Building riser on rear half of flag - Flagstone stairs

[scotpot]

I am laying a set of 7 stairs which are 6m wide with sawn flagstones which are 600mm x 900mm. The risers will also be clad using the flags so that no brickwork is seen.

My designer has recommended that the riser is built on the rear half of the 600mm deep tread of the step below to ensure step treads do not come loose over time. (I guess this is opposed to butting up to the riser?)

Is this the best approach?

FYI: total rise is 1020mm;
Step: 380mm tread; 145mm rise

[lutonlagerlout]

sounds like a plan but make sure the steps are built on concrete
i.e each flag must be laid on concrete
LLL

[Tony McC]

145mm rise is a bit awkward to arrange if you are bedding standard bwk on top of the preceding tread.

1 course of brick gives you 75mm, so you've 70mm to make up including the depth of the tread. No problem if the tread is 55-60mm, but if these are only 20-25mm thick, then you're 40-50mm short - less than a brick, but achievable with bits of flag offcuts (seeing as it's all being clad).

For awkwards size risers such as this, I usually suggest building the riser on a separate footing at the back of the preceding tread so that its height can be set precisely as required using basic bwk.

[scotpot]

Thanks Tony. Apologies in advance, I'm a complete novice and just want to ensure my designer isn't going to land my landscaper with a headache!

The flags are 20mm and my total rise is 1020mm. A 145mm was selected as we'd anticipated 7 steps [(7*145)+(7*20)].

So, an alternative is to lay two course of brick on a separate footing at the back and approx 10mm lower than the tread of the preceding tread, giving a rise of 145mm.

Would you say this is more beneficial than the extra stability provided by building on top of the lower tread? (Or is that marginal anyway?)

[lemoncurd1702]

Building on top of the paving slab leaves little scope to change the tread in the future.

Personally I would build the flight and lay the treads after so that each slab butts against the next riser.
Get your first riser right allowing for the 20mm paving slab plus the 20mm bed. Concrete behind riser far back enough to provide a sound footing for the next riser. Use extra raipid cement in your concrete to fast track the project.

I'm guessing there will be retaining walls to the sides of the steps also, so would definitely do it this way as the brick work will not stay in course with paving slab tread.

How critical is that 1020mm? If it's leading to a garden area, surely there's scope to adjust.

[scotpot]

I've seen another person mention that about there leaving little room to change the tread should it need doing . That was the ONLY comment I could find on this subject anywhere so it's good that somebody else thinks the same.

My landscaper is going to have these flags cut prior to starting the project, that's why I'm stressing a little over getting this right!

Yes there is some scope to adjust but probably only by -20mm / +40mm.

There will only be a retaining wall at one end. The other end will be clad with flags. Issue?

[lemoncurd1702]

If your building with brick and the side walls are on top of slab also, when the side wall meets the next step the coursing will be out of sync by 35mm.
Two courses 150mm + slab 20mm + bed 20mm = 190.
Three courses of brick 225mm. The third course will be 35mm higher than the slab on the next step.

What are you attaching the cladding to? If its brickwork the coursing will still be out making for some messy brickwork.

[Tony McC]

Thge only bissue with the cladding is getting the flags to properly and permanently adhere to the masonry. A standard sand/cement mix is not going to do it. There are special stone cladding adhesives from the likes of Mapei and BAL which are well worth considering.

[lutonlagerlout]

if the blockwork is true exterior tile adhesive works
LLL