installing new interior stairs

Old 06-25-05, 12:36 PM
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installing new interior stairs

Right about now I could use all the help I can get!!!! The stairs in our home have come down and I am "trying" to figure out how to replace them. Had a friend from work explain to me how to calculate the measurements on making new stringers but, for some reason, it's just not working!!!!! The original stringers were "notched" out and the treads were shimmed in. This time, I'm trying to go with, the best way to describe it, I guess is ... saw tooth.... and it's just not matching up right!!!!!!! So... before I buy out the whole lumber yard, could someone please guide me in the right direction?!!! Where should I be measuring from? The landing upstairs, the ceiling? Or do I have to stay with the same way they were put in originally? Any help will be greatly appreciated! Knew this would be alittle harder than deck stairs but had no idea!!!!!
Old 06-25-05, 02:32 PM
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This is fairly advanced stuff here. I'm an amatuer and I just did a housed stringer rebuild and I also replaced the framing stringers (2x12 Doug Fir). I assume you're talking about the latter. By the way, you should get kiln dried 2x12's because the typical HD stuff is way too wet for this type of precsion work. I had to get those from a full service lumber yard. Many carpenters are laminating 2 strips of 3/4" plywood to make stringers nowadays since they are dimensionally stable. Anyhow here is the procedure (You need a good square with stair gauges.

First measure the total run of the stairs. This is the distance from the first riser to the last riser (horizontally). Now measure the total rise of your stairs. This is the distance from the floor to the landing (all meas to finished floor).

Now divide the total run by the number of treads. Divide the rise by the number of risers (treads +1). Note that for now you are counting the last riser even though it may not be part of your stringer.

Now set your stair gauge for the rise and run you calculated. Draw your first run and rise on the stringer. The run represents the floor (as a ref) and the rise represents the first riser. Then continue as accurately as possible and draw in the last riser and landing also as a ref. It is highly recommnded that you check yourself by measuring from first run (actually the floor as if there was a tread there) to the last run (actually the top front edge of landing) and check this with pythag theorem (sqrt(total run +1(sqrd) + total rise(sqrd). If it's not within a quarter inch do it over.

Remember that code requires all rises to be consistent with 3/8" or so. This means you actually have to make the cut for the floor a tread thickness higher (shorter) than the line.

Draw a picture of all the risers and treads with dimensions so you don't get confused.

Also I learned a great trick from a carpenter to cut these more accurately (applies mostly to mitered skirt but can also be used for carraige). Even though a 12" sliding compound miter saw does not have enough capacity, you may still be able to cut the carraige by dropping the saw blade into the work and pulling the blade towards you. Using this method my mitered skirt fit my risers good enough to be stain grade which is saying alot.

By the way, you should really do an online search of the librarys in your area
for "Basic Stairbuilding". He covers this subject very well. Also, is this going to be hardwood treads or carpeted? It makes a difference in the required accuracy - they say paint grade hides all your sins then I suppose with carpeted treads you can hide a capitol offense

Good luck

Last edited by AlexH; 06-25-05 at 03:22 PM.
Old 06-26-05, 12:52 AM
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AlexH, you explained that very well. I should have come here when I was building a porch for my stepdaughter. When I was doing that I did my fair share of searching, and this page has a calculator that came in handy.

Hang in there fordmann. It'll all work out in the long run. ( I made a pun and didn't notice until right after I posted.)
Old 07-05-05, 02:47 PM
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so far you have been given good info. Don't for get to allow for carpet or what ever type of flooring you will be using. Also, to keep from cutting up alot of lumber, you can use a story line. Cut a scrap of wood the height of your stair, prop it up where your stair goes and mark all your riser measurments on it to be sure they all work. Math that you dived up will work, but you will need to allow for the framing material and flooring.
Old 07-16-05, 10:16 PM
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Home depot and lowes has a calculator just for that kind of stuff it cost about $50. bucks but think of the money you are saving doing it yourself and you won't have a pile of scape when your done it also comes with a book that is easy to understand. It will give you the angle you need to cut your stringers the lenght the size of each riser each tread where you want them to hit on the bottom floor an so on as well as roof framing and alot more you will be pleased try it,it will make you look like you know what your doing

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