want more insulation in the roof section what we do when we build a cathreal type ceiling where the ceiling is close to the roof we add another 2x4 to the 2x that is there for the roofing - that will give you the depth that you need for thicker insulation MTCW

 

[flatheadfisher]

I just stapled the insulation to the 2 x 4 rafters in my shop. I had a bunch of large sheets of card board that I used to cover the insulation. I just stapled the cardboard to the rafters. I shot the cardboard with several light coats of ceiling white and it works great. I have plenty of light and the frost doesn't melt on the roof even when I have the heater cranked up.

 

[Mike Davis]

What about the solid foam sheets of insulation? Couldn't you glue that to the bottom of the rafters leaving a space for ventilation.

 

[decibel]

Yes if I wanted to go with thicker insulation I'd have to do something similar to what Phillip suggested and add another 2X4 to get the depth I'd need. As far as the whole "up to code fiasco" I've already pulled and had the building permit completed. Inspector wasn't very concerned about much since it wasn't a living space. However the electrical is a whole different ball game as an electrician I know did it as a "side" job so it's up to code but not permitted, now either I can go pull one (after doing some codebook reading to pass that f#@#%# test) and hope they don't kill me because I backfilled the trench and started some of they drywall:swoon:

I do plan to cover the insulation with drywall whenever I'm done I'd like to stay with R13/R15 I'll find the load calc the havc guys ran to make sure but I believe I can get by with R15 in the ceiling. So next question where can I find those baffles I couldn't find them in home depot or lowes..

Here's some pics of what I'm working with full size pictures are in my members gallery.