Insulating detached garage - check my startegy

[Quijote]

Insulating detached garage - check my strategy

I have a 22'W x 34'D detached garage with 10' walls. It has a 4'x4' window, a 30" double hung window, and a 16'x8' garage door. Construction is 2x6 on walls and engineered trusses on roof - all on 16" spacing.

It has a 100A panel to it, but that's it. So any heating/cooling will have to be electric.

My plan is to insulate walls with faced R19 fiberglass and the ceiling with unfaced R30. Blue board and skim coat over all of it.

Since I am in the Boston area, winters are not consistently brutal temperature wise, but we can certainly stretches of a few days with awful cold.

My hope is that when I am working there, to keep the garage at a manageable temperature range. That is, in the dead of winter, be able to get it up to the 40F's, and in the summer down to 80 or so.

My plan was to use a space heater (that I don't yet have) in the winter and a window AC (10,000 BTU) in the summer that I already own from my previous home.

How feasible do you think this is?

If I were to heat the garage to say 55F, how long do you think it would keep the garage above freezing if the average temperature outside is ~30F?

Anyone have a similar setup?

 

[Quijote]

Well, I used an online calculator for heat loss, and assumig a 30F difference between inside and outside (say 20F outside and 50F inside), I should be loosing ~6000BTU's/hr.

Any 1500W space heater should produce over 5000BTU and my fluorescent bulbs (56 @ 32W) should chip in another 1000BTU.

So, in theory, One space heater and the bulbs should maintain the temperature that's already there. I may need to buy a 2nd space heater to bring the temperature up. Still, not bad. I can spend less than $200 on two space heaters for the occasional winter use of the garage.

 

[Falcon67]

I would put at least a 5kW heater in there. I use one in 960 sq/ft, insulated and it works well but takes a bit of time to bring up the 24x28 area. But I have no problem - keeping all the doors closed - running the place in the 70s with it 20s outside. My walls and ceiling are R13. And the 5kW heater does cycle once things are up to temp. If it's really cold, I use a 60K propane turbo heater as a booster. Used it maybe 3 times last year. Just sitting, I've never seen the shop go below 45F and that 45F was this year after a string of mid 20s days. Not unheard of, but not common here.

The 10K may work. I use a 10K Samsug to cool the 28x24 car area. Will keep it in the 80s with about a 1 hour head start. Will maintain 70s if fired off in the morning. Note I have less volume in that space than you because my ceiling is 8'. You have 40% more volume, so I'd say a 12K is going to be more like it.

The 12x24 tool room uses an 8K LG unit that works great. I was using a 6.5K Fridgidare in there - it didn't do squat, but may have been wounded from the factory. I had it two years, plugged it in this year and no cooling. Hence the new 8K unit.

The biggest deal is air movement. One thing I should have done is caulk the siding to the sill and top plates inside the walls. Everything on the inside is caulked. Sealing it up to prevent air movement makes the insulation work a whale of a lot better.

 

[yeldogt]

You will want to seal it as best you can -- and you should have a vapor barrier on the ceiling.

Mine is about twice that and very tight -- I have a net 29k propane that will easily keep it at a nice temp -- but it takes it a while. When everything is cold -- it is not like heating an empty room.

with the electric rates in MA -- you may have wished for a mini split in a couple of years.

 

[Highbeam]

I was witb you until you mention blue board and skim coat. Is that blue xps with some sort of stucco on it? The ceiling should be r30+ batts on top of a vapor barriet with some sort of ceiling under it. Maybe metal.

The walls, faced insulation, should also be covered with something like metal, osb, drywall, etc.

 

[Quijote]

I would put at least a 5kW heater in there. I use one in 960 sq/ft, insulated and it works well but takes a bit of time to bring up the 24x28 area. But I have no problem - keeping all the doors closed - running the place in the 70s with it 20s outside. My walls and ceiling are R13. And the 5kW heater does cycle once things are up to temp. If it's really cold, I use a 60K propane turbo heater as a booster. Used it maybe 3 times last year. Just sitting, I've never seen the shop go below 45F and that 45F was this year after a string of mid 20s days. Not unheard of, but not common here.

I see. Well, like I said, I'm not looking for 70F. I wouldn't want it that warm anyway (other than the tools would feel cold, but I'll get over that), I would get uncomfortably warm at over 60F with winter clothing if I'm working on a car.

Also, I am technically prohibited from anything other than electric heating. The other big factor is that I don't need the entire garage to be warm. If the space heater is on, it will locally be warmer in the area where it is, which would be near where I am working.

 

[Quijote]

I was witb you until you mention blue board and skim coat. Is that blue xps with some sort of stucco on it? The ceiling should be r30+ batts on top of a vapor barriet with some sort of ceiling under it. Maybe metal.

The walls, faced insulation, should also be covered with something like metal, osb, drywall, etc.

Let's work from the outside in. Fiber cement siding, then house wrap, then plywood, then faced R19 fiberglass, then drywall, than plaster.

It is my understanding and that of anyone I know who seems to know about this, that when you apply a 1/8" thick plaster skim coat over the whole wall (instead of mud & tape), you need to use "blue board" (labelled as such at Home Depot and Lowes) so that the plaster properly adheres to the drywall. So the plaster will cover every square inch of wall & ceiling.

Here's the blue board:

http://www.homedepot.com/p/Gold-Bon...ypsum-Board-GB22800800/202090532?N=5yc1vZbb52

 

[Highbeam]

Weird. So you're sheetrocking the interior, that's good. What is your reasoning for using a vapor barrier on the walls but not the ceiling?

 

[Quijote]

Weird. So you're sheetrocking the interior, that's good. What is your reasoning for using a vapor barrier on the walls but not the ceiling?

I don'y think I need to use vapor barrier at all. I got the faced insulation on the walls for ease of installation, primarily.

That said, I'm not against vapor barrier on the roof if there is a real advantage.

My understanding of vapor vapor barrier use is to keep humid, warm air for hitting cold surfaces and condensing in the winter.

My garage will be used seldomly in the winter, and there are no sources to provide humidity (baths, any water, etc).

 

[Highbeam]

Since you are sheetrocking, the paint will likely be all the VB you ever need anyway. Moisture is in the air, even if you don't do anything to add it to the room.

I use the VB as an air sealing barrier too. I want to keep the conditioned air in the shop.

 

[Falcon67]

I see. Well, like I said, I'm not looking for 70F. I wouldn't want it that warm anyway (other than the tools would feel cold, but I'll get over that), I would get uncomfortably warm at over 60F with winter clothing if I'm working on a car.

Also, I am technically prohibited from anything other than electric heating. The other big factor is that I don't need the entire garage to be warm. If the space heater is on, it will locally be warmer in the area where it is, which would be near where I am working.

I keep it mid 60s. My wife's hair dryer puts out 1500 watts, I would not even try to space heat a square foot with it. I think you'll get tired of that pretty quick. But your call. IMHO you'll not generate enough heat/moisture with a 1500w space heater to create any issues requiring vapor barrier.

Something else to consider is that your 1500w heater is going to run pretty much continuous, and that's going to chew power. And your power up there runs a whale of a lot more than our power down here. My 5kW cycles about 4 times per hour for a total of 15 minutes run time at 65F in the shop. Just sayin'. I'm about $5 cheaper per hour that I expect what you'll pay. Also, I'm in the shop a lot in the winter because I have two race cars to maintain plus other projects, so it makes a difference to me being able to work comfortably.