Insulation Questions

[Rinkydink]

Disclaimer...I am a complete idiot when it comes to energy topics.

 

 

I have a two car garage with a floored attic and at a 90 degree angle to that I have a separate single car garage (two cars deep 400 sq ft) for my shop. I am able to isolate the shop totally from the two car garage. All outside garage walls have cellulose and all doors/windows are insulated. I have put a window unit in my shop and I am wanting to insulate both attics with blown insulation as they have no insulation at all. I am wondering if this will be worth the $$ as far as helping the shop and overall home heating/cooling bill. I have been told that it will actually hold the garage heat/cold in if the garage ac/heater is not running therefore doing more harm than good. I find this hard to believe because the garage is already stifling in the summer. The house itself is very well insulated and at 2600 sq ft my energy bill has really not been that bad. I will just be cooling my shop and not the two car garage. Should I insulate both garages or just the shop? TIA

 

 

[Natche]

Coming from an HVAC background, the most effective dollars spent on insulation will be in the ceiling. Heat rises so your heating dollars are leaving the garage via the ceiling at a higher rate than anywhere else. As far as cooling is concerned, insulation is designed to inhibit the transfer of heat to cold so, in theory, if your garage is hotter inside than the outside temperature (not likely), then the insulation will trap heat inside. To say that that is enough reason to not insulate is preposterous. Once you have the garage cooled, you want to keep it that way so the insulation will work for you. You should get the ceiling to R30 - minimum. I think this is money well spent. Stay cool - or warm.

[Bob Palin]

I can't see how insulating the garage would trap heat inside. My house is insulated but not cooled and as long as I close the windows during the day it remains significantly cooler than the outside. What the insulation does is slow the transfer of heat so in a closed system the temperature should vary less over the 24 hour cycle. It will be warmer than the outside at night and cooler during the day. If you open the windows at night you can have an overall cooler indoor temperature, sometimes a bit too cool for Florida visitors...

 

(Assuming of course that it does cool down at night where you are)

[Ken H.]

You garage(s) are hot now because the sun striking the roof is heating the air in the structure and there is nothing in the un-insulated ceilings to impede the transfer of that heat into the lower (occupied/used) portion of the structure. That’s what insulation does, shows down heat transfer, in either direction. By adding insulation to the ceiling you will be creating a thermal barrier between the two areas, thus the lower one (the work spaces) will be cooler than the upper area (the attic).

 

Understand though that in addition to the insulation, adding proper ventilation to the (now thermally isolated) attic space will be key. A step often skipped in garages for some reason. We know houses need to have attic ventilation, why would the other building be any different? Soffit vents to allow air in and roof top, or even better ridge vents to let air out will create a stack effect (hot air rises) moving air through the attic. This air movement brings outside air in (which is cooler that the sun supper-heated air in the attic) then even further lowering the thermal heating of the entire structure. This makes the new insulation even more effective at keeping the lower part cooler.

 

People seem to thing insulation is just for the heating season. It’s not. The material doesn’t know what season it is, it’s just sitting there slowing down heat transfer. During the cooling season from the sun beating down on the roof into all the space below.

 

[Rinkydink]

Thanks guys. that's just what I thought, I'm insulating it.

 

 

Ken brings up another topic I've pondered. I have 3 turbines on my roof. I have heard good things about ridge vents but had a roofer tell me you don't want to use both. He says it actually will just transfer the air from ridge vent to turbine (or vice versa?)and negate your soffit vents. Any experience with this?

[eddd]

Thanks guys. that's just what I thought, I'm insulating it.

 

 

Ken brings up another topic I've pondered. I have 3 turbines on my roof. I have heard good things about ridge vents but had a roofer tell me you don't want to use both. He says it actually will just transfer the air from ridge vent to turbine (or vice versa?)and negate your soffit vents. Any experience with this?

 

Absolutely true, one or the other, and if you go with regular vents be sure they are all on the same side of any peak or they will do the same thing.

[markgoodrich]

Does your shop's garage door face the sun? Is it metal? Our garage is Insulated all around. When we installed an insulated garage door it made a very significant difference.

[eddd]

One other thing to consider is adding a radiant barrier if you have the access to do so. The type of barrier will determine how much of a benefit you will get.

 

When I had my last house built I was able to specify TechShield for my roof sheathing. The results were fantastic.

 

Post-construction barriers are not as effective, but might still be a valuable addition to your project.

[Rinkydink]

Mark, my garage is part of my house, brick and the garage door (insulated) faces north. The exterior and interior walls are insulated with cellulose.

 

I made an appt. with the insulation company for Monday. Thanks for the advice.

[Quinn]

There's a payback to having a whole house fan in the ceiling of the shop if have an insulated cover over it when not in use. It's the same as rolling down the windows of your hot car when you first get in. Gets rid of heat buildup before turning on the air conditioner. Also useful for getting fumes out of the garage if something spills. Sucking that much air up into the attic will really get your turbines spinning.

 

Also be sure you don't block your soffit vents with insulation so they can do their job.

 

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