[Greenbuilding] Outgassing of Sheathing & Insulation fasteners

[Eli Talking]

As noted by my earlier message, I was advocating predrilling 2x furring strips to achieve accurate alignment of long screws through thick layer of foam that could reliably hit the intermittent studs.  I had the issue of hitting the rafters through 3” foam and .5” paneling installed under existing sheetrock of cathedral ceiling.  However, on the exterior of my house that had 5/8” textured plywood siding, I did not need to be accurate because the plywood had sufficient grip.  I could run GKR screws anywhere and it would grip suffieciently to allow the head to countersink into the exterior furring strip.  In the house I am designing, we are planning on putting all the insulation on the outside, 6” or 8” EPS, still to be determined.    I am wanting to know if the withdrawal strength of .5” plywood or osb would be sufficient.  I like the simplicity of assembling a very solid conventional sheathing enclosed framed structure.  

Because this is a new structure, I am planning on setting the EPS and the 2x furring strip directly on metal termite shield, insect barrier, flashing that is in direct contact with the foundation.  In so doing, the fasteners are no longer fully supporting the weight of the 2x furring and the selected siding.  Fasteners would only be resisting horizontal loads from wind or vibrations.  2x4 studs commonly get away with 4 16d nails.  Fasteners for furring  could be located at band joist, top plates or other horizontal framing, allowing more location tolerances and avoiding the need to predrill.   

All insulation in exterior mounted foam makes the structural sheathing over the conventional 2x4 framing on the interior side of the thermal envelope. Can some on the list point me to issues relating to outgassing in plywoods and oriented stranded boards?  I expect to achieve near passiv haus level of tightness.  We will install ERV for ventilation.  

Also, we are considering alternative bracing to rely on the EPS for the exterior sheathing.  In this approach, there is not tendency for foam to sag from weight.  Then we would have to achieve accuracy and predrilling would be appropriate.  Also detailing the bracing becomes more important.  However, it would save a whole layer of sheathing from project cost.  

Still probing for more knowledge and insights from this list.  It is exciting to be moving forward in achieving a new level of performance.  Your help is very appreciated.  

Eli 
www.conservationarchitect.net 

From: John Straube 
Sent: Tuesday, November 20, 2012 5:12 PM
To: Green Building 
Cc: Chris Koehn 
Subject: Re: [Greenbuilding] Insulation fasteners

Thats an interesting idea Chris! never seen it done, but it sounds really worth it for 2nd stories etc.  


Dr John Straube, P.Eng. 
www.BuildingScience.com
On 12-11-20 3:47 PM, Chris Koehn wrote:

For thick insulation, take the time to pre-drill before installing. If the structure is accurately framed, studs are at predictable centres, and it's much easier to drill straight holes when the sheet is on horses than when you're standing on a ladder. We snap lines and pre-install the screws, which makes running them in while working at height a much simpler process. As well, choosing a screw that self-taps into existing (and often hard) materials makes life easier.

Best,

Chris Koehn
TimberGuides
Vancouver Island

Eli wrote: "I know from experience there is a lot of labor from missing the stud and 
trying again, as well as creating additional holes to the the thermal 
barrier.  The thicker the insulation gets, the more difficult it becomes to 
hit the stud with hand held drills."


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