Messages and Online Forum Q&A

Re: Correction to above

From: info@builderswebsource.com
Category: Structural
Date: 26 Feb 2000
Time: 10:45:44
Remote Name: 63.198.181.43

Comments

Thanks for the detailed description. I now have a much better understanding of the structural configuration.

First, let me preface my response by stating again that I would advise you consult with a licensed structural engineer to look at the actual "as-built" configuration -- since it clearly differs from the blueprints.

But here are some general comments:

1) It sounds like 12"x12" beams were used in lieu of the glulams. This may have been a decision to keep the entire perimeter substructure at a consistent depth, to match the rim joists and the 2x12 floor joists. In checking the building code, it seems that your floor structure itself is sound based on certain assumptions, such as the use of Douglas Fir with an elasticity modulus of 1,500,000 @ 16" centers, with a worst-case 40 lbs/sq-ft live load and 10 lbs/sq-ft dead load. In other words, a 17' span appears to be within acceptable limits for the floor.

2) The ceiling joists should probably by 2x6 based on the span (assuming the ceiling joists go the short direction of 14'). This is based on a typical sheetrock ceiling.

3) As far as the suitability of the 4 4x4 columns are concerned, this requires more information based on the expected total load. For example, it the structure subject to earthquakes? Or heavy snow or wind loads? This must be known in order to properly determine the expected axial, and shear loads imposed on the structure and the columns.

A few areas concern me in particular: First, the fact that 4x4 posts were substituted for 6x6 posts is a flag. Second, I'm concerned about the actual foundation situation. If the posts are simply resting on a slab with some "L" brackets, then if the slab were to slip or settle on the downslope, this would undermine the structural integrity of the entire structure above. Generally, in situations like this where there is a cantelevered structure, sizable footings and/or drilled piers should be set well into the ground. Furthermore, proper attachment to the foundation and the beams is essential, including as you mentioned, proper separation between the slab and the wood. Otherwise, the potential for rot at the base of the columns increases significantly.

Finally, if there is no lateral bracing between the posts, then the entire structure could "wiggle" in heavy winds or during an earthquake -- possibly causing structural damage or worse, collapse.

There are enough unanswered questions here that getting an expert onsite is essential. Considering the cost of purchasing a new home, this is a drop in the bucket compared to the peace of mind you'll have, knowing for certain whether the structure is sound or not.

Keep us posted and report back when all is said and done.

Good luck with your new home,

Builders Websource.

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