How should I insulate my shed?

kbizzle

Hi everyone,

I'm new here and just wanted to say that I've already learned so much from researching this site. It's a great resource.

So, I'm having a 16' x 16' shed built in the backyard. I plan to use it as a workspace / project studio / retreat and I want to finish it with insulation and drywall. I plan on using a 12,000 BTU portable A/C in the summer and some sort of portable garage heater in the winter. I'm in Durham, NC so the summers are hot and winters can be quite cold. The shed will be a mostly shady spot because we have a nice canopy of trees in the backyard. I thought insulating the shed would be relatively simple but after almost a week of research I'm puzzled.

I plan on using R-13 fiberglass batts in the walls and finish them with drywall. The ceiling / roof is where I'm running into problems. The roof is framed with 2 x 6 at 24" on center. There's a ridge vent that runs almost the full length of the shed and a gable vent on each side. I've included some photos here so you can see exactly how it's setup. The photos are of a 12 x 16 demo shed on the lot (mine is just now being built).

The contractor says not to staple batts between the rafters because it will most likely hold moisture up against the roof decking. That makes sense to me. They suggested rigid foam board or possible some foil backed bubble insulation. Rigid foam board insulation kind of pricey and I'm not sure it's the best option.

Here are the photos and any suggestions would be most appreciated.

Thanks!

kbizzle

Forgot to mention that I'm concerned that if I just insulate the roof with foam board or a product like Prodex Total Insulation (http://www.insulation4less.com/prodex_Ffmf.asp) that the ridge vent and gable vents will allow so much air to escape that it won't be effective.

I'm considering finishing the ceiling by attaching horizontal 2x4's (maybe 2x6s) to the rafters at 24" on center to create a frame for hanging drywalll to the ceiling. I could then use R-19 fiberglass batts or Prodex in the ceiling and then there would be a continous air space above the insulation so the ridge and gable vents could work as intended. There are no soffit vents in the eaves. The ceiling would form a seal between the shed workspace and the shed attic. Does that make sense?

The outside walls are 8' but if I drop the ceiling where the framing meets the rafters that's only about a 7' 8" headspace. I was thinking of hanging the ceiling a little higher on the rafters to form at least an 8' ceiling. I don't plan on using the attic for storage so I don't think that would cause any structural concerns.

Scuba_Dave

Having a shed built....or already built?
I prefer a bran style shed - lots of extra storage room up top




You use a rafter vent against the plywood for ventilation
Then insulation
With 2x6's you could still use R13

kbizzle

Thanks, Dave. I've seen those rafter vents before but would that require cutting holes into the eaves for them to function properly? Or do the vents just keep the batts from pressing up against the OSB roof plywood?

Yeah, I like barn roofs for that exact reason too but had to compromise because my wife hates the way they look (???).

Scuba_Dave

They keep the batts from pushing up against the roof decking
Heat will rise & cooler air will sink
It would work better with soffit vents

Have you thought about putting joists across for a flat roof?
That would reduce the space that you would need to heat/cool
It would eliminate the need for rafter vents & allow ventilation up there w/the gable vents/ridge vent

kbizzle

Dave,

Yes, that's what I was trying to explain in my second post. I think about raising the joists up about 8" to 12" to increase the headspace. There would be an angle on each side of the ceiling close to the wall. That may be the best way to go.

Scuba_Dave

Ah, I missed that - must have been typing up my post - slow

Yes - I'd run 2x6's straight across even with the rafters
You should be able to sit them on the wall if you angle cut each end
But to go 16' you would need to go to 16" OC
-even that would be pushing the span allowed
2x8 would be better - angle cut each end

kbizzle

dave,

thanks again for the info. so, here are a couple of updated illustrations of what i'd like to accomplish. ideally, i want to create a raised ceiling for more head room. check out the illustration with the red beams.

in the raised ceiling scenario, i believe the span would only be about 10'. the only weight these joists would bear would be the weight of the 1/2" drywall. i would not be using the space for storage of other items in the attic.

if there's no good way to accomplish that then i could go with the scenario the blue joists illustration. you think 2 x 8 at 16" on center would be necessary there though, right?

thanks again for all your help so far!

kb

Scuba_Dave

2x6's 24" OC will span 10'
They will act as rafter ties too = keeping the walls together
This is the span calc I use
You enter the wood species, size, use (joist, rafter etc) & calc & it tells you the distance you can span

http://www.awc.org/calculators/span/...rcalcstyle.asp

Up here we have to worry a lot about snow load
I actually re-used 2x10's as rafters for my 10x10 cabana addition
They came off my house whan I dormered the back
With snow I stick to 16" OC here

kbizzle

dave,

thanks for the link and for all the super-quick replies. much appreciated!

kevin

Scuba_Dave

Your welcome
I just happened to come down off the roof (new roof on addition)
Going back up now

beerdog

Don't you have to have open eave vents or some type of equal amount of intake with ridge venting? it could actually work in reverse from what I have been told and read a bazzilion times in the roofing section. Then again it is a shed.

beerdog

Also, the roofers will say that ridge venting and gable venting in the same roof is a big no-no. both are considered exhaust venting and there should only be 1 type of exhaust vent. The visitors of the roofing section have been lectured a million times by "Ed the roofer".


By the way, great looking shed. Wish it were mine.

Scuba_Dave

That's actually the 1st shed I've seen a ridge vent installed
If it was a house I might change it
But as someone pointed out...heat will rise
So it may not be the perfecxt setup - but it will work

Just make sure those gables have very good screening to keep wasps/bees out
In my MIL's house they came loose & she had quite a few nests

kbizzle

thanks beerdog and dave. my shed is actually just being built this week. i may take your advice and request that the ridge vent not be installed since there are no soffit vents in this design.

dave, great idea about doubling up the screening on each gable vent. i can't stand bees and wasps!