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One Room School House

RJJ

RJJ

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Joined
Oct 17, 2009
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Location
about 1' east of the white water
Like to get some feed back on Floor loads. Have a one room school house. OC load will be 25 or less. Used one maybe two afternoons a year. I would like to see some feed back of floor loads. I have run some numbers and want to see if others agree or where they would place the load. This is a historic building with newly made desks a total of 18. Only load will be by visitors with the max to be 25. Real number would 15 to 20 people at a time.

Size of the building 35' long & 23 feet wide. Joist run the long length. floor covering is 3/4 yellow pine flooring 2 3/4 x 3/4.

Joists are 3x8" hem fir in good condition spaced in 2 sections 24" oc. The front third is 16" oc. The spans are broken in to three section. From the front at 16"oc joist run from stone walls to stone wall. This would be the first third. From the first intersecting stone wall to an 10/22 I beam and then again to a stone wall. A bearing points are 6"+/-.
 
Unfortunately, it may fall down on who declares it historic. If it's national (George Washington slept here, for example), you usually are not allowed to change the structure. If it's locally designated, you usually have more latitude in requiring changes. 3x8 isn't a standard size (anymore); if the joists could be 2x8 and work no problem, if 2x8 doesn't work, but 4x8 does, you need an engineering analysis.

We had a home on the National Registry of Historic Sites with a floor issue - it took the owner 3 years to get approval from the NPS to make appropriate repairs.
 
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A couple considerations--

Are these old 3x8s 3x8 actual? If so they are a little stronger than 2 new 2x8s-- 1.5x7.5 actual.

Also consider that they are likely old growth wood that also increases strength ove new fast grown wood--ref the southern pine derating proposals.

Classrooms get a 40 psf loading.

#2 Hem fir at 12 in oc gets a 13-2 span so the 2x3 actual at 24 oc would be more than adequate for a 13 ft span.

That and as long as the wood is in good condition it has stood the test of time.
 
RJJ said:
These are actual 3x8" and I would classify them as #1 or SS. They are in pretty good shape.
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If it's a change of occupancy, then an engineering analysis should be performed. Adding some intermediate supports shouldn't be a big deal, if required.

I wouldn't count on 25 max.

If it doesn't work with the owner's budget, it's not a big deal to lose something used once or twice a year.
 
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