How to hit studs through exterior insulation
Greetings All,
I have been lurking on this site for a couple months and have recently become a member. I want to say thanks to all the regular contributors; I think the technical content on this site is amazing!
My question:
Can someone explain to me or point me to an article that explains the technique that builders use to hit studs with long screws when installing exterior insulation?
Background:
I have a residential building lot and will, hopefully, soon be building a new, energy efficient home. I am in the design stage now and I am trying to get as many design details specified as I can so that I can get reasonably accurate estimates from builders/contractors. I have read many articles that discuss the advantages of continuous exterior foam insulation both on walls and above roof sheathing. However, when I talk to prospective builders in my area about these designs they generally have no experience with them. When I explain that the screws that retain the rain screen and insulation need to hit wall studs, they look lost and lose interest in the job. Sometimes I have problems hitting a wall stud just going through 1/2″ drywall after marking it with a stud sensor, so I can understand their hesitation. What is the technique? It is really just a matter of careful measurements and driving the screw in square to the surface? Seems like there would be a lot of misses that no one would ever know about.
Thanks,
Jim
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Replies
Jim,
The easiest is to mark out the stud location where it will be visible after the foam goes on. Snap a chalk line for longer runs or eyeball for shorter ones. Usually it is good enough for 2"-3" of foam. Sometimes it helps to drive a long screw out from the inside beside the stud to mark the stud location.
For thicker foam go for a guide to keep the screws straight (lot of extra labor, so mostly for DIY). TJIs with wider flanges are also your friend for roofs with thick foam.
You will still occasionally miss a stud, just check from the inside after install and fix the shiners.
Engineered nail base can be installed directly over sheathing without hitting studs but usually need a lot of screws.
It's all careful measurement, and going by feel when driving the screws. It's Much easier when drywall/insulation is not done on the inside.
Also consider 3/4" plywood for sheathing. I saw a risinger video a while ago where he did that for screwing the battens over the insulation and get around having to find studs. Where the plywood is supposed to have enough grab for the screws. I personally think the extra cost of sheathing would outweigh the extra cost/time in labour of carefully finding studs.
It's a question of how much insertion of the screws you are comfortable with. Maybe the mechanical eng's on here can talk about that.
Hey Jim! As you can look up my story here on GBA, you'll see that I do a lot with 6-8" of exterior insulation as I get used polyiso so cheap from roofers. Anyway, I screw recycled plywood or 2x4 under the eaves and stake to ground with rebar, then using a large square, mark all studs out away from the wall.
https://www.greenbuildingadvisor.com/article/one-mans-quest-for-energy-independence-part-1
Kuennllc.com
Malcolm was recently very disappointed when I shattered his dreams of a new tool purchase after describing a simple tool (a piece of 2x4 scrap with a slot cut in it) that could help keep a screw aligned perpendicularly to the face of the insulation to ensure you drive it straight through to hit the stud. If you can’t find the drawing I can repost it.
Mark the stud locations vertically as you put the insulation up, then use an aide like I described to keep the screws from skewing off your mark and missing the studs as you drive them in. As the foam layer gets thicker it does get trickier to hit the studs reliably, but is certainly possible to do it if you’re careful.
Bill
Zephyr 7.... I read the thread and am interested in the "tool" you designed... I'm only screwing through 3" foam but still manage to miss the stud 20% of the time :(
Can you post that drawing? I searched for it but found nothing...
Thanks
Here is the pic. It should basically just a scrap of framing lumber with a slot cut in it. Ideally you want that slot to have a square end, not a rounded end like if you cut it with a circulator saw the usual way. Cut across the edge so that the bottom of the slot is square, which will keep the screw straight as you drive it. The wood acts as a guide to keep the screw going in straight. It’s really easy to drive the screws at angles even though they “look straight”, and end up missing the studs if you don’t use some kind of alignment guide. As the foam gets thicker, it gets even more critical to keep the screws straight as you’re driving them.
Bill
I have not forgiven you.
:-)
I'm curious if under some conditions, glue would suffice to hold the outer/upper layers on. Screws into sheathing could hold it till dry.
I think the effectiveness of glue depends on the material you’re hanging. I wouldn’t trust glue with lower density EPS, for example, since I’d expect the glue would pull out a chunk of the EPS beads and the sheet would fall. Polyiso would probably glue up OK. I have some XPS in my own house that has been up for about a year with glue (PL for foam board), and screws. I have a second layer (polyiso this time) going up this fall so I can check how well the glue is holding. I used the glue mostly for an air seal.
Based on past experience gluing up rigid insulation, I think screws/nails is much easier. Glue has more variables and a tendency to hold for a little while before falling off which drives me crazy. Just about when you think you’re finished, you look behind at what you’ve already done and see several sheets separating from the wall...
Bill
For those who DO want to buy a tool:
https://www.amazon.com/Milescraft-1318-DrillMate-Drill-Guide/dp/B014A1Z92I?ref_=fsclp_pl_dp_2
(no affiliation or review of such).
That being said, it looks like it would be quite heavy and unwieldy.
I'd go for the slotted 2x4 route first before buying the attachment.
Or, in the less heavy and unwieldy department,
http://www.leevalley.com/us/Wood/page.aspx?p=32318&cat=1,180,42311
Sold as a drill guide but can’t see why it wouldn’t work for screws.
>"Sold as a drill guide but can’t see why it wouldn’t work for screws."
For one, screw heads won't fit through a guide properly sized for the shaft/thread diameter.
I suppose if you used one for each screw a it would work great, assuming you wanted a rainscreen that deep! :-)
Yup, obviously. Pretty silly of me.