Aluminum Screen Enclosure to Fascia

[Wbruseski]

I am a structural engineer and I design screen enclosures typically for pool areas which attach to the fascia board of the home. My question regards capacity of the house truss to take the additional wind loads (up and down)from the enclosure. (A typical load is 150 lb/ft of fascia or 1350 lb at a 9' spacing along the fascia up or down.)

1. Where the screen enclosure attaches to the end of a truss, is there a simple way to calculate the load capacity of the truss and the design load of the truss to find the "excess capacity" in order to approve this additional load? For this project the Truss Engineering Drawings cannot be found. (If they were found, would this information be there?)Does the size of the overhang raise additional bending concerns for the top chord of the truss?

2.Of course the truss connection must be checked in uplift loads. I found the capacity for toe-nailed connections. Is there any information on mechanical connections?

3. In some situations, there is "gable end framing" (the fascia board is parallel to the truss and there are "ladders" connecting the truss to the fascia board). Is there a calculation or somewhere to find detailed drawings of how this is constructed to estimate the capacity of this type of framing?

Thank you for any information provided.

 

[dik]

I assume that the trusses use the metal connector side plates.

In this area, the competition for factory fabricated trusses is so high that there is little excess capacity built in.

The loading you descibe is sufficient to possibly overstress the members or the plates. The Truss Plate Institute (TPI) or the Canadian equivalent (TPIC) has information regarding assumptions used for analysis and the only 'correct' method is to check a truss for the new loading using their assumptions using one of the analysis programs available. The truss manufacturers have software specifically tailored for truss design; it's quite expensive and is often set up for the specific truss plate involved.

Alternatively, you may want to contact an engineer that designs trusses for a fabricator and see if he can/will take on the work (truss plates, although different, are similar). I use a fellow out of Winnipeg that has 20 years experience with trusses and it costs about $150 for simple trusses.