What type of fasteners in a thick roof deck?
Wango1
| Posted in Construction Techniques on
Come spring I plan to rip off my roof and add 3 layers of 2 inch foam insulation and then re deck it. I plan to use 2 x 6’s at the eave with some plywood to equal the 2″ foam.
My question is what kind of fastener should I use to hold the decking to the lower decking/rafters 6 “s + below? Timbermates? Ledgerlocks? 8” screws?
Also what kind of fastener schedule should be used? I am worried of the fastener bending with time.
BTW, 8 pitch roof, soutnern WI, architectural shingles, not planning to vent it.
Thanx Guys!
Replies
They typically sell the screws for this where they sell the insulation. Construction adhesive and H clips are also your friend.
Wango
Did you think about hoisting up SIP roof panels? (if your framing can handle it.)
But even if you don't use them, they should have suggestions on type and length of fastener.
Fasteners
Your local building official will help with a fastening schedule, based on you application and location. As for the screws, check these out, available in long lengths up to 16". Test results for shear, pullout, etc. are available for your inspector.
You uploaded the thumbnail images -- microscopic in size.
Limits
Well, okay, there is a limit on the file size that can be posted here. Maybe a link would be more appropriate, for you non-extrapolaters.
Gary
150 kb is good. 400x600. The size adjuster here doesn't seem to cut the mustard for me.
I used timberlocks in a similar situation. You want something self drilling with a relatively flat head. Fastening schedule would be the same as any roof sheathing for your area. Wind exposure will probably rule. This upper sheathing doesn't replace the lower for shear... does it? These screws will poke through the lower sheathing. Will you see them in your living room?
sap
He'll be going into the rafters, no?
That's a good point -- probably best to put some screws into the rafters and some between rafters, to keep the sandwich together better.
strap as you go
I did a similar retrofit - in my case only two layers of 2" foam
I started with a full length of 2x4 fastened along the eave edge, flat on top of the sheathing.
I then placed a row of sheathing (4x8) flat on the roof with another row of 2x4 against the top edge.
Continued this to the ridge.
I ripped the next layer of foam to 21 1/2" , placed a 2x4 along the rake edge and placed the ripped foam against it and followed with another 2x4.
Took this same patten across the roof.
This left me with a 2' oc spacing to attach my sheathing. I found that if I held my sheathing fasteners close to the edge of the foam sheets, it did not distort the sheathing at the butt joints.
This method gave me gave good attachment with minimal thermal bridging.
Terry
Thanks for the info. Did you add plywood to the 2x4's? (2" foam)
Also, what kind/brand/style of fastener?
Wango1 and Sapwood
Wango1:
I had considered ading a strip of 1/2" to the top of the 2x4's, but found it wasn't necessary.
I used 20d sinkers to attach everything (a bit more length then 16's). The first ply of 2x4's was firmly nailed down to the rafters.
The second ply of 2x4's was nailed to the first layer of 2x4's.
I wasa bit concerned that nailing the 1/2" OSB along the butt ends would pull down enough to show and as a result had some 4' strips of 1/2" to place on the 2x4's. I found if I crowded my sheathing nails close to the edge of the foam, no noticable dip from nailing it down.
Sapwood:
Sorry for such a vague discription.
After stripping the existing shingles, I ran a single 2x4 the full length of the house along the eaves.
I placed the foam against that 2x4 and followed with another 2x4 running the length. Effectively having flat 2x4's on about a 4' center with foam in between. Continued that pattern up the roof.
Then starting along one gable end, I attached another flat 2x4 along the rake. Alternating a strip of 21 1/2" rippers of foam and another 2x4.
This resulted in a 2' on center spacing for the sheathing.
To get 3 layers I suppose you could put the first layer on as I described, start the second row of 2x4's 2' up from the eave and again run the foam with the 2x4 strapping on (about) 4' centers, then the top layer as I described.
Terry
Chalk it up to my advancing age if you want... but I cannot visualize what you did. You started with a sheathed roof, placed rows of 2x4's, added rows of sheathing, then added a "next layer" of foam (where was the first one?), then added another 2x4 and a foam sheet at 21 1/2" to give you 24" spacing. Do 2x4's come in 2 1/2" widths in your neck of the woods?
Sorry, I can't follow it.
As I see it...
If I am following what he is saying, the 2x4s ran flat on the deck the length of the roof parallel to the gutter, one on top of another (similar to an ice dam). This serves as a toe board to prevent the sheets of insulation from sliding off the roof, and to have something to nail the fascia to.
What I am unable to follow is how the layers of 2xs (at 1 1/2" ea) are the same final thickness as the 2" foam. Hence, I asked if he screwed on some 1/2" ply on top to even them out.
I looked into 10" screws from several sources, and have now realized how expensive this will be. I may have over $1000 in screws if I have to follow the same fastener pattern.
I am also assuming I will need to tape the seams of the foam.
Thank you everybody for your help.
1/2" ply ?
The 2" sheets of styrofoam was ridgid enough that the 1/2" shim to make up the 2" wasn't needed.
The 20d nails (3 1/2" long) that I used to nail the second layer of strapping (the rows that ran up the roof and on 2' centers) did not crush the styrofoam noticably.
I was most concerned with the sheathing sucking down. As it turned out, the only place of concern was the butt ends and carefull placement of the sheathing nails (hugging over close to the edge of the styrofoam) took care of that issue.
By all means, pad the 2x4's out with 1/2" ply if you feel it is needed - I just couldn't justify it.
Terry
I case you didn't check these guys: http://www.twincreeksloghomes.com
They were the least expensive of all the sources I checked into. But, yeah, those long beefy screws can add up to some money.