Modifed 20x30 single floor roofing

[alex trent]

I have decided that the 20 foot wide and plan-wise 30 feet long single floor house downsized to 20x 20 fit me pretty well.  Manageable size and relatively simple construction.

Some questions..

1. Planning on a ridge board not a beam.....at 20 feet wide this should not be a problem. Or is their something I am missing? Load on the roof is light...using galvinized and cane underlayment...about 2 psi for that.

2. I do not see anything on this site about or with hip roofs. Any special reason?  They do seem a bit more complicated, but certainly doable, given all the other stuff done here.  Reason not to consider?

[Don_P]

1) As long as there is a ceiling forming a triangle of rafters and ceiling then a ridgeboard is fine. As soon as the ceiling is omitted or raised too high the rafters push against the walls and a ridgebeam is needed to hold the rafters up.

2) A hip is a bit more complex. At 20x20, assuming equal pitches, there would be no ridge, it would be a diamond hip. You'll still need ties, in both directions, or across the hips, or a post in the center, or steel holding a tension beam in place around the top plate.

[Texas Tornado]

Don can you post a picture/drawing of what you are saying?

[alex trent]

Looks like it will be joists, although that is no5 the first choice.  Be difficult to do a beam on this.

Is there anyplace to go on line that you know of to see the hip bracing techniques you point out.  I have been searching a lot and find next to nothing.

[Don_P]

Alextrent, Texas Tornado, anyone else,
I have an article on cathedral hip roof framing that might be of interest. PM me your email if interested and I'll forward it.

Edit; found the article online here;
http://www.jlconline.com/cgi-local/viewnew.pdf/0/92052e82a1e8c5d41337213177306148/www.jlconline.com/cgi-bin/jlconline.storefront/4eccd7a605b78cd227190a323cb406cb

Mt Don also found an interesting article here;
http://www.chandlerdesignbuild.com/files/fhbIss178.pdf

On another thread you were using very low numbers for the dead load of the roof. This is ok but in that situation wind is usually what controls the design. In the US the design load doesn't drop below 20 psf for this reason.

[alex trent]

Good stuff and very doable to do down here.....even the steel rafter sandwich.

As for the old loads I used. The material load for my roof is about 6 psi...so the lowest USA overall load is adequate...20 lbs, I guess.  Contrary to some general thinking, being in the tropics is not the same as being in a high wind or hurricane zone.  We have less occurance here then in NJ. Nevertheless wind is  heeded...hard to build for the max, as one never knows what that really is in these changing times with the weather.

With my situation roof uplift is more of a concern as is racking the building...due to the shape of the building and where the strong winds will most likely come from.

I have an anemometer at my site...max velocity was gusts of 34 MPH and an average of less than 12 mph over any 24 hour period.  This is in 16 months. The indigenous folks say that is about right. No wind generation electric for me is possible.

Here is a very good site for those who are interested in what the various loads are on different kinds of roofs. Get by the complex equations in the first few pages and on to practical explanations and charts.

http://www.ce.udel.edu/courses/CIEG407/CIEG_407_Protected/Chapter%206%20Wind%20Loads.pdf

[Don_P]

That's an excellent link.  With that info you can also figure out the lateral load you'll be delivering to the piers.
We don't see high winds often but I've also seen the cheapo wind guage we had come apart. I suspect in ~25 years I've seen one 90 mph blow here... but it only takes one.

[alex trent]

Yeah, that's the one thing I left out of my windy post.  If you get the 50 year storm two years after you build, you will not get all those years of saying, well, see I got by!

I doubt I can figure all the lateral forces from the link...so I will just do what I have learned on here thus far:1. plenty of piers.  2. Dig the piers deep.  3. Big bases  4. good ties of posts to piers and...5. Brace it all both ways.

i think I about got the deck figured out...now for the building. I think the only way i will feel safe is to put plywood in all four corners..both ways (I saw a post on here about relative bracings and was impressed at the plywood numbers). Is 4 feet per side enough?  The outside will be horizontal wood 8" boards and the inside will be uncovered studs so not much way to brace walls without ruing the look.  Bit if the plywood is not enough, I will do what I have to.

[MountainDon]

Plywood or OSB works well.

The examples you saw were based on a 20 ft wall length too, just what you are planning. Sheet sheathing all the way along the wall is stronger but you have to decide according to your budget if it is worth the extra sheathing. Also if only the corners are paneled, what goes in the space along the rest of the wall? Does it matter if there is nothing in those areas?  Full length sheathing may also haelp with wind blown debris penetration of the walls. The horizontal boards won't add to the racking resistance of the walls .

[alex trent]

The uncovered inside walls are a "design" just for looks.  My idea and may not stay once I see it.  The reason to consider it is the siding is great looking stuff front and back...yes I ill post a pic soon. It is T&G so not worry about stuff blowing in. The back side is as good looking as the front..color striations from tan to reddish brown and a great grain. So why cover.  I am paying more for finished 2x6 studs to complement that look. May evn be a different type of wood (stronger but more expensive than cedro) for accent.

But,as you know this poses some stability problems. Hence the plywood in the corners, which will also beak up the all wood look.  The entire rear wall is also plywood as that is kitchen and bath.

As you will see when I finally post pics, the front..which is also the side where the most wind comes..is open 12 of the 22 feet. I have concern about this getting in and not out...seems like lots of uplift on the roof. Need to do something in the back...which right now does not have a lot of open spaces as it has a bathroom and closet wall

Questions

1. Does the plywood thickness make a big difference?

2. Does putting some other bracing behind the plywood..like a Simpson brace...add or is that not additive because in the same area?

[MountainDon]

1. Does the plywood thickness make a big difference?

2. Does putting some other bracing behind the plywood..like a Simpson brace...add or is that not additive because in the same area?

1. It will make a difference, but not sure how much

2. It should add up... adding a layer of sheathing is sometimes done to add extra stiffness when the available panel area is narrow. That's my impression, which could be wrong.


The look of the variety of wood grain, colors etc could be very attractive.