# Insulating garage ceiling..... the smart way?



## jeffpas (Feb 21, 2011)

I have a small garage which I use occasionally as a workshop, too much of a pain to get the car in and out, so it basically gets used for this and storage........ but its cold out there half the year. I would like to insulate the roof.

The garage was built with two old fashioned gable vents at each end, which I'm told are the best way to go for ventilation- better than ridge vents, advice given such as in this article below: 

Article here:
http://tedsenergytips.com/2011/12/20/attic-insulation-problems-and-solutions-part-2/

I don't want to put a ceiling in as I need the overhead storage space, and really can't mess with hatches. I want to insulate further up and still have the 'vault'. I know its not as good, but its better than nothing.
But my question is all about venting.

My understanding is not to staple fiberglass bat insulation between the vaulted rafters directly under the roof- as there would be no way for the moisture to escape, especially considering there isn't a ridge vent (even if I left a space behind the insulation for air flow).

However, if you look at the article I posted above, Tedsenergytips, he recommends Closed Cell Spray Foam, right up there on the rafters directly below the roof. 

Why would this not cause any moisture damage? Because he says, as the warm air rises and condenses, there would be no way for it to actually get to the roof, it would be just as if you had a thicker roofing boards.

OK fine, but we all know Closed Cell spray foam kits go for like $1000.00, not cheap by any stretch. 
My question is: What about foam polystryene sheets, stapled directly against the roof underside between the joists? Such as this:

http://www.foamular.com/foam/products/foamular-250.aspx

The theory being, practically no rising moisture will even touch the roof underside- and air can still ventilate out the gable vents as the builder intended.
This seems the only affordable solution for me.

Smart? Crazy? Dumb? please comment.... thanks!


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## Windows on Wash (Aug 30, 2011)

Don't bother with the spray foam. The froth pak and propane canister kits don't give near the yield or quality of a rig.

Are their soffits on the garage? 

Will you actively be conditioning the space?


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## pondball (Dec 9, 2013)

Hi jeffpas I was about to post the same question... Where are you located? Im In ontario Canada and today it was a balmy 3 celsius... Which might be as warm as it gets until next March. I'd intended to get the insulation done sooner but... I actually have a ridge vent (have had for the last 5 years since we put on a metal roof. I've found both the house and the garage cooler in the summer and warmer in the winter since switching to the metal roof... But it's still too cold to do anything in the garage in the winter without more insulation. I bought what I think will prove to be a decent portable heater for when I am out there, but on,y if I get some ceiling insulation in place... The walls have fibre pink in them.. No other source of heat or ventilation available, Nor will space permit anything else even though it's a double car garage with a higher than normal floor to joist ceiling... Unlike your situation I would be able to insulate along the the flat ceiling and was wondering if simply adding rigid 2x4 insulating panels would be enough to get me through the winter. It seems the quickest and least messy way... Being panels I was thinking if I did need to store anything above them I could and then just slide a few aside to have access to them.. Is this something that might work ... And if it did would it work in your situation where you require the overhead storage space... Something like an attic?

Just found this... Might be relevant... Dunno... But it talks about much of what you have asked

http://www.trainedeye.ca/articles/ventilation/insulatingGarageRoof.html


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## jeffpas (Feb 21, 2011)

There are no soffits.... no ridge vents, nothing but the two gables. 
The garage was built around 1940..... later it was sided, but still original tongue and groove board outside the studs. Its all open on the inside of course. Though far from air tight.

I won't ever be air conditioning if that is what you are asking by 'conditioning', the most heat will be one or two oil heaters when it is very cold out and only when I'm in there for a few hours. 

I have read that since there are no soffits, there is no way for any moist air to get up behind whatever is covering the cathedral rafters, say you did that. Still the thought of doing all the work of putting insulation in and then rotting a roof out isn't appealing..........


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## jeffpas (Feb 21, 2011)

@pondball if you mean covering the horizontal rafters and then removing them to get to the overhead space.... I have far too much stuff stored above, and large items to make that workable I think.
A one car garage needs every square inch of storage. But what about the waterproof polystyrene, stapled or glued directly against the underroof between the vaulted rafters? surely air would still circulate below and out the gables as before and nothing would really get behind them.

? ? ?


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## pondball (Dec 9, 2013)

Yeah .. Was thinking insulating along the horizontal rafters might be a solution but on.ynif you had an access door like what you might have in the attic. It would still require some venting though... And anything I've been reading recently says without venting rot is a sure thing. 

Not so sure my rigid board is as quick and easy a solution as I originally thought either as research suggests it would not be to code... Mainly due to the fire and subsequent toxic fume problem. It would have to be covered with drywall or some other fire retardant material... Unless there is a rigid solution that comes with a fire retardant layer already built in???


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## High Gear (Nov 30, 2009)

Are the walls insulated ? If not I would concentrate my efforts there first.
I had a similar situation at my old place with a 24x24 garage .
I insulated the walls left the ceiling open but made hinged covers for the vents for when I heated it.
A 18000btu wall heater would give me a 40f rise from ambient, good enough to take the edge off.
Insulating the floor may be something to consider also.


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## jeffpas (Feb 21, 2011)

The walls are not an option for me. They are loaded with shelves, hanging yard implements, hoses, etc etc. the shelves are between the studs, a huge project just not worth the trouble.

I would think doing the roof would be more bang for the buck than the walls at least heat wise, since heat rises. The vaulted ceiling rafters are bare now, would not be much work to just cut some polysytyrene into strips and tack it up between them.
I wish some knowledgeable person could tell me if this would be bad for the roof or not..... oh well. :surrender:


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## pondball (Dec 9, 2013)

Hi ... Sorry, I'm just a DIYer like you... But if you're going to cut the polystyrene and tack it between I see two things you will have to consider. 

First, we did this over a kitchen extension, on a side wall above that had been way too cold for our son to even put his bed up against. We used the 2" thick (I think that was the one) rigid insulation on that side wall and because it was of this nature we were told a vapour barrier was not needed. On the ceiling of that kitchen area we also used the white (non-itchy) batting over a vapour barrier. Keep in mind though that the rigid was on an interior wall facing what was essentially a mini-attic. There was plenty of air space behind it as well as soffits for air flow. The wall, now however, is very bearable and he has his bed up against it with no issues of getting cold.

Second, my understanding of any readings here or at other forums is that the rigid or poly is not to be left uncovered by a fire retardant material (such as drywall) as there are fire and subsequent toxic fumes issues... Would not pass code. 

I think the things you may need some answers to are:
If you put the cut poly up can you leave some space behind it?
Can you form some type of soffit if one does jot presently exist. In another forum (sorry, can't remember which) it was suggested that cutting holes and covering with animal proof screen would allow for sufficient ventilation behind the insulation.
You, like, I, need to find out what type of non-drywall fire retardant can be used to cover the rigid foam and still be to code... So as to satisfy fire and thus insurance regulations 

Sorry I can't be of more help


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## jogr (Jul 24, 2007)

You are way too worried about condensation of vapor. In a garage you won't have that issue. You aren't running showers, cooking steaming food or filling it with people giving off moisture. Your only moisture will come from your heaters and you say those not be used that much. Your structure will stay dry and any slight condensation will have plenty of opportunity to dry.

Since you are infrequently heating it it makes no sense to put in an expensive insulation system. It will never pay for itself. # 1 Seal all air leaks with caulk and use good door seals on all doors. That's the most cost effective way to make the garage more comfortable. If you want to go 1 step further then insulate with faced fiberglass insulation, place the facing on the inside and tape the seams. That will prevent what little moisture is there from causing a problem.


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## Windows on Wash (Aug 30, 2011)

Keep in mind there can be moisture from sources other than those listed. 

If you can ensure the ceiling will be airtight, the likelihood of condensation is very small. If, however, any moisture can enter the assembly, the roof will suffer and the sheathing will take the brunt of it.


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## jeffpas (Feb 21, 2011)

What about then just making little doors to cover the gable vents? It makes sense to keep the heat from escaping there but something tells me I'm messing up the original design of the garage. 
If I close the gable vents with doors, and run the heater for a few hours surely no problems? What if you left the gable vent doors closed all winter?

yes I've read articles like the one attached. Many people preaching on about not closing vents.


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## MT Stringer (Oct 19, 2008)

Insulate between the ceiling joists, not the rafters. I had R38 insulation blown into the ceiling of my garage. The outside walls are also insulated with the standard kraft paper style roll insulation.

102 in the summer (Houston, Tx area); 77 inside the garage with a split system air conditioner w/heat pump. You will be glad you did.


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## jeffpas (Feb 21, 2011)

I have no ceiling joists..... only a couple and like I said its not workable, its a small garage and I need the overhead storage space. 
Attic doors are just not going to work... not enough room :/

As I said, I know a ceiling is the most efficient. Its just not workable for me so I'm making the best of it.


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