Quesitions on a Slant Roof

jk333

Im debating putting a slanted roof on my pole garage. Im in the building proceess and not to the roof yet, so i thought i' ask. My building will be 22' by 38'. My main concern is strength. Compared to a conventional styles roof with trusses, what is the strength difference compared to a slanted roof and what bracing will i need to do with a slant roof?

iMisspell

Im no engineer, but i would think if you have a 22' span and used a slanted roof your "weak" point would be at the 11' mark.
If you have a 22' and used a gable style your weak point would shift to two spots at 5-1/2 foot marks (which would seam stronger to me), thats if you used the same dimensioned lumber for both.
With a gable roof i would think wind would be more an issue then with a slant roof.
Could be completely wrong with all that, so take it with a grain of salt

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Marvin Gardens

Shed roofs stay up by shear brute force. There is no shifting of weight like other types of roofs. It is just a cap on a building.

If you want to go that route you will have to consider things like snow load and water shedding abilities.

I didn't see where you live but if you are in a snow zone then you will have to have some massive rafters to span 22 feet and be able to handle snow. The calculations show 2x12 with 16" centers. If the angle of the roof is not all that steep then you will have to have closer spacing or bigger rafters or maybe both.

When bridges are built the architects have to consider water drainage as a hard rain can put so much water on a bridge that they have collapsed. The water just can't get off quick enough and the weight exceeds the design and down she comes.

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Wildie

I'm planning to install a shed roof on a raised concrete deck!
Its attached to the house at the high end.
As I live in an area with a snow load of 50 p.s.f. the 2X6X9' rafters must be supported by a beam that consists of 3, 2X10X12' planks laminated together.
In your case, I would think that you would have to have a mid span beam and 2X10 rafters if snow load is a consideration.
For a building the size that you are considering, truss's with a high pitch on the roof, would likely be a better option.

jk333

Thanks for the replys. so, what if i put support posts at the center point of 19'? do you guys think that that would provide enough strength so that my roof wouldn't collapse? and as far as snow load goes, I barely ever get snow in my area Tacoma, WA.

jk333

Can you please explain this? im still a little confused. THanks

Wildie

A beam at the center point of the rafters, effectively reduces the rafter span to 8 1/2 feet.
I would think 2X6 rafters would work in this case.
The size of the beam is dependent on how wide the building would be.
You're lucky that you have little snow. I'm in the Great Lakes area and its a major consideration.

Note: 2X4's on 8" centers are the equivalent of 2X8's on 16" centers. And so on!

Marvin Gardens

Span tables show how far you can reach out with a beam to hold up a fixed amount of weight.

You can change the amount of weight a structure can hold in several different ways.

Go with thicker beams like a 2x10 instead of a 2x8 or you can put the beams closer like 16 inches apart rather than having them 24 inches apart.

This is the simple explanation and it is more complex than that but this is the general idea.

It does snow in Tacoma and when it does it has high water content (it's called Cascade Concrete). This means when the snow comes down it has a lot of weight compared to snow with a much lower water content. Or even worse freezing rain that can't get much heavier.

You don't want to have to worry about rushing home and shoveling off the roof every time it snows or worse yet, wake up to see your roof on the floor of your shop.

Tacoma has a snow load code that you should search out and see what they require.

With a shed roof design my guess is that you will have to put in a center support of some sort.

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