Insulation help please

[STClurker]

Hi all, so I'm working on insulating the garage (because why do it in the summer when you can do it when its 2* out). I am putting up R13 on the walls (menards had a sale on it) but I am trying to figure out what to do with the ceiling (sp?)...I am very attached to putting stuff on the bottom cord of the truss...but I understand I am loosing any heat through the roof.
Pic attached to see what I am dealing with, not really any room to hang anything (8' walls). Any ideas or suggestions appreciated



Adam

 

[logboy]

i'm no expert but i have done some insulating. R28 is the preferred stuff in my area for ceilings. but you need to have some air space above it, meaning don't have it right up against the osb. don't forget the poly. it makes all the difference

 

[matt_i]

Imo unless you enclose the ceiling, you are going to fight with retaining heat forevermore, especially when heat is being picked off by a 2F exterior temp.

I would put in an attic stairway access and you will have plenty of storage.

 

[R_einan]

Does you roof have soffit vents and ridge vents? If it is not a vented roof design, you 'can' insulate directly against the OSB without an air space. It is known as a hot roof, and while not ideal for an asphalt shingle roof, it can be used depending on your climate.

I recently moved into a property with a detached 24x24 with just over 8' ceilings, it was built is '75 and is 2x4 construction with an unvented roof. Living in an area with little moisture, and not wanting to lose the rafter storage, I went ahead and insulated directly against the roof sheeting. I am aware that it will accelerate the failure rate of the asphalt shingle roof and hide any leaks. However, I believe it is the original roof and plan to replace any damaged sheeting and add an add'l 2" of foam and a metal roof in the next couple of seasons.

 

[D45]

Does you roof have soffit vents and ridge vents? If it is not a vented roof design, you 'can' insulate directly against the OSB without an air space. It is known as a hot roof, and while not ideal for an asphalt shingle roof, it can be used depending on your climate.

So if you have soffits and 6 roof vents, you cannot insulate directly onto the roof sheathing?

Is this because of moisture and air flow that needs to travel from the soffits to the vents?

 

[R_einan]

My understanding is that you can still insulated against the roof sheathing, however with a vented roof it is ideal that the air flow from the soffet vents to the roof vent be maintained for moisture control. We are talking strictly about fiberglass insulation in this, spray and rigid foam is another story.

 

[D45]

Good to know, thanks

So basically with a soffit and vented roof, an air channel needs to be maintained for the entire length of the roof, from the soffit up?

Is it as simple as using the foam baffles all the way up, then attaching fiberglass insulation?

Like these?

The are pretty reasonably price:

14" Wide:
http://www.homedepot.com/p/ADO-Prod...t-Attic-Ventilation-System-UPV14480/100533902

22" wide:
http://www.homedepot.com/p/ADO-Prod...t-Attic-Ventilation-System-UPV22480/100561170

22" wide:
https://www.lowes.com/pd/ADO-Products-Durovent-22-in-x-48-in-Rafter-Vents/3012019

It looks like most are all 1" gap standard........just depends on the material and price

Foam vs plastic and about 40 cents more, per baffle, for the plastic

 

[R_einan]

Baffles all the way up the rafter cavity is the only way to maintain the air path. The reason behind it is moisture can build up on the inside of the sheeting if it is warmer than the exterior. The air flow lowers the temp of the sheeting and limits the temp variation. With 2x4 rafters, the issue is with baffles, you can only use r13 and it will be compressed at that. Definately not ideal. In that instance, 2" thick rigid foam installed flush with the rafter will provide better air flow and almost the same r value. Another consideration is the cost, after figuring up the cost of fiberglass and the baffles, rigid foam might be more cost effective.

 

[matt_i]

Suppose you insulate the rafters (glass or spray foam) and provide the vent channels.

The majority of the heated air is naturally going to collect in the attic, needing some sort of blowing device to get it back down.

That's why I like the ceiling despite the tradeoffs. Fit sheet goods to the ceiling, dump cellulose or roll out glass and call it a good day. Less "cube" to heat and more of it will heat you.

 

[R_einan]

Suppose you insulate the rafters (glass or spray foam) and provide the vent channels.

The majority of the heated air is naturally going to collect in the attic, needing some sort of blowing device to get it back down.

That's why I like the ceiling despite the tradeoffs. Fit sheet goods to the ceiling, dump cellulose or roll out glass and call it a good day. Less "cube" to heat and more of it will heat you.

Matt is correct, I have a ceiling fan in the center of mine to help push the heated air back down.

 

[STClurker]

Ok, so looking at it again there doesn't seem to be any ridge vent. So does that mean I can insulate right against the roof or would I nees to put those channels in?

Thanks all, keep the thoughts coming

 

[D45]

Ok, so looking at it again there doesn't seem to be any ridge vent. So does that mean I can insulate right against the roof or would I nees to put those channels in?

Good question

Do you have any square or round vents?

Do you have soffits?

I do not have a ridge vent, but rather soffits and 6 roof vents

 

[Firebrick43]

I would highly suggest not insulating against the roof with fiberglass, and sealing off below , as it never ends well. Moisture always gets in. Air flows to well through fiberglass and forms convection currents which cause continuous condensation . Spray foam or xps put in place with foaming adheasive such as foam2foam, have at it.

Are you wanting to heat all the time or just when working in the shop?

 

[DeltaWye]

What about putting rigid foam boards perpendicular to the rafters and leaving the cavity open?

 

[BearsFan315]

here is what i did with mine in a similar situation Garage Roof/ Rafter Insulation... To Vent or Not to Vent ?

i am very happy with it, PTAC has been maintaining a constant 61 deg which is where the eat is set for now. really nice to be a in 61F garage when it is 30F outside !!

 

[Firebrick43]

What about putting rigid foam boards perpendicular to the rafters and leaving the cavity open?

If you vent the cavity!

 

[R_einan]

Again, the reason I chose to insulate with fiberglass in my case, unvented roof, is the asphalt shingles are old and nearly due to be replaced, I had easy access to the fiberglass, and intend to put 2" of xps foam and a metal roof on in the next couple seasons. I also do not heavily condition the space; only run a little occaisional heat in the winter to keep things from freezing. Everything is a trade off, and in my climate (SE WA) we have little humidity and some of the lowest precip rates in the country at about 10" of rain annually.

 

[Randy in Maine]

Spray 3" of high density foam up the bottom of the roof and there is no need to worry about any venting. You could then infill with rigid foam.

Be sure to put poly over the fiberglass in the walls.

 

[D45]

here is what i did with mine in a similar situation Garage Roof/ Rafter Insulation... To Vent or Not to Vent ?

i am very happy with it, PTAC has been maintaining a constant 61 deg which is where the eat is set for now. really nice to be a in 61F garage when it is 30F outside !!

Looks good!

Any idea on how much you spent?