Fixing open stair tread(s) (moved from Projects)

[Boone76]

Hi all,
Sorry, I am a newbie here. I saw that this forum has specific stairs forum.
I need advice from experts here, I have open stairs (treads only, no risers) in my condo. The stairs are pretty old and badly needed some fixings (as I heard occasional creaking noises when I step on some of them).
One of the stringers is touching the wall so I have no access to the side touching the wall. Now, some of the treads are gaping from the stringers (as you can see from picture attached), and one of the tread actually caved in because the 2 nails which was holding the treads snapped. Currently I just add aluminum brackets to support the treads from underneath but I want more permanent and safer solution.

My questions are:
1. Should I remove the tread which caved in and replace it with new tread which is wider? FYI, the width of the space in between the stringers are 35.5" and there are 0.75" cut-out on each stringers to fit a 1.5" x 11.5" treads.
If yes, what size of treads should I pick? 37" width (because 35.5" + (2x0.75)) or standard 36" width. If 36" wide, is it safe because there will be gaps too? How can I make sure it's safe?

Also, any recommendation of the type of wood for this application? I am leaning toward red oak because I heard it is the cheapest hardwood for this application but they are hard to find at that thickness (2" x 12") and pretty pricey. Do you have recommendation on a good place to get them? I am on a budget so cost is important.
If not, how do I fix the treads, can I add wood to it, just insert to the gap and glue them? How do I safely mount to the stringer which is touching the wall, since the broken nail was on that side?

2. How do I fix the existing gaps of the other treads which had not caved in? How do I reinforce it?
Any suggestions?

Thanks in advance,

 

[Boone76]

One more question: Are these cheap douglas fir from Home Depot any good for my purpose?
http://www.homedepot.com/p/2-in-x-1...nd-Better-Douglas-Fir-Lumber-707195/202094201

 

[Doggit]

First check the width of the stairs at the top, middle and bottom, and see if there is a difference - is the outer string lose, and moving sideways, hence the gaps on the treads.

Unless there's something obvious, I think you'll find that this is a job for a carpenter. You're either going to add risers to the back of the treads to reinforce them (after have glued the treads in to the strings), or you're going to put noggins/supports under each tread either side of the strings. You can't add new treads, as they were slotted in to the strings, so you'd need to be able to take the complete stairs down to do any repairs.

 

[Boone76]

Hi Doggit, Thanks for the response. I checked and the gaps look pretty much the same, except the middle ones are a bit wider (<1/4" wider), I believe the previous owner has replaced one of the treads on the middle sections as I can see some nails from the side of the stringers that is accessible. I think he may have cut the old nails out and forcefully insert a new tread on that section.
About the noggins, what are they like? are they pretty reliable? I currently placed heavy duty aluminum L- brackets but I think it's not a safe solutions.

 

[Doggit]

Essentially, you want a piece of wood attached to the stringer, that supports the stair tread. You can glue and screw it in to the stringer, and then just glue it to the tread unless - you've got an angle drill of course. A piece of 2x1 should be sufficient, and a local woodyard may be able to knock up a moulding that look a bit more decorative, rather than just utalitarian. And you want a good quality PVA glue from a woodyard, not the local diy shop.