want to insulate garage roof

[Itsa Pole Bender]

My wife and I bought a house in late Novemeber. The house was built in 2004 with the garage cieling being insulate. After the original construction a previous owner cut in a really nice stairway and constructed a great storage area in the garage attic. The problem is, that due to this the garage does not stay warm. I want to insulate the roof of the garage and install an overhead heater this summer.

Question is: will just using the space of the 2x6 rafters be enough insulation for what I want?

or - Should I build a door covering the stairway and only heat the parking area of the garage.

I am tired of scraping ice out of the garage.

Thanks in advance.

[WaveWacker]

So it's insulated already? And...the hole through the ceiling for the stairs was left open? I insulated my garage with only 4" roll insulation (not really that high of an R value. I forget exacatly what) and it's just fine. So I would assume that yours would be just fine. Either build some sort of insulated cover for the top of the stairs or take them out and put in a drop down ladder.

[Itsa Pole Bender]

So it's insulated already? And...the hole through the ceiling for the stairs was left open?

[B@ssmaster]

If I understand you correctly, you are thinking about insulating the roof itself? Above the ceiling? That could prove to be a problem for you if you heat the space below. You could create a moisture issue between the insulation and the roof decking material, resulting in mold, rot, etc. This could also cause major ice dams outside. Presumably when you talk about insulating this area, you are also thinking of blocking all the venting to hold in the heat? If so, that will compound the problem.

I know the basic concept of an attic is to keep the rain/snow out via the sloped roof, but let the outside air circulate above the ceiling insulation via the vents in the eaves and vents above, helping to vent any warm air and moisture. Ideally there is enough circulation through the attic so that the attic air and the outside air the same temp and humidity level.

Maybe there is a way to insulate the roof deck itself that I am not aware of that prevents condensation, but be careful. You don't want any moisture/heat building up between that insulation and the deck layer. Heating up the deck material causes ice dams above and no air circuilation can cause condensation in between.......

Maybe they put insulation in the rafters NOT full thickness, creating a small airspace between the insulation and the bottom of the deck plywood, then vent both the peak and the eave of each joist space...just guessing on that one......

[King Canada]

In the southwest many new homes are built this way. Just run the chutes from top to bottom and use a kraft backed product. A continuous ridge vent would complete the system. Do you really have rafters or do you have trusses and are the trusses designed to carry the extra load?

[Itsa Pole Bender]

sorry all for not replying in a while. My wife gave birth to our first future outdoorsman and life has been hectic for the last two weeks.

My current plan is to insulate between the rafters. I will first place a vapor barrier on the underside of the roof, then I will place vent baffles in between each rafter. The vent baffels will run from the eave to the ridge vent. After that is complete I will then place the insulation over those two things.

Given that the ceiling of the garage is already insulated and I have an approximately 4 1/2 foot by 12 foot hole in the ceiling to accomadate the stairs into the garage attic will roughly 5 1/2 inches of insulation do the trick to keep the garage above freezing in the winter??

[motley man]

There is a plastic piece that goes between rafters be fore putting insulation in to prevent moisture build-up. Check with lumber yard, FF, M, they can help.

[Itsa Pole Bender]

King Canada.... I am assuming the system is a pre engineered truss. However I cannot confirm. To give you an idea of the system....

The attic of the garage has rafters on each side of the roof as typical. joists are connected to the rafters and are covered by plywood. There are also braces between the rafters and the joists that run vertically and are placed approximately 5 feet each side of center along the length of the garage.

[Surface Tension]

If the attic is just storage I'd not waste money to heat it.

Depending on your layout.

Frame in the opening in the attic leaving a small landing and put in a door.

Or frame in the stairway with a door at the bottom of the stairs.

That could be studs from slab to ceiling or from Stringers to ceiling.

If you do insulate the rafters as said you'll need a ridge vent and vented soffits.

Leave a space between the roof and insulation, the more space the better. You can gain space by furring out the rafters with 2x2s. I'd attach 3/4" nailers to the rafters spaced 2" from the roof deck for your air space and use rigid foam compression fitted to the nailers. There is your shoot and with some r-value. Follow that up with batts. Vapor barrier goes over the interior side of the insulation then your sheet rock. DO not put a VB on the exterior side of the insulation.

[LightningBG]

Yeah, I dont think you want to be insulating right under the sheathing. You need airflow and you need to keep that roof COLD in the winter. If that roof heats up the runoff will travel down the roof to the overhang. At that point the roof is cold and runoff will freeze. Major ice dam.

The vent baffles may be sufficient, but I would be apprehensive about it.

I would try to build some type of hatch that lays horizontal over the opening that can be flipped up when you want to access the storage area. Could use weights or gas shocks (like the liftgate on a SUV) to assist if there is a weight issue. If you wanted to be real fancy you could hook it up to an electric hoist to the hatch. Push a button and the hatch opens up. (Now I almost want one)

Even if you do insulate up there and have a garage heater, all of the heat is going to go right up there. So you'll have a hot little room up top (not great for storage) and a chilly garage below.

[LightningBG]

Could you take pictures of what this stairway/opening looks like?

[Steve Foss]

I'm in favor of doing the staircase in either of the two ways Surface Tension mentioned.

Since it's a fairly big expense to buy vapor barrier, vents between each set of rafters and insulation for the whole roof, you should look carefully at laying a new floor out of 2x4 on top of the existing attic floor, and then insulating between that floor, which would double the existing R value. And with a door built for the stairway, you'd have a barrier against cold that way.

There's so much rigamarole to insulate an attic in ways that stop moisture issues that you may find it less hassle in the end, and not even a whole lot more expensive, to do what I suggested. You'd have to be sure that the existing ceiling joist/truss system can handle the added weight, of course, so there's that to watch out for.

Honestly, with a good heater you'd be fine with your current insulation setup as long as you take care of the hole in the ceiling by adding a door somewhere. If I were in your position, that's what I'd do.

[B@ssmaster]

IPB, Congrats on the future sportsman!

[Tom7227]

Is the garage attached to the house? If so I would be concerned about a fire break cause if things get going that attic is going to go fast and theres a problem if there isn't a fire break - I think at least 1/2 inch gypsum on the common wall with the house. Unless you really want that extra room for regular use I don't see any value in insulating it. Figure out how to put a door on it and let it go cold and avoid all the issues with condensation/ice dams and whatever else.

[SFC]

I would go with the door as others have suggested, if not the door get someone who knows for sure the steps to do this. Products are changing all the time, codes change all the time, usually because they didnt work as planned. It may take years to find this out & be costly. A door & a properly vented roof should have no issues.

[Tom7227]

The other thing I would be concerned about is the amount of weight you put up in the attic. There's a limit on what a truss can hold when putting weight on the horizontal members. I don't know what it is or how to figure it out but you may want to pay some attention to that before you start hearing cracking noises.

[vister]

you'd be creating a hot roof. to do it, you'd have to run shutes from eave to ridge, assuming your garage roof has a ridge vent. then insulate with the itch, or fiberglass. but you'd also have to put foam sheathing on such as thermax to the bottom of the rafter top cords to prevent cold transfer. do that, then youd be fine