Ridge Beam Sizing

[Josh Morgan]

First, this is for my house I'm building and not the shop but it's construction so I thought this would be the best place to ask.
I'm building a 24' x 32' house. I will have a loft in the back half at 16' and a roof pitch that can be as low as 10/12 or high as 12/12. I would probably prefer the 10/12 as I don't loose much room in the loft and it's a little better to put the roof on. The 24' wide and 16' deep section at the front will be vaulted. I will have 2x6 exterior walls. I'm concerned I'm not doing the calculations correct for a load bearing ridge beam.
If I'm not mistaken I can use a 3-1/2"x 11-1/4" beam with 2x10 rafters. I was doing some additional reading with people commenting and I've seen it recommended all the way up to a 5"x14" beam.
I'm out in the county with no code enforcement, inspections, or other government help.
I'd like to make sure I'm not going to have issues in the future.
house_plan3.jpg

[Bill Dufour]

snow load, wind load, seismic load all affect the needed structure. Will roof be tile or composite? that alone is several of tons of difference. any solar panels in the works? I suppose big skylights may affect things as well.

Which way does the ridge run long or short. Will it be centered side to side or offset to one side.

Depending on where in the world you live it may be cheaper to use a steel beam. If you use an I beam you can use it for a hoist trolley to get stuff into the loft.
Bill D.
USA

[Wayne Lomman]

You will get all the info you need from the Building Code of Australia. I know you aren't here but the timber frame engineering it contains is generic. The entire code is available free on line. It will answer this question and everything else you need to know. Since you have no compliance oversight, you can just use it as a reference. Cheers

[John K Jordan]

I'm concerned I'm not doing the calculations correct for a load bearing ridge beam.

Josh,

I didn't see where you mentioned where you live (hurricanes? heavy snow?) Some unknowns, besides what Bill mentioned: how and where will be beam be supported? by posts or braced 2x6 walls? In my 36' barn I used a single 2x12 nominal ridge beam (with 2x8 rafters, lightweight metal roof, low snow load) but it is supported by 4 or 5 posts to the ground. Will your beam be supported in the middle only by the wall at the stairs?

So much better to be sure of the calculation, especially for the house for the family. In a recent thread I told about hiring an engineer to do a beam calculation for me. I've done a lot of construction and was "pretty sure" what I planned was OK but it was inexpensive to hire a structural engineer to do the load calculation - $100 or so. He was recommended by an architect friend who uses him often since they don't have a structural engineer in house. You might visit a local architecture firm and ask.

I sent the engineer the details and he quickly emailed a drawing back to me. (In my case it was a 16' span supported only at the ends) I'd recommend the engineer over engineering by forum response.

BTW, my own house is timberframe post-and-beam construction, 2 stories, with 12/12 shingled roof with multiple skylights, 6x6 rafters on 4' centers. From the floor it looks like the main beam running the length of the house is a solid 6x12 pine beam supported by 6x6 posts. We are not in an area that gets more than a few inches of snow. A second 6x12 beam below it holds up the second story floor.

JKJ

[Malcolm McLeod]

...used a single 2x12 nominal ridge beam (with 2x8 rafters, ...

^I would call this 2x12 a 'ridge board', since I suspect the rafters rest against it, in direct opposition to each other, and so, the 'ridge board' carries no real load, rather it is there just to stabilize the rafters. Since the 'board' carries no load, it may not have a vertical support under it - tho' in most cases the framer puts some vertical member to hold it up while installing rafters (and then leaves it in place).

A true 'ridge beam' (by my admittedly limited understanding) is positioned at the ridge, but under the rafters. The beam is supported by posts, and the rafters rest on the beam - so the rafters need not necessarily be in direct opposition to each other. Rafters may also have a birdsmouth cut into them at both the plate and ridge beam.

And this semantic difference points out the need for expert advise...

...
So much better to be sure of the calculation, especially for the house for the family. In a recent thread I told about hiring an engineer to do a beam calculation for me. I've done a lot of construction and was "pretty sure" what I planned was OK but it was inexpensive to hire a structural engineer to do the load calculation - $100 or so. He was recommended by an architect friend who uses him often since they don't have a structural engineer in house. You might visit a local architecture firm and ask.
...

^+1 - - A forum is unlikely to even get a consensus on what a given structural member is called, let alone the proper sizing, material, strapping, and installation.

[Malcolm McLeod]

...
I'm out in the county with no code enforcement, inspections, or other government help.
I'd like to make sure I'm not going to have issues in the future.

I'm looking at building a house (again), so doing my due diligence now. Many code enforcement locales now require "engineered framing" (as well as foundations). As explained to me, this is just a stamp by a Professional Engineer (PE), indicating that the design is structurally sound, suited for purpose and site. In the grand scheme of things, that PE stamp can be cheap insurance, especially since no building inspector will be reviewing the suitability of work in your build.

...Might help you sleep at night knowing the structure is unlikely to fall on you or the next 6 owners?

You can over-build something and pay up front (for excess material & labor). You can under-build and pay on the back end (to fix it). Or engineer it. Hope this helps.

[Josh Morgan]

I should have included more details with my original post.
Snow load 15psf
wind load 90mph
2x6 walls, window dead center of the vault so it would have a header and load bearing posts all the way to the ground.
5/8" decking with 29ga tin roofing, no skylights, spruce ceiling.

I've tried to find a local structural engineer but I may have to go about 1-2 hours drive to find one. The ridge beam is the only thing I'm concerned with.

[Josh Morgan]

I'm going to do three beams from front to back. I can make all three load bearing if that will significantly reduce the top load.

[Ken Fitzgerald]

Josh,

When I needed to replace a poorly design and executed header in the carport of the home we bought, I went to a local lumberyard. I provided them with the information and they called the structural engineer for the company that manufactured glue-lam beams. He took that information and gave them a recommended size for my header. I bought the header from them and they delivered it.

Something to consider.

[John K Jordan]

^I would call this 2x12 a 'ridge board', since I suspect the rafters rest against it, in direct opposition to each other, and so, the 'ridge board' carries no real load, rather it is there just to stabilize the rafters. Since the 'board' carries no load, it may not have a vertical support under it - tho' in most cases the framer puts some vertical member to hold it up while installing rafters (and then leaves it in place).

You are absolutely correct, I was sloppy in describing it and plum forgot about the difference in the loads of those two types of ridges. Could probably even get by with a 1x8 in the barn with rafters pinching it. The original roof, probably 80-100 years old, had a pretty stout ridge, perhaps because they nailed it to flats on posts made from cedar trees. But as you indicate, don't mess around, get a professional.

It's interesting to see what kinds of wood they used in these old buildings - I've ripped out poplar, walnut, oak, cherry, cedar, chestnut, and a number of "wonder what that is" boards. A lot of the bracing is with 4-5" round sections of tree instead of board, probably cut from the smaller tops of the 15 cedar trees they used for the posts.

JKJ