10' x 20' rafter size

[justinae]

Hi all. I got great advice on the electrical so I though I'd try a framing question.

My garage is 10' w x 20' d with gables on the short end. I framed up the walls with 2x4 24" oc with double top plates. I know it's a bit light, but the structure is small, will have 1/2" CDX ply and roofing material is metal shingles so lightweight.

I was planning on using 2x4 rafters 24" oc with probably a 7/12 pitch and 2x6 ridge. I think it will be fine since I'm using a metal roof and would collar tie about 2/3 way up. I also plan to either block between each rafter or use Simpson ties.

Thought I'd run the idea past those that may have done the same or at least thought about it.

It's not too much more money to go 2x6 but I have a bunch of 2x4 material I'd like to use and it's not crappy either.

Many thanks.
Justin

 

[tskills10]

Depending on the area of the country you are in you may need to consider 2x6 instead, due to snow load. Just a thought from the Ohio snowbelt.

 

[justinae]

Oh I forgot to put that part. I'm in Portland, OR. We get a dusting usually each year, sometimes not, every once in a while we get a snow. But that's why I'm going with a steeper slope.

Thanks!

 

[5lima30]

2"x6" without a doubt! Years down the road you will be glad you did for a relatively small increase in cost.

 

[wnstwolf]

2"x6 and for the extra $50 or so try to make them 16" OC. Rafters at 24" beg for sag to happen even when clips are used. You are using metal so I beleive 24" are fine since you will need some sort of nailer run across the rafters anyway will add structure.. 2"x4" for the nailers and 2"6 for the rafter 2"x8" ridge

 

[Dead Skunk]

My house has 2x4 roof trusses on 24" centers and I'm in Michigan. It was the first time I'd seen 24"centers. We used to live in Ontario and my house there had each roof joist over a stud,so 16" centers.

 

[BARN ONE]

At only 10' wide 2x4 would be plenty! Use them up.

 

[pattenp]

2X4's are okay for engineered truss but I'd go with the 2X6's for your stick built roof.

If you're determined to use the 2x4's go 16" on center.

 

[wnstwolf]

Good point Pat.. a lot of today's engineered truss design is 2x4. ^^^ x2 if your stick building..

 

[rsa]

See my sig

At only 10' wide 2x4 would be plenty! Use them up.

Yes, for most available woods, minimum building code allows use of 2x4 rafters here, but the OP wanting to raise his rafter ties could require larger rafter members.

Prescriptive code only allows raising rafter ties 1/3 of the height between the top plate and ridge. When raising the rafters the allowed 1/3, a Rafter Span Adjustment Factor reduces the allowed rafter span by 1/3, so raising the rafter ties can require increasing rafter size past 2x4's.

Here's the part of the 2012 International Residential Code for One- and Two-Family Dwellings that prescriptively sizes roof framing members.

You could also dispense with rafter ties completely by using steel flitch plates. See this article by Michael Chandler.

I have seen an article by an architect describing a similarly sized building where he created a vaulted ceiling using only plywood gussets at the roof peak. The principle is the same as the Chandler article, where the plywood gussets perform the same function as the steel fitch plates. The small size of the building allows the plywood to be substituted for steel. Darn if I can find the link now.

 

[Gary S]

We have big snow loads here, and a 2x4 engineered truss is totally adequate to handle 24' span and beyond. Just don't cheap out and try to get by building your own.

Check with your local building inspector for details before you take advice from the internet from people who don't build.

 

[camarotoolman]

2x4 will be good. I would build my own trusses on the ground and put them up yourself. 2x6 is over kill for a 10 foot spand. Gambrel or barn roof would give alot of storage for not that much more cost.

 

[stafford]

Your rafter is only gonna be 69.45" long minus half the ridge board thickness. That's from the birds mouth to the center of the ridge board. Are you also gonna have ceiling joists or just use the collar ties? I'd hate to see the snow that would break that roof down. The worst thing I see wrong with using a 2 x 4 for a rafter is not having much of a birds mouth, and if you cut it too deep it weakens the tail of the rafter, (or the overhang). I would not be afraid to use the 2 x 4 on that building that is only 10' wide. The steeper roof actually helps. Most folks really like to go for the overkill. If you've gottem I say use'm.

 

[justinae]

Thanks for all the replies. Very helpful. I think I'll stick with the 2x4 and go 16" o.c. Great conversation.