Snow Drift on Existing Roof

[BubbaJ]

I am working on a project where it is proposed that an addition will be approximately 12 feet taller than the existing building. Due to the length of the existing roof, there is potential for a 4.5' drift to form at the junction.

Unfortunately, the existing structure is joists and joist girders, which were not designed for this type of loading. Since reinforcement of the girders is almost impossible I was considering another avenue. I have heard of similar cases where a sloped roof, mono-slope type structure was erected on the existing roof that represents the anticipated shape of the potential drift.

Have any of you heard of this practice?

 

[geoffdale]

We have done analysis on open web joists and reinforced them many times, including girders. Unfortunately, being an existing building, its tough to find the manufacturer most times, so we do our own calcs, and add rods, angles or plates to reinforce the existing over loaded members. Also check the columns and footings as well. Hope this helps.

 

[jike]

Reinforcing joist girders are much more of a problem then the joists or the deck. The main problem is trying to reinforce the top chord with joists bearing on top and the diagonals and verticals allowing little if any clearnace underneath. I have found an effective way to do this is to add a column at mid-span and reinforce the web members as needed (the chords are generally OK).

 

[civilperson]

The sloping roof added over the old roof is a normal proceedure and has been done on many structures. It is cost effective since the added loads are only the new roof elements, the snow loads stays the same. I have even seen examples in text books of this method of drift prevention.