Using T-shape 2×4’s instead of 2×6
RedDenver
| Posted in Green Building Techniques on
Has anybody used two 2×4’s arranged in a T-shape in a wall? Just use standard 2×6 wall construction otherwise. Seems like it’d mostly solve the exterior insulation issue of hitting the edge of a stud with a long screw. I’m guessing this has been done before and there’s a reason not to do it, but I couldn’t find anything online.
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Replies
Jason,
My suspicion is it hasn't been tried because it's a bit like trying to kill an ant with a sledge hammer. You gain a larger surface to screw to, but have to use two studs where before one did, rip down all top and bottom plates, figure out what to do at openings, jack-studs, corners and headers, can't easily use batt insulation... that's just off the top of my head - I'm sure there are more consequences.
If your concern is just hitting the stud with a long screw when attaching exterior insulation why not get a can of spray paint and mark where the studs are on the sheathing at the top and bottom of the wall when you're putting it up? Then when you come to attaching the exterior insulation run a chalk line between the marks and you'll know there's a stud behind it.
Scott,
I'm not an experienced exterior insulation installer, but on the two small projects I used it on the difficulty of hitting the studs seemed to get exponentially harder once I moved to 2". With thickness beyond that I can see how misses would quickly increase just due to the angle of the fasteners as you applied them.
On an episode of https://www.youtube.com/user/MattRisinger he did a project where they used 3/4" sheathing so they could just hit the plywood with screws. Supposedly engineered that way
I haven't crunched any numbers.... But I'm going to go on wild limb to say you'd save so much more money and time by just doing regular framing with 3/4" plywood for the sheathing... That way you can screw anywhere to your heart's content.
It would depend on both the thickness of the foam, and the type of cladding. James Hardi has tables showing various permutations, some of which would require more than 3/4" plywood.
@Malcolm
I kind of figured there were a number of reasons that it didn't make a lot of sense. I suppose you could also just add 2x4's on the flat to the outside of the wall and get the same effect.
Jason,
Hitting the studs through thick foam is definitely a problem. I'm just not sure what the best thing to do about it is. Adding a layer of 2"x4"s outside the sheathing would mean cutting down a lot of foam to go in between them. And given that you are also attaching more strapping outside the foam to support the siding, the two layers begin to represent quite a bit more lumber.
I bet there is a market for a screw gun with a flat base, like a router has, which would help align the fasteners for these types of applications.
Imagine performing the task when the interior has exposed studs and every miss would show. That's pressure! https://architizer.com/projects/perfect-wall-house/
Find an old light portable drill press (very old) as they can hold about any drill and you can just sit it in position on the wall and pull on the lever to sink the screw straight in. Mine has 7" of drop so I can use 6" screws with no problem. Found mine at a rummage 20 years ago for $5. Good deal!
Paul,
What an excellent idea!
I was about to suggest you use engineered I-beams for the studs instead, but then I realized that you wouldn't really need foam in that case :p.
Paul's idea is excellent though. I'm actually intending to build a home with exposed studs like the "perfect wall" build Malcolm linked, so that advice is very helpful. I was intending to post asking for tips on hitting those studs once I got closer to the project, but now it looks like I might not need to.
I haven't found it too difficult to hit studs through 3" of foam. I did use a speed square to mark center on 1x4 furring, then predrill screw holes with a spade bit, get the screws started before lifting the furring.. generally easy to eyeball the screws are square to the furring this way.
3/4" sheathing would be miserable to lift and install. Definitely makes it a 2 person job. Assembling studs would be a ton of extra work, and would do a number on cavity insulation. Also now you're at 3.5+1.5= 5" cavity thickness which rules out batts.
Anyway, of all the difficulties from installing thick foam - mainly corners, window and door flashing, sinking screws was one of the easier tasks.
There are a bunch of options similar to this drill guide that should help a lot working with thick foam.
https://www.amazon.com/Milescraft-1318-DrillMate-Drill-Guide/dp/B014A1Z92I/ref=sr_1_3?keywords=drill+guide&qid=1557761710&s=hi&sr=1-3
There is no need for any fancy drill stuff, and horizontal drill press attachments tend to be a bit on the heavy side and I wouldn't want to use one for the tons of screws needed while putting up exterior insulation. I think there are only really two important steps to get the screws lined up:
1 - Mark the stud locations! This is what I've seen missed the most.
2 - Make a simple screw guide jig like I show in the attached sketch. A piece of 2x4 is usually sufficient. Cut a slot that will clear the threads of the screw just barely, and make sure the back of the slot is square to the face of the 2x4. When putting in a screw with this jig, hold the slot vertically and put a bit of pressure on the jig and the driver to keep the screw pressed against the back of the slot. Once you get started into the stud, pull the jig off and finish driving the screw. The simple jig serves to keep the screw square to the face of the insulation as you drive it so that you go straight through the foam to hit the stud.
The biggest problem with thick foam after forgetting to mark all the studs is to drive screws at a slight angle and then miss the stud that way. My simple jig helps to keep the screw straight as you drive it to avoid that problem.
Bill
Bill,
You have taken the fun right out of this. Here we were happily anticipating buying a new tool, and you go and spoil it with a scrap of 2"x4" that would work just as well.
Sorry for spoiling the fun Malcolm :-) Perhaps take the savings and put it towards the job site pizza or beer fund? Or, I’d be happy to machine the jig out of a piece of aluminum and you can pay me too much money for it :-) some of the fancy tools out there are crazy expensive for what they are, and since I have some experience machining metal I frequently make custom tooling for screwy problems.
For the poster about rockwool, I imagine my jig would work for that too. All the jig does is help you keep the screw square to the face of the insulation in two axes at the same time (fancy engineer word for that is “orthogonal to the insulation”). It will work whenever you need to keep the screw straight while driving, which is surprisingly difficult to do by hand, especially while working off of a ladder.
Bill
I haven't worked with the rockwool board and am wondering if they are too soft for this to work. The jig requires the surface it's contacting to be parallel to the studs and rigid.
You could screw a fair sized piece of 3/8" plywood to a small 2"x4" jig. That might work with something softer like rock wool.
#20
Good idea, thanks Malcolm.
Do you think that would also work on rockwool installs?
I like Malcolm's idea to attach a good sized piece of plywood to the back of the jig. All you need to do is to distribute the force of you pressing the jig against the wall over a large enough area that you don't significantly deform the insulation while working.
The only thing I'd do differently from Malcolm's suggestion would be to use some thinner plywood like luan or maybe 1/4" plywood. Keeping weight down will make the job easier as you'll be constantly re-positioning the jig as you go.
Bill
I'm with Nathan on this one. I've never had problems hitting studs through 2" to 3" foam (no pre-drilling or guides). Something like Densglass sheathing makes it even easier as you know right away when you miss a stud.
Key is to mark out the stud locations where you can see them after the foam goes up.
Putting up exterior insulation is one of the easier house building task. Here and there you might miss a stud, easy enough to go back and fix afterwards.