Framing the Super Insulated Garage Workshop
Intro:
Framing up this 1200 square foot garage started out pretty easy. We (family/friends) built and stood up all four walls in just one day. Nice! I was feeling like we would be driving into the garage by next week.
Well, a year later and we had finally finished the project. I say finish, but there are still a couple minor cosmetic things that will be done “some day”. I joke to Alaina (my wife) that “some day” is going to be the day before we sell.
Anyways, let’s get into the details of framing up this garage and shop.
Sill Plates:
Arrows show the sill plates on the foundation walls
After the concrete slab was cured I bolted down the sill plate. This is the first piece of wood to be attached to the concrete foundation using anchor bolts. This element is critical. The walls of a buildings walls act like big sails that grab wind. Everything relies on this sill plate being firmly connected to keep from blowing away.
The building code requires this sill plate to be pressure treated. They did this after too many sill plates were rotting due to contact with the concrete. You see, concrete is porous and soaks up water from the ground. Which means that anything in contact with it might also be wet. Wood rots when it stays wet over a long period of time. Bad things happen if the sill plate rots. I’ve seen this first hand and have actually replaced a few sill plates in my day. Ha! I got to say “in my day.” So, I understand why they did it, but this is a prescriptive method. I would have preferred a performance code requiring measures to protect the sill from rot. It is almost like the building code is just throwing up their hands and saying it is impossible to build a sill that won’t get wet. Well I capped the foundation with Grace Ice and Water shield. This is a thick rubberized membrane. This is going to separate the concrete foundation from the wood sill. It is called a capillary break. So, if I keep water out of the wood sill then I think I should be allowed to build the sill using non- pressure treated wood; but unfortunately I don’t get that option.
Wall Framing:
Framing the walls, 24 inches on center, 2x6 studs
Once the sills were down we laid out our top and bottom plates for the walls. The walls are framed using 2x6 studs, spaced 24 inches on center. I bought 10 foot studs, and trimmed them as needed so they were all exactly 10 feet long. Very little waste this way. 24 inches on center is one of many details used in “Advanced Framing” which is something I wanted to try. I’m glad I did, but it meant that I used a different wall sheathing then normal.
Common wall sheathing is 7/16, or 1/2 inch OSB or plywood. I thought about using this but choose instead to use much thicker 3/4 inch OSB (actually 23/32). This is sold as a subfloor product and is not usually used as walls or roofs, but is absolutely acceptable and legal. Because it is usually used as a subfloor it has tongue and groove edges. When installing this on the walls I had the tongue face up and groove down. I did this because framing will be rained on periodically while you build. I wanted the sheathing to naturally shed the water away. I was worried that if I had the groove up, then rain would run into the groove and puddle, soak in, and swell the joint. Structurally the direction of the tongue and groove makes no difference. All the sheets are laid horizontally so that the strength axis is perpendicular to the studs. Some builders run sheets vertically, which is allowed when you’ve upsize the thickness. However, I saw no benefit to running them vertically on these tall walls. I do see the benefit if it is a shorter wall and can tie the top plates and bottom plates together.
Why did I decide to go this route on my garage? Let’s take a look at what I did on my house. On the house I framed the walls much more typical with studs spaced 16 inches on center, and sheathed using 1/2 inch plywood. I noticed the sheathing was slightly wavy between studs. Even from one sheet to the next they would sometimes be wavy, in a different way. This was noticeable even when they are facing the same way and from the same unit (stack). So, if one sheet bends inward, and the sheet on top bends outward, I was having large un-evenness in the wall plane. I assumed this was going to cause me issues when trying to make the sheathing air-tight as this was going to be my air boundary. I also assumed it would transfer outward and create un-evenness in my siding. I might have been wrong assuming this, but I went about correcting it. I cut and installed blocking in-between each stud bay at every sheathing joint. Then I nailed the sheathing horizontal edges to the blocking. This corrected the un-evenness and made the plane of the wall much smoother. But it was extra time and material.
That experience with my house led me to want to use a tongue and groove product on the garage. And because I spaced the studs farther apart then the house, I wanted to use a thicker product. It turns out that my local lumber yard stocks two types of subfloor product fitting the requirements. One is “Advantech” made by Huber; the other was “DryGuard” made by Georgia-Pacific. Both meet the same exact code requirements of strength. However, Advantech seems to have an extra water protective layer on it. At least it feels that way when I have used it; more slippery compared to Dry guard. Also, Huber does a great job marketing their product in magazines and at trade shows. The key difference for me was that DryGuard was $12 less per sheet! DryGuard was actually slightly less per sheet then 1/2 inch plywood. Wow! I think that is a great value.
Now that I have built both style walls I highly recommend the garage wall over the house wall. The garage wall assembly was faster, less material, less cost, it feels more solid, and is definitely smoother. The smoothness matters when trying to make it your air boundary. Just a note to clarify, I’m not discussing the merits of double stud vs. single. All my comments are referring only to the structural (outer) wall.
Air Sealing:
6.5 inch wide OSB strip nailed to top plate
Green tape to air seal joint between wall and OSB top plate
Once the walls were framed up I had one more detail to complete before roof framing. The air-sealing detail would be easy to do at this point in the build, but extremely difficult to accomplish later. Being an owner/builder it allows me to mix it up. This would be very difficult to manage if you were hiring out to a framing crew. In my experience, they’ve been known to not slow down to do an air sealing detail. They will just fly right through and leave it up to the insulation contractor to do what they can later on. If you decide to use these details on your upcoming project please keep that in mind. If you are hiring a crew then you may want to go with a different air sealing detail that won’t require you to micro manage.
To incorporate the air sealing I ripped OSB sheets into 6.5 inch wide strips by 8 feet long. I then laid the strips on the top plate, flush to the outside, and with a one-inch lip overhanging to the inside. These were simply nailed in place. This inside lip was going to provide me a way to carry the air boundary from inside to outside. I then taped the joint between the OSB strip and the outside wall sheathing. Now I could set trusses on top and not have the joint broken.
Roof Framing:
Looking up at the trusses
I chose to use trusses for roof framing. I think they make a lot of sense with this style building, and are not very expensive. With a lot of family and friends to help, we raised the trusses into place by hand. One at a time we set them onto the top plate of the wall, tilted them up, and nailed them into place 24 inches on center. The trusses are located directly over the wall studs for a nice load path to the foundation. We secured the trusses against wind uplift by using timberlok screws instead of the more common twist strap. This was because the timberlok could screw up through the top plate and through that OSB strip we had installed. These trusses are very heavy and I would not attempt to lift anything larger by hand.
On the north side of the garage we wanted to incorporate a deep porch. This was framed up starting with 6x6 fir posts set on concrete piers. Alaina and I cleaned up the posts and coated them with boiled linseed oil before setting them in the post bases. On top of the posts we ran a continuous beam. This was 3 layers (plys) of LVL’s, 7.25 inches tall. All three layers are secured together using TrussLOK screws. Unfortunately, these screws stripped out the holes 30% of the time. Needless to say, I will not use them again in the future.
Finally, we cut rafters to span from the wall of the garage out to the beam. These were framed normally, one at a time. They are 2x8 lumber. The porch roof is in the same plane as the garage roof for an un-interrupted water shedding layer.
Porch framing
I wanted a deep overhang all the way around the building for water management. This is no big deal at the eaves because the rafters just stick out past the supporting member. But it is harder on the gable end walls. Many times, framers just add blocks of wood for support. This is OK if the overhang is less than a foot, but my overhang was 2 feet deep. So, I used “ladder blocking”. There are supporting members (2x4’s) spanning from the second truss, over the gable end truss, out to the fly rafter. These 2x4’s will prevent the overhang from sagging in the future. You can’t notch a truss, so when I placed the order I asked for the gable end trusses to be dropped by 3.5 inches. The truss manufacturer knew exactly what this meant and they showed up exactly as I had hoped. This process worked great. There was extra blocking and nailing to keep everything from rolling.
Finally, it was time to sheath the roof. This is the same sheathing I used on the walls. 23/32 OSB tongue and groove. The only downside is how heavy these sheets are. I think about 80 pounds each. But the roof is a 6:12 pitch, so it was manageable. I did this with a helper (usually my dad or neighbor) to lift the sheet from the ground and I grabbed it from the roof and dragged it up.
Conclusion:
It took two months to complete the framing. I think that is pretty good considering it was not hired out to professionals. All the work was done in evenings and weekends. I’m very pleased with the framing details. I recommend 24 inch on center stud spacing when it is combined with thicker sheathing. The porch roof took as much time to build as everything else combined. This is just another example why I like roof trusses. They are just so fast. Framing costs were $10,847 for lumber, sheathing, trusses, nails, and structural screws.
Thank you everyone who helped.
