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WILL1E
Moderator
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# Posted: 5 Aug 2021 07:57am
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My plan if i go the gambrel route was to make separate rafter tails. This way i can have the rafter ends terminate fully on the top plate (gives me the warm and fuzzies structure wise). This gives more options on looks, angles, etc. plus gives more room to get the baffles in and more area to either do vent holes or a screen on the soffit end.
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Brettny
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# Posted: 5 Aug 2021 11:19am
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Why vent it at all? Spray foam directly on the bottom of the roof/plywood.
I also did separate rafter tails(for a lack of a better word) it was very easy doing it after, it also help use up some scrap. This was on a 19' wide shed though.
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travellerw
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# Posted: 5 Aug 2021 01:23pm
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Quoting: Brettny Why vent it at all? Spray foam directly on the bottom of the roof/plywood.
Middle of nowhere so I can't get a spray foam company in there. Not to mention spray foam is WAY WAY out of my budget up here (even in a big city). I have no interest in messing with the DIY stuff.
Traditional insulation techniques are really my only option.
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travellerw
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# Posted: 5 Aug 2021 01:24pm
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Quoting: WILL1E My plan if i go the gambrel route was to make separate rafter tails.
I have looked at that... but I'm not to excited by another change in the roof angle. It complicates roofing materials and introduces a possible leak or ice damn location.
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travellerw
Member
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# Posted: 30 Aug 2021 12:14pm
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Well, we have begun to move forward and things are coming along nicely. Hope to get it buttoned up before the snow flies.
I decided on a gambrel roof with a 2.5" overhang (no different than a birds mouth). I will make that a soffit with a ridge vent at the top. I will then "baffle" the rafter bays with 1/2 foam all the way to the top (there is a trick used up here, I will post details later). The remainder of the bays depth will be filed with batt insulation. The gambrel gives me excellent head room, but makes for a pretty tall building (28ft at the peak).
We will do a 1/2 loft. We beefed up the top plate to 3 laminated 2x6s (glued, nailed and screwed). We will then use 2 316 stainless cables spaced out in the open area to hold things together and counter "kick-out"!
Its been a fun project so far (if a little expensive with material costs these days).
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snobdds
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# Posted: 30 Aug 2021 07:10pm
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Why did you put the plywood on like that. It takes all the sheer strength out of the walls?
28 feet is one tall building. Almost too tall for ladders, are you going to bring in some scaffolding?
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travellerw
Member
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# Posted: 30 Aug 2021 11:40pm
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Interesting you said that.. An engineer I talked with said it does not matter with OSB the direction its installed. The strands in the boards are placed randomly and it has the same strength in either direction.
I decided on this orientation as it was easier with 10ft walls and the crew I'm working with (kids and a wife). We didn't have to use ladders for these initial boards. We could hang them with fasteners half way up, then I did all the high up work. The last portion is about 12 feet off the ground and will be done from an 8ft scaffold.
Sorry, I mistyped.. I meant 18ft at the peak (from the floor), 20-21 ft from the ground. However, we will still be working off scaffold.
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Brettny
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# Posted: 31 Aug 2021 06:04am
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That is going to be tall. 10ft walls too?
Usualy people put the OSB on flipped 180* so the lines are on the outside. Even if they dont fall on a stud it gives you a line to follow when you do find the stud.
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toyota_mdt_tech
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# Posted: 31 Aug 2021 08:19am
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I'd of put the OSB down over the rim joist. Actually, I would never use OSB, plywood, but its just my preference. I actually cant stand OSB.
Laid sideways would of gotten rid of the full length seam, and makes it easier to install, working bottom row at ground level, then following rows, the lower section holds the next section in place, stagger to get rid of long seam/breaks.
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ICC
Member
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# Posted: 31 Aug 2021 08:39am - Edited by: ICC
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Panels are available in longer lengths but not at big box stores. I've used lots of 9 and 10 foot sheets. Overlapping the rim is very good.
Where you have a seam there should be a 2x nailer on the inside. Panels need to be nailed all around the perimeter for shear strength.
One other thing to keep in mind when using partial panels is to try and keep the smallest width to 24" or more if possible.
Staggering the joints is always a good idea; walls, floors, roofs. That adds to shear strength.
Be sure to leaves gaps at panel edges.
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snobdds
Member
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# Posted: 31 Aug 2021 11:24am
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Quoting: travellerw Interesting you said that.. An engineer I talked with said it does not matter with OSB the direction its installed. The strands in the boards are placed randomly and it has the same strength in either direction.
The reason you put the sheeting goods on horizontally is due to shear strength, or to prevent the walls from moving side to side. Instead of spanning 4 studs, it spans 6 studs which locks in more studs on one sheet.
I also understand why you had to do what you had to do. For a small cabin, it should be fine.
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travellerw
Member
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# Posted: 31 Aug 2021 01:53pm
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Quoting: snobdds The reason you put the sheeting goods on horizontally is due to shear strength, or to prevent the walls from moving side to side. Instead of spanning 4 studs, it spans 6 studs which locks in more studs on one sheet.
This post has already taken a turn on how to sheet, and I don't want to take it further, but a quick google "Sheathing horizontal or vertical" will show that it makes no difference on a wall. Around here OSB sheets are sold with the markings going in both directions and its very common to see builders of big houses installing sheets vertical.
Lets just say there were "reasons" for each decision (not sheeting the rim, flipping the boards, horizontal, 8ft OSB sheets, ect).
I have begun working on the roof trusses here in the city. My plan is to manufacture all 22 here and then haul them on a trailer the 2 hours to the site.
I have setup a jig on my garage floor to make each truss as close to identical as possible. I used the blocklayer.com website to figure out the lengths and angles BUT I will warn others, the website has some bugs in the calculations. The centre height is definitely calculated wrong. I verified ALL my measurements and angles and my centre height is about 5" higher than the websites calculated height. At least one other blog I read found issues too and he suggested using sketup instead.
Anyway, I decided on a slightly different sweep angle to reduce waste. The uppers are 5ft so I can use 10ft OSB sheets for no waste. The lowers are 7'10' (ish) leaving only 2 inches of waste.
I have had a rethink and will probably be creating rafter tails. It dawned on me that with only a 2" overhang much of the watershed will be right on the foundation. Kicking out 1ft should really reduce that, but I'm sure I will be swearing when putting on the metal roof (extra pieces.. extra sealant.. extra costs and stuff is SUPER expensive these days).
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ICC
Member
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# Posted: 31 Aug 2021 03:13pm - Edited by: ICC
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Quoting: travellerw a quick google "Sheathing horizontal or vertical" will show that it makes no difference on a wall.
For that to be correct, all the panel edges need to be nailed to a 2x piece of framing. That requires blocking. For that reason most wall sheathing is done with vertically placed panels. Longer panels where needed. That saves on the labor more than on materials usually. Be
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Brettny
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# Posted: 31 Aug 2021 03:40pm
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Laying all the trusses out on the garage floor and making them all the same in an assembly line fashion and towing then 2hrs away is going to be far easier than making them in place. When you put them in place run a string line from front to back and at the peak to keep things all inline.
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snobdds
Member
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# Posted: 31 Aug 2021 03:53pm
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I make one rafter that is perfect. Then I take that one rafter and use that as the template for each one. Then you know they will all be the same and the roof looks straight and level.
Make the template at the cabin on the actual structure. I tried an online calculator and compared the rafter to the actual one used. The two were different enough to make the online calculator one useless. I have been wary of those things ever since.
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ICC
Member
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# Posted: 31 Aug 2021 04:54pm
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Quoting: snobdds Make the template at the cabin on the actual structure.
I second that. Experience speaking.
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travellerw
Member
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# Posted: 31 Aug 2021 05:19pm
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With the distance I am from the site, making a template at the site is going to be problematic.. Trucking it back and forth isn't really an option.
The only real measurement that seems to count is the inside measurement between the lowers of the rafters. As long as that measurement is the same on all the rafters and matches that of the distance between the top plates, everything should work fine... No?
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Brettny
Member
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# Posted: 1 Sep 2021 05:41am
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Quoting: travellerw The only real measurement that seems to count is the inside measurement between the lowers of the rafters. As long as that measurement is the same on all the rafters and matches that of the distance between the top plates, everything should work fine... No
Essentially yes. As long as your walls are level and square to each other. Did you measure diagonal across the top plates corner to corner?
If your putting on a lower gabel (kick out) and doing it after the trusses are up you have a good amount of fudge factor. Like the trusses put each end up and run a string line to follow.
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travellerw
Member
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# Posted: 1 Sep 2021 01:09pm
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Yes.. Measured between top plates at multiple locations. Then corner to corner and was out 1/2 inch.. Thought that was pretty good over 16X28.
I will do rafter tails, but I'm more concerned on the inside. If I make the rafters distance between lowers too short, then it will overhang inside and make drywalling a PIA.
Anyway, gonna be a busy week building stuff. I went to buy fasteners and was shocked when it turns out I will need 1200 for just the rafters.. That is insane.
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travellerw
Member
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# Posted: 6 Sep 2021 11:20pm
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Well its moving along and things worked out building the joists in the garage.. Sigh, however, even though we used a jig it quickly became apparent that the right and left of the joists were just slightly different. So that meant that the right side of every joist had to go to the west. If you flipped them, things were just a tiny bit out and it was clear the inside ceiling would be very "wavy". Sigh, 2 joists had to come back down and be flipped.
Unfortunately I didn't get as much done as I hoped. I lost 2 of my helpers to a COVID infection and had to scramble to find others. We only got up 14 out of 22 joists this weekend.
I may have lined up a picker truck for next weekend, so we should be able to finish the joists and sheathing in one go.
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WILL1E
Moderator
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# Posted: 7 Sep 2021 08:57am - Edited by: WILL1E
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travellerw couple questions for you:
1. What size joist did you use in your floor?
2. Any bounce in the middle with only 2 beams?
3. How are you securing your rafters to the top plate both as you are building and for final?
4. What are you doing on your gable ends for the overhang?
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travellerw
Member
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# Posted: 7 Sep 2021 01:05pm - Edited by: travellerw
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1. I used 2X10s with a 6 inch cantilever over the main beams. This is code according to the span tables I have seen.
2. Very little bounce. If you jump up and down (I'm 220lbs), there is a small amount of bounce. None with just walking.
3. Rafters are secured to the top plate with hurricane clips, then 4 toe nails and 1 toe screw (for final). For getting them up quickly we used just the toe screw (came back later in the day and added the other attachments).
4. Unsure at this point. Many builds don't do an overhang, some do. I'm thinking of overhanging the sheathing 6 inches then coming back and building a 2x4 eave later. However its pretty damn tall and will be a pain to do that.
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WILL1E
Moderator
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# Posted: 7 Sep 2021 01:19pm
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Thanks for the info!
How wide are your gussets?
Are they on both sides of the rafters?
How did you nail the rafter sections and gussets?
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travellerw
Member
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# Posted: 7 Sep 2021 07:11pm
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Gussets are 24 inches and on both sides of the rafters. They are made out of 3/4" floor grade OSB.
I choose structural screws and glue (PL) to attach the gussets. The screws are rated at 90lbs/screw and each gusset pair has 20 screws (12 on one side and 8 on the other) the screws are long enough to go into the gusset on the other side. (if you choose nails, you NEED a nail gun as hammering 1200 nails is gonna kick your butt).
If you are thinking of doing something similar, then it may be important to understand the scope of work. Those rafters took 3 people (myself, my wife and my teen) about 30 hours to manufacture in the garage. A bunch of it was planning and laying out the jig, then its just boring monotonous assembly work. Once manufactured, they required a 14ftX8 foot trailer rated at 3500 pounds to transport on site (with tons of straps and flags). Actual unloading and installation of the 14 we have up took 4 people about 16 hours (including the screw up and reinstalling some).
I'm guessing once the shell is up, it will be close to 250 man hours of work! Just some information to help you plan!
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carlveil
Member
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# Posted: 30 Oct 2021 01:29pm
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I'm doing gambrel too, on a 14' x 24'. I see that your lower rafters are longer than the upper. can you tell us what lenght and angles you used? I was going to do same lenght for both but if i can get more headroom that would be nice.
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travellerw
Member
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# Posted: 30 Oct 2021 06:56pm - Edited by: travellerw
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I used block layer until I found a roof I liked and it seemed right. Then I went with that.. However, be careful with blocklayer as it has bugs and sometimes the measurements dont' work. You need to build one truss and make sure it works.
By making the uppers smaller, you reduce the snow load, but increase the push out. I think I found an excellent balance.
I don't have the exact angles on me right now. I will dig them up and post them later. However the uppers are 5ft (ish) and the lowers are 8ft (ish)
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travellerw
Member
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# Posted: 31 Oct 2021 04:07pm - Edited by: travellerw
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Here is an image of the dimensions and angles.
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