Insulation retrofit

[Johnhg7]

Hi all,

I'm looking to add insulation to my detached garage so I can work out there in the winter. My plan right now is to add an electric heater. I live in central Illinois where it typically hits 10 or so in the winter and a humid 100 in the summer, although we did go down to -20 for a few days this year. Only looking to bring it up to 55 when I'm out there.

There are no eves and no vapor barrier, just vinyl siding and asphalt shingles on OSB. There are two vents near the ridge.

My current thought is to add faced R15 in the walls and against the roof. I want to keep the trusses open for storage. I would cover the walls with OSB for durability.

Would this set up trap moisture or should it work out?

Thanks,
Jack

 

[strutaeng]

Welcome to GJ!

So you are only planning on R15 to the deck? Same as walls, right? Do you need to comply with the building code? If so, R-15 is not enough for the "lid." Don't you need like R49-R60 in Zone 5?

As far as leaving the trusses exposed, the best solution is rip off the singles, add rigid insulation (again, to meet thermal code requirements) and another layer of deck and new shingles. That gets expensive quickly!

Even spray foam under the roof deck won't give you enough R-value if you fill the 2x4 top chords.

You can also use a combination of fiberglass and rigid insulation or fiberlgass and spray foam. Do a search, this a commonly asked question.

I hope this helps.

 

[D45]

Soffits or not?

I am also currently looking for add insulation to the roof deck, like you

I want to leave the joists open for added storage

 

[strutaeng]

No soffit vents if you add insulation above the deck like the method I mentioned. It is a non-vented system.

Essentially, it is like a commercial application. Typical warehouse roof construction consists of metal deck with polyiso insulation (many times tapered to achieve the roof slope.) No vents.

 

[xyster101]

Welcome! With a space that large you are going to go bankrupt using electric as your heat source!
I would suggest that you put a ceiling in and insulate above the ceiling with a minimum of R-30. Code in your area for a home is probably R-49. If you don't put a ceiling then all your heat is going to go UP. That means the top peak inside will be 90 and the floor area where you work will be 40. On top of that, R-15 will just let the heat go through the roof, literally!

If you are determined to not put a ceiling in (which will give you more light too) the put the thickest fiberglass you can up there. Screw 2" ridgid foam over that, 2 layers of foam if you can afford it.

I suggest using a propane or natural gas "Hot Dawg" forced air heater. It will be about the cheapest gas type heater you can get. If you install it yourself, around $1200.





Search craigslist for poly ISO foam. It is used foam from commercial roof jobs with a high R value and super cheap used. I did my whole shop with the stuff. $600 for R-30 in the walls and R-50 in the ceilings (1200sqft)

 

[Dragfluid]

Welcome to GJ!
You need to put a ceiling in and blow it full of cellulose. At least 16" of it.
I've said this before and I'll repeat. Keeping the rafters open for storage is a lesson in futility. The stuff that gets put up there will still be there 10 years later.