Overhead structure for patio

[AlmostDone]

I am having a 20x20 concrete patio poured and I would like to build an overhead open slat (arbor) structure over it. I would like to use only 4 posts (one on each corner inset about 1 to 2 foot from patio edge) My problem is that I don't know what size post, beam and rafters I should get since the span is larger than what is covered in most do-it-yourself books. Also the height of the structure needs to be at least 12 foot above ground since the door to the patio is about 4 foot above the level of the patio.

I am thinking of a structure roughly 12-14' high by 18 ft square.

1. Can I get away with only 4 posts, If so what sizes should I make my posts, beams, and rafters

2. Do i need to sink my posts in the foundation of the patio or can I attach them to the top of the patio with metal post anchors?

Any help is REALLY appreciated.

Thank you.

[Wgoodrich]

First concern is the foot print. Is this patio and planned structure attached to the house or a detached structure ? Makes a difference.

Second how deep is the concrete of this patio ?

Third how deep was the footer under the patio along the perimeter of that patio, and was there any peirs installed to support inlet posts setting not on the perimeter footer?

Fourth location dictates depth of frost line. What is the depth of frost line rating in your area and was this a unipour? If a Unipour and only say 12" deep was this footer a frost protected footer?

Lets look at a proper foot print first then work on the rest.

Curious

Wg

[AlmostDone]

Wgoodrich Wrote :First concern is the foot print. Is this patio and planned structure attached to the house or a detached structure ? Makes a difference.

Almost done: The Patio will be poured next to the foundation of the house. There will be no direct connection to the homes foundation and the new patio other than the patio being poured right next to foundation (no rebar to connect them.) In addition to the poured patio there will be a set of poured stairs leading up to the door at approx 36" height.

Wgoodrich Wrote: Second how deep is the concrete of this patio ?

Almost done: The patio has not been poured yet. It can be done as deep as you would suggest.

Wgoodrich wrote: Third how deep was the footer under the patio along the perimeter of that patio, and was there any peirs installed to support inlet posts setting not on the perimeter footer?

Almost Done: The existing patio will be broken up and removed before the new patio will be poured. I am unsure if the old patio even had footers, will know more when the old pad is broken up. My Concrete man will dig holes for concrete post piers before pouring the patio that will be about 12" round by 42-48" deep (to go 1 foot below 30" frost line) Would additional footers be required? or would 4 corner post piers suffice? My Concrete guy is not a licensed contractor so I don't know that I would completely trust his suggestions about concrete depth, footers, and pier size.

Original Posting :I am having a 20x20 concrete patio poured and I would like to build an overhead open slat (arbor) structure over it. I would like to use only 4 posts (one on each corner inset about 1 to 2 foot from patio edge) My problem is that I don't know what size post, beam and rafters I should get since the span is larger than what is covered in most do-it-yourself books. Also the height of the structure needs to be at least 12 foot above ground since the door to the patio is about 4 foot above the level of the patio.

I am thinking of a structure roughly 12-14' high by 18 ft square.

1. Can I get away with only 4 posts, If so what sizes should I make my posts, beams, and rafters

2. Do i need to sink my posts in the foundation of the patio or can I attach them to the top of the patio with metal post anchors?

Any help is REALLY appreciated.

Thank you.

[Wgoodrich]

If you dig post holes below frost line and either put a concrete donut at bottom of the poles or sack crete in the post while under ground then no further footing is required to support those posts. Those posts in the ground would be your footing or foot print.

You may dig your posts set them frame your building then pour your concrete around the posts minimum of 4" deep. This is called a pole construction design. Footer being the poles. Concrete only being the floor.

If it were me I would dig a footer for the floor above Code requirements at least 12" below undisturbed dirt with 1" styrofoam insulation board verticle from finished grade along the side of that unipour concrete floor then at the bottom of that concrete a 1" styrofoam insulation board 12" out horizontally. This will protect your concrete from frost heave and keep rats and other critters out from under you concrete floor and pestering you around the house over time.

If it were me I would install line posts along the perimeter of the building and install header boards to support the roof line. 20' span to support the ends of rafters would call for a rather large header board. Can be done but cutting the distance between the corner posts to 10 spans would make for a much stronger roof supported by the header boards.

The roof and ceiling I would contact your lumber company for truss set up or if cathedrawl an I joist or web joist rafter combination design. They will assist you with this type of spanning and design if you go trusses. I suspect the above suggestion will be less expensive that rafters and ceiling joists.

However if you wish to use spanning lumber then I would suspect if your are in central Missouri you will have a 20 pound roof snow load. I suspect a 20 foot area you will probably have about a 12 foot rafter span depending on roof pitch. A 12 foot rafter span for a 20 pound snow load would call for a 2 x 6 if SPF lumber repetitive 16" on center. The celing joists would be a 20' span calling for a ceiling joist if no storage in attic of a ceiling joist sized at least 2 x 8 SPF lumber 16 on center.

Hope this gets you on your way to filling your information

Good Luck

Wg