Any structural engineers here?

[lethal289]

Or people with experience converting attic spaces.

Opinions welcome! I'm involved in a project that is converting an existing attic space into a third floor master suite (Why anyone would want a third floor bedroom is beyond me). Anyway, the existing structure because it was an attic, has two by six floor joists. I've questioned the builder on integrity of the supporting structure. The tub alone full of water will weigh close to 500 lbs. sitting on 2x6's that span 14 feet. I envision this thing crashing down to the bedroom below.

Couple that with a few of the joists not under the tub getting a 2-9/16" hole drilled through. What possible strength could remain?

Naturally there are other penetrations through the lumber (electrical wiring, alarm, water lines, etc...).

The builder doesn't want to follow my advice. Which is pull back all wiring, etc... Sister in a minimum of 2x8 preferably 2x10"s by nailing them to the existing 2x6 from baring point to baring point. He prefers to leave the 2x6" saying they are strong enough. he says he will "compromise" by putting 2x4s on top of the 2x6"s screwing down through them joining them together every foot. Effectively making a 2x9. Where any future penetrations will be the lumber will get gusseted together with plywood.

Is this a strong enough way of doing something? I may just bid this job high enough not to get it.

 

[Horseplay]

Don't even bid that job. No way is that close to code. I take it there is no permit on this project?

 

[lethal289]

yes there is a permit. I just don't think they realize whats underneath the plywood sub-floor. At the staircase, there is a framed opening with 2x10s, you cant really see it anywhere else. They basically raised half the roof by adding a large dormer to make room for the bathroom, and a huge walk in closet.

I will never risk my license. Everything I install will get the appropriate inspection. However, a plumbing inspector wont care a bout structural integrity.

 

[Horseplay]

That span is far too long, in my opinion, for 2x6 joists. Obviously I do not know they type of wood etc. but here is an example of requirement.

http://www.awc.org/calculators/span/cal ... pan#answer

It says about 10' max which is about what I would have suspected. Even then, that floor is going to deflect. That also doesn't take into account the drilling of the joists. As you know, that will reduce the strength. No way is that right, Jake. Laying a 2x4 on the flat on top is not going to make any difference. I would suggest sistering in 2x6 that could sit on the existing headers (nailing wider along the length but not resting on the headers is not as good).

 

[Anonymous]

I wouldn't even consider using that space as floor space. Also the first and second floor "walls" should be a 2X6 (or 2X8) on 16" or closer centers. "If" the walls are strong enough then I would consider using a "11 7/8" I" joist on 16 centers with the original 2X6's nailed into the bottom. 2x10 "YELLOW PINE" would work also and is a LOT cheaper. I would bid it at two times your estimated cost with the provision that an engineer give you a drawing approved by the local building inspector.

 

[nymustang]

There is no way that is safe. 2x6 is not enough for a floor joist. I wouldn't be comfortable with anything less than a 2x10 sistered to each joist and I would want to know what walls below will bearing weight. I guarantee they aren't designed to be bearing walls. Someone at the buildings department needs to know what is really going on there. Walk away don't bid on it.

 

[Anonymous]

No way I'd get involved with a clusterpuck like this. Regardless whether you do YOUR job correctly, it'll be going into a sub standard place. You rep will go down when that ceiling collapses. Listen to your "rare" sense and over ride the contractor's lack of.

 

[Mach1Mark]

I agree with those above, and the contractor is an idiot. Where did he get his engineering degree? I got mine from the University of Alaska. Attic spaces are usually not designed to bear the load of a floor. The 2x4 over the 2x6 joists is a solution, the 2x6 will snap at the end where it meets the top plate. To do the job properly you neet to remove the attic structure, add a proper top plate to all walls and then install properly engineered floor joists, walls trusses etc. Dont bid this job, low bidder isnt always the one chosen for a particular job. Tell client to add on the ground floor or buy/build a different home. JMHO.

BTW: Ive never met a building inspector or permit clerk with an engineering degree. Thats why its smart money to hire an engineer, we LOVE what we do and we are very good at it.

 

[JeffTepper]

I wouldn't get near a project like that without seeing wet stamped engineering drawings with calcs showing the load can safely be carried. Out here the engineer of record is responsible for the design specifications on something like this. You do not need the liability for a half assed non-engineered design. Keep you fingerprints off of it.