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Old 05-27-2020, 04:56 PM   #1
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Insulating a 900 sq ft workshop


Greetings! I'm new here so first let me say hello to everyone!

I'm planning to finish the inside of a 900 sq ft workshop (30 ft x 30 ft) that comes with a house I'm purchasing and I'm trying to decide the best way to insulate it; I wonder if anyone here can offer some advice. This space will need to have walls, floor and ceiling that are smooth and easily cleanable, so my material decisions revolve around that requirement.

Here is a short video of the workshop to give an idea of its current state:

I plan to finish the interior walls with this plywood: https://www.homedepot.com/p/15-32-in...0496/206093575

I will screw ceiling panels into the underside of the rafters, these are the panels I will use: https://www.homedepot.com/p/Suntuf-2...1890/100087758

My plan is to:
1. Move all electrical outlets outwards (so they are in line with where the plywood paneling will be)
2. Add insulation (foam or roll - if it's foam I'll hire a pro for that part)
3. Panel the walls with the above-mentioned plywood
4. Seal the concrete floor
5. Install a split a/c unit (will likely do this after step 1 but still undecided on exactly what step this will be)

As you can see from the video, the roof area is ventilated (you can see the outdoor light coming in). I was originally leaning towards using open cell foam to insulate the walls and roof, but I'm not sure if this will work with the vents. Do they need to be prepped somehow if we use foam? I assume they are ultimately plugged with the foam, but is there some modification needed first? And if we do use open cell foam, will the air get stale? Do we need some kind of vent system for this little building?

I could use roll insulation everywhere, I'm just weary that it won't be very effective. However it would actually make use of the vents that are present since it would be rolled up between the rafters. We're in southern Alabama and want to try to get our utility bill down (the building will be occupied by one person frequently, two people occasionally).

Any advice is appreciated, as I'm not the handiest of handymen.
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Old 05-27-2020, 04:58 PM   #2
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Re: Insulating a 900 sq ft workshop


Also I should mention that I'm open to advice on other parts of the project as well (wall finishing, ceiling etc.) if anyone has a suggestion. I'm trying to keep costs down while still ending with a nice looking space.
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Old 05-27-2020, 05:04 PM   #3
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Re: Insulating a 900 sq ft workshop


How is the out side finished, type of siding and roofing?
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Old 05-27-2020, 05:10 PM   #4
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Re: Insulating a 900 sq ft workshop


Thanks for your reply!

It's vinyl siding with a shingle roof. Here's an image (sorry you can't see the roof):
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Old 05-27-2020, 05:11 PM   #5
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Re: Insulating a 900 sq ft workshop


Well the image didn't work... here's the URL: https://ibb.co/Bz5CDFV
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Old 05-27-2020, 05:20 PM   #6
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Re: Insulating a 900 sq ft workshop


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Old 05-27-2020, 05:29 PM   #7
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Re: Insulating a 900 sq ft workshop


You want the roof vented to add life to the roofing and allow radiant heat to escape.
When you cool a space, you are making the air smaller and the room will suck air in. If you allow air to get passed insulation it will bring with it humidity and dust which are both food for mold. 2 layers of thin plywood with offset joins would do a better job on the walls and I would reconsider the ceiling it needs to be sealed.
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Old 05-27-2020, 05:29 PM   #8
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Re: Insulating a 900 sq ft workshop


Thanks for posting the image. Not sure what I did wrong. Anyhow that's the only image I have or I would post one showing the rooftop, but it's a standard asphalt shingle. I haven't moved into the property yet so I can't get more pictures, I'm currently trying to plan the project before we move in next month.
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Old 05-27-2020, 05:32 PM   #9
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Re: Insulating a 900 sq ft workshop


Quote:
Originally Posted by James414 View Post
Thanks for posting the image. Not sure what I did wrong. Anyhow that's the only image I have or I would post one showing the rooftop, but it's a standard asphalt shingle. I haven't moved into the property yet so I can't get more pictures, I'm currently trying to plan the project before we move in next month.
Why not just do it with drywall?
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Old 05-27-2020, 05:38 PM   #10
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Re: Insulating a 900 sq ft workshop


The plywood aesthetic is more what I'm going for, things can be hung from anywhere without regard to studs, not as susceptible to humidity/moisture. These are the main reasons. Also the price isn't much different, especially when you consider the finishing work drywall requires, and I'm willing to spend a few extra bucks per panel for a space this size (we're not talking very many panels either way).

But the insulation is the thing I'm still trying to figure out.
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Old 05-27-2020, 05:42 PM   #11
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Re: Insulating a 900 sq ft workshop


Quote:
Originally Posted by James414 View Post
The plywood aesthetic is more what I'm going for, things can be hung from anywhere without regard to studs, not as susceptible to humidity/moisture. These are the main reasons. Also the price isn't much different, especially when you consider the finishing work drywall requires, and I'm willing to spend a few extra bucks per panel for a space this size (we're not talking very many panels either way).

But the insulation is the thing I'm still trying to figure out.

I would look at insulation as R value per dollar or dollar per R value.
They all fail with air leaks.
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Old 05-27-2020, 06:48 PM   #12
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Re: Insulating a 900 sq ft workshop


2x4 or 2x6 walls?
Will you be adding heat and what type?
Will you be heating and cooling this 365 or intermittently as needed for use?
Will any of the activity in there be moisture related, wet cars or other?
Do you know what was used for rafters, trusses, 2x4's, 2x6's or other?
Are you planning on any use for the attic space?

I'm guessing that summer heat is your main concern and if so as Neal mentioned you will want ventilation from those soffits up to a ridge or high vent. The answers to above questions will help with the recommendations.

Bud
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Old 05-27-2020, 06:53 PM   #13
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Re: Insulating a 900 sq ft workshop


Quote:
Originally Posted by Bud9051 View Post
2x4 or 2x6 walls?
Will you be adding heat and what type?
Will you be heating and cooling this 365 or intermittently as needed for use?
Will any of the activity in there be moisture related, wet cars or other?
Do you know what was used for rafters, trusses, 2x4's, 2x6's or other?
Are you planning on any use for the attic space?

I'm guessing that summer heat is your main concern and if so as Neal mentioned you will want ventilation from those soffits up to a ridge or high vent. The answers to above questions will help with the recommendations.

Bud
Vaulted trusses so insulation and venting is not a problem.
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Old 05-27-2020, 07:07 PM   #14
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Re: Insulating a 900 sq ft workshop


You watched the video, that's cheating .
Also saw the skylights in the roof that will need a solution.

Thanks,
Bud
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Old 05-28-2020, 05:18 AM   #15
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Re: Insulating a 900 sq ft workshop


Foam has more r value per inch but not greatly more. I think fiberglass gives you more value. I think even more value in your area and without any shade cover would be powered attic exhaust fan or even big cfm bath fan high in the gable and adding some intake mushroom vents on the other side.



I would:
1. gable vent fan (both heat and moisture) rated close to attic space you'll have after closing off with insulation. Equal or greater intake vents. All measured in CFM. You'll want to reframe for access later for replacement/repair. About 30x30 inches and put a ladder there to see if more is more comfortable/access.



2. Spacer baffles along the eaves. Minimum required is 1.5" but 2 or more is better.


3. fiberglass insulation. Along eaves, as much space as it will fit. Stuffing more does not give you more r value.


4. As spaces get bigger, switch to at least r-40. I read that after r60 there is no more return on cost.


5. Cover the whole thing again with xps foam board. Min 1.5" or more if budget allows. XPS will give you greater air seal too. If xps, use faceless fiberglass insulation to avoid double vapor barrier.


Don't use inside vapor barrier on walls. South is a region where "vapor drive" is out to in, so you want inside sheathing to allow vapor to pass.
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