# Putting A Gable Roof on my Garage **URL:** \ **Category:** Factual Questions\ **Created:** [June 18, 2014, 12:29am UTC](https://boards.straightdope.com/t/putting-a-gable-roof-on-my-garage/691023 "2014-06-18T00:29:17Z")\ **Posts on this page:** 15\ **Page:** 2
**Author:** ![The\_Man\_In\_Black](https://avatars.discourse-cdn.com/v4/letter/t/bcef8e/32.png) [@The\_Man\_In\_Black](https://boards.straightdope.com/u/The_Man_In_Black)\ **Post date:** [June 19, 2014, 11:58pm UTC](https://boards.straightdope.com/t/putting-a-gable-roof-on-my-garage/691023/21 "2014-06-19T23:58:15Z")
Thank you for all the replies. It’s a lot of info to take in. For what it’s worth, the existing “flat” roof (which will remain in place, I see no point of removing it after the gabled roof is built) uses 2x10’s on 16" center, running long ways. Starting at the garage doors, the 2x10’s span 16’, where they are supported by 2 thicknesses of rough-cut 3x12’s which span the 25’ width, supported by a house jack in the center. From there the 2x10’s span another 16’ to an interior wall. On the other side of the wall the 2x10’s span another 10’ or so to the outside wall. If the bottom of the trusses can’t support significant weight, I could support the bottom of the trusses against the “flat” roof. I’d think it is plenty strong enough. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [June 20, 2014, 12:01am UTC](https://boards.straightdope.com/t/putting-a-gable-roof-on-my-garage/691023/22 "2014-06-20T00:01:25Z")
> [@The\_Man\_In\_Black](#): > > For what it’s worth, the existing “flat” roof (which will remain in place, I see no point of removing it after the gabled roof is built) uses 2x10’s on 16" center, running long ways. Starting at the garage doors, the 2x10’s span 16’, where they are supported by 2 thicknesses of rough-cut 3x12’s which span the 25’ width, supported by a house jack in the center. From there the 2x10’s span another 16’ to an interior wall. On the other side of the wall the 2x10’s span another 10’ or so to the outside wall. > > If the bottom of the trusses can’t support significant weight, I could support the bottom of the trusses against the “flat” roof. I’d think it is plenty strong enough. If you are getting permits, your engineer will make that decision. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [June 20, 2014, 5:26am UTC](https://boards.straightdope.com/t/putting-a-gable-roof-on-my-garage/691023/23 "2014-06-20T05:26:29Z")
There’s also the possibility that if you replace the 2ea3x12’s crossbeams with metal beams, maybe you can move those posts to a post against each wall leaving an open garage. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [June 21, 2014, 2:07am UTC](https://boards.straightdope.com/t/putting-a-gable-roof-on-my-garage/691023/24 "2014-06-21T02:07:06Z")
> [@md2000](#): > > There’s also the possibility that if you replace the 2ea3x12’s crossbeams with metal beams, maybe you can move those posts to a post against each wall leaving an open garage. That would be pretty expensive. I’d first look at engineered wood beens. ---
**Author:** ![cornflakes](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@cornflakes](https://boards.straightdope.com/u/cornflakes)\ **Post date:** [June 21, 2014, 3:17am UTC](https://boards.straightdope.com/t/putting-a-gable-roof-on-my-garage/691023/25 "2014-06-21T03:17:43Z")
It sounds like you have a LOT of wood up there already. Even if an engineer isn’t required, I’m sure that they would be worth it. Trusses are meant to span from wall to wall, not rest on other lumber. It sounds like you need supporting beams that will allow the existing ceiling to work well as an attic floor. Thinking about it, you have a built-up roof, right? If so, that’s a lot of weight. The ceiling may already be carrying an attic floor’s load. ---
**Author:** ![Renee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/renee/32/287_2.png) [@Renee](https://boards.straightdope.com/u/Renee)\ **Post date:** [June 21, 2014, 5:16am UTC](https://boards.straightdope.com/t/putting-a-gable-roof-on-my-garage/691023/26 "2014-06-21T05:16:11Z")
Yeah, I agree. Personally, I wouldn’t even consider not removing the old roof. Leaving it on is kind of a kludge, and is going to complicate the project. I also doubt code enforcement is going to allow it. ---
**Author:** ![cornflakes](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@cornflakes](https://boards.straightdope.com/u/cornflakes)\ **Post date:** [June 21, 2014, 11:12am UTC](https://boards.straightdope.com/t/putting-a-gable-roof-on-my-garage/691023/27 "2014-06-21T11:12:15Z")
> [@cornflakes](#): > > Thinking about it, you have a built-up roof, right? If so, that’s a lot of weight. The ceiling may already be carrying an attic floor’s load. After rereading this, I realize it might not have been too clear. I could be wrong, but it sounds like the current roof might work well as the attic floor. I’d run it past an engineer, but you may be able to strip the asphalt and rock, trim off the gables and set rafters on the old roof, using the old roof as the new attic floor. An engineer may want to see additional beams, and you would probably want to add some sort of sheathing or other flooring on top of the old roof sheathing. ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [June 21, 2014, 11:29am UTC](https://boards.straightdope.com/t/putting-a-gable-roof-on-my-garage/691023/28 "2014-06-21T11:29:02Z")
Theres a lot of good advice in this thread from 2 weeks ago. > **[Please Help With Shed Rafters](https://boards.straightdope.com/sdmb/showthread.php?t=725568)** > > Hi Everyone I am working on a shed (12x12, 7.5 tall). I have done a fair bit of amateur framing before, so it’s coming along well. However, I need to make the rafters, and I want to seek math guidance here. Despite working in a STEM field, geometry... framing a roof is not difficult if you understand how to lay it out with a framing square. The earlier thread has several excellent links that explains the framing square. Use the right materials. 3/4" plywood exterior grade. [Use ring nails](https://www.disastersafety.org/wp-content/uploads/ring-shank-nail-illustration1.gif) Use an underlayment like thick roofing felt (tar paper) and Select a quality shingle. 20 year minimum. Heres an article on the importance of ring nails in heavy storms. [https://www.disastersafety.org/high\_winds/re-nail-roof-deck/](https://www.disastersafety.org/high_winds/re-nail-roof-deck/) ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [June 21, 2014, 12:04pm UTC](https://boards.straightdope.com/t/putting-a-gable-roof-on-my-garage/691023/29 "2014-06-21T12:04:25Z")
Also, we have a lot of flat roofed homes in my 1950’s subdivision. They are constantly getting patched. Fed up homeowners often have a gable roof erected over the flat roof. Its the one guaranteed method of eliminating leaks. ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [June 22, 2014, 4:20am UTC](https://boards.straightdope.com/t/putting-a-gable-roof-on-my-garage/691023/30 "2014-06-22T04:20:57Z")
Get the permit. If you’re spanning 24 feet, you’ll need engineered trusses. Just give the truss company the specifications for the attic storage and they’ll make sure you’re safe. If it’s just a simple gable roof, you’ll be money ahead buying trusses. “I live in north east PA.” That’s snow country, feet of the stuff is heavy. This is a very challenging project for a do-it-yourselfer, be prepared and be safe. ---
**Author:** ![The\_Man\_In\_Black](https://avatars.discourse-cdn.com/v4/letter/t/bcef8e/32.png) [@The\_Man\_In\_Black](https://boards.straightdope.com/u/The_Man_In_Black)\ **Post date:** [June 22, 2014, 10:00pm UTC](https://boards.straightdope.com/t/putting-a-gable-roof-on-my-garage/691023/31 "2014-06-22T22:00:06Z")
I just want to add for the people saying I’d have to use 2x12’s, a house my parents own uses 2x6’s for a span of around 36’ on 20" center with a peak height of over 8’. I wasn’t able to measure the length of the 2x6’s, but they must be pretty damn long. I will of course build it to code, but apparently 2x6’s are more than capable of spanning 25’. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [June 22, 2014, 10:43pm UTC](https://boards.straightdope.com/t/putting-a-gable-roof-on-my-garage/691023/32 "2014-06-22T22:43:33Z")
> [@The\_Man\_In\_Black](#): > > I just want to add for the people saying I’d have to use 2x12’s, a house my parents own uses 2x6’s for a span of around 36’ on 20" center with a peak height of over 8’. I wasn’t able to measure the length of the 2x6’s, but they must be pretty damn long. > > I will of course build it to code, but apparently 2x6’s are more than capable of spanning 25’. In my best Peter Seller’s [Inspector Clouseau] voice: _Not anymore!_ ---
**Author:** ![cornflakes](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@cornflakes](https://boards.straightdope.com/u/cornflakes)\ **Post date:** [June 23, 2014, 3:02am UTC](https://boards.straightdope.com/t/putting-a-gable-roof-on-my-garage/691023/33 "2014-06-23T03:02:02Z")
> [@The\_Man\_In\_Black](#): > > I just want to add for the people saying I’d have to use 2x12’s, a house my parents own uses 2x6’s for a span of around 36’ on 20" center with a peak height of over 8’. I wasn’t able to measure the length of the 2x6’s, but they must be pretty damn long. > > I will of course build it to code, but apparently 2x6’s are more than capable of spanning 25’. The 2x12 requirement is for ceiling joists. Your parents’ house has 2x6 rafters that span 18 feet–rafter spans are measured from the ridge to the wall, and the slope of the roof is not a factor. Also, by code, they would need to use 2x8s if they rebuilt today, but 2x6 rafters may have been allowed in the past. Span tables have become more conservative over the years, partly because the engineers are more cautious and partly because the wood they grow and mill today is pretty crappy compared to lumber from the 1970s or before. ---
**Author:** ![The\_Man\_In\_Black](https://avatars.discourse-cdn.com/v4/letter/t/bcef8e/32.png) [@The\_Man\_In\_Black](https://boards.straightdope.com/u/The_Man_In_Black)\ **Post date:** [September 17, 2014, 11:19pm UTC](https://boards.straightdope.com/t/putting-a-gable-roof-on-my-garage/691023/34 "2014-09-17T23:19:34Z")
UPDATE: I decided I don’t have time to do the roof myself, so I have a roofing company doing it. They have it framed out and are going to start sheeting it tomorrow. And guess what the building inspector and the contractors agreed on, 2x6 rafters! ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [September 18, 2014, 12:03am UTC](https://boards.straightdope.com/t/putting-a-gable-roof-on-my-garage/691023/35 "2014-09-18T00:03:22Z")
Please post pics if you get a chance. I love some good framing porn. [Previous page](https://boards.straightdope.com/t/putting-a-gable-roof-on-my-garage/691023.md?page=1)