Another detached garage insulation thread...

[CarCrazyRDM]

I've read through a number of posts using the search function but haven't quite seen the answer I'm looking for. So I figured I'd just save myself some time and ask the questions specific to my garage.

I'm currently in the process of having a 24x36 detached garage built (see pics below). It has 12ft ceilings downstairs and a interior staircase leading to a second floor. It will have an 8x18 insulated garage door on one end, a 9x7 garage door on the other end, and 4 windows downstairs, two upstairs and a single man-door.

I'm in NC, where we see below freezing temps each winter but usually nothing excessive (single digits) and usually not for any extended period of time (more than a week straight of below freezing temps). There is no plan now or any time in the near future of finishing the upstairs. It will likely remain storage. I also have no near future plans to add HVAC to the building. When I need heat I'll likely use some kerosene and/or propane heaters I have and in the summer it'll likely just be fans. This garage/shop will be used for automotive work and other "shop" work on a regular basis but it isn't like I will live out there every weekend.

So there are all the parameters that I think might be necessary for advice to my questions. I'm going to do all the electrical work once the building is complete and then I think I've decided soon after that I will likely want to do insulation and drywall.

Given the intended use of my building is it worth spending the extra money for R19 or will R13 suffice?

Would it be of any use to put R19 in the ceiling if I only put R13 in the walls?

I hadn't planned on insulating the roof rafters now but I will likely install a door on the stairs somewhere to isolate the upstairs from the down. Or do you think I should just go ahead and insulate the rafters when I do the downstairs?

I don't need the thing to stay at some perfect 55-75 degree temp... I really just want to not have to worry about any liquids inside freezing in the winter and I'd like to have enough temperature barrier that it stays maybe a good 10-20 degrees hotter or colder than the outside temps in the extremes of winter and summer.

Thanks in advance for any advice,
Ryan

 

[deserthawk]

I recently insulated a 100 year old house and after discussion with the power company, I went with the good stuff in the walls. They directed me to this article, take a read. From what it says majority of heat is actually lost through the walls. Something to consider.http://www.greenhomegnome.com/energy-loss-homes-insulation/

 

[rayra]

If it's cold enough to have that muck peak to the roof, and you have 2x6 wall studs, it would be foolish NOT to put R19 in.
The R19 'only' costs about 45% more. Which oddly enough is the same % increase as the R value. Funny how that works.

 

[Kamhillbilly]

I would defiantly go r19 , and bite the bullet and insulate the ceiling with the highest r value you can afford then its done ,so much easier to do now before it fills up . I have made that mistake ,plus it will be much cooler upstairs in the summer months

 

[rvieceli]

Another vote for the R19 and also do the attic before you load it up with stuff that you'll have to move later.

Since you are in or near a big city, you might want to get some bids from insulation contractors. I don't have any personal experience, but there have been more than a few mentions on the forum of situations where the insulation contractor's price was either cheaper or the same as the owner buying the just the insulation and that included the labor for installing.

You also might want to consider insulating the ceiling in the garage as well if there might be a big temp differential between the spaces. But I'm not sure of the return on investment there.

 

[CNGsaves]

I'd even recommend going further . . . . . with SPRAY FOAM.

Your underside of roof is perfect candidate of couple inches of closed-cell foam.

This would give you tight sealed upper "envelope" of building, then you could fill rest of space with at much batt insulation higher R value you can. This mix of foam/batt would minimize cost, as it would be expensive to completely fill cavity with closed-cell foam (which is ultimate choice, if money is no object). Yes, put AS MUCH INSULATION AS YOU CAN. This is one chance to Do It Right !!

Your choice on what you'd put in walls, but 1" of foam would do wonders to keep your entire building airtight and easy to heat / cool. Then fill rest of space with as much batt insulation as possible.

Also your climate would be perfect for mini-split system.

With open studs now, this is your chance to also . . .
. . . . . PLAN AHEAD for absolutely all Rough Electrical and Lighting . . .
that you think you'd ever need in the building. Thus, 240v runs for compressor and welder, lots of 20A outlets using 12 gauge wire, etc. Don't forget low voltage wiring for internet, CATV, security, speakers, phone, etc.

If you ever consider putting DISH-style TV antenna up on roof, then put a conduit in wall for that wiring that goes does down to a centralized distribution box where the end runs terminate. Again, best chance to get it right the first time. Put a pull string in that baby and you'd be REALLY ahead of the game !!

 

[CarCrazyRDM]

Yeah CNG, I will be doing all electrical before doing any insulation. I'm going to plan out all my lights, outlets, 220V plugs (welder, lift, maybe larger compressor one day), garage door openers, etc. If money were no object I'd consider foam insulation but I've already gone over budget on the garage and I really want to go ahead insulation and drywall within a reasonable amount of time from the structure being complete so that I don't fill it up with stuff and then never do it or it be more difficult. I will likely do the rafters as well but it may not be right away since I can always come back at a later date and do that... there won't be much of anything upstairs for quite a while.

 

[Jack D]

I'm also starting to look at insulation for a small garage that I am now obtaining the building permits for. I have two bids on my foundation and as I was reading this I was thinking along the lines of doing it 'right' out of the box providing it doesn't drive the costs too far out of control. But I am pretty much out of control already.

My winters in the northeast are considerably colder than NC and because I decided to do an LVL as my ridge beam I will have an open room similar to what CrazyCarRDM has upstairs. I'm planning to go with closed cell foam but had not thought of combining foam and batt insulation but I intend to look into it.

My question is has anyone decided to insulate under the slab. I've pretty much decided on a 5000# 6" floor. If this was living space I would certainly insulate. I don't, at least at this time, intend to heat the garage except maybe to use a portable heater to take early winter or early spring chill out of the space.

Any thoughts?

Jack

 

[bczygan]

You didn't give enough info.

What size are the ceiling joists? And how about the roof rafters.

Typically we use R38 in the ceiling and R13 in the walls, for standard construction.

If you don't have enough space in the ceiling joists, other methods need to be used.

Bill

 

[derosa]

My understanding is that the greatest heat loss is through the ceiling since heat rises though windows will let a lot of cold or heat through. Here in NY new requires r19 walls with r38 ceilings, renovation only r15 in the walls but r30 in the ceiling, if walls lost more then ceilings I'd expect the ceiling requirement to be lower, actual recommendation is more like r60 in the ceiling but that seems ridiculous to me. It really does make a difference too. I have all electric with wood stove backup, the main part of my house has r19 walls with r23 in the ceiling above the upper bedrooms. While above the kitchen/mudroom and side room there is a minimal amount of blow in insulation, maybe r13 but mixed depth, in the ceiling with only attic space above. The main part of the house can easily maintain 70-72 but the kitchen is always colder and the mudroom despite having its own heater is freezing. The middle room does ok but all have r19 in the walls as well. I expect when I finish sealing the attic with r15 walls and r34-38 in the ceiling there will be a considerable difference in the kitchen/mudroom. Any insulation helps a lot.
Jack D, I understand there is high density foam board that can be laid under the slab and does make a difference. I was in a shop with a poured cement floor that had insulation and radiant heating under it and it was a beautiful thing. Not a bad system for a shop and affordable to install yourself.

 

[CarCrazyRDM]

Bill,

The ceiling joists are 16" tall wooden I-beams spaced at 19". The roof rafters are 2x8's 24" on center.

 

[bczygan]

Bill,

The ceiling joists are 16" tall wooden I-beams spaced at 19". The roof rafters are 2x8's 24" on center.

Then your solution is to fill that ceiling joist space completely, with the least expensive insulation.

You could partially fill the space, but why not completely fill it. Insulation is cheap.

That will take care of your insulation needs whether heated or not. Now, understand that if left unheated, the space will stabilize at the outside temperature. Insulation does not heat a space. It only slows the loss of heat from a warmer space to a cooler space.

It will help slow the loss of heat gained from daytime temperatures.

So the plan is this:

Insulate the ceiling joists fully, and the walls with the maximum R value.

Later, to finish the upstairs space, either foam the rafters fully or install insulation, leaving a 1" airspace between the insulation and roof deck. Since this leaves the insulation value low, add layer(s) of rigid insulation to the bottom of the rafters.

You can almost never have enough insulation.

Bill

 

[K'ledgeBldr]

For your intended use, I wouldn't insulate it at all. You'll never see any ROI.

As for the build, you could have done something to help temper the summer heat- but you're too far along. Should have used radiant barrier decking.

As for the slab (since it's not there yet[?]), put 2" of rigid board (EXP) over the base and vapor barrier, then reinforcing wire, and concrete. This will help to greatly reduce heat loss through the concrete and virtually eliminate sweating.

 

[4cyclic]

Go R-19 in walls and R-38 in ceiling, 100%. You won't regret it ever. It will keep your garage from freezing in harshest winter.

 

[jgorm]

I'd even recommend going further . . . . . with SPRAY FOAM.

Spray foam is awesome, if you are a billionair! It's usually $1 for 12x12x1" or $60 for one 8' x 16" x 5.5"

 

[DougWil]

Spray foam is awesome, if you are a billionair! It's usually $1 for 12x12x1" or $60 for one 8' x 16" x 5.5"

Spray foam on wood framing can cause lots of serious problems. Close cell foam doesn't allow the wood to breathe or pass water vapor and dry out, causing rot.
Any water leakage is trapped between the foam and the framing, undetected.

Open cell can actually soak up moisture like a sponge up against framing.

One of many articles.
http://www.energyvanguard.com/blog-...ll-Spray-Foam-Insulation-Really-Rot-Your-Roof

The OP roof/ceiling framing needs to be properly designed as vented or unvented and not taking all the proper precautions will result in poor insulation performance or worse.

 

[CarCrazyRDM]

I'm nearly certain I won't be using any spray foam any where in this building so it really shouldn't be an issue.

 

[CNGsaves]

^ ^ ^ For your climate, that is wise choice to not pursue foam insulation. Now if you were in much colder climate (northern USA or Canada) then the foam decision would have been more involved.

Good luck on gameplan but agree with the R19 walls and R38 ceiling as minimum.

 

[theoldwizard1]

Given the intended use of my building is it worth spending the extra money for R19 or will R13 suffice?

Most heat loss/gain is through the roof.

If you are on a budget, do R19 in the ceiling and skip the walls, but don't seal them up.