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Old 02-09-2017, 11:45 AM   #1
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Insulate Metal Roof Garage with loft


New garage with metal roof for wood shop. Not currently heated or cooled, but intend to add this in the next year. It is insufferably hot in the loft in the summer (western MA). Want to insulate the ceiling for heat reflecting in summer and then the floor joists to retain heat in winter. Walls are fiberglass and OSB covering.
I am thinking reflectix for metal roof over storage loft and then fiberglass for ceiling joists with drywall face. Can anyone direct me on the reflectix? It seems running this in each bay (24"oc) will be better/more effective than just the reflective wrap installed horizontally. Also, their graphic seems to want reflectix AND fiberglass. Wouldn't that be overkill if I am not interested in real climate control in loft area?
Any help will...help.
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Old 02-09-2017, 12:51 PM   #2
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Re: Insulate Metal Roof Garage with loft


It is always difficult to advise people when they are considering one of the foil faced bubble wrap products because those mfgs have often exaggerated their claims to the point where few professionals believe them or even want to talk about them. What the professionals are reading are the test results, and there have been many, that demonstrate the limited benefits of reflective barriers in any place other than the deep south. Down there the roof sheathing is available with a foil facing on the bottom.

The testing that has been done has compared the radiant barrier approach to traditional insulation and ventilation. When properly ventilated and with sufficient insulation in the ceiling below, there is very little benefit to having the foil up top. Insufficient enough to say it doesn't pay for the application.

In your case it sounds like you want the attic space to be cooler in the summer and then shift your attention to insulation in the ceiling for heating in the winter. Trying this split approach can complicate moisture issues as I don't see specific guidance for it.

One element that would be needed in either approach would be ventilation. What have you provided?

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Old 02-13-2017, 03:06 PM   #3
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Re: Insulate Metal Roof Garage with loft


There is a ridge vent and soffit vents. I am also going to put in a window in the loft to ventilate further while up there in the summer. I need to do something about the heat up there in the summer. It makes the wood shop an oven as well. I also need to be able to contain heat in the shop area in the winter without heating the loft... Also thinking of a ceiling fan to help circulate air in both winter and summer.
So, it sounds like the foil is unproven and not worth the time... bummer because of ease of installation.
Now that you know the vent situation do you have any further suggestions? Any help is much appreciated.
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Old 02-13-2017, 06:28 PM   #4
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Re: Insulate Metal Roof Garage with loft


As long as there isn't anything in the attic area that needs to be cool, then focus your effort on air sealing between the garage below and that attic, then add tons of insulation. I prefer Roxul over fiberglass as its density performs better.

If you still need or want to control the temp in the attic beyond what natural ventilation is providing, then consider a powered exhaust fan.

Note, check to be sure the ridge and soffits are open and venting.

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Old 02-15-2017, 05:59 AM   #5
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Re: Insulate Metal Roof Garage with loft


this is quite helpful! Thank you so very much! Makes good sense.
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Old 02-15-2017, 07:26 AM   #6
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Re: Insulate Metal Roof Garage with loft


For cooling a wood shop, with or without loft, I would install a 30" belt driven whole house fan in the gable, opposite end of the door. Cools very well and removes dust efficiently. Recommend a fiber glass filter on the motor air intake and changed on a regular basis as needed.
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Old 02-18-2017, 07:11 AM   #7
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Re: Insulate Metal Roof Garage with loft


I was just reading about how a ridge line vent does not want a gable end vent because it would mess up the flow of air and pull it in from the ridge line. I think the vent is the least expensive and easiest option for me but I worry about the combination. Should I be?
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Old 02-18-2017, 07:46 AM   #8
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Re: Insulate Metal Roof Garage with loft


Hi Linee, if you have both ridge and soffit vents, leaving the gable vents in place (or adding them in some cases) simply improves the air flow. The old "short circuit theory" is hard to kill, but it has been wrong since introduced many years ago, a total misunderstanding of attic air flow. I can explain more if needed, but in most cases (we don't know what your application is) both work well together and both act as exhaust vents.

Do you also have soffit vents?

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Old 02-18-2017, 07:57 AM   #9
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Re: Insulate Metal Roof Garage with loft


yes, soffit and ridge vent are in place. I am going to insulate the wood shop ceiling/loft floor to retain heat in winter in shop and prevent heat build up in summer from metal roof and loft. I still want more ventilation up there as it is incredibly hot! So you suggested the vent and the gable is the easiest for me to install. Then I read an article re not mixing the two.
Sounds like I don't need to worry about the "short circuit theory" and should proceed with the additional exhaust fan on the gable end. Was going to get the thermostat ones to just kick on as needed.
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Old 02-18-2017, 08:17 AM   #10
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Re: Insulate Metal Roof Garage with loft


Natural venting is passive and struggles to move enough air to cool an attic like yours. Passive venting is not really intended to cool. It helps, but a fan, despite the cost to run it, will move a ton of air. Now, with that much air being exhausted, where the replacement air comes from can be an issue. Rain can be pulled in either the opposite gable vent or the ridge vent, soffits are well positioned to avoid this.

My vote would be to go with the fan and keep an eye out for any water issues. Even up here in Maine, getting rid of that accumulation of attic heat does make a difference.

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