Will This Sag?

[thiggy]

A little old lady wants me to build a cover over her 2nd story deck, approx. 16’ long by 10’ deep. She drew up the plans supporting the two outside corners with 4 X 4s and the rear rim joist bolted to the house under the eaves. She visualized using 2 x 6 x 10’ for the rafters, attached to a doubled 2 x 6 x 16’ with a steel flitch plate bolted between them for rigidity. The roofing material is to be a PVC sheet product she described as Palruf PVC. It sounds to be a lightweight transluscent panel. She says it is not corrugated. She is spacing the rafters 16” OC using saddle hangars. I told her that the flitch plate will probably be rather expensive and I don’t know for sure where to purchase it. She would prefer not to have a support post in the middle of the front rim joist. Could just a doubled 2 x 6 span 16’ in this installation without sagging?

[homebild]

2×6 rafters “might’ be able to span 10′ but only if the snow or wind loads are less than 50psf.

A girder made from 2x6s can only span a maximum of about 6′. No way will a 2×6 girder be able to span 16′ even with a steel flitch plate. (Girders made with flitch plates must be designed by an engineer and approved by the building code official.) Flitch plates are purchased at steel suppliers.

You’ll need at least 3 support columns for this girder no matter the design. Even a girder made from 4 2x12s can’t span this distance. Only other alternative may be to have a steel girder, glulam or other engineered designe, but for a 16′ span will be excessively deep.

The roof will also not meet code. The roof needs to be designed and installed just like any other roof. Unless she can demonstrate to the code officials that the PVC panels can support up to 40psf, it will not be allowed.

[Author]

Posts