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Some of the discussions and issues about rafter postions over studs, using double or single plates, sheathing or not sheating; etc, are lost in the ventilation string. I would like to hear more from people in a string I can follow.
I say double sheating (top and bottom of rafters) in stick frame construction of conventional roof is a waste of material. I have even ventured that any sheating on roofs is a waste — that cross bracing and purlins will do everything required structurally. Sheating is a bed for shingles but not necessary for structure nor for weather protection.
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Here a couple of posts out the recent ventilation discussions:
Gabe Martel - 08:42am Mar 24, 1999 EST
I'd be interested in your comments on the use of a single 2x for the top plate and the use of metal clips and plates to hold the corners
and plates together.
Ron Schroeder - 09:37am Mar 24, 1999 EST
Gabe,
I have used the single top plate method before. It works fine. You MUST line up the rafters/trusses within 3/4" of the studs. It is harder to line the walls. It is also harder to attach the top of the dry wall sheets. Splices in the plate are harder. Less thermal bridging. Pre-cut studs are too short. Inspectors have to look in their code book. Rafters and studs that line up with a single top plate is STRONGER than a double top plate where they don,t such as 24" o.c. roof with a 16" o.c. wall. I often mix single and double in the same house, other than 8' 0" walls or how straight the lumber is for the plate is often the deciding factor, but I slightly lean to the single plate because of cost, environmental conscience and thermal reasons.
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The discussion is academic at best since the use of this "streamlined" construction would not be allowed under the OBC.
*tedd - one problem. Metal roofing to span these purlins will cost 3-5 times as much as ply and shingles. The non- structural metal roof I am using cost me $252/square for metal materials only. Who will pay for this?The metal and purlins you referred to in previous posts gave me the impression that you were referring to corrugated, exposed fastener metal panels. These are the kind used on pole barns, etc. These panels may be self-supporting, but they do not meet residential standards for snow loads with that method of installation. In fact, after a few years you can usually see those dipping between the purlins.I am unaware of anyone that double-sheathes as a matter of practice. Of course, what do you consider to be sheating? RFBI is considered sheathing, and I think it a good idea on the underside of a roof deck.-Rob
*Gabe,Many codes DO allow single top plates and 24" o.c. framing.Ron
*RobMetal roofing for residential applications, to be applied over purlins (1x4 or larger)in Ontario is onlyb 50% more per squarethan OSB/ 25 yr.shingles. 'Heavy guage' (we have a different guage numbering system than the U.S. so mentioning guage numbers is misleading) coloured Galvalume is around $150cdn./square. The saving in labour between the two systems is b huge!!! with steel/purlins winning in a cakewalk. And we still haven't factored in the lifespan of the steel (50 yr.'s conservatively) with shingles (25yrs maybe). I am indeed talking about i "corrugated, exposed fastener metal panels"but they certainly b do meeti ". . . residential standards for snow loads with that method of installation."and there isb never anyi "dipping between the purlins." on any that I've installed, or for that matter seen on other installations. This may be a case of totally different products available on opposite sides of the border.
*Ron,I'm sure if you looked hard enough, by combining all the codes, you can quote a loophole from one and then a loophole from another until you find enough of them (loopholes)to build to your standards.Your objective to build to minimum structural integrity is weird, but well within your rights.Just don't try to include me in your quest.
*Mornin' Gabe,I absolutly do NOT believe in building to minimum structural integrity, in fact the building inspector often comments about the strength and stiffness of what I build. I allways build at least to code. I just don't believe in using "extra" where it isn't needed. Safety factors and redundancy against single point failures are important. I evaluate every thing that I do that is different from the way "Grandpa" did it on the basis of structural integrity, cost of materials, cost of labor, code, life span, apearance, future maint., energy use, recycleability and the environmental impact of the materials and their manufacture.Ron
*The heavy guage (24 ga U.S. .0269")- painted galvalume pan & batten panels from metal sales cost $150 u.s. per square. As an option you can get 22 ga - .0329". The 24 ga are still not structural - they want sheathing under them.The corrugated panels used here (NYS) are typically referred to as "Agricultural Panels" and come in various thicknesses. These corrugated panels are indeed stronger than the same guage pan & batten, or interlocking concealed fastener systems with one problem - washers. It's a fact they will, by design, leak. Thus (in my mind anyways) making them unsuitable for residential work. In a barn there is no insulation and drywall to get ruined.Regardless of which panel you use a square of decent shingles can be bought here for $35.00 and a sheet of 5/8 T&G plywood costs $22.00. This totalled still costs only $103.75 per square. Is there really $45 per square labor savings? I will concede that the metal goes on fast. The pan & batten system I am using will take 12 screws to secure 15 sf at a whack. What about the fact that a roof framed with trusses and purlins is difficult to construct if for no other reason than lack of footing and safety concerns?-Rob
*Good Day Ron,Grandpa never had the materials or choices that we have today. What he had that we don't, is time.The time to pick out the right piece, the time to make it fit just so right, the time to stand back and take a second look at what he was creating.Putting in that little extra is not waste, it's just another way to do things that seems to work for me.
*I wish I had Grandpa's lumber.............
*RobIt would appear that we are talking about the same product when we refer to "corrugated panels". I'm not aware of a 'non-corrugated pan and batten panel'. Our 'Ag. panels' tend to have a low rib (3/4") while residential/commercial panels are available with both low & "high rib" (1"-1.5"). All are available with slightly different 'profiles' and some are meant only for side wall applications. Perhaps it is these profiles that make the panels that I use more structurally sound for residential use (more bends, more & higher ribs = strength). The guage thickness seems to be the same,(my mistake) and I use 26 guage(.021")corrugated, high rib panelsb screwed through the ribinto 1x6 Spruce strapping on 24"o.c.. . . trusses require 2x4 purlins.You writei " It's a fact they will, by design, leak."The screws we use are colour matched with metal over neoprene washers and areb very water tight when applied through the rib!!!The purlin/rafter construction is dead easy, very fast and a i real joyto work on compared to typical roof sheathing. . . you've constructed a permanent roof ladder, piece by piece, and you can scramble up and down a 12/12 pitch like it was the boardwalk. . . the last sheet of steel and ridge cap in the run is a bit problematic, requiring padded removable ladders hung from the ridge, or ropes and safety harness.So yes, using your figures, there is $$ savings. Whether it's as much as or more than 2 man hours/square would depend on several other variables, such as pitch and total squares- the larger, steeper roof emphasis the efficiency of steel. But you still haven't considered i lifespan,which makes the $$ savings considerably greater. And then there'si ice dams.Gene L. has said elsewhere on this forum that steel roofs can have them too, and while I know better than to say iti won't happen, I'veb neverseen them, and I live in ice dam country!!! Ya gotta watch out for those roof avalanches though. . . they can be a real killer!!!
*I don't have a problem with the system, and I agree that it is worth the extra cost - metal is what I am putting on my own roof. I went with concealed fasteners because of the washers. The neoprene lasts about 15 to 20 years then you have to "re-screw" the roof. In my opinion, the exposed fastener panels look cheap on a house, they interrupt the lines of the roof. Check out new style screws with silicone (or some type of clear silastic coatin). My cousin just used these on his barn. They are softer, but they should last longer.-Rob
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Some of the discussions and issues about rafter postions over studs, using double or single plates, sheathing or not sheating; etc, are lost in the ventilation string. I would like to hear more from people in a string I can follow.
I say double sheating (top and bottom of rafters) in stick frame construction of conventional roof is a waste of material. I have even ventured that any sheating on roofs is a waste -- that cross bracing and purlins will do everything required structurally. Sheating is a bed for shingles but not necessary for structure nor for weather protection.