I-Joist Hole Spacing

[Andrew Kolar]

I-joists in a home run from the front foundation wall to the rear foundation wall (approximately 25' span) and are supported by a steel I beam at basically the center of the basement. There is approximately 9" between the top and bottom flanges, or 12" total joist height, which I beleive allows for a maximum hole size of 8 5/8". Can this size of hole be cut through just one of the I-joists, approximately 3 ft. away (in a perpendicular direction) from the central support beam?

[Randy Mayo]

Andrew

What is the brand of I-Joist? Usually stamped on the side of the web.

[Andrew Kolar]

LP I-Joists. Specifcally LPI-20PLUS SERIES 11 7/8".

[Randy Mayo]

Andrew

According to the manufactures technical data you could cut up to an 8" hole and you have to be at least 2'-6" from the edge of the support to the center of the hole. Here is the link please read all the fine print at the bottom to make sure your application falls within their criteria. http://www.lpcorp.com/WorkArea/DownloadAsset.aspx?id=419

[Andrew Kolar]

I think that link was actually to a different model / serires of joists. Here is the link to the technical info. for the specific joist I am talking about.

http://www.lpcorp.com/WorkArea/DownloadAsset.aspx?id=422

The web hole specifications are on page 14. I am having a hard time deciding which side of the table would be appropriated. The closest bearing position is the central steel I beam (but there is no cantilever). So would the "Distance from the End Support" or the "Distance from interior or Cantilever - End Support" be appropriate?

[Jerry Peck]

The closest bearing position is the central steel I beam (but there is no cantilever). So would the "Distance from the End Support" or the "Distance from interior or Cantilever - End Support" be appropriate?


"Distance from interior or Cantilever - End Support"

The "or" is the critical decision maker, when if the holes are closer to the interior support ("or" cantilever end support) you need to use those columns.

If the holes are closer to the end support you would use those columns.

[Andrew Kolar]

That is what I was thinking, but I just wanted to make sure. Thanks again!

[Randy Mayo]

Andrew

Technically you can cut an 8" hole 3 feet from the center support beam, but you need to read the design assumptions and notes at the bottom of the table on page 14 to see if you meet all the criteria. Your actual loads need to be considered before anyone, including myself, could give you an answer that would be considered acceptable from an engineering standpoint. If you have any concentrated loads on that floor such as support walls that table becomes worthless. Without getting too technical the closer you get to the beam supports the Shear forces get higher and the web is one of the major components that supports that load. That is one of the main reasons the tables limit the size and locations of holes near the supports.

[Andrew Kolar]

There are no load bearing walls that run perpendicular to those I-Joists on the floor above. It is open formal living room and kitchen area. In fact the only wall is a central half wall, which does not extend to the vaulted ceiling. It is only there to frame in a pantry closet. So I believe this meets all the small print criteria below. I am curious how you came up with 3’ (as opposed to 3' - 10")? Is it because the span between the I-beam and the foundation is closer to 13' ft and the table lists 14'?

[Randy Mayo]

Andrew

You approximated the total length of the I-joist to be 25 feet. I used 12.5 feet for one span and interpolated between 10 & 14 feet in the table. The table is designed to use clear span so without exact measurements I rounded off to 3 feet. I am being very simplistic with this information, your situation may be different. An 8 inch hole at 3 foot from the center support is obviously at the upper end of what the manufacture is comfortable with. This floor joist is just one part of the entire structural system of the house. The correct design procedure starts at the roof by applying the loads for you location and following the load path down the walls and into the floor joist. Realistically very few floor joist are supporting the same loads. Typically the joist size is dictated by the few that carry the greatest load or has the greatest span. The remaining joists could technically be smaller but that is not always the most economical design. The joist you want to put a hole in might be one of those joist with the greatest loads or it could be one of the other joists. Any structural advice you receive through a forum like this should be followed up with real design information based on your exact situation.

[Andrew Kolar]

Randy. That was the answer I was looking for! I appreciate your insight and completely understand that the info. you are providing is SIMPLISTIC at best... I was more interested in how your were using the tables as a reference guide. Thanks!

[Andrew Kolar]

Suspecting that the Tables were slightly oversized for "fudge" factors I contacted the manufacturer. As far as they are concerned an 8.5" hole at 2.5 ft (on the 13' span side) would be acceptable, which would differ from the table. I attached a link to the document they sent me from their software analysis...

http://i303.photobucket.com/albums/nn125/KolarPhotos/WebHole.jpg