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Monopitch Roofs

April 11, 2020, 1:06 p.m.
Posts: 11905
Joined: June 4, 2008

I'm planning on building a 14'x16' workshop on four 6x6 skids.

I will be doing a monopitch roof.  This will be in Whistler, so we will have heavy, wet snow.  For those in the know, am I asking for trouble for just using say 2x10's every 12" on centre?  Or is this something that will need structural joists?

April 11, 2020, 2:18 p.m.
Posts: 2001
Joined: April 25, 2003

Ex carpenter here. I didn't design much on the job, but I was trained to. If you want to do this up to code, you'll need access to a BCBC 2018 and someone who knows how to read span tables. I don't have a copy any more so I can't help you there.

Additional info that you'll need:

- roof slope.

- roof sheathing material.

- Available material. For example, sometimes Doug Fir #1's are are to get locally in your size, so you'll have to design around what your local yard has, generally SPF #2's. Or you don't want to pay for Doug Fir, so you have to design around something else.

- Snow load for Whistler. That's in one of the appendices. (Appendix C; Table C-2?)

With this info you'll be able to use the tables to determine how big a span you can do with each material and size.

Looking at that drawing you'll need to add:

- Lintels over the doors and windows at the front walls to transfer the roof loads to the foundation.

- Hurricane clips on the roof joists to prevent wind uplift.

- Blocking between the roof joists

Notes:

- It's not necessarily "wrong" but I've never heard the term "monopitch roof" before. I'd call that a shed roof.

- What do you mean by "structural joists"?

Or you can just give it a go and if it sags put in a beam and posts at mid-span.


 Last edited by: tashi on April 11, 2020, 2:18 p.m., edited 1 time in total.
April 11, 2020, 3:26 p.m.
Posts: 899
Joined: March 15, 2013

Kind of off topic, but I made sooooo much money as a teen shoveling snow off houses with flat-ish roofs in coastal northern bc.

Food for thought.

April 11, 2020, 3:53 p.m.
Posts: 1637
Joined: Nov. 23, 2002

tashi has it right.  The size of your roof joists will depend on the slope of the roof and roof material,  personally I’d go at least 6/12 or higher. Based on the size of those openings you’ll want a 2x10 header (lintel) for sure. Steel roof would be great and let you get away with a lower pitch, asphalt shingles are cheaper but you’ll want a higher pitch, maybe 8/12 so it sheds the snow better. 

And yes, shed roof you numpty.

April 11, 2020, 6:37 p.m.
Posts: 11905
Joined: June 4, 2008

Thanks all. As has been guessed correctly, I am not a carpenter. (Good catches on the diagram, I just grabbed the first one I saw to give an impression of what I was going for).

I would like a super low pitch. 1.7143:12. (Why does the pitch end at 12?) Two foot rise, fourteen feet wide... 10 foot wall to 8 foot wall. Will be going for a metal roof.

Local Rona has Fir. Will be buying that.

tashi, the attached seems to be what I want.  It seems grade 2 Fir 2x10's at 12 inches apart will handle 3.0kPa across 14 feet.

April 11, 2020, 7:12 p.m.
Posts: 1637
Joined: Nov. 23, 2002

Pitch = rise/run in inches and there’s 12” in a foot which is why it’s measured in x/12. Your 1.7/12 is too low imo, it’s basically a flat roof. But as long as the structure is strong enough then give’r. 

Oh and you clear span will be a bit longer than 14 ft, but no enough to really make a difference.

April 11, 2020, 9:41 p.m.
Posts: 1455
Joined: Nov. 8, 2003

Just watched this whole 4 hour video on building sheds. Feeling ready. 

https://youtu.be/BLk_CAMmQPc

Right off the bat he recommends pouring a slab.

April 11, 2020, 10:15 p.m.
Posts: 11905
Joined: June 4, 2008

Definitely pouring a slab.

April 11, 2020, 11:11 p.m.
Posts: 2001
Joined: April 25, 2003

Clear span will be inside - inside dimension between the top plates, so if your shed is 14' to the outside of framing, your walls are 2x6 and sheathing is 1/2" than your span will be 13'.

I think that's the right table, as long as you're using the right table for your slope and the right snow load for Whistler.  9.23.14.10 seems to guide you to those tables.

I found this link to 9.23 of BCBC, the wood framing section. The info is there, if you can understand it. I had to help my wife out when she needed to use the BCBC for work and she's a government lawyer. It's clear as mud.

http://free.bcpublications.ca/civix/document/id/public/bcbc2018/bcbc_2018dbp9s923


 Last edited by: tashi on April 11, 2020, 11:23 p.m., edited 1 time in total.
April 11, 2020, 11:15 p.m.
Posts: 11905
Joined: June 4, 2008

LOL, thankfully it's finally all online now.

Thanks, will have a look!

April 11, 2020, 11:28 p.m.
Posts: 2001
Joined: April 25, 2003

I'll note that I wouldn't stand a chance of building that without permits in Victoria. Whistler may be a different story, good luck on that end! A proper foundation may be required.

The Full BCBC 2018


 Last edited by: tashi on April 11, 2020, 11:30 p.m., edited 1 time in total.
April 11, 2020, 11:51 p.m.
Posts: 11905
Joined: June 4, 2008

Posted by: tashi

I'll note that I wouldn't stand a chance of building that without permits in Victoria. Whistler may be a different story, good luck on that end! A proper foundation may be required.

The Full BCBC 2018

Not gonna lie, I'm quite shocked too.

Tell me, am I missing something here?

April 12, 2020, 12:42 a.m.
Posts: 1637
Joined: Nov. 23, 2002

That’s not really the shocking part. Basically you’re twice as big as you should be. Building that with permits will probably cost you $60k or more up there, especially if you want power in it.


 Last edited by: syncro on April 12, 2020, 12:45 a.m., edited 1 time in total.
April 12, 2020, 12:59 a.m.
Posts: 1637
Joined: Nov. 23, 2002

I say go for it without permits just so you can regale us with your harrowing story of dealing with RMOW afterwards

April 12, 2020, 1:05 a.m.
Posts: 11905
Joined: June 4, 2008

Posted by: syncro

That’s not really the shocking part. Basically you’re twice as big as you should be.

In relation to my skill-set or with the bylaws?

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