# Insulating back yard workshop in a hot climate



## beanu (Jun 28, 2016)

Hey folks,
I have a 10×20 shed in the back yard, and as my wife and I get increasingly addicted to woodworking, it is becoming "the workshop" where we spend a lot of time on our shared hobby. We live in Austin [where it will be 101° F today] so we're focused on making the building cool enough. Heat isn't much of a concern.

We're still very new to building stuff-I'd classify us as "advanced novices"-so forgive any silly mistakes below :-D

*More specs on the building*
Again the size is 10×20. It sits on a mostly-stable concrete slab and we have a bare concrete floor. 2×4 studs (unevenly spaced) which are skinned somewhat loosely with painted plywood and exterior trim. Totally unfinished on the inside. Gable roof with the ridge running along the major axis, probably about 20 - 25 degrees, plywood decking and galvanized steel on top. The "attic" space is not separated from the general interior space-there is no ceiling, only open trusses. The attic is not vented in any way, but we do have two good-sized operable windows (at typical interior height) at either end of the shed, which we usually leave open with the screens. And finally, there's a well-sealing pre-hung door in the middle of the broad side.

This building is definitely leaky in terms of air flow, because hey it's a wooden shed right? :-D
As we add insulation here, I don't imagine we would choose to make it more airtight; that might be a losing battle, and we're not that concerned about energy efficiency anyway.

*What we're up to so far*
The building has a subpanel of its own, and a half dozen outlets and a couple of switches. All of this is (unfortunately) wired on just one breaker from the subpanel, so I know I'm going to need to do some re-wiring (utilize multiple breakers) in order to e.g. separate the lights from the eventual table saw, etc.

Meanwhile we purchased a refurb 6000 BTU window A/C unit, and this morning we are in the process of mounting this in a thru-the-wall fashion. We're going to get it rigged up and probably test its cooling capabilities even before we've done any insulating work.

*The plans from here*
My thinking is, we're probably not going to be spending long hours in this shop except on the weekends, so I don't see us leaving the small AC unit running when we are not in it. This means the temperature and humidity levels will be changing frequently inside. Am I already on the wrong track here?

If not, then here's what we're thinking for insulating / closing in the shed:

Some kind of moderate insulation (batts or rigid foam) in the stud spaces and roof rafters
Close over the insulation (perhaps loosely) with thin plywood sheathing as the interior walls
Leave the "attic" space inside the gable open to the interior with the trusses still exposed, so that space can be used as an overhead storage loft, or a place to route wiring and dust collector hoses, etc.

*Finally, the questions*

I know that if I was working on a true interior space, or I was in a colder climate, I would definitely have to worry more about condensation and dew points, etc., think about vapor barriers, and so on. But, given that this is a leaky building that will probably always remain so … do I need to worry about that or am I doing fine with the plans above?
The hottest part of the building right now (by far) is the metal roof and the heat coming through it. Will insulating here in the rafters be enough to make a difference? Or do I also need to consider adding some kind of attic vent or fan (passive or forced) to move the hot air out of that space?
What have I missed? What would you do here? What are we about to do wrong?

Thanks A BUNCH for reading this far. Appreciate all your help.


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## patcollins (Jul 22, 2010)

I would say go with rigid foam insulation, since you want the attic area open I would try to put some insulation under the metal roof. If you can seal off an area between the insulation and metal roof like a cathedral ceiling type setup you definitely need to vent to the outside some how.

Most of the heat gain in the shed is going to be coming from the sun beating on the roof and maybe two walls.

What you end up with will be determined by how much work/money you wish to put into it.

You might also try this stuff, i had good luck with it and my old cheap fiberglass garage door that allowed the evening sun to beat through it. Got it at Lowes reasonably priced a $50 roll was enough to insulate my garage door, water heater, additional insulation for my lunch box, and a bunch of can koozys.

http://www.reflectixinc.com/basepage.asp?Page=Double+Reflective+Insulation&pageIndex=622


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## GR8HUNTER (Jun 13, 2016)

This means the temperature and humidity levels will be changing frequently inside

keep your machines waxed well


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## clin (Sep 3, 2015)

I think you are on the right track. However, I would stress sealing the building. It's not just air infiltration, but moisture and insects you want to keep out. Without seeing some photos I can't say what you would need to do, but if the exterior siding is that bad, perhaps just add some new siding over what is already there.

The uneven stud spacing complicates insulating. But fiberglass batts are going to be the least expensive. You may have to buy 24" wide batts and cut them down as needed, but you'll most likely have plenty of odd sized places to use the scraps.

For the roof, I think foil sided foam board might be a good way to go. Just attach it to the underside of the roof framing with the foil side up, facing the metal roof. The foil helps to reflect heat back. But it must not touch the metal roof. For a radiant barrier to work, there needs to be an air space. Which you would have by attaching the underside of the framing. Doing this, you don't have to worry about fitting insulation between odd spaced framing.

If possible, create a ridge vent and have the lower edge of the roof open. This creates an open air channel between the foam board and metal roof. This will eliminate any possibility of condensation on the roof and will help remove heat.

You could just leave it at that, but the foam board will get damaged as you use the overhead space for storage. So I would still cover that with something to protect it.

For the walls, after adding the insulation, I'd add thick plywood on the walls. That allows you to attach things to the walls wherever you want. That might be real helpful in a small shop space where putting a lot of cabinets for storage is not practical.

I'd consider painting all the interior walls and ceiling a light color. The paint will help seal the plywood, that is on the walls, and of course improve lighting.

Given that you plan to be weekend warriors, I agree with using a window AC unit.

I don't think you have much to worry about as far as condensation and vapor barriers. As you mentioned, you're not in a cold climate. And you won't be generating much moisture in the space (no kitchen or bath). Moisture will mostly be limited to what comes from you. Though I think some might come up through the slab. So painting the slab might be a good idea.

Sealing and insulating will reduce temperature and humidity extremes, and will slow temperature changes. That should help mitigate the tendency for moisture to condense on tools. Of course running the AC unit will pull moisture from the air.


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## Blindhog (Jul 13, 2015)

As with most things, money will be the determining factor. Ideally, if you want to leave the trusses open, you could spray foam insulation directly onto the rafters/roof deck. This would provide a good insulation/sound barrier and some air seal as well. That product is quit expensive but very effective.
I live in Austin also and I have been converting my 3-car garage into a shop for the past year. Definitely insulate the walls with batt insulation. Covering with s/r or some type of osb is fine. But the most heat gain will be coming from your roof/attic space. You can install cheap roof vents that will help relieve heat build up but it will not be enough to overcome with window unit. To keep the space cooled you'll have to insulate the attic or resign yourself to using large fans to move air and suffer through the summer.
If you want talk further, you can PM me with contact info and I'll be happy to share what I know.

Rick


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## tmasondarnell (Jul 2, 2013)

+1 on Blindhog.

I am in Manor, so I know what you are up again. You need to seal the building better to give that AC unit a chance. If it is in the budget, I highly recommend doing closed cell spray foam. Even 1or 2 inch layer will make a big difference.


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## rwe2156 (May 7, 2014)

You definitely will gain an advantage insulating the roof, probably more than the walls because this is where most of your heat gain is coming from, especially if the building is not shaded.

If you use standard fiberglass insulation against a metal roof you really need a vapor barrier (plastic or housewrap), which means either lining each joist bay.

I put a couple layers of foam board.

I seriously doubut 6000 BTU is not going to be enough for that space in the kind of heat you're talking about unless it is extremely well insulated and sealed. I think it will take too long to cool it down and my guess it will never turn off so you'll need to keep it running when you're not using the shop.

I think you need at least and 8 and probably a 10K (which may put you to 240V).

I have an 8000 BTU unit in my studio which is 14×16 (well insulated) and shaded and its just about right.

Years ago the big thing where I'm from (FL) was putting soaker hoses along the ridge until everyone figured out it accelerates rusting.


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## patcollins (Jul 22, 2010)

> Years ago the big thing where I m from (FL) was putting soaker hoses along the ridge until everyone figured out it accelerates rusting.
> 
> - rwe2156


What was the idea behind the soaker hoses?


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## splatman (Jul 27, 2014)

+1 on spray foam insulation, if you can afford it. Especially because of the (I presume) "right about here looks good" stud spacing, and the air-untightness issue you describe.

And +1 on using strong plywood on the walls after insulating and wiring. Lets you hang cabinets and tools anywhere you wish.


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## WhoMe (Jul 9, 2009)

The op also mentioned something about a storage area in the attic. 
If they do the spray foam and then create that storage area, if sealed from the main shop, that will also add an additional heat barrier for part of the shop which should reduce the cooling needs for the overall shop. And at that point would a ridgeline vent with soffit vents help evacuate the sealed attic of more hot air?


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## splatman (Jul 27, 2014)

Put something below the roof deck to provide the needed airspace. Maybe the foil-faced foam board clin mentioned. Spray the insulation over that.


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## jwmalone (Jun 23, 2016)

cool seal on the roof helps a lot, if you do have problems with moister you can get a dehumidifier for less than a hundred bucks that solve that problem. it will run constantly but doesn't pull much juice.


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## rwe2156 (May 7, 2014)

> Years ago the big thing where I m from (FL) was putting soaker hoses along the ridge until everyone figured out it accelerates rusting.
> 
> - rwe2156
> 
> ...


Keeps the metal cool.


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## patcollins (Jul 22, 2010)

> Years ago the big thing where I m from (FL) was putting soaker hoses along the ridge until everyone figured out it accelerates rusting.
> 
> - rwe2156
> 
> ...


lol, I was thinking they were trying to make a swamp cooler some place with 100% humidity. Personally I would have just put some of that building camoflage stuff over it like the buildings in MASH had.


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## Finn (May 26, 2010)

I have a little larger shop than yours. Mine is 23×13 insulated with a drop ceiling. I am in Lubbock where it was 101° today. I have two window AC units. an 8000 and a 6000 and they just barely keep me cool. I think you will be putting another unit in one of your windows. IF I was you I would insulate the walls and roof rafters and put pre painted white Masonite on the walls over the insulation and wiring in conduit on the surface of the wall.


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## BurlyBob (Mar 13, 2012)

Put a good epoxy floor coating down. I found mine helped reduce humidity quite noticeably. Do it in a light color to help with brightening the space.


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## devann (Jan 11, 2011)

Another vote for sprayed on insulation. Walls & ceiling. You mention uneven stud spacing, foam insulation will also strengthen that situation. I'm very familiar with the climate at your location having spent many years there. I can tell you from a personal experience of a job I did in Cedar Park area where the owner had a large (150' x 80') metal building erected for warehouse/office use. The owner used sprayed on insulation on the walls & ceiling. I was amazed that they were able to spray the insulation 8" thick on the ceiling. It was a pleasure building the office spaces inside the building compared to the typical metal building chicken wire / roll type insulation metal buildings I have built inside of in the past. Around a 15° difference of pleasure while working. The job was built during the summer. All work I did in the building was before the HVAC was installed. Compared to an uninsulated metal building you would have thought the HVAC was already working in the foam insulated building.


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## beanu (Jun 28, 2016)

Hey all, 
Thanks again for all the feedback. We worked up spreadsheets and priced out all these various upgrades. In the end we decided to start with closing off the interior gable, aka creating an insulated attic to reduce some of the massive heat gain from the metal roof. We also trawled craigslist for a couple of weeks because we wanted to do this project cheaply.

Today was the first big work day! My wife and I scored a ton of unfaced fiberglass insulation, reused MDF for the decking, and 2×2x8s for the "joists". We decided to do a slightly 'arched' ceiling in order to preserve a little more interior space and use the exposed trusses to mount lights and other ceiling stuff. Anyway, we got the whole thing done in a day… First we added gable vents and a powered gable fan to circulate some air. Then put in the 2×2 framing, cut lots of MDF panels for the ceiling decking, and finally added in those unfaced batts. By the time we were done it was late afternoon in full Texas sun, and the temperature differential between the attic and the interior space must have been 25 degrees or more. Not a bad start!

Thought I would share some photos of the day's progress: 
https://goo.gl/photos/b9gAgmzRSZ5JJbJb8

Thanks for the support!


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## clin (Sep 3, 2015)

Looks like you're off to a great start.


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## youdidntbuildthat72 (Dec 21, 2016)

Google Radiant barrier. It looks like a big roll of aluminum foil and works great. I put some in my attic up near the metal roof of my building and I didnt have enough to do the whole building. Where I didnt do it you can really feel a difference in the radiated heat coming from the ceiling. The rest of the building is much cooler because it is radiating that heat back the the roof and not into the room. I stapled mine to the rafters.


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## OSB (Dec 16, 2016)

This is a late reply but if full spray insulation is too expensive, you could cut rigid foam to fit between your studs and then use canned spray foam to seal it to the structure.

Hilti brand spray foam is the best I have used by a large margin.

For the roof, I would have removed the steel and used two layers of OSB backed 2" foam insulation, then put the steel back on over that. Put the two foam sides together to have an OSB foam OSB sandwich, use an overlapping pattern so the joints don't line up and seal them with spray foam.

If you want to reduce your cooling requirements you need to seal the building envelope so you don't get conditioned air leaking out and warm air getting in. Spray foam will help with that but after what I have read about fine dust separation, you will either need a very expensive cyclonic system or a system that vents outside which will act like a huge air leak.

I think it might wind up too expensive to aircondition but with insulation and some air flow it might not be too bad.


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