Maximum ceiling deflection 1

[obzpae]

I have a wood frame house that has ceilings that sag. The house has plaster. What is the maximum deflection allowed before cracking will occur such as inch/foot? Also any suggestions on how to repair a sagging plaster ceiling?

Thanks

John

 

[TAF]

In the uk, the deflection limit for timber joists is 0.003 x span, with an upper limit of 14mm. This upper limit is to avoid excessive vibration to the ceiling under load.

With regard to eliminating the deflection, you have three options. Firstly, you can reduce the load on the existing joists by installation of additional joists between the existing, effectively halving the joist centres. Secondly, you can increase the section of the existing joist by supplementing with another section. Lastly, you can reduce the span of the joists by the addition of a binder or similar within the loft.

Hope this information assists!!

 

[rbg]

I have a wood framed garage that was in built in 1963. The layout of the garage is 26 x 26 with a gable roof(12/4 pitch) and storage area above the joists floored with 3/4 plywood. The garage finished ceiling is 1/2 sheetrock.

The garage was framed with 2" x 6" joists that span the entire 26 feet (from one side of garage to the other) with no connection to the garage door header or house structure other than bridging or cross braces. Needless to say, the ceiling has dropped (or deflected) over 5 5/8 inches in the center.

Recently, I temporarily supporterd the ceiling/joists over their entire span, and installed (2) 1 3/4 x 9 1/4 LVL beams sistered running perpendicular to the joists along the centerline (approx. 13 ft from each wall). Each joist was connected to the LVL with Strong tite Joist hangers and the LVL beam was glued and bolted together along the entire length.

These two LVL beams have a maximum load of 63lbs/ft over a 26 foot span. I have temporarily supported the center of the beam (at 13 feet) with a column to increase the load capacity of the beam to 539lbs/ft (per allowable uniform load tables, 115%Snow, Georgia Pacific)

My question is this, I want to remove the center support column and replace it with a single steel I-Beam (running perpendicular to the LVL, parralel with the joists, just below the finished ceiling) down the opposing centerline of the garage. What size steel beam do I need to carry the load and span the 26 feet?

I have contacted several Structural Engineers in my area and none of them are interested in calculating the requirements for a residential homeowner. I am willing to pay someone for this, but I am quite frustrated with the engineers in my area lack of interest in "small jobs".

Please provide some advice at your convenience.

Best regards,

RBG
Detroit, MI
USA

 

[JAE]

RBG:
Its tough to design via the web, and I hesitate to do so. Without knowing the actual dead load of your ceiling/attic etc. I'd have a hard time engineering it for you. I would suggest that you keep trying the local engineers in your area. Especially the smaller firms (one-man firms) etc.

As a rule of thumb, the required beam depth in inches is approximately .45 times the span in feet. So for your 26' span beam you'd need about a 12" depth. Now the weight size would depend upon the actual design loads. Is the attic accessible? If so, a heavier beam might be needed for possible storage loads as opposed to a 10 psf attic live load.

The LVL's you sized look plenty strong for the new 13' span.