Small Cabin

# Posted: 11 Nov 2022 11:41am
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I'm also going to build a 20' wide gambrel roof. We are going to do 2x12 framing for the roof to get the proper R value. I'm also useing the floor joists to tie the walls together along with a horizontal 2x6 at about 7' above the loft floor joists to help hold things together. We are also going to screw and glue plywood gussets on each junction of the truss. I'm cutting no birds mouth in the trusses and am going to make a lower gambrel to keep the drip line away from the building. With the pic shown I should have about a 12' wide area that's 6' or higher above the floor joists.

I'm not sure what the first or second link is showing and your blocklayer.com link dosnt show what you input. You need to take a screen shot and post it for that to work.

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Steve_S
Member

# Posted: 11 Nov 2022 12:24pm
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Blocklayer can output PDF with the info & design.

There are MANY Gambrel Roofed buildings here (region) and a common Gotcha is that there is little to no Eaves which result in several issues. When considering the JLConline info, it is more appropriate in general WITH eaves extensions added.

# Posted: 11 Nov 2022 01:46pm - Edited by: jbirdmotox
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Thanks guys! Few more details

Thanks Brettny for the pic of your design.
I also will be tying the trusses into the 12" oc 2x12 floor joists already installed. No birds mouth either.

1st link is showing a gusset design for a 22' span by an architect.

2nd link shows detailed braced truss design for a 20' span using 2x6.

With blocklayer I wasn't really trying to show my proposed design. I'm just unsure what size rafters/gussets I need minimum for 20' (but obviously still rugged). 2x6? 2x8? Bigger?

Playing around with www.opticutter.com it seems 40" gussets get the most out of a sheet of plywood (7 per sheet). Smaller still only yields 7.

For insulation I'm leaning towards unvented with spray foam.

Steve_S
Deff planning on adding 12"-16" eaves to whatever design. Want to keep water away from the building.

# Posted: 13 Nov 2022 07:35am
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Quoting: Steve_S

There are MANY Gambrel Roofed buildings here (region) and a common Gotcha is that there is little to no Eaves which result in several issues. When considering the JLConline info, it is more appropriate in general WITH eaves extensions added.

That got ya issue of no overhangs is prety easy to fix. This is how I did my 19' wide shed. Its only rough cut 2x6 but able to hold about 900sqft of 1in ash boards drying for flooring. It's a pile of stickered wood about 4ftx5ftx9ft. I have a center wall under 2x8 floor joists there. It is just a shed though.

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# Posted: 14 Nov 2022 10:28pm
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Built something very similar to W1llie. If you search my username there are quite a few posts with pics. We are 16X24. Manufactured all the trusses in my garage, then trailed them to site (as building onsite would have been near impossible). Trusses are 2X8 screwed and glued. We used foam insulation to create a 1 inch channel in each truss bay, then put fiberglass insulation in the remainder. We have stayed in there at -40C and were able to easily maintain +20C with our wood stove (it would be about R25 in the roof). We were also out there this summer at +34C and the cabin was pleasant.

Five things I learned. First if you build offsite, you need to ensure you mark all sides of the truss. They must all go up exactly the same or you will have a wavy roof.

Second, Bricklayer is not without bugs and will put out PDFs that aren't right. Measure, plan and ensure things are right before starting construction.

I will NEVER use PL400 or Polyurethane glues again. Its cheap, but the bond is not great (based on the trusses I pulled apart). Foam based glues (like Great Stuff pro) are the future. They bond WAY better and are easier to use (with the right tools).

2X8s are heavy. The completed trusses were a nightmare to put up. My brother and I aren't small (both over 6ft and weigh just over 200lbs), but the trusses were almost at the limit of safely handling. We got 1/2 up and then brought a picker truck for the other 1/2. It was WAY safer and easier.

20+ feet is high! Higher than most people are comfortable working at. Gambrel roofs are also steep and not conducive to working on without experience or equipment. I tried sheathing and gave up. I ended up renting a lift to finish the sheathing and metal roofing. Personally, I could not have done it any other way!

Good luck.. We absolutely love our cabin. That high soaring roof is lovely inside!

# Posted: 15 Nov 2022 08:23am
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Did you have your loft subfloor up before putting trusses up?

# Posted: 15 Nov 2022 08:53am
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Thanks travellerw.
I have a complete 2nd story subfloor installed so hoping truss assembly and standing them up won't be too bad using the 2nd floor deck. I was planning on using PL400 so I'll check out alternatives.
Sheathing is one thing I'm NOT looking forward to. I know it's going to be painful.
I have moved all materials by pontoon boat or snowmobile so any sort of lift is out of the question for me.

# Posted: 15 Nov 2022 10:01am
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Quoting: Brettny

Did you have your loft subfloor up before putting trusses up?

Back then our loft was 1/2 the building. So those are the trusses we put up before using a picker truck. Even then, they are top heavy which makes them hard to handle. Getting them in place, then holding them in place, while trying to screw them to temporary perlins all the while ensuring things are square was a PIA. Our trusses are only 2X8.

As to sheathing, I could have built some temporary supports and got the sheathing done. The metal roofing is another story. I'm not sure how I would have done it without a lift.

# Posted: 16 Nov 2022 06:16am
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Dont sheeth it at all. Use perlins. If you really feel the need to sheeth it you could just do the top or side section of roof. If I was pulling all the materials out via boat/sled theres no way I would be useing sheet goods for under a metal roof. If your worried about racking you can buy rolls of metal strapping and cross your walls/roof with it. Simpson strong tie makes a metal strap just for this.

Useing perkins is still within most all metal roof manufacturers specs.

# Posted: 16 Nov 2022 04:03pm
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What about if I didn't do spray foam? You and travellerw got me thinking about using deeper trusses and fiberglass insulation. I know a metal roof can sweat like crazy.
I see the live edge siding on your shed and doing the same. Got maybe 25% milled so far. I have already felled, milled, and trucked all the framing lumber 4+ hours to the boat launch. Then it's boat/sled. Why stop now?

No one has ever accused me of being smart.

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# Posted: 17 Nov 2022 05:34am
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I plan on doing 2in foamboard above the trusses and below the perlins. I want a good thermal break. Then I will fill the rest with fiberglass. Technically it's still not enough R value for my area.

With solely fiberglass or rock wool you need to vent the roof alot and in trying to avoid that because of issues I have had with a shingle roof. Metal is just far worse.

# Posted: 17 Nov 2022 08:53am - Edited by: jbirdmotox
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I'm in zone 6 so never going to get the R value without going crazy. Camp will only be used 3-4 times for short 2-3 night stays in the winter.
Cost is going to be waaaay too expensive for DIY spray foam. Even just 2" would be around $2500. Then would still need some glass.

Need to do something that is "good enough".

# Posted: 17 Nov 2022 01:35pm
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We did 3/4" airgap (under sheathing), 3/4" of foam and then 5.5" of pink fiberglass. Walls are 5.5" of pink. Then well sealed vapor barrier. We also have 2 inches of foam over the main subfloor with another 5/8" sheathing over that.

Does it meet code, nope! It would be near impossible to meet code here with a Gambrel roof. R60 requires a lot of space.

Our wood stove has no problem keeping up in the coldest temps (below -30C). Actually it won't just keep up, it will cook you out if you keep feeding it.

I was going to do Rockwool, but I couldn't justify the cost for no insulating benefit. Sure its easier to install and not as itchy, but its really a one time job. Mast/suit and I was fine (even without a functioning shower).

gcrank1
Member

# Posted: 17 Nov 2022 04:01pm
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For over 30 years we had a 12 x 24 c/w 12 x 12 loft cabin in south central Wisconsin with no ceiling insulation, just the 1/2" CDX plywood topped with tar paper and bargain asphalt shingles. We used it in all seasons, heated with an antique upright woodstove I rebuilt. We did fine, lots of times in winter sitting around in t-shirt of an evening. Gettin cool?, throw another log in.
Not saying some insul between the rafters wouldnt have been a good thing (in our case that would have been <6"), but it never became a big enough issue to 'get around to it'.
Of course I didnt have to deal with code, inspection sign-off, etc.

# Posted: 17 Nov 2022 04:56pm
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Insulation under a metal roof isnt about code or how warm you will be. It's about how much condensation will form on the underside of the metal and cause mold or the wood to rot.

What the specific R value needed to not have condensation happen is I'm not sure.

# Posted: 18 Nov 2022 12:12pm
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Quoting: Brettny

Insulation under a metal roof isnt about code or how warm you will be. It's about how much condensation will form on the underside of the metal and cause mold or the wood to rot.

That is why you use new synthetic underlayment. Well that and because it stands up to the heat under the metal roof.

gcrank1
Member

# Posted: 18 Nov 2022 02:31pm
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Link to a product or product type?

# Posted: 18 Nov 2022 03:12pm
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Quoting: travellerw

That is why you use new synthetic underlayment. Well that and because it stands up to the heat under the metal roo

Air leaks that your going to have with batt insulation can cause condescension on even that. I have seen it on wood too.

# Posted: 19 Nov 2022 12:21pm
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Quoting: Brettny

Air leaks that your going to have with batt insulation can cause condescension on even that. I have seen it on wood too

That is what the vapor barrier is for, to stop the air leaks. We were super anal when we put it up and even taped the staples. Sealed all the junction boxes with Poly Hats and sealed the wire penetrations with acoustical sealant. Drywall, then mudded and taped seams over that. Essentially code here in Alberta.

That is also why there is an airgap under the sheathing which is open at the soffit and peak. If warm moist air actually makes it past all of that, it should rise out the peak. Even if it condenses on the underside of the sheathing, it should vent out once the roof warms.

As to the underlayment. I used a locally manufactured product BigFoot, but there are tons of synthetic underlayments made for metal roof. They all seem to be made from polyethylene, polyolefin, or polypropylene. No idea if they are all created equal though. I used the Bigfoot stuff as all the roofing companies around here seem to be using it now.

# Posted: 19 Nov 2022 07:00pm
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Appreciate all the input. A woodstove is in the plans as I have easy access to free wood.
At this point I'm planning on 2x8 rafter depth. Fully sheathed with 5/8 ply and full coverage ice/water shield. Then the metal over that. With R21 fiberglass I should get ~1.5"-2" of air gap for venting. Interior finish is a looong way off for me but with a sawmill and almost endless supply of white pine I'll do something with that.

# Posted: 20 Nov 2022 11:07am
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Are you going to use a ridge vent or gabel vent?

# Posted: 21 Nov 2022 08:39am - Edited by: jbirdmotox
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ridge vent with soffit venting

# Posted: 21 Nov 2022 01:53pm
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Those dont flow very well and if the ceiling is right up to the peak of the roof theres no plan B if you cant get ridge vents to work.