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Brettny
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# Posted: 11 Jan 2025 06:03pm
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I would definitely wrap the siding down below the rim joist. I even did this with my sono tube foundation that I dont plan on skirting. It really helps keep the rain that runs down the siding away from important framing. I put the 8' t1-11 sheet at the bottom so my Z flashing and second smaller piece was at the top and well under the overhang of my roof.
It worked out that all the top of my windows are also at the Z flashing. You can also see that I used upside down T1-11 to cover the bottom of the overhang.
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JD0
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# Posted: 12 Jan 2025 10:43am
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Lots of great information here, I may not respond to everything individually but I appreciate all the input.
ICC, I will look into helical piles and see if that's something feasible. I've assumed they would be too expensive but maybe for a small building it wouldn't be too bad.
I'm thinking about the floor framing now too...I guess in order to cantilever at all, the joists would have to sit on top of the beams vs using joist hangers. In the past I've always used joist hangers but the more I think about it, sitting the joists on top would be preferable anyways - no worries about corrosion or having adequate bearing on the hanger.
I will see if I can adjust my plans to include two beams vs three, you're right, that sounds easier and simpler to have all the blocks near the perimeter if the span will allow it.
You mention doing twin beams will change the requirements for the loft joists. What do you mean by that? With two beams, would the joists now have to support the entire span vs being able to use the interior wall to bear the load? I guess that would make sense, since you would want that weight to have a direct path to the foundation vs over a floor joist.
Regarding inspection/code - absolutely, I agree that generally these things exists for a good reason. My comment wasn't meant to imply that I intend to carelessly disregard code, just recognizing that sometimes sound practices can exist outside code and I have some flexibility.
Regarding the walls, I definitely will have the sheathing go down over the rim joist. Menards does sell 5/8 t1-11 in 4x9 sheets. The manufacturer website states they are "Grade-stamped and span-rated by TPI". I guess that means they are structural but I'm not sure. I think it's a moot point anyway, I'll almost certainly do sheathing underneath the siding. It comes out to about the same cost either way considering the thicker t1-11 is more expensive.
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JD0
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# Posted: 12 Jan 2025 10:47am
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Quoting: Brettny It worked out that all the top of my windows are also at the Z flashing. You can also see that I used upside down T1-11 to cover the bottom of the overhang.
Looks great. Whats the purpose of covering the bottom of the overhang here?
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ICC
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# Posted: 12 Jan 2025 12:52pm - Edited by: ICC
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Quoting: JD0 You mention doing twin beams will change the requirements for the loft joists. What do you mean by that? With two beams, would the joists now have to support the entire span vs being able to use the interior wall to bear the load? I guess that would make sense, since you would want that weight to have a direct path to the foundation vs over a floor joist.
That is pretty much what I meant. I am not an engineer, but if a more or less mid-span wall was inserted under the loft joists I believe that would create a point load on each main floor joist. I think that is where an engineer's expertise enters the planning.
My quick calcs with a triangle calculator make me wonder about the roof pitch combined with the desire for a loft. Using 18 ft as the width and a 6/12 (26.6 degree) pitch the height of the rafter triangle looks to be about 4.5 feet. Roughly.
With 8/12 (33.7 degrees) the height is about 6 feet.
With either it seems that anyone up there is going to be stooped over or crawling unless they are laying down.
Not to mention my main dislike for lofts; it is always warmer/hotter up there than on the main level. But that is just me and my thought about a loft.
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Brettny
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# Posted: 12 Jan 2025 04:09pm
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Quoting: JD0 Looks great. Whats the purpose of covering the bottom of the overhang here?
Keeps mice out and seals things up. I have no blocking at the top of the walls. This does the same thing but wat easier to install.
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JD0
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# Posted: 13 Jan 2025 09:49am
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Quoting: ICC My quick calcs with a triangle calculator make me wonder about the roof pitch combined with the desire for a loft.
Yeah, actually it's only around 5 ft with an 8/12 pitch once you factor the width of the rafters and floor joists. I am with you on the general discomfort of lofts. In the first place I built I had designed the main sleeping area as a loft, and it was much smaller and only gave me maybe 3 or 3.5 feet of headroom up there. Many nights in the summer the heat was pretty miserable, but with the window open and a fan running it was tolerable. I would never build a place with the intention of always sleeping in a loft unless I really had to, and with more attention to air circulation and ventilation.
My intentions here aren't to make it a primary sleeping spot, just some extra space to have guests, and only if it's preferable to sleeping in the living room. Even if it ends up being mostly storage and seldom used to sleep in, it's a pretty minimal investment for the extra space. I guess I just can't think of a better way to use the space since I don't really care for the entire cabin to be open. It would be great to have a 12/12 pitch and make it more liveable up there, but...heights aren't my thing and I don't know if I see myself willingly working on a roof that steep.
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JD0
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# Posted: 13 Jan 2025 09:49am
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Quoting: Brettny Keeps mice out and seals things up. I have no blocking at the top of the walls. This does the same thing but wat easier to install.
Ah, nice. Yeah, that does seem much easier than blocking.
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Grizzlyman
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# Posted: 13 Jan 2025 03:37pm - Edited by: Grizzlyman
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Quoting: JD0 It would be great to have a 12/12 pitch and make it more liveable up there, but...heights aren't my thing and I don't know if I see myself willingly working on a roof that steep.
I hear you there. It’s definitely a different ballgame when you have to ACTUALLY go up there. But. Keep in mind 12/12 is really no different than 8/12- you ain’t walking up there either way. If it were me and I was considering 8/12 I would just 12/12. Plus the snowload difference is significant- especially in the mountains- and especially when you’re not around to check in on the place. Adds a lot of peace of mind when you’re not there and headroom to the loft. Just my .02
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JD0
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# Posted: 14 Jan 2025 04:59pm
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You've got a point...I was thinking it would be easier to move around on an 8/12 (with a harness, of course), but you're probably right...either way it's going to be a slow process of repositioning ladders and equipment and not much freely walking around. I'll give that some thought and come up with a better plan
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JD0
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# Posted: 2 Mar 2025 09:13pm
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Thanks again to everyone for the help...planning to get building started next week. Earlier than planned but taking advantage of some unexpected time off work. Plans have changed slightly but not substantially - decided on 18x26 for the size, with a 16 ft loft.
A couple minor points...
For the roof I'm going to do 2 1" layers of polyiso over the OSB deck. On top of this I'll lay flat 2x4s horizontally every 24" and the metal will be screwed into the 2x4s. For securing the 2x4s I bought a case of 6" structural screws. They will be long enough (1.5" + 2" foam + 1/2" OSB leaves 2" to go into each rafter) and my thinking is that screws will be better since uplift forces should be more important than shear forces here. But is there any reason nails would be better for this?
30# tar paper will go over the 2x4s, directly under the metal panels, I'm thinking this will be the best place in case there is any condensation on the metal that would otherwise rot the 2x4s over time. Any reason for another barrier under the foam? Thinking it will be better to run the tar paper vertically.
I'll make another thread and share some pictures when I get some progress
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MtnDon
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# Posted: 2 Mar 2025 10:32pm - Edited by: MtnDon
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The structural screws will be better than nails in that application because of potential uplift forces.
FWIW, polyiso performance falls in colder and hotter temperatures. It is best around 75 F. In extremes it might be better to go with XPS as the extra R-value the polyiso can deliver will be reduced in the extremes. Something to think about.
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JD0
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# Posted: 3 Mar 2025 08:22am
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Thanks for the link, I didn't know this about polyiso. I can't find any specific numbers for the brand I'm using (Johns Manville) but it's good to know.
I think polyiso will still be marginally better since I don't plan on being there much when it's very cold (anything below 40F looks to be a slight advantage for XPS). There's no cost advantage for XPS for me...I think normally it's cheaper but for the brands I have access to, it is about the same. If I do end up spending alot of time there in the winter and the insulation isn't cutting it, at least I'll know why. I can always add something to the inside in the future.
As a side note, it seems sort of interesting to have an insulation product that drastically loses effectiveness in the extreme cold or heat- especially when that could be at least partially designed away with the use of different blowing agents. I'm sure there's a good reason, just seems odd.
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Grizzlyman
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# Posted: 3 Mar 2025 09:48pm
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JD0
Sounds great. Your roof sounds exactly like what I did. 6” structural screws through purlins and through foam into the rafter.
Food for thought. If you lay them(the 2x4s). horizontally (perpendicular to the rafters) they will block any airflow up the ridge.the only airflow is through the corrugation of the roof panels. If you put 2x4s vertically(parallel) it will allow airflow up and through any ridge venting. This will allow the roof to vent and airflow can dry things out if need be and prevent any rot.
You can just do one 2x4 directly on top of each rafter
The problem with this is that you need perpendicular purlins to affix the roof sheathing. For this reason I put a perpendicular board on top of the parallel board. This made a 2’ cross hatching with spacing underneath to allow airflow. I just used regular decking screws for this.
…But then with 2x4s as the purlins you’re creating 2 layers of 2x4s laid flat… a 3” space underneath the tin- which is just inviting animals to nest (especially if you’re not around all that often.).
I did mine with 1x4’s so there’s only a 1.5” space underneath. . True squirrels or mice need less space than that but it is a smaller target.
So far I’ve had 3 summers and no pests in the roof…. And we have a buttload of red squirrels.
I also put tarpaper under the foam instead of under the steel. Not sure if this was the best way to do it or not but I figured the foam wasn’t going to rot if it got wet. And I’d rather have the last line of defense directly on the roof sheathing.
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Brettny
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# Posted: 3 Mar 2025 11:13pm
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I did 4in polyiso In between my 2x10 rafters. Took forever and I used a ton of caned foam to seal around every piece. I was paying about $12 (2023 price) per 4x4' piece of polyiso. It was scrap so the 4in wasn't exact, some was 3.75 and 4.25. Because of this putting above the rafters wouldnt work. I used no plywood on the roof and rough cut 1x4 perlins.
Seeing how tar paper deteriorates I wouldnt use that stuff under a metal roof. Synthetic underlayment is prety cheap now.
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gcrank1
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# Posted: 4 Mar 2025 07:38am
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I agree, use a syn membrane up top
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JD0
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# Posted: 5 Mar 2025 10:26am
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I hear ya guys on using synthetic. I don't know why, I just always used regular tar paper/roofing felt for everything....I'll look into switching to synthetic.
Grizzly, thanks for the perspective on that...I had thought about that and was wondering if what I'm doing is going to work- having adequate airflow under there is important to me since I've seen how bad a metal roof can drip in the winter.
Wouldn't there still be some airflow to dry things out if the purlins went horizontal though? Is it common practice to install ridge venting on a metal roof in this application? I'll admit I've never installed a ridge vent with metal roofing before, but then again I've always installed metal directly on the roof deck so it wouldn't do much anyways
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Grizzlyman
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# Posted: 5 Mar 2025 04:12pm
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I don’t know about ridge vents per se on a steel roof… don’t know if that’s a thing.. maybe it is….but typically there is a gap created where the horizontal ridge cap meets the vertical corrugations. You can either buy shaped foam solid blocking to block this or they do make a vented blocking as well to allow air flow while keeping pests out.
My thought was that if I simply install horizontal purlins then there’s only a small space through which the roof can take in air…And I wanted to have more airflow. I didn’t think the corrugations themselves would provide enough venting. True it’s just the corrugations at the top that allow venting but like a jet engine I figured a bigger intake is probably better. I thought the 1x’s were a nice compromise over 1.5x dimensional lumber.
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gcrank1
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# Posted: 5 Mar 2025 05:37pm
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Imo doing the 'crosshatch', even with 1x, will provide enough air flow even though it isn't a straight shot up.
As to a cap, I seem to remember seeing a ridge foam to go under the cap but who knows lifespan as foam deteriorates and aggressive bugs and critters like to chew. A real wire mesh you could count on.
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Malamute
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# Posted: 7 Mar 2025 10:06pm - Edited by: Malamute
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Several points.
I skimmed some of this,...but dont guess on frostline depth. Im several hundred miles farther north, footers/foundations here need to be 4 ft below grade. Water lines need to be 6 ft. Find out whats required at your location.
ive used the bigfoot footers with sonotubes, they are cones made by sonotube, cut to correct diameter (they are stepped to work with various diameter tubes,and at least 2 sizes depending on tube size and expected load) screw them onto the bottom of the tubes, backfill, and pour concrete. Simple, fast, dont shift sideways or pull out in 130 mph winds. You can drop several sticks of rebar in them once poured, or make a cage of rebar if you want before pouring.
I dont think theres any way to auger and get a good footer under the tubes. Backhoe or mini excavator should work well. The ground is so heavily rocky where I am I dont think an auger would work in any event. Check your area if you intend to use one. Hand digging is a brutal exercise in breaking up a few inches with pick at first, then heavy digging bar once down a ways, cleaning out the loose stuff with shovel. Ive hand dug fence post holes, posts being power poles set 4 ft deep. Quite brutal.
Ridge vents work well with versa vent for ridge cap, the air comes under the sheathing, leave a gap of a couple inches at the top. Insulation between rafters needs to be the C type with a gap, or blocked to give free air space, or the ceiling insulated. Eaves vented with strip or round vents or facia with stepped facia and hidden edge venting works ok.
Br sure the roof insulation doesnt block air flow at the wall, use the durovent type styrofoam channels if need be to keep them from getting blocked there.
Instead of a door on a side wall and adding a porch to cover it, likely involving a pitch break in the roofing, if you extend the roof on one end 6-8 ft it gives a protected porch with simplified roof over the door, and more outdoor living space under cover to enjoy the rain etc.
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neb
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# Posted: 8 Mar 2025 09:43am
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Great advice Malamute. Good to hear from you.
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gcrank1
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# Posted: 8 Mar 2025 10:04am
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We have the door end overhang on our new cabin, it is GREAT. Ours is 5', I wouldnt really want shorter because rain doesn't often come straight down.
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