joists strong enough?

[Myke Simonian]

Hello, All!

I was hoping to get a little advice. I have a back area on my second floor I would like to finish off. The space is roughly 11 x 17 ft. The support is eight beams, 3x9", 16.5" on center, running parallel to the long dimension. It's old stuff-- house was built in 1870s.

Seven beams end on a header that spans the short dimension and goes onto the eighth joist on the one end and the external wall (brick on stone) on the other. The header encloses an old staircase, torn out below to enlarge the kitchen a number of years ago. The old stairwell is 31" wide, the header is also 3x9", and the joists the header supports are thus just over 14' long.

The eighth joist -- the one the header is hung on -- also supports a partition wall, also an old monster, plaster and lathe. This eighth joist is supported on the back wall, also brick on stone.

I want to put in two partition walls, parallel to the header and therefore crossing the joists. The space will thus be partitioned into three rooms, one of which will be a laundry room: washer, dryer, water heater, sink. At this point I am concerned about weight. I only have the one joist and header supporting the entire floor on the one end. So, what do I do? Remove the header and marry the joists into the opposing wall? Extend the seventh joist to the wall, and then hang a shortened header onto this? Extend 7, 4 and 1 to the wall, and hang two shorter headers on these, to which I hang 6,5,3 and 2? Nothing at all?

Attached is a very primitive diagram that I hope is enough to give an idea of the setup.

Thanks!!!

[Lee Schierer]

A 17' or 14' span is way too much for 2 x 10's. They should be at least 2 x 12's and ideally should have a support mid way along the length to prevent sag. As a crude rule of thumb, the length of span in feet should never exceed the nominal height of the board. A 2 x 6 should span no more than 6 feet, a 2 x 12 should span no more than 12 feet. Check the sag in your existing floor with a tight string from one end to the other along the side of one of the joists near the center. I think you'll be amazed at how much the floor is sagging.

It isn't clear if you are putting the new partitions above or below the joists. If below they should be perpendicular to the existing joists to add additional support. Adding more weight above without additional support below will result in sagging floors.

[joe milana]

Not really enough information to give you sound advice, and I hate to say a structure that has stood for 140 years is inadequate, but it is.

[scott vroom]

No offense, but your question is not suited for this forum. Asking people on a general woodworking forum for advice regarding residential structural safety issues is bad idea. Hire a structural engineer.

Mods, please lock this thread.

[Van Huskey]

No offense, but your question is not suited for this forum. Asking people on a general woodworking forum for advice regarding residential structural safety issues is bad idea. Hire a structural engineer.

Mods, please lock this thread.

That is a gross overreaction IMHO. By that logic ever electrical question should be locked and the OP told to hire a EE, since far more death and property damage results from improper electrical work than residential structural collapse. The VAST majority of residential structures in the US are built with no direct involvement with a structural engineer other than their involvement in the standard conventions and codes such as span charts. If it was new construction cantilevered out over a gorge or other special circumstance I would agree however.

[Jim Andrew]

A modern 2 x 10 measures 1 1/2 x 9 1/4. Sounds like your joists are like having 2 2x10's nailed together for joists. Years ago, when I built my house, I had an area where I had to use 2x10's 18'. Was only a few feet wide, and I put the joists on 12" centers. Of course they were douglas fir joists, and the code book allowed this. Do you know what species the joists are? Either syp or doug fir are much stronger than the common hem-fir or especially spruce boards, spf. Does the floor sag now?

[phil harold]

A 17' or 14' span is way too much for 2 x 10's.
Can be done if engineered 2x10 no.1 can easily span 14 foot on 12" centers with bridging and possibly 17' with a plywood diaphragm

Adding more weight above without additional support below will result in sagging floors.
True True


Not really enough information to give you sound advice, and I hate to say a structure that has stood for 140 years is inadequate, but it is.

Yup Yup

we need to know a lot more than what is provided:
species
construction method
subfloor
king post
foundation
live load
dead load

and you dont even give us a picture to speculate...

[Rick Fisher]

Google a span table for 2x10 ..

Typically the number for 2x10 SPF is about 14' .. Changes if glued, and strapped ..

[Stan Krupowies]

I find it interesting that all the comments thus far are regarding the spans for the 7 joists and not one comment yet on the eighth joist that has to support the wall and roughly half the overall load that is on the header. That is what I would be concerned with more than anything. That last joist has a tremendous job to do and as only a 3x9 I would be seriously concerned about its ability to do that job safely. Up to this point it has only had to support the dead load of all the existing lumber and, like others have said, I would venture to guess that you already have significant sag. If you were to add additional dead load in the form of walls and then the live load that will go with that with the washer, dryer and sink. Not to mention the significant concentrated load of a water heater (you don't say the size but a full 30 gallon water heater would weigh close to 400 lbs in a space of about 2 sq ft).

I'm not an engineer and don't pretend to be one, but logic and span tables tell me that what is there now is not nearly enough to support all that you want to add. If it was me, I'd hire an engineer to look at it.

[Kevin Bourque]

If a Douglas fir 2x10 can safely span 14'-6", then these 3x9's should be more than adequate for your span.
The problem is not the joists themselves, but with the header joist that they tie into.
It's grossly undersized for the load you plan to put on it, unless its got a bearing wall or support column underneath.
If there's no way to support the beam underneath you have a few options:
1) Remove all the joists and replace them with engineered joists designed for the span/load.
2) Remove the support beam and replace with one designed for the load.
3) Move to Poughkipsie

[scott vroom]

Van, I couldn't disagree more. The guy's house is 140 years old, with one of the main load bearing stuctures being a "brick and stone wall". Without being on site you have no idea what the poster is dealing with, you don't know the condition of the existing beams, the proposed load, nor do you have a clue as to the local building codes with respect to load bearing structural support. Need I go on? The proper response is to direct the guy to a structural engineer and to his local building department for guidance.

Although I doubt you have any data to support your statement that more houses burn from electrical fires than collapse from structural failure, you are probably correct. I wonder how many of those electrical fires resulted from folks asking questions on a forum and getting dangerous responses from DIY hacks?

The mods chose to not close this thread; so be it, it's their web site and their liability/conscience.




That is a gross overreaction IMHO. By that logic ever electrical question should be locked and the OP told to hire a EE, since far more death and property damage results from improper electrical work than residential structural collapse. The VAST majority of residential structures in the US are built with no direct involvement with a structural engineer other than their involvement in the standard conventions and codes such as span charts. If it was new construction cantilevered out over a gorge or other special circumstance I would agree however.

[Carl Beckett]

An interesting thread

And brings up an age old issue, that of regulating human behavior.

'should' he consult a structural engineer? Well.... From a liability standpoint yes. From a functional standpoint lack of a formal license does not mean an individual does not possess the knowledge

And for sure, by telling someone what they ' should ' do, in no way ensures they 'will'. So one side of this could be that he is going to go forward, and any info that points him in the right direction is a relative improvement over what he might do independently.

I know I have done things without a permit ( but I grew up on a farm.... There was no such thing as an inspector... Nor structural engineers for that matter.... If something fell down, someone could get hurt, we did the best we knew how. And sometimes someone did get hurt, the nature of farming)

[scott vroom]

I guess I'm not being clear. This isn't a philosophical qustion about "regulating human behavior", nor should he consult a structural engineer solely "from a liability standpoint".

It's simple: You've got a guy asking technical structural load questions on a woodworker forum. He doesn't know the people he is consulting, nor does he know if they are qualified to provide responses that will guide him to a safe and code-compliant conclusion. The guy has a 140 year old house with brick and stone load bearing walls.

This is a woodworker forum; let's stick to woodworking and not try to represent our community as anything else. Obviously some here don't agree; so be it.

To put it another way, If a guy comes here complaining of angina and asking for inputs on what to do are we going to respond other than to suggest he see a physician?



An interesting thread

And brings up an age old issue, that of regulating human behavior.

'should' he consult a structural engineer? Well.... From a liability standpoint yes. From a functional standpoint lack of a formal license does not mean an individual does not possess the knowledge

And for sure, by telling someone what they ' should ' do, in no way ensures they 'will'. So one side of this could be that he is going to go forward, and any info that points him in the right direction is a relative improvement over what he might do independently.

I know I have done things without a permit ( but I grew up on a farm.... There was no such thing as an inspector... Nor structural engineers for that matter.... If something fell down, someone could get hurt, we did the best we knew how. And sometimes someone did get hurt, the nature of farming)

[Phil Thien]

It's simple: You've got a guy asking technical structural load questions on a woodworker forum.

Scott, I would call this a woodworking forum, as opposed to a woodworker forum. Woodworking is a hobby for most guys here. There are engineers, electricians, building inspectors, and some incredibly knowledgeable "others" that visit this site every day.

I often do research by asking questions in these forums. While I don't always rely on the answers exclusively, they can be invaluable when it comes to getting pointed in the right direction for additional research, and also very helpful when it comes to double-checking what a professional may have told me (sometimes the pros get it wrong, too).

While I agree that we don't always know the qualifications of a responder, and I will stipulate I've seen some bad office offered-up in a few regards, I think that the answers are (on average) helpful and I'd hate to think that we'd no longer have the users here available to bounce questions off.

[Carl Beckett]

Yes, the power of community knowledge is incredible.

And much much greater than what I might know as an individual.

For the occasional 'bad advice', the community jumps on it pretty quickly and redirects. Certainly I have had MUCH better experience here, than I have relying on a single individual (professional or not). A very knowledgeable group here, and very generous and willing to share that knowledge. For me, that is something that sets this forum apart from others, and establishes a sense of community.

The posts in general are almost exclusively woodworking related. I suppose if we got over run by DIY questions it would be a problem. But its not.

As for data, the best estimates I could find were that there were approximately 28,000 fires each year caused by electrical (and 280 deaths). I couldnt find anything on structural failure (some roofs failing from heavy snow, but not complete collapse and injury...). Earthquakes and tropical storms seem to cause the most structural damage - this is real and could contribute, but I wasnt able to separate damage from unfit structure from structure fully to code.

If a guy comes in asking about a medical condition, Im guessing he will be pointed to a doctor - and at the same time will be given any advice the community has to offer (both, not either/or). In fact, I bet there are a number of doctors on here (although at least two of the doctor woodworkers I know quit due to seeing too many accidents - this of course shared with me while being in the ER for my own tablesaw accident). Hmmm.... I would bet there are more injuries each year by woodworking, than there are from structural failure (wild conjecture, no verifiable data).

Scott - I think you ARE being clear. Its just that some here dont fully agree 100% on your position. I get your point. I hear you. Its just that I dont agree that this type of thread has to be 'locked down' (other than for liability reasons - which may be enough I dont know, maybe we have some lawyers here than can advise).

I replied to this thread because I felt this was a valuable dialog about governance and forum topic boundaries. I for one believe its healthy to explore these type of boundaries. In no way am I trying to be disrespectful or upset anyone.