# Insulating detached garage



## wrbrb (Aug 18, 2020)

We have a detached unheated garage with walls that are insulated up to the few ceiling joists but not apparently beyond, and there's no insulation between the rafters either. The garage is about 24' x 24' with a 10' high door and no ceiling below the roof. 

I bought a couple electric space heaters, but the heat from those is clearly just being lost through the roof. I'm guessing the cheapest way to make it a little warmer during cold Midwest winters would be insulating between the rafters, but I've seen some conflicting information on what R value to choose. 

With just space heaters used occasionally when working out there, does it make more sense to go with something like R11 or would it be worth it to spend for a higher R value? Does paper or foil faced matter? Can this just be stapled to the rafters face side down and will there be a noticeable temperature difference with or without the space heaters?

Thanks!


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## Bud9051 (Nov 11, 2015)

Although this is not living space there is guidance that advises ventilation above the insulation you suggest. And they do so for good reasons. 

Other than the occasional electric heaters what other use is intended for that garage, such as parking vehicles in there?

Bud


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## wrbrb (Aug 18, 2020)

Wet, snowy vehicles will be parked in the garage, and it will be used for working with power tools and as a place to get out of the rain during a cookout, etc. There is a medium sized (5' x 2') window on the south wall with two louvered/vented windows that can be opened or closed, and there are two vents just to the north side of the ridge at the top of the roof, one a few feet from the east wall, one a few feet from the west wall. I assume those should remain uncovered...


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## Bud9051 (Nov 11, 2015)

When that snow melts that moisture has to go somewhere and without a traditional ventilation approach all too often it masses through the insulation and freezes on the inside of the exterior shell.

The unvented attics you may have read about follow specific guidance, one being never installing fiberglass insulation against and exterior cold surface.

Wish you the best but outside of following traditional guidance I'm no help.

Bud


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## Ryanhutzel (Dec 29, 2020)

Drywall the ceiling and blow in cellulose to R-38. This would help. If you wanted to go real fancy you could spray foam the underside of the roof prior to drywall and then do the insulation. This would be very effective. 


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## joecaption (Nov 30, 2011)

You've got a real mess going on there.
Looks like the dry wall was put on backwards, no tape on the seams, no clue why they would have left 1/2" gaps and used those small pieces.
Rafters are way to far apart to properly hang new drywall, more would have to be added to add new drywall and not have it sag..


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## Ryanhutzel (Dec 29, 2020)

It’s definitely a mess. I don’t think that’s drywall. Looks like they stuffed insulation in the walls and covered with sheets of cardboard. 


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## chandler48 (Jun 5, 2017)

Combining the other posts, installing a ceiling with more joisting would allow you to install a sheetrock ceiling and either blow in or lay in insulation. You want the attic area to be as close to the outside temperature and humidity as possible to prevent moisture damage. It appears you already have some in one of the pictures. No comment on the erratic wiring on the gable. The only choice, IMO, if you leave it like it is, would be to have the rafters spray foamed, but it isn't cheap.


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## wrbrb (Aug 18, 2020)

Thanks for all the feedback and observations. It is actually 1/2" drywall and yes it does appear to have been put on backwards. I believe they used 8' pieces from the floor and then 2' sections to get to the top of the 10' walls.

The functional wiring is done fairly well, 99% in EMT along the walls. There is one free wire stapled to the rafters for the garage door opener. The wiring on the gable looks like it was actually just used as some kind of storage system and is now all undone and unused - not used for electricity at any time thankfully.

I would like to do this the right way - it looks like some of the ceiling joists are a bit precarious and may have shifted but they support the garage door track. It would be nice to lower the ceiling to have less to heat. I suppose I'll head over to the carpentry area and discuss some ceiling framing. Thanks everyone.


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## 3onthetree (Dec 7, 2018)

wrbrb said:


> It would be nice to lower the ceiling to have less to heat.


NOOOO, don't do it! If you do turn in your man card.


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## wrbrb (Aug 18, 2020)

3onthetree said:


> NOOOO, don't do it! If you do turn in your man card.


Okay, what I meant was not "lower the ceiling" but "have a 10 ft ceiling" meaning not having to heat attic space up to the rafters.


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## Porsche986S (Dec 10, 2017)

Another option for a ceiling would be to install metal roof/wall panels like installed on a pole barn . My man cave garage started as a 24 x 26 pole barn and the rafters are spaced aprox. 5 ' apart . I had the local manufacturer cut my panels so I only had one overlapping seam . Screwed the panels directly to the bottom of the trusses . These metal panels easily bridge the 5 ' space with no sag . I went with white panels so when installed there is no painting/taping/sanding etc. you are done once they are installed . They reflect light very well .

My pole barn has a full length ridge vent and I installed full length soffit venting on both sides . For ceiling insulation I had left over R19 kraft faced fiberglass insulation from the walls so I used that . I placed the kraft face against the metal . I am in GA. so we don't get extreme cold but I easily heat/cool with a 24k Mitsubishi mini split . My walls are just under 12 ' tall . If you can purchase metal roof panels locally I highly recommend them as a finished ceiling . I installed 13 ' long panels BY MYSELF just by renting a sheetrock jack and I was 61 years old when I installed them . Good luck with whatever you decide to use .


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## wrbrb (Aug 18, 2020)

So I would be able to get away with adding no additional framing, use metal panels to bridge the 4' gaps between the rafter ties, and place rolls of insulation paper side down on top of the panels as I'm going along?

Could 6 mil vapor barrier be used in this same fashion, stapled to the underside of the rafter ties and with insulation placed on top?

Looking for a cheaper option as this space is only for occasional use, but when used it would be nice to have it heated if desired. 

Thanks again


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## Porsche986S (Dec 10, 2017)

Yes on your metal panels questions . I have no idea if plastic can bridge 4 ' AND support the weight of insulation . My gut says no .


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## wrbrb (Aug 18, 2020)

Would it be okay to attach 1x2 furring strips every 16 inches perpendicular to the 48" oc rafter ties, use those as framing to staple the insulation to, and cover the whole thing with plastic sheeting as a vapor barrier, so the ceiling would just be sheeting with insulation visible through it? No insulation anywhere farther up and the two ridge vents allowing the attic space to breathe?


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## 3onthetree (Dec 7, 2018)

I think the 1x2s would sag. Stapling insulation meaning you want faced batts? The paper facing is the vapor retarder, you wouldn't use another poly sheet over that. Enclosing the ceiling would make your inadequate attic venting become a problem.

You should zero in on your budget vs use. You just want to stop the heat from escaping, but won't use it often and want it cheap. How about just lining under the rafter ties with a scrim sheet - no insulation. Once you insulate you have to address the venting and maybe the 48" rafter tie spacing to hold whatever.


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