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Small Cabin Forum / Cabin Construction / are 2" x 6" enough for 14' gambrel roof?
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carlveil
Member
# Posted: 5 Nov 2021 15:23
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are 2" x 6" enough for 14' gambrel roof? It's not for the cost but rather for the weight.

WILL1E
Moderator
# Posted: 5 Nov 2021 15:25
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Depends on which lumber you use and what your snowload, if any, requirements are.

carlveil
Member
# Posted: 5 Nov 2021 15:28
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Quoting: WILL1E
Depends on which lumber you use and what your snowload, if any, requirements are.


Sorry, ground snowload is 46 and would use standard hardware store spruce and fir.

Brettny
Member
# Posted: 5 Nov 2021 15:33
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Why gambrel a 14' wide building? Typicaly this is done for head room and with 14' wide you would have 7ft from the level of the top plate to the peak of the roof. Then you subtract the height of the rafters and height of the floor joists. Your not left with much if your putting the floor joists on the top plate.

With 14' wide you can do a steep roof with normal box store lumber with out much trouble.

carlveil
Member
# Posted: 5 Nov 2021 15:49
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Quoting: Brettny
Why gambrel a 14' wide building?

I need to keep it under a certain height so gambrel would be ideal for me.
I'm not sure for the snow load, i'm in Qu├ębec Canada and it seems to be 3.6kpa in metric, is it possible it is over 70psf?

travellerw
Member
# Posted: 5 Nov 2021 17:12
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No.. Not if you want to vent it and still have room for insulation.. A minimum 2x8 is required for that.

I think a 2x6 has enough structural strength, but not enough depth. If you want to use 2X6 and then extend underneath with tacked on 2x2 to gain the depth that could work. However, I would check with an engineer to make sure you would have the strength.

While I agree the weight is a big factor as your completed trusses will be like 75 lbs or more with a 2x8. Equipment makes things WAY easier even with lighter trusses. A picker truck or towable man lift, makes the job super easy for one person!

carlveil
Member
# Posted: 5 Nov 2021 17:32
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Quoting: travellerw
No.. Not if you want to vent it and still have room for insulation.. A minimum 2x8 is required for that.

Hi travellerw, i was hoping you'd chime in. I didn't mention that i will be sheathing with tongue and groove and insulating from the top with foam panels so the rafters will be exposed. So i don't need space for insulation, but if 2 x 6's is not enough then i will go for 2 x 8's like you did.

travellerw
Member
# Posted: 6 Nov 2021 01:29
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Quoting: carlveil
Hi travellerw, i was hoping you'd chime in. I didn't mention that i will be sheathing with tongue and groove and insulating from the top with foam panels so the rafters will be exposed. So i don't need space for insulation, but if 2 x 6's is not enough then i will go for 2 x 8's like you did


That would be super cool.. Open rafters and insulated on the outside..

I'm actually out at my cabin so I have limited access.. I will look into some span tables when I'm back.

However, one comment I have.. Some areas have a minimum code on R value in roof. R30 is required to pass in a ton of places. If you are getting it inspected, makes sure you can meet that with foam.

carlveil
Member
# Posted: 6 Nov 2021 07:13
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Quoting: travellerw
However, one comment I have.. Some areas have a minimum code on R value in roof. R30 is required to pass in a ton of places. If you are getting it inspected, makes sure you can meet that with foam.

No inspections here, officially it's a shed/garage.
https://www.youtube.com/watch?v=_ib0YRE-PMI
I'm planning to do something like that for the insulation.

travellerw
Member
# Posted: 7 Nov 2021 18:55
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Quoting: carlveil
No inspections here, officially it's a shed/garage.
https://www.youtube.com/watch?v=_ib0YRE-PMI
I'm planning to do something like that for the insulation.


That is exactly how I'm insulating my floor.. 2 inches of foam, then 5/8 tongue and groove over it..

WILL1E
Moderator
# Posted: 9 Nov 2021 08:37
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It might be because i'm still fresh off of my build yet, but i don't think i would ever do a gamrbel roof again. And i'm 6'5" and i need the head room in the loft. It's overly complex for the benefits you get. Have you thought about just doing taller exterior walls and then a standard gable roof? But if you have others helping or have equipment like Travellerw mentioned, then life might be a little easier.

travellerw
Member
# Posted: 9 Nov 2021 10:55
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I will disagree with Will1E on this one.. I think the Gambrel roof has a ton of benefits (not to mention character). Is it more difficult and more work, yep.

You have all the same drawbacks with an A-frame roof if you do a loft. You still need to insulate and vent it, thus 2X8s or joist extensions. To do a loft in an A-Frame you have to have such a steep pitch to get head room that roofing it becomes a real problem. Taller walls and a dropped loft won't pass code in many areas (A-frame roofs have more push out). Stair configurations would be super limited in an A-Frame (most likely switch back required in the centre of the building), or a ladder!

I'm not sure how I feel about insulating on the outside and leaving the inside open. Either way you are working at heights to insulate, however on the outside you could use equipment easier. You sheathing costs will be over double and I worry that if you use no wood between the sheets, you could have a blow off issue in high wind. You would also need to take a lot of care when making the gambrel roof members if they are going to show. The plywood gussets at each hip aren't the prettiest to look at. You would probably have to step up to sanded one side ply.

On the plus side.. No worrying about interior ceiling finish (however, a definite fire code violation).

Its a novel idea, but I don't think I would take the gamble on it. I'm not getting anything inspected either, but I stuck to code everywhere.

carlveil
Member
# Posted: 9 Nov 2021 11:12
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Quoting: WILL1E
Have you thought about just doing taller exterior walls and then a standard gable roof?

I did think about it, it was my initial idea but like travelerw said, to much height for same headroom and steeper roof. Anyways, i already cut my rafters yesterday. As for insulating from outside, that is the plan for now but could change. I used 2 x 8's so plenty of room to do it from the inside.

carlveil
Member
# Posted: 9 Nov 2021 11:13
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Rafters
IMG_20211107_1621443.jpg
IMG_20211107_1621443.jpg


carlveil
Member
# Posted: 9 Nov 2021 11:24
Reply 


Quoting: travellerw
The plywood gussets at each hip aren't the prettiest to look at. You would probably have to step up to sanded one side ply.

Definitly a challenge There. About costs, i think it wouldn't be much more. Tongue and groove over the rafters, membrane,1 1/2" foam, 2x4's flat vertically every 2' with 1" foam in between then furring strips horizontally and metal roofing. Anyways this will be for another thread.
IMG_20211107_1621513.jpg
IMG_20211107_1621513.jpg


travellerw
Member
# Posted: 9 Nov 2021 13:18
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Quoting: carlveil

Rafters
IMG_20211107_1621443.jpg
IMG_20211107_1621443.jpg

Looks great..

When its time to assemble make a jig on the floor on sheet material. Make sure your jig keeps the rafter legs secure AND THE PLYWOOD ON BOTH SIDES AT THE HIPS. (I did not do that and every piece of plywood at every hip is just slightly set different. Its hard to see with the eyeball, but if you put a straight edge on them its very clear.)

Mark the lower legs (left and right)! When putting them up ALWAYS keep left and right to the same side of the cabin. No matter how well you build your jig there will be small variances between the sides. Doing that will make all the rafters on one side the same and you won't see it.

I'll be interested to see your results.. Its kinda like a SIP panel construction with rafters below.

(as an aside, I have been researching glue for foam as I want to make a laminate sandwich for the floor. Great stuff pro construction adhesive is the winner. Its bond is insanely strong.)

Brettny
Member
# Posted: 10 Nov 2021 05:48
Reply 


If total height is the limiting factor a gambrel roof or a second story with a flat roof is really the only two options if you want an upper floor. We all know a flat roof will or has alreaty leaked.

Tallguy
Member
# Posted: 8 Dec 2022 06:29
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I am planning a summer cabin in Vermont. Very basic 20x32 gambrel. I plan on a long steep pitch part and a short shallow pitch part. Hoping to do metal roofing over purlins. I need to plan for a 70lb snow load. Assuming 16 spacing, will 2x6s cut it, or should I do 2x8s. Insulation is not a concern as we will only use it in July and August.

curious
Member
# Posted: 8 Dec 2022 13:58
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It would be the connections at the joints that make the gambrel shape that would concern me most.

Brettny
Member
# Posted: 9 Dec 2022 07:18
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Thata where plywood gussts typicaly go. You can also add strength by adding a horizontal 2x6/8/10 at the lower two joints. Then the loft floor joists would tie the walls and rafters together. All need to be proper thickness lumber.

Brettny
Member
# Posted: 9 Dec 2022 07:20
Reply 


Quoting: Tallguy
will 2x6s cut it,

Not a chance for a 20' building. Shooting from the hip with that snow load I would be useing 2x12. I'm sure theres a calculator to figure this all out.

ICC
Member
# Posted: 9 Dec 2022 14:53
Reply 


The wider 2x's will enable the use of much larger gussets. A good idea IMO.

Factory built trusses will usually be built with MSR lumber, not common #2 stuff like most diy will use.. with MSR each stick is first visually graded and then tested for bending by a calibrated machine. There are about a dozen grades so the engineers can carefully spec the design depending on what the truss factory has access to

Machine Stress Rated

Aklogcabin
Member
# Posted: 10 Dec 2022 12:05
Reply 


Around here the lumber for trusses is the same stuff from the lumber yard. Actually the lumber for the local truss plants sits out in the yard

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