Mount steel staircase to floor

I'm getting a steel staircase built for my basement. The welder is using a 5x5" steel tube, 5/8" thick and he told me it will have a total weight of approximately 1000 lbs.

He somehow needs to attach the bottom plate to the floor. Usually this wouldn't be an issue, although the basement has in-floor heating (water/radiant) so drilling into the floor is a risk.

On top of the concrete floor I am going to install 7mm vinyl planking. If possible, I want to lay the floor under the bottom plate (continuously) so I don't have to work my way around it.

I'm assuming the only way to figure out where the tubing for the in-floor heating is exactly positioned in the floor is cranking up the heat and use a thermal/infrared camera. I don't have one and I found out they are very expensive.

Would there a way to avoid drilling into the floor and yet have the stairs attached safely to it?

Hi, I'm assuming this staircase is spiral as you wouldn't need to secure it if it was straight. I'd bite the bullet and epoxy the steel to the floor and install the vinyl around it.

Just did a quick lookup. 1 person rented a camera and another person mopped the floor with the heat on high. the water dried over the tubes first. The only other thing I cann think of is hire someone to map out the whole floor for you and then you have a map for future reference.

It's a regular staircase with a 45 degrees angle (the last 3 or 4 steps) at the bottom. Not a spiral staircase.

I'll look into renting a camera since buying one is not really cost efficient in this case.

There's not that many options around here, so if renting is not possible, we will probably try epoxy.

I would try the heat on high and mop the floor trick first - fast and easy. If that doesn't work well enough then try renting a camera.

Two thoughts...  Do you have to attach it to the floor if it's attached at the top?  It's likely but maybe it's not as critical as you think.  Or maybe you can do very short stubs into the concrete.  It's likely that all you need to do is keep the bottom from "sliding away" from the connection at the top.

My second thought is that you may or may not want the vinyl going under the stairs.  Is the vinyl rated for that amount of pressure in one spot?  Or might it compress and then buckle up nearby?  Or does it need room around the edges for expansion/contraction with temperature fluctuations and now you're pinning it down in one spot?  The vinyl manufacturer should have details on that in the instructions (I think).

I am with Mike.
If the system is attached at the top it will not move. Its simply a physics issue.
Its heavy enough not to be accidently moved from a kick at the bottom.

I'll try to do the mop trick tomorrow, hopefully that will already give me enough information since it's only a small area I need to figure out.

I was only asking since the welder told me he wants to secure it to both the ceiling header and the floor.

The stairs that I took out were just made of 2x10's and 3 stringers. They were only nailed into the ceiling header. Those stairs indeed never moved back and forth in the 11 months we live in this house. Of course it was way lighter than my new stairs, about 200 lbs.

The floor plate will be very small, probably something like 6x6". I will double check if this will cause any problems when the stairs will be on top of the vinyl. They said it shouldn't be an issue...

Turns out the stairs will have an approximate weight of 550-600 lbs and not 1000, I misunderstood the welder.

The past few days I did two tests with water to figure out the in-floor heating without any luck. We will most likely drill a few small holes at 1 inch deep to put steel stubs or bolts in, like Mike said.

This week we also tested the steel tube to see if the angle is correct, see attached images. Just the tube already weighs 260 lbs.

The only thing that keeps worrying me is how the top plate is going to be attached to the header at the ceiling. I keep thinking that one day it will come down and drops on one of my kids 😖

The welder said it's absolutely strong enough, but it keeps bugging me...

Interesting, the stairs bend in the middle.  That's information that could change things...  Is there just one tube down the middle with the treads attached to it?  How big is the plate that will be attached to the header?  If he's a professional metal worker, I'd trust that the plate won't come off of the tubing.  Now if the plate is 4" by 4" and attached to the header with small screws, those are different failure points.

Another way to maybe find the water is to turn the heat on and use an infrared heat gun to measure the temp of the concrete floor.  Yet another way might be to use a stud finder to see if it somehow finds the water in the lines.  It would probably also find rebar or not find anything at all.

Maybe your welder could add a foot to the central tube that attaches where the tube bends and goes straight down to the floor.  That would help give the stairs more support at the bend.  And distribute the weight for the vinyl flooring

He's a professional metal worker / welder indeed, he does very complicated projects and stairs like these are just an average job for him.

The steel plate at the header will be about 13" high and 36" wide.

It will be just one 5x5" tube (5/8" thick) with steel plates (8" x 36") welded on top. I will put pine treads on top.

I'll keep thinking about finding the water lines, I can try my stud finder this weekend. It's just hard to find and/or get something done around here. I could buy an infrared heat gun but they're about $500 CAD and I don't really have use for it after this project.

I use an Infrared temp gun for my racing sidecar tyres and exhuast pipes, it cost about $50. Not $500

John, can you please share a link or let me know the brand and model so I can look into it?

Ok, then as long as your header is a solid piece of wood that's well attached, the metal should hold the staircase just fine, likely regardless of the bend in the staircase.