Stair Calculations; calculation check please

[Chris Hogg]

I'm planning a step down from a utility lobby into our garage (there is a solid fire-door at the top). I want the minimum intrusion into the garage, as it's narrow and the car won't get in if the step sticks out too far.

(I hope this graphic works!)

door | | _|_|______ lobby floor level | | _________| | | garage floor level_______|

The difference between the two floor levels is 420mm. I read that for a private stair, regulations require that the risers should be between

150 and 220 mm, so two risers of 210mm just fits those requirements. I also read that the going should be between 220 and 300mm, and that twice the riser plus the going (2R + G) should be between 550mm and 700mm. For a riser of 210, that means that the going can be between 130 and 280mm. 130mm would suit me nicely! But I also read that for a private stair, the maximum pitch allowed is 42°. Tan42° = 0.9, so 0.9=R/G, or G = R/0.9, or in my case with a riser of 210mm, G = 233mm, which is between 220 and 300mm, so that's OK.

Can someone confirm that the calculation is OK?

[Andy Burns]

One of the online stair designers (that restricts number/sizes of steps based on total height) came up with two steps of 210 height and length of 234 even though that produced an angle of 41.9

[Chris Hogg]

Thanks Andy, I guess that's close enough.

[Andy Burns]

I guess 233mm rounds to above 42 degrees, so it disallows it?

[Chris Hogg]

Yes, it looks like it. But I can't think that anyone is going to notice 0.1°, and my measurements might be out by a mm or three anyway.

[John Rumm]

Looks ok to me. Can't see the pitch limitation really mattering for this application anyway.

[John Rumm]

When I did the stairs for my loft conversion the actual pitch cam out at a little bit steeper than the maximum permitted. Just had to make sure to answer the BCO's question carefully... After he had wandered up and down and looked and measured etc (I think he was quite impressed that someone had actually built their own from scratch rather than ordering them made to measure), he asked the question "And the pitch is 42 degrees or less?", "Yup should be", was my answer. He seemed happy with that!

[GB]

I measured the staircase here. It's a modern house, built in 1972 (as cheaply as possible!). It's an open staircase, and the treads overlap by

40mm. The treads are 240mm and the rise is 200mm, making an angle of about 45 degrees, because of the overlap.

It seems somewhat steep these days coming down, but fine going up. I don't remember a problem when I was a teenager. :)

If space is really at a premium, the OP could consider a hinged step, but that would be limited to a tread length of 210mm. A tread of less than about 200mm would be uncomfortable to go down as you would have to turn your foot sideways to get it on the step. You might want to add a grab handle.

[Chris Hogg]

An idea I hadn't considered. Yes, might be useful, thanks.

[ss]

It may not be relevent, when we got our house built and the door from the utility room in to the garage we had to have a `platform` built for the door to open on to, roughly a sq metre. This was due to building regs (Scotland) after the building was passed the `platform` was taken away and just the single step remained.

[Chris Hogg]

I suspect not relevant. Door opens into the lobby.

[Andy Burns]

:-)

[Vir Campestris]

How's that then? My foot doesn't fit on a 200mm step. It's actually about a foot long (amazing isn't it) which is 300mm.

Last year I slipped on a step and ended up testing the German hospital system :( - it was wet, and smooth at the edge.

No long term damage though.

Andy

[Tjoepstil]

I've never heard a health service described that way before...

[Fredxx]

I thought there were rules where you couldn't open a door onto stairs, and that there needed a platform of a certain size before descending any stairs.

This might depend on which way the door opens.

Others might be along shortly to shoot this concern down, or otherwise?

[GB]

My foot is also about 300mm long (funny coincidence), but only about

150mm wide. Turned at around 60 degrees, it fits onto the 200 effective length of these stair treads. Or I can walk down the stairs with my feet straight, but my toes projecting over the edge of each tread.