Heating, cooling, insulating garage in NC

[HAVEaSigAR]

Hello from Charlotte, NC

I'm in the process of restoring a 68 mustang, and would like to make my garage a better environment for it when it comes home.

It's a 25x25 attached garage with one garage door, one regular door, an attic, concrete floors, and drywall with rubber panels around the bottom, ceiling is OSB. I'm fairly sure there is no insulation in the walls, because there is none in the attic. The wall opposite of the wall shared with the house seems to let some water in under the rubber panel "baseboard" during a heavy or extended rain. Not the entire wall, just a couple foot section close to the garage door.

I've researched for hours on here, but it seems a lot of variables come into play. Here is what I want. I want to first fix the leaky wall, which I'm sure will require pulling down drywall. While I'm in there, I'd like to add insulation. I'm not sure whether a vapor barrier is necessary or not. I will be spending a lot of time out there working on the car, so I would like for it to be heated and cooled, as cheap as possible. My buddy (hvac guy) suggested I just get a hotel room PTAC style unit. I'm assuming batt insulation would be sufficient, and probably the cheapest.

My questions are, do I need vent fans in the ceiling? A dehumidifier? ANY step I can take to prevent this car from rusting would be helpful.

 

[DC73]

Before you pull down the drywall to check out your water leak, double check the ground situation outside the wall. You could have a drainage problem allowing water to enter your building at the bottom of the wall.

Here are a couple of good websites to check out for info on insulation, vapor barriers etc:

BuildingScience.com

GreenBuildingAdvisor.com

Walls have to be able to dry so one issue with vapor barriers is to make sure you don't have multiple barriers that could trap moisture inside the walls. Whether vapor barriers are needed and at what location is climate dependent. What works in the cold north may not work in Charlotte. The building scientists don't even use the term vapor barrier any more. They prefer to use vapor retarder. Here's one article to check out: http://www.greenbuildingadvisor.com/blogs/dept/musings/do-i-need-vapor-retarder

A ductless mini-split HVAC could be a good choice for your situation.

I don't have any answers to help with preventing your Mustang from rusting. My climate is dry and we don't have the same issues with humidity as you.

DC

 

[HAVEaSigAR]

Thanks for the help. Another question- I don't have any vent in the attic. I think the soffit is vented, but I'm not sure. It's the kind that has holes in every 3rd section, but I haven't climbed up there to see if it is actually vented or just the soffit plate has holes. Do I need to insulate the roof, the ceiling, or both? The ceiling will be difficult as it is just osb with gaps, and I put plywood over the joists in the attic for storage.
So what do I do for vents? And how should I insulate?

Thanks

 

[sands35]

The walls need a vapor retarder, not a vapor barrier. Though where the retarder goes is different in warm humid climate than in cold ones. The wall needs to be air tight (caulk gaps and joints), but also needs to dry out. So poly is a very bad idea.

Is your siding vinyl or something else? The soffit vents are different given the type of siding and soffit trim you have. Ridge vents are either continuous or a vent cap every so often at the ridge. Either one is needed. You should be able to see daylight through the soffit and ridge vent when in the attic, even thought the gaps should be small enough to not allow bugs in.

These need to be installed prior to insulating the attic:

http://www.homedepot.com/p/ADO-Prod...h-Built-In-Baffle-10-Ctn-UDVB234610/202389935

Commonly called "soffit baffles", they prevent insulation from filing in the air gap at the soffit. Detailing them at the soffit to prevent cold air blowing down the surface of the attic is important where temps can get down to freezing, probably not so much in NC.

 

[OccupantRJ]

From my life experience here in NC, faced R13 in the walls, soffit baffles with blown in insulation in the attic. Caulk all ceiling joints for air leak sealing. Gable vent(s) or continuous ridge vent in the attic, along with soffit venting will do the job. If you are not removing drywall, blown in inside the walls by making hole at the top of each stud cavity. A ceiling fan will usually handle moisture problems. Some people run them 24/7. These are the basics of my detached shop. It was 47 degrees inside last January when the outside temp was 24, with no heat inside at the time.

 

[burnedzr2]

If you have vinyl siding on the outside wall you may want to pull it in the area of the leaks. you may find no Tyvek or some type of house wrap. or the wrap may be there but not installed correctly. The wrap should be taped at the joints with Tyvek tape. Vinyl siding does get water behind it if it is not done right. Do you have a window near the leak? that can cause a problem also. Go to your local hardware store and get a siding unzipper its like 7-8 dollars, find the siding joint push the unzipper up and over and unzip the siding. really not hard.

 

[DC73]

. . . Another question- I don't have any vent in the attic. . . . Do I need to insulate the roof, the ceiling, or both?
So what do I do for vents? And how should I insulate?

Thanks

You can go with either a vented or unvented attic but both require proper attention to details. See the two websites I linked and search for vented attics, unvented attics and/or non-vented attics to get a feel for what needs to be done. On the GBA site, look for an article titled something like "How to Build a Cathedral Ceiling". It has good info.

For a properly vented roof, you can calculate how much vent area you need. One good option is to have vents near the peak of the roof for exhaust and then use the soffit vents for intake.

The best way to construct a non-vented attic is to use spray foam but the cost may be a factor. It wouldn't hurt to get an estimate before making a decision.

DC

 

[russelljones48]

I'd like to piggy back on this thread. I also live in the Charlotte area and need some advice on HVAC for my garage. I'm contemplating a mini-split but I have a 1300SF garage with a shed roof at about 22' in the back which tends to trap heat in the summer and winter. It's insulated and fully sheetrocked so I'd prefer to disturb that as little as possible. I have clerestory windows (not operable at the moment) at the top/back and have an estimate to make a couple of them operable. That will probably cost me about $1200 but should really help vent the heat out in the summer. I've tried using a large fan to push air into the garage but it will only cool it off by about 5 degrees and that doesn't help much in August. I'm now using a pedestal patio propane heater which makes cold days bearable but would like a more permanent solution to heat and cool it.

 

[HAVEaSigAR]

Thanks for the replies. The siding is wood, and I think the leak is due to the space between the siding and the concrete slab on the outside. I'm assuming caulk would do the trick. I'll probably install a gable vent, as it will be cheaper and easier than the ridge vent. On a positive note, I installed 2 220 connections today, so all I need is some insulation and a ptac unit, plus the gable vent of course.

Now I just need help picking out a unit. Can someone suggest a BTU rating for me?

 

[HAVEaSigAR]

Also, one contractor advised me to install radiant barrier on the roof rafters, and that this would eliminate the need for cellulose insulation on the ceiling. I'm not sure if I believe this, I would think I'd lose more conditioned air through the attic vents if there was nothing but open space above the ceiling, all the way up to the radiant barrier.

 

[sands35]

Radiant barriers can work in specific applications - but only for radiant heat transfer. i.e., reducing the heat transfer during hot summer days. Blown in (cellulose or fiberglass) or batts will reduce convective heat transfer - which is what matters all year long.

It will help, but blown is pretty cheep.

Leak - make sure that you take care of grading the outside lower than the top edge of the concrete. More than 6" inch gap. If you just caulk it up, eventually the caulk will fail.

 

[DC73]

Also, one contractor advised me to install radiant barrier on the roof rafters, and that this would eliminate the need for cellulose insulation on the ceiling.

Radiant barriers can work in specific applications - but only for radiant heat transfer. i.e., reducing the heat transfer during hot summer days. Blown in (cellulose or fiberglass) or batts will reduce convective heat transfer - which is what matters all year long.

Sands has it right. Radiant barriers get a bad rap and are somewhat known as snake oil in the insulation business because of advice like you got from that contractor. The science behind radiant barriers is sound but the cost is hard to payback if contractor installed. You might make a case of it working well if you do it yourself. But, it does not eliminate the need for proper insulation and after installing a proper amount of standard insulation, the incremental gain from a radiant barrier requires an even longer payback period.

Radiant barriers could help reduce attic temperatures which might be important if you are storing things in a hot attic but even then it would probably be best to just create an unvented attic and insulate at the roof level.

DC

 

[HAVEaSigAR]

I have an opportunity to buy a 14000 btu PTAC for $200, it's made by Amana. Will this be sufficient? Keep in mind, I'm not trying to make the garage liveable, just want to dehumidify and make it a little more comfortable during extreme heat or cold.

 

[ascott172]

I also live in Charlotte. My attached shop has radiant barrier on the ceiling an r13 in the walls. I have a large window unit mounted in the wall 10ft up. It has a heat pump that will keep it warm unless it is below freezing outside. Then I get the torpedo heater out. I think your 14000 ptu heater will help make the temperature more comfortable but until you insulate it won't be able to keep up with heat loss when it's really cold.

 

[BoostAddiction]

I'd check out the efficiency of that PTAC unit. Most modern minisplits are extremely efficient and over time, make for a much better experience than the PTACs, IMO.

My own garage, about 800 sq ft, is well-heated and cooled by a 12K LG minisplit, though it has insulated doors, walls and ceiling.