ledger board construction concern

[truppo]

I just bought a house and have some concerns, or perhaps I'm a bit paranoid, about the weight I'm placing on the 1st floor.

The idea of ledger board construction was new to me, and I really never considered it until after buying the house. The whole concept is distressing. How do I know when I am placing to much weight on the floor? I have the rooms packed with chairs, tables, and couches. I also have several thousand books in cases made for me. In a month I will have 50 people over for an event. How do I make sure the floor is safe? Should I just get some lolly (spelling?) columns and a 4x4 to reinforce the pressure put on the main beam and the small strip of wood that was run along the main beam 90 years ago to sit the joists on?

Thanks in advance,
Jeff

 

[dik]

I'm not familiar with ledger board construction, but, if it the the manner of securing a horizontal member to a stud wall and bearing the ends of the joists on this member or supporting the ends of the joists using joist hangers, then the strength is dependent on the fastening of the ledger to the stud wall.

You may want to have a local engineer review the connection in view of the large number of people (liability, not load) and the large number of books. My bookcases are distributed around the home and not concentrated. Loading for bookcases and filing cabinets can easily exceed the normal design loads for a home. A 40PSF live load (common home loading) will usually accommodate people on a 2'x2' grid... not likely to be achieved unless it's a real cozy party!

 

[JMcNPE]

Ledger construction
The usual ledger construction is a 2x2 or 2x3 nailed to the side of beam with notched joists bearing on the ledger. In this case the joist load is limited to that which will have a joist reaction that will not exceed the cross grain allowable bearing on the joist end or the the ledger. The usual case 1 1/2 x 1 1/2 inch area times allowable bearing stress for the wood species and grade (in the neighborhood of 400 psi)is approximately 900 pounds. The lateral load capacity of the ledger nailing must also be adequate to safely sustain the load. The nail spacing should be such that the joist reaction (live + dead loads) does not cause nail loads that the exceed the allowable. See the NDS manual for fastener loads on wood of a given density. Hire a structutal engineer.

 

[dik]

JMcNPE:
Thanks for the enlight; I hadn't encountered "ledger board" construction as a common method, before.

 

[Taro]

JMcNPE's advice about having a structural engineer come look at the framing is good. But if the structure has been standing for 90 years, it has probably been fairly well load tested unless the occupancy has changed or there is evidence of deterioration.

 

[Trussdoc]

I have run into ledger boards in old houses....and many times they aren't 2x material, but 1x, barely 7/8 of an inch across! Fortunately, code loading is quite conservative, and there's a very large safety factor in allowablew nail strength. Also, the wood used a hundred years ago is considerably stronger than currently harvested material.

If it were my house, I would replace the ledger with joist hangers.Make sure that any hangers you get are wide enough for the joists, because the old sawn lumber standard was somewhat wider than current 2x material.

 

[dik]

With the reference to 'old' framing. Is the manner of construction similar to what we refer to as 'balloon framing'?

 

[boo1]

I only use ledger strips for a construction guide till the joist hangers can be installed.

 

[truppo]

What about installing a few columns with the metal plates at the top? If the plate covers the strip of wood that the joist hangs on, it should in theory take load off the ledger board, at least I think? Since I only use the basement for storage, the columns seem like an easy, quick, and cheap solution to my fears. Does this make sense?

Thanks again in advance.

 

[boo1]

Consider installing a beam (column supported) under the joists.

 

[RG88]

Ledger construction for floor joists in quite common in my area. Typically the code covers the method by which the ledger must be installed. Granted your house pre-dates most building codes. The strength is provided as the others have indicated, through shear and compression. Where I see most of them fail is through rotation and subsequent deflection as the support. Calling an engineer is a good idea, but perform a common-sense double check first, does ledger look like it is sagging or rotated under the current 'furniture' load. If there are hardwoods above, does the flooring have significant gaps or undulations? If you do have a problem and the ledger is in good shape, you may be able to simply screw it back to resist rotation and nail it under the joists to provide shear.

 

[10k]

Recently had a question regarding a ledger for a deck, and followed your thread hoping for answers. With one or two exceptions, the responses were not comforting. The most confidence inspiring comments came from Trussdoc and boo1 (mechanical!!!).

RG88 mentioned rotation and screws. Both are good points, but I have difficulty believing that a 2x2 can be made to work for anything beyond minor loads.

Assume 12' floor joists, 16" on center: Live load of 40 psf, dead load of 5 psf, self weight of 4 lb/ft, so that the uniform load is 64 lb/ft and the end reaction is 64x6= 384 lb. I don't have an NDS, but the allowable shear load for a 16d common nail is only 108 lbs, and that will need to be reduced for edge distance, spacing, moisture, penetration, species, etc. Say it's 80, so that 384/80=4.8 or 5 nails (and a 16d "sinker" commonly used by builders may not be rated the same as a "common" nail). I don't think you can put 5 nails close enough together in a 2x2 to provide this capacity.

Rotation is even scarier. The 384 lb vertical load must be assumed to act at the center of the 1.5" support width, and taking moments about the bottom corner of the 2x2 shows that the pull-out resistance (before rotation even occurs) will need to be 384 lb. Once rotation begins, the problem gets worse. Again, the NDS will tell you what the pull-out resistance is, and I'll bet it's less than 80 lb per nail.

Joist hangers or direct support via beams and columns are preferred. When you have to use a ledger, use at least a 2x4, and use lag screws with washers or through-bolts.

While your example is interior, the problem with ledgers is even worse on exposed decks. At exterior locations, pressure-treated wood is essential, fasteners should be galvanized or stainless steel, and there must be provision to prevent moisture intrusion at the connection.

There was considerable discussion about deck supports and deterioration in the Pacific NW a few years ago. Maybe someone reading this remembers where to find it?

One more thing. The 40 psf floor load typically used in residential and office-type construction is not really as conservative as we like to think. Consider a 200 lb male occupying 2'x2'. That's 50 psf. Don't have any relatives who weigh 200 lb? Now consider a wedding party or family reunion on your deck squeezed in real tight. Now pretend someone puts their favorite brand of foot-stomping music on the stereo. The impact factor can easily exceed 2. This scenario happens all the time (two weeks ago +- here in Atlanta a deck failed for reasons just like these).

 

[redhead]

Before the days of steel joist hangers, ledger board construction was standard for flush framed beams. I do a lot of work in old and historic houses. The typical ledger strip is a 2x3 nailed to the main beam. The most common problem I see is a slight rotation of the strip away from the beam. But I have yet to see an actual failure. Obviously the load value we assign to nails has a sufficient safety factor to compensate for most contingencies.

On another note, unless you are regularly having "luv-ins", I find a 2'x2' assignment per person would leave me rather breathless. That is getting close to the subway train density at rush hour.

 

[ERV]

"One more thing. The 40 psf floor load typically used in residential and office-type construction is not really as conservative as we like to think."

Maybe someone should mention that residential floors are designed at 40 psf with a live load deflection of L/360 (and not fail if we exceed that), that means that if loaded to 40 psf we can expect the floor to deflect 1/360 of its span. I think that is conservative enough for my house. If the room was 15'x 15' wide under full load (45-"200 lb males&quot it would sag 1/2" at center span.

 

[unclesyd]

I just checked and ledger bearing is still allowed but discouraged. The ledger strip has to be a 2X4 min. 1 1/2" bearing. If the joist are level with top of wood beam then a steel tie strap has to tie the 2 joist togather across the top of the beam. If the joist are above the bean a scab tie across the beam is required.
If you replace an older wooden beam with a steel beam the top flange is below the top of the joist at least the thickness of the nailing strip a scab tie is used to tie the joist togather.

Pull out strength
SP DF
12D 55# 38#
16D 60# 42#

A friend who also works on older houses here on the Gulf Coast said that there is no nailing per say on beams. They used a lot of drifts and cut nails for the heart pine. To use a common nail you predrill. Also leveling a floor is chore as he said you are nearly picking up the house, even tough there maybe sag the thing is still pretty ridged. Nearly all balloon framing (not allowed now) 26' 2x framing no problem except when you try to replace it.

 

[bylar]

I encounter this situation all the time and most of the time the 2x2 ledger is insufficient. It is dicouraged in this area. Normally i find 1- 16d comm per joist sometimes 2 16d comm. but never have i found the nails to support the load required by the joist.

As far as a building being 90 years old and not failed, do you think the structure was ever fully loaded. I doubt it but some time it may be and that is why we have a code requirement.

 

[ELIofVA]

Load capacity of toenails and nails in general is my question.

I am an architect in Virginia. I have specified 2x ledgers with number of 16d nails = #/LF X nail/100#. A contractor that has put one or two 16d nails/joist (1'-4&quot has challenged my assumptions about the required nails on the ledger. He makes a claim that the toe nails have similar capacity as a square placed nails on ledger. I found different ratings for loads of 16d nails in different references. "Simplified Engineering for Archtects and Builders 9th Addition" in table 7.2 list 141#'s for 16d common nail through 1 1/2" member (like a 2x ledger). There should be a reduction for coated or neumatic nails. My concern about toenails is the penetration. Because the answer is not clear, I choose to use the more conservative assumptions that all load is on the ledger. Especially since this standard is not expensive. Since a 2x12 girder w/2x10 joist leaves a full 2", I ask coarpenters to install a full 2" depth to allow more space for quatity of nails required.

On exterior decks I have concerns about the corrosive affect of the new pressure treated wood on nails and fasterners. I have been told by Simpson Fasteners Engineer that beam and joist hangers must be Z max and nails and bolts should be hot dipped galvanized. They are also not guaranteeing their fasteners in this new material.

I do not like exterior decks. I am trying to design away from exterior deck. At my house, I am repacing an old deck with a composit concrete deck. I have questions about this technology that will be posted on another question.

Comments on load capacity of toenails and nails in general will be appreciated

 

[ERV]

A wire nail driven parallel to the grain of the wood shall not be subjected to more than two thirds of the lateral load allowed when driven perpendicular to the grain. Toenails shall not be subjected to more than FIVE SIXTHS of the lateral load allowed for nails driven perpendicular to the grain. (UBC 97, allowable lateral loads, Section 2318.3.1)

Nails driven parallel to the grain of the wood shall not be allowed for resisting withdrawal forces. (UBC 97, allowable withdrawal load, Section 2318.3.2)

Box nail values for single shear, for 16d with side member of 1 1/2", for southern pine is 113#, for DF-L is 103# and for spruce-pine-fir is 88# (normal fo nail guns).

Common nail values for single shear, for 16D with 1 1/2" side member, for southern pine is 154#, for DF-L is 141# and for spruce-pine-fir is 120#.

Nail withdrawal for common and box nail is 42# & 50# for southern pine, 33# & 40# for DF-L and 21# & 26# for Spruce-pine-fir. These values are pounds per inch of penetration into side grain of main member. (UBC 97 Table 23-III-C-1, C-2 and Table-23III-D.

 

[10k]

Chapter 3 of the Forest Products Society, "Wood Decks, Materials, Construction, and Finishing" has a lot of good advice for deck design. It specifically rejects the use of 2x2's for ledgers. Design according to Chapter 3 of this document is required by Section R502.2.1 of the Georgia State Amendments to the 2000 CABO One and Two Family Dwelling Code (Jan 1, 2002 Revision).