Ok I’m going to take the plunge, call in all my favors and try my first house on my own-my house. I know just enough to be dangerous.
The house is a simple(I’m finding out nothing is simple) 28’X40′ ranch. Downstairs I’m trying to get a walkout to work so I can put two bedrooms and a bath down there with the Master Bed/Bath on upper floor. So, ceiling height and clear spans of space are important issues. First floor would not have any interior bearing walls as I’m using 28′ scissors trusses for ceiling/roof.
The guy doing my drawings has suggested I use a 40′ 5-1/4 X 14″ lam carrying beam and hang 14′ 2X10’s. Three problems 1) beam needs two lally columns in places I’d like to keep open, 2) beam price is killing me and 3) hanging floor joists just doesn’t seem the strongest way to set a floor system. I’d also have a bump at bottom of beam to finesse around because of dimensional differences between the 2X10 and the LVL.
Using a haunch (right term for footing between foundation walls?) and build carrying walls for beam could work at one end of building but not other.
Should I be looking at using I beam joists to run the entire 28′ span? If I’m reading the span charts correct, it appears I might be able to use an I beam that has 3-1/2 flange and 14″ depth @16″oc. Can’t find a price online for those.
I’ve read all the pros of using I beam system- seems like better than conventional system but costs more. While price is always an issue, I’m looking for a balance between what’s best and how much more that will cost.
Thanks for any help.
Replies
Skippy, no way would I use 28' I-joists. No matter what your span tables say, you'll get excessive deflection and vibration. If I were you I would look into another I-beam system: use a steel I-beam for a carrying beam.
Set the ends into beam pockets in the foundation wall, pad out the sides with lumber, and hang the joists. Strong, relatively cheap, and in something around a 14" depth you will be able to get by with one lally column (get an engineer or the steel co. to size the beam).
You'll be able to use conventional lumber for the joists, which will offset the cost of the beam.
Have you read the Spec House from Hell thread ??? The reason I ask is that it was my first house, it's 28' wide, and I wanted a clear span floor. Just thought the conicidence was funny. (-:
My first thought in reading your post is that hanging 2X joists on a flush LVL beam is a bad idea. The beam would make it difficult to get any mechanicals through from one side to the other. You can't drill holes in LVL beams.
I would suggest you refer to I-joists as I-joists, not "I-beams". I think most folks think of steel I-beams when you use that term.
There's no way you'll get a decent floor using 14" deep I-joists spanning 28' - I don't care what any chart says. There's a thread on Floor Vibration that covers a lot of reasons why I believe that.
On my house, I went with 24" deep clear span wood webbed floor trusses. I wanted plenty of depth to make sure I got all the mechanicals up in the system. And it worked great.
Wood webbed floor trusses are expensive. But the cost is offset by the fact that you don't need beams, posts, or footings. And there would be a lot less labor.
If you're not familiar with wood webbed floors, I can post some sketches if that would help.
I'm with you. I worked on a house that was over 40' in the short dimension and had trussed floors. Deep trusses too, as you might suspect. But that place was solid. And the basement was clean. Man I hate bumping into soffits all over the place."If you pick up a starving dog and make him prosperous, he will not bite you. This is the principal difference between a dog and a man." - Mark Twain
BossHog,
Thanks for the story and sorry!
Thanks for the headsup with utilities and the hanging joists. While I've kept all my plumbing to one side of the beam, I am thinking about radiant floor heating and that beam would complicate things.
An interesting suggestion from someone on the list was to flip my carrying beam from the 40' dimension to the 28' one and then run sets of 20' trusses. Still got the headroom issue with that beam but maybe can configure the layout to burry it in walls there. Have to think through the utilities issue.
I will look into the webbed floor trusses.
Thanks again.
Skippy,
You didn't mention what your foundation walls are going to be? Around here, the standard wall for a walkout is a 9'H. poured wall. Why not use a W8x__ steel beam to break up your span? This would be a simple cost effective approach, and you could stick with 2x10's for your joists. Break your beam span into 3, and your good to go.
Regards
Your statement "First floor would not have any interior bearing walls" is wrong. Those walls will carry weight. How much I don't know. In any case those walls make nice line loads.
I would have used a 28' beam rather than a 40' beam.
Good design/construction using I-joists will provide good floors.
GHR,
Your statement "First floor would not have any interior bearing walls" is wrong. Those walls will carry weight. How much I don't know. In any case those walls make nice line loads.
Help me to figure this out. If I'm spanning the entire building with 28" roof trusses what loads are my interior bedroom etc. walls bearing? Is it the load of the dry wall etc.? I'm not using ceiling joists as I'm going with T&G on the scissors truss.
Your suggestion that I run my carrying beam over the 28" dimension is interesting. I'd then use two 20' I-joists. Running my utilities would be more complicated.
Thanks for the suggestion.
>> Help me to figure this out. <<
I'm not sure he understands the concept of a load bearing wall.
"I'm not sure he understands the concept of a load bearing wall."
He claims to be an engineer. But he either gives dubious advice or smart-assed answers - Never anything helpful.
He's never given me any reason to think he really *IS* an engineer.
Avoid suspicion: when your're walking through your neighbor's melon patch, don't tie your shoe. (Chinese proverb)
I don't get that impression at all Boss.
I got the impression that there are two different opinions about what constitutes a bearing wall in this thread.
blue
I was speaking mostly from past experience - Not just this thread. To the best of my knowledge, he's never posted one useful comment in any thread I've seen.But he's happy to cry to the moderators when you say something he doesn't like...
Q: Why do blondes wash their hair in the kitchen sink?
A: That's where you clean vegetables.
I am just an engineer. All walls that are capable of carrying a load, will carry a load, and are load bearing. Most people on the internet use very simple engineering models and are happyand oblivious when they provide wrong results.
Skippy,I'm not sure why you wouldn't run the main beam the 28' way. Either way you do it you will have to either have a flush beam and use hangers or you have a smaller dropped beam.The only thing from my past experience with steel is that you wont need any columns wether you go the 28' way or the 40'way. With wood you can probably get away without a column the 28' way but not the 40' way.When I framed my friends house it was 6600 s/f and and he had two 40' I-beams running parallel to each other about 6' in between with one end on the right side of the foundation and the other end in the middle of the house with each end on one column. No other columns in between the 40' span.The I-beam was 24" high and 13-3/4" wide and 3/4" thick.You have to make up your mind what you want. Going the 28' way is the easiest way to do it using a smaller beam.Joe Carola
Framer,
I guess I was using the shorter dimension for the floor joists when I was going to use a conventional built-up 40' 2X10 carying beam and 14' 2X10 floor joists-again a 40X28 foot print. Seemed to be the best use of lumber. Set my stairway running between (parellel with joists) to minimize lumber- also helped with running plumbing up in the floor system. I still had problems with dealing with headroom and lally columns everywhere.
Flipping the carrying beam has got me rethinking where my stairs could/should go. I'd still have 20' joist spans to. I guess I should talk with an engineer to discuss the steel I beam option.
Thanks for the suggestions.
I think 20' spanned I-joists are not going to be the best choice... Unless you go with some fairly expensive I-joists. There are always exceptions, but the normal way to tackle this would be to run the beam the long way so that you can have the 14' joist span. If you for some reason want to run it the short way, I suggest having 2 beams with 3 fairly equal spans. I suggest you go to your lumber yard and have them design an I-joist floor system - they will do it for free so they can sell you the floor system. They will probably want to see a (complete) set of plans though... For a structure this size, I'd guess that you will be looking at $400 of extra expense to go from dimensional lumber to I-joists (running the joists the 14' span).
BTW - when looking at span tables, use about 75% of the max spans given unless you like bouncy floors.
Re designing a building, material usage is always taken into consideration (from a conceptual standpoint), but generally a house layout is drawn and then you figure out how you are going to frame it - not the other way around. Sounds like you need help with the plans before you worry abut how it is going to be framed...
Edited 10/25/2005 6:21 am ET by Matt
"...when looking at span tables, use about 75% of the max spans given unless you like bouncy floors."
I'm pretty conservative on floor design, but even I wouldn't go that far.
My suggestion would be to use the vibration formula to figure out what's O.K and what isn't.
If that's too complicated, just check out what span something will owrk at if it's places 24" O.C. If it works at 24" O.C., it almost certainly isn't overspanned. Then you can set it at whatever spacing you want. (less than 24" O.C., obviously)
Children have more need of models then of critics. [Joseph Joubert]
Ron: I get that you don't like my method... and you would know... but are you saying that my method is too conservative?
In some situations, I think your method could be way too conservative. Let me take a shot at an example:According to the GP span charts in the books they gave us, 11 7/8" deep I-joists can span 19' 1" at 16" O.C. Using your 75% rule of thumb, you would limit the span to about 14' 3". Using the vibration formula to check the vibration limits the span to about 19' 6". That's more in line with my experience. (I prefer to limit them to around 18' or so).There could also be situations with heavier loads, like for tile floors. The spans would already be limited by the heavier loading. So limiting it further probably wouldn't help the "feel" of the floor. Remember that the "feel" of a floor is controlled almost entirely by the length/depth of the floor members. The spacing has little to do with it.
The dead fish goes with the flow.
"Remember that the "feel" of a floor is controlled almost entirely by the length/depth of the floor members. The spacing has little to do with it."
You are correct but please allow me to elaborate; the spacing does have an effect it's just that the effect of the span has more influence.
I think the following is true: Spacing is essentially linearly related to the deflection. In other words if you double the spacing, you double the load and that would double the deflection. If you double the span that will cause an 8 fold increase in the deflection as deflection is a function of the cube of the span (i.e. 2 cubed = 8)
You're preaching to the choir here.
Check out the thread I did on Floor Vibration.
Ambiguous headline: POLICE BEGIN CAMPAIGN TO RUN DOWN JAYWALKERS
Perhaps you should read a good book on engineering composite plates. Most cost about $150. I can read about 10 pages of engineering per hour - 40 hours to read a book. Your speed and ability may differ.Most contain a formula for the vibration frequencies of anisotropic plates. (I expect you will need to do a lot of work to verify the formula given is also suitable for anisotropic plates, but ...)I suggest this for several reasons:1) The floors I have information about vibrate at the frequencies these books predict.2) The formulas in these books are different than the formulas you might "find" on the internet. The internet formulas you might find simply have the wrong "form" to be correct.3) If you are an engineer, you can save your clients a lot of money.
Thanks for the advice- after further thought I've gone back to my original plan of conventional framing with 14' 2X10's. I'll use a 40' 5.25X14" LVL and burry the lally col's in interior walls. With 9' walls the LVL should not create a headroom problem. As you suggested, I guess I'll figure it out as the frame goes up.
Thanks
Well... didn't quite mean figure out as you frame. What I meant is that you draw the floorplans, elevations, etc of the house so that the interior spaces work for you and then on a structural copy of the floor plans you fill in the joist, header, beam size and locations. Then a structural roof plan. Then a footer plan is drawn with piers footers, etc where needed. In the areas where I build plans must be stamped by either an archi or PE, so the structural plans are done by an PE, etc. Of coarse, if the roof is to be trussed that is done by the truss company/supplier (or any other engineered system for that matter) - these end up getting stamped too (do all truss companies get their plans stamped?). THEN, get a permit, order material, and start building...