Are these second story floor joists overspanned?


I am not an inspector or a professional in this trade, I am the homeowner. I looked around the site to see if there were posting rules about non-professionals or non-inspectors posting as some sites do have those rules. So I hope it’s ok that I ask.

My house is a 2-story Cape Code modular home, built in 1988. We bought it in 2011. Despite having been through 3 previous owners, to this day the second story is still completely unfinished, and apparently it was built as an attic space with stairs, ceilings are 7.5’ in the center. By unfinished I mean no wiring, mechanical, framing, not even insulation when we moved in. An empty shell.

I’m wanting to finish this space and put 2 bedrooms and a full bath up there. I am going to pull the permits and have been trying to get a hold of our inspector but he hasn’t gotten back to me yet regarding this issue: the overspanned floor joists are 2x8, spanned 14’ and…24" on center. The span starts in the middle load bearing wall and goes 14’ out each side to the exterior load bearing walls (house is 28’ wide). The distance from the center to the knee wall is 7.5’ each way. The floor isn’t bouncy, I suspect it’s probably because all the usable/livable interior space is within the first 5-6’ of the span.

I want to know if the inspector is going to require these joists to be sistered. Right now I’m ripping up the OSB as it was installed very poorly and incorrectly and will install a new subfloor properly with good materials. The time to sister the joists would be now if required. The only other caveat is I had the second story spray foam insulated, so near the eves the floor joists disappear into about 10-12 inches of open cell foam. I’m not excited about having to rip some of that out to install another joist and break the barrier, but will do whatever is right and necessary nonetheless.

Thanks for your time.

I would at least sister them. Your local AHJ (Authority Having Jurisdiction) may require something different/more. Here’s a link to some general information on joist spacing and spans. There’s also a basic chart at the end.

Those are ceiling joists. You’ll need to beef it up for a floor.

You have options.

Sister the joists.
Put 2x8 joists in between what you have
Get some engineered joists

14’ is easy to comply with if you get the proper set for the bearing ends.

I would draw it up and submit. I doubt a building inspector would give advice over the phone.

Better yet, hire a structural engineer. You said you wanted to do it right correct?

If the home is a single story, the footings may not be adequate for a two-story home. You may want to get a structural engineer involved. You may have to confirm the size of the existing footings and possibly address what to do to carry the second floor load. You want to do it right. Correct?

Thanks for the feedback.

The building inspector called me back this morning and in short, he would not require me to add additional joists, he said the house would have already passed inspection when it was built (which is not comforting given the level of craftsmanship on this in some places). He said they wouldn’t make me rip up the subfloor, but I already have (because subfloor absolutely must be replaced). But it does take the pressure off me with regard to the home being in compliance by their standards, and now anything I do would be ‘bonus.’

I asked my question to the forum because I wasn’t sure he’d call me back. However at your encouragement I’ll consult with a structural engineer. My brother is an architect and he’s been kind of back and forth on this. Thanks again.

Smart move…


I just ran through some quick calculations and adding one 2x8 to each existing joist would get you close to the required 30 psf live load for bedrooms. The weight of the tub full of water will probably require a little more floor strength in that area. The city gave you some bad advice. Get an engineer to do the calculations. $300 to $400 should be the maximum cost depending on what else needs to be done.

I had a structural engineer out yesterday to look at it. His recommendation is to sister up all the existing joists (glued and screwed) with SPF2 and then add a second set of doubled up SPF joists at 12" on center. I almost fell out of my seat. I’m just working on the first half of the floor right now, which has 21 joists. If I’m sistering them up and adding another double at 12" OC that’s 63 additional 14’ 2x8 just for one half of the second story. I want the floor to be strong, but wow.

He said he believes it’s best to use only one type of wood. It would have made life a lot easier (and cheaper) if I were able to run a single MSR 2400 SYP at 12" OC in betwee the existing joists with a sister.

At $9/board that’s $567 for half the floor, not counting screws and glue.:shock:

It is possible and likely that the 2x8 ‘ceiling joists’ you observed are actually the bottom chords of pre-engineered roof trusses. Many are designed with future floor loads in mind. I would check with the modular home manufacturer (if they are still around). If not, I would spend a few dollars and hire a professional engineer to write me an opinion on them.

Experience is a wonderful asset because sometimes you will know what appears minor can be a major future problem and on the other hand what appears to be a major problem is of no concern.

I have remodeled a lot of attics and working on assumptions is no way to build.

The engineers findings seem like overkill but the great thing about engineering is its based on math and math is reliable.

Why don’t you just look at some span tables and decide

Here’s one for hem-fir The Maximum Horizontal Span is:
12 ft. 10 in.
with a minimum bearing length of 0.77 in.
required at each end of the member.
Property Value
Species Hem-Fir
Grade Select Structural
Size 2x8
Modulus of Elasticity (E) 1600000 psi
Bending Strength (Fb) 1932 psi
Bearing Strength (Fcp) 405 psi
Shear Strength (Fv) 150 psi
My favorite link to span tables

That’s the span table I use too, what I can’t do however is fine the span of doubled up 2x8’s. When he gave me his recommendation he didn’t include any of the deflection numbers and what the live and dead load was.

I have started working on the first joist and it’s not going so hot. The problem is I have about 32" of open cell foam blocking off all the eves inside that the joists just kind of…disappear into. If I was doing this before the upstairs was foamed it would be a walk in the park. It was $5700 to foam it at the time, and if I have to rip all this out along the eves, I was told it would be about $700-1000 for them to come back and reinstall it once I’m done.

And ripping out that foam ISN’T fun! The foam itself gives easily, it’s laying on your back and contorting and trying to reach clear back in there. I think I’m going to buy one of those tree pruners with the blade on a pole and that will help a lot. Lots of fun words too in the process. I could probably make a sailor blush.


Select Structural lumber is a couple of grades higher than any box store carries around here. No. 2 is about as high as you can go without special order.