Yes, chord size is highly dependant on the span and design load. Trusses I set last week are 28' span, 2x6 chords and 2x4 webs.
Roofing questions - going with a metal roof
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alia176
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Thank you gents for the education as I'm learning quite a bit about roofing.
Per my blueprint, 2x10 rafters with 16"OC and there doesn't seem to be any type of venting or spacing above the bat insulation.
@KLF, thank you for that article, very informative.
So, it sounds like having a ridge vent would be a good idea, even though there hasn't been a problem. Sounds like the water marks are from the vapor barrier not installed correctly on the ceiling.
Per my blueprint, 2x10 rafters with 16"OC and there doesn't seem to be any type of venting or spacing above the bat insulation.
@KLF, thank you for that article, very informative.
So, it sounds like having a ridge vent would be a good idea, even though there hasn't been a problem. Sounds like the water marks are from the vapor barrier not installed correctly on the ceiling.
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nailed it on the 16"o.c.
.yeah, wth? they've got the soffit vented, @alia176 , you're not missing a thing, the print sure is though
I was wondering that too... vent the soffit but not the ridge? 
But, actually my garage was originally built that way (1995). No ridge vent, wow it got stupid hot up there, so I put in a gable fan on a thermostat/humidistat. Some days it would run all day. When I had the roof replaced 4 years ago I had them cut the ridge and install a vent, and now it never runs. Made a huge difference. I do still run it if I'm doing any welding, so at least it still has some use.
But, actually my garage was originally built that way (1995). No ridge vent, wow it got stupid hot up there, so I put in a gable fan on a thermostat/humidistat. Some days it would run all day. When I had the roof replaced 4 years ago I had them cut the ridge and install a vent, and now it never runs. Made a huge difference. I do still run it if I'm doing any welding, so at least it still has some use.
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alia176
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I was wondering that too... vent the soffit but not the ridge?
But, actually my garage was originally built that way (1995). No ridge vent, wow it got stupid hot up there, so I put in a gable fan on a thermostat/humidistat. Some days it would run all day. When I had the roof replaced 4 years ago I had them cut the ridge and install a vent, and now it never runs. Made a huge difference. I do still run it if I'm doing any welding, so at least it still has some use.
This is very interesting so let me inquire some more. So, you have a shingle roof and cut a 2" or so strip off the OSB on both sides of the ridge? The ridge vent deal that are made for the shingle roof seems to have a decent size hole and seems to be able to exchange air more easily, at least from my newbie eyes.
The ridge vent for a metal roof are using some sort of a mesh deal that gets squashed with the ridge top piece (don't recall the name). I was curious if the air exchange as good with this mesh vent thing.
Our regular roofer out here hates the typical product offerings for asphalt comp(shingle) ridge vents. In a vaulted ceiling though, cutting in a bunch of the typical passive attic vents doesn't really work, as you would need one every bay, and would look like crap. I think his big gripe is that they don't move a ton of air, and if they get stepped on during install or maintenance of the roof, they get crushed pretty easily. This is not to say don't use them, just passing along some gripes from an old timer in the industry whom I trust.
I've only been involved with one metal roof house, and one metal roof garage so my personal experience with metal offerings is admittedly thin.
I've only been involved with one metal roof house, and one metal roof garage so my personal experience with metal offerings is admittedly thin.
Re trusses, I was just curious if due to a higher snow load your trusses out there were always 2x6 bottom chord min, and went up depending upon span. as I type this, I realize they could also be double bottom chord, less spacing (24" o-c down to 16") and lots of other engineering shenanigans.
Yes, the sheathing needs about ~2" gap between the ridge beam (or, in your case, the blocking at the plumb cut of the rafters) so air can escape the ridge. Here's what it looks like in my garage:
That black stripe is the gap between the ridge beam and the sheathing.
Best ridge vent I know of (after looking at a bunch of them) is the GAF "Cobra SnowCountry" vent. Very nice rigid plastic piece that bridges the gap, has about a 1" opening along wach edge, but they also include a thin screen at the openings to keep bugs out. It's the only thing my roofer uses, and I'll be putting it on the Habitat house in a couple of weeks when we do the roof.
Boost Attic Ventilation with a Roof Ridge Vent | GAF Roofing
This Cobra® SnowCountry® roof ridge vent features an easy tear design for less waste during installation. Protect your roof in winter weather with these vents.
Oops. ya sorry I should have clarified, that ridge vent is for traditional shingle roofs only.
Personally, I'd strip the existing shingles off whether you're doing new shingles or metal roof. It allows a chance to assess the existing roof deck for any issues rather than just hoping for the best.
Concealed fasteners are a much longer lived solution than exposed fasteners. The exposed fastener typically has a neoprene washer, which dries out over time and then you have thousands of perforations through the metal panel. It's like the roofers who install an Architectural shingle with a 40 to 50 year warranty, but then use caulk with a 7 year lifespan instead of properly flashing things. The shingle warranty doesn't cover everything you have to rip out and replace in 10 years when the caulk fails...
Metal roof systems can be vented too. It's a slightly different detail, but basically works the same.
The fact that you have the soffit vents and not a ridge vent is poor design/execution. The soffit vents don't do a thing without the ridge vent and a path between the two. As one poster mentioned, the alternative is spray foam and moisture/vapor barrier so that you don't get any condensation in the space.
Concealed fasteners are a much longer lived solution than exposed fasteners. The exposed fastener typically has a neoprene washer, which dries out over time and then you have thousands of perforations through the metal panel. It's like the roofers who install an Architectural shingle with a 40 to 50 year warranty, but then use caulk with a 7 year lifespan instead of properly flashing things. The shingle warranty doesn't cover everything you have to rip out and replace in 10 years when the caulk fails...
Metal roof systems can be vented too. It's a slightly different detail, but basically works the same.
The fact that you have the soffit vents and not a ridge vent is poor design/execution. The soffit vents don't do a thing without the ridge vent and a path between the two. As one poster mentioned, the alternative is spray foam and moisture/vapor barrier so that you don't get any condensation in the space.
PAToyota, that is a great ridge vent screen detail.
When using the ridge vent detail above we use 24g galvanized perforated sheet metal.
We did a major renovation to a house that was build in the early 90. Builder used window bugscreen material.
When pulling down the drywall on the ceiling we saw lots of yellow stains, this was from the rats.
After pulling all of the insulation out we saw that the soffit bug screen, ridge vent bug screen and the rainscreen bug screen was all compromised by the rats. Metal perforated bug screen is the way to go.
When using the ridge vent detail above we use 24g galvanized perforated sheet metal.
We did a major renovation to a house that was build in the early 90. Builder used window bugscreen material.
When pulling down the drywall on the ceiling we saw lots of yellow stains, this was from the rats.
After pulling all of the insulation out we saw that the soffit bug screen, ridge vent bug screen and the rainscreen bug screen was all compromised by the rats. Metal perforated bug screen is the way to go.
If not rats, squirrels can be just as destructive.
Insulation is a double edged sword. My crawlspace is still completely bare, and I have zero rodent issues. We did a bathroom remodel for a lady that had had her crawlspace cleaned, re vapor barriered, and insulated about 1 year before we got in there; Rat and/or mouse city. Granted, I'm sure the exterior of her house has some ready access places for the critters, but all that fiberglass batting is just ready made nest material.
Another reason I hate fiberglass. Mineral wool is where it's at, they hate the stuff, won't touch it. Plus it's a better R value (among other advantages).
alia176
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That one is a Metal-Era: Hi-Perf Ridge Vent Slope to Slope, Standing Seam - https://www.metalera.com/Products/Details/Metal-Era/Hi-Perf/Hi-Perf-Ridge-Vent-Slope-to-Slope-Standing-Seam
EZ-Vent-N-Closure is another one: EZ-Vent-N-Closure | Two-In-One Vent & Closure for Metal Roofing - https://ezventnclosure.com/
I'd start by checking with your metal roofing manufacturer to see if they have something similar in their product line. If not, these other ones can usually be adapted to any system.
EZ-Vent-N-Closure is another one: EZ-Vent-N-Closure | Two-In-One Vent & Closure for Metal Roofing - https://ezventnclosure.com/
I'd start by checking with your metal roofing manufacturer to see if they have something similar in their product line. If not, these other ones can usually be adapted to any system.
