Dog gone it, here I am with all my degrees and license and such and I’m failing to find info on wood strength in home construction.
I’m having a half-story internal staircase built to go between two levels of a side-side split (as part of a major expansion of my house), and I am told by the contractor the following:
This staircase (about 7-8 steps total) will be 2x12 fir jacks with 2x10 treads, OR
I can go with 2x12 “micro-lam” wood for the jacks for a substantial price increase (4x the material cost).
What is the actual strength difference between 2x12 fir and 2x12 “micro-lam?” Is there a spec sheet on that? Are there long-term stability issues with possible de-lamination? For a half-story internal flight of stairs, is 2x12 fir good enough? And for those of you skilled in home improvement, are there some questions I should be asking or specifications I should be making for construction of stairs? (I did specify counter-sunk screws to hold the stairs together, instead of nails, and I think the contractor isn’t pleased with that. Any reason why, if I’m willing to pay for the extra labour?)
Try looking up LVL (laminated veneer lumber) or Glulam instead of the term “micro-lam”. I found a few pages of PDF specs on the laminated product here. Required a free registration, which means I’ll probably be getting some SPAM from them, but the data seems fairly detailed.
I’m assuming you can get the basic strength characteristics of fir from an engineering textbook.
As for the countersink screws, he’s probably grumbling because it makes the job longer and it’s kind of a pain. Nails can be powder-actuated and shot into place quickly; countersunk screws are a major hassle by comparison.
Just sent you a ~5MB PDF with their most general construction guide - it lists compression, bending, and tension specs for all of the different grades. On a first look it appears that 2x12 glulam will be much stronger than fir, and you could skimp on size to save cost… but then you’d have to redesign the construction.
I received the PDF you sent, thank you very much. It seems though that with Douglas Fir being 1.6M Modulus of Elasticity, it’s not a whole lot off from the laminate, unless one specifies a really high grade.
The cost doesn’t bother me as much as the value - if paying 4x the materials cost doesn’t give me any real difference, then I’m not sure if I want to do that. I just want to guarantee that I get solid stairs people can jump up and down on and not creak ominously. If I do this project (the overall one) it means I’m committing to staying in this house for a long time, and I don’t want to be 80 years old and walking up creaky, rotten stairs. Of course a large amount of the solidity is a result of the tread design I know. Overall, I guess I’m wondering if for a half flight of internal stairs if a well-built 2x12 and 2x10 fir construction will be more than solid enough.
The only time I use engineered lumber is when the project needs dictate their use, typically load to size ratio or span rating. A short stair run doesn’t strike me as a reason to depart from solid sawn dimensional lumber.
So long as a pair of stringers is carefully picked by the contractor, load shouldn’t be an issue. Example: I put up a set of stairs using 2 x 12 x 24’ to provide access to the storage rated ceiling of a separate structure about 12 years ago, and the customer has employees up and down them six days a week. Knock wood (yes, pun) they are doing fine.
Not sure if the d was intentional, Jurph. Powder actuated fasteners are used for attachment to cementitious substrates-I don’t use a Hilti gun for stairs. If you meant power, as in pneumatic nail guns, then yes.
If you want the stair treads screwed and countersunk, or countersunk, plugged, and flush sanded, that’s your choice. It is a bit more labor intensive, but not that big a deal for a short run. If you want a long term squeak free project, then have the treads glued with polyurethane adhesive, and screwed.
I can’t help you with engineering data,but have some observations you may find helpful.
These days,glu-lams (micro-lams) always have an advantage over sawn lumber as there is no continuous discontinuity.Any de-rating due to knots,etc. stops at the glue line and the glue joint is stronger than the wood.
The problem with traditional stair construction is that the "notches" that form the seats for tread and riser remove a large portion of beam integrity.Depending on the pitch,I've seen risers that leave less than 2" of continuous wood from floor to floor.Any grain runout diminishes carrying ability further.Of course the notches themselves are stress risers.
The strongest stair is made by seating the tread in shallow mortises in the stringer,easily made with a router and a site made template.Adding risers under the tread decrease their deflection and depth of mortise required.
There is an old saying about “glued & screwed” for a reason.
Are the stairs going to be covered with carpet? Completely open? What look are you going for? If it is all going to be boxed in and covered, you can have the side runners solid without notching or mortising.
In a big job, an extra 4 man hours is no deal and I wonder why he is not liking this? Maybe has no one who is skilled enough for a open wood finished stairs? Should just add in to his bid…
I do want it finished, wood, with later on to have brass carpet runner holders and carpet in the center.
However, the actual look is something that depends a lot on what I want to do with the upstairs.
Why are they complaining about countersunk screws if I say I want to pay them extra? The same reason that ALL contractors I know (even my really good plumber) give me funny looks - they live in a cookie-cutter world, and any time you try to step outside their comfort zone they freak. I’m sure there are lots of “outside the box” contractors out there, but damned if I can find them. It’s like when I told the electrician that I wanted “code plus”, and he looked at me like I was crazy and said “you don’t need that.” and I said “but I want it, how much extra will you charge me?” and he said “nothin, because we don’t do that.” :rolleyes: