Getting cold feet on how I want to do my stone lintel detail - Any thoughts?

[GEO-PAR]

I need to order my stone cills and lintels asap but getting cold feet on how I planned to do it.  Interested to know what others think - Whether I'm being a little mad or if it will be okay?  

 

My intention was to have a natural limestone lintel self supporting. I only wanted it to bear onto the stone walls either side by 50mm (for visual reasons) but now questioning if that's enough.  I'll then stick a Catnik CN71A (or similar) above it with a 10mm gap for deflection (so the steel doesn't crack the stone if it deflects).  This steel will have your typical 150 bearing each side.  I want to keep this above the limestone lintel so when you look up at the window, you don't see any steelwork. 

 

 

 

Edited October 20 by GEO-PAR

[nod]

Why don’t you just sit the stone lintel in a catnic 

[scottishjohn]

If you do not use a catnic  with inset limestone  

then a lintel will need to be at least 150mm into wall each side and thick 

 you will need to be very specific on size with stone supplier if you want to set a one piece  one in wioth planty of clearance to fit it in as the steek defllects 

does not need to be thick as its just for show 

Is this a new build or extension on exsisting stone building 

[scottishjohn]

3 hours ago, GEO-PAR said:

10mm gap for deflection

19mm would be normal gap for bedding it --so maybe a bit more clearance 

you need to knpw the deflection to work out how big gap for bedding you will need,so it looks right 

[GEO-PAR]

3 hours ago, nod said:

Why don’t you just sit the stone lintel in a catnic 

Because then you'll see the underside of the steel when you look up below the window

 

[GEO-PAR]

3 hours ago, scottishjohn said:

If you do not use a catnic  with inset limestone  

then a lintel will need to be at least 150mm into wall each side and thick 

 you will need to be very specific on size with stone supplier if you want to set a one piece  one in wioth planty of clearance to fit it in as the steek defllects 

does not need to be thick as its just for show 

Is this a new build or extension on exsisting stone building 

I did wonder this.  I've seen it don't before where the edge of stone head aligns with the opening reveal (I.e so no bearing at all). No idea how you'd do this. 

[GEO-PAR]

3 hours ago, scottishjohn said:

19mm would be normal gap for bedding it --so maybe a bit more clearance 

you need to knpw the deflection to work out how big gap for bedding you will need,so it looks right 

Okay cheers

[nod]

55 minutes ago, GEO-PAR said:

Because then you'll see the underside of the steel when you look up below the Sounds an expensive way to go about it

[nod]

Just now, nod said:

57 minutes ago, GEO-PAR said:

Because then you'll see the underside of the steel when you look up below the Sounds an expensive way to go about it I would push your frames forward to hide the lintels It would cut your exterior reveals down to 50 mil 

[GEO-PAR]

44 minutes ago, nod said:

 

Yeah I appreciate it will make it a whole lot cheaper but it's not a house I'm intending to flip, so want to get it right.  But equally think what I've drawn may cause issues.  I'm wondering how they managed to achieve this - Super deep reveals with no exposed lintels.  My guess is that they cast the stones into some kind of concrete lintel. 

 

[Mr Punter]

With just 50mm end bearing I think the stone lintel will look wrong.  Go with 150mm minimum.

[GEO-PAR]

6 minutes ago, Mr Punter said:

With just 50mm end bearing I think the stone lintel will look wrong.  Go with 150mm minimum.

Yeah I think I'm going to boost it up to at least 100 if not 150 like you suggest.  

 

I found this picture where the bearing looks about 50mm, but it's granite so being a harder stone, I guess this makes it possible 

 

[scottishjohn]

8 minutes ago, GEO-PAR said:

Yeah I think I'm going to boost it up to at least 100 if not 150 like you suggest.  

 

I found this picture where the bearing looks about 50mm, but it's granite so being a harder stone, I guess this makes it possible 

 

still wrong ,

thelintel will be ok buy could crush those small bits under it

[Gus Potter]

On 20/10/2024 at 12:38, GEO-PAR said:

I need to order my stone cills and lintels asap but getting cold feet on how I planned to do it.  Interested to know what others think

@GEO-PAR I do like what you're trying to achieve, very elegant Architecturally.

 

On 20/10/2024 at 15:54, scottishjohn said:

you need to knpw the deflection to work out how big gap for bedding you will need,so it looks right

Deflection is a key.. will come to that in a bit.

 

I think you will have trouble with that at the clear span of some 1800mm. The way it is detailed is potentially risky in terms of failure of the stone lintel and bits falling on folk.

 

Here are a few comments (with my SE hat on) on the structural design of something like this at this span.

 

Firstly though for all stone lintels can work well if the span is short (image by @scottishjohn) and you have masonry above that is bonded to the top of the stone (no dpc / cavity tray as this acts as a slip plane) the composite action (stone lintel and masonry working together) form an arch thus the actual load on the stone lintel is small.

 

For a piece of stone spanning ~1.8m say with a shallow depth of 150mm the primary design force is going to be a bending force, unless you have a huge uninterrupted wall above which forms a bigger arch.

 

@GEO-PAR the detail seems to show the bottom of the Catnic in contact with the top of the stone. The Catnic is more "bendy" than the stone thus the stone could carry a lot more load than you expect not just its self weight. It takes a lot of finesse to design something like this that is not common bedtime reading.

 

I would revisit your detail before progressing. The quality of the stone, type, mechanical properties and knowledge of that is vital. If you have ordered and paid for the Catnic then you need to work around that. This is something that interests me as I love a bit of stone.. but to make more detailed comment I would need to know all the loads from above and how the floors etc are supported on the inner leaf for example.

 

In summary.. I would recommend that you check with your SE that your detail is ok... as it look a bit off to me based on what you have posted so far.

 

 

[jfb]

Can you not cut a slot in the back of the stone lintel to fully cover the catnic?

pretty sure that was what we did for our French doors (though we had an external steel beam not a catnic and were using bricks to finish)

[GEO-PAR]

Sorry - Didn't see these additional comments until now.

 

I'm attempting to go down the precast route...  50mm stone veneer to the front and underside (using the joint to form a drip detail) pinned into a reinforced concrete lintel. This way the stone will only need to oversail the opening by 50mm and the concrete can oversail by the typical 150mm. Just exploring the option not so not sure how expensive it will be. 

Edited November 6 by GEO-PAR

[GEO-PAR]

On 23/10/2024 at 09:09, jfb said:

Can you not cut a slot in the back of the stone lintel to fully cover the catnic?

pretty sure that was what we did for our French doors (though we had an external steel beam not a catnic and were using bricks to finish)

Not really sure what you mean - Are you able to sketch?  Did you just cut the slot about an inch above the bottom of the brick?  

[Russell griffiths]

In a former life I was a bricklayer, I remember doing a job to clad a concrete car park in brick, the brick continued over the openings in a soldier course. 
there was no catnic lintel instead a very thick 10-12mm stainless steel angle was used, this was bolted back to the concrete structure. 
the brick soldiers had a groove cut into them that fitted around the steel. 
This can probably be explained better by @Gus Potter

 

ive recently done some stone cladding on my place and did something similar 

@GEO-PAR not sure if this is any help to you. 
large angle instead of a catnic recessed into the back of the stone. 
poor picture I’m afraid  

[jfb]

15 hours ago, GEO-PAR said:

Not really sure what you mean - Are you able to sketch?  Did you just cut the slot about an inch above the bottom of the brick?  

Correct. Though it was a little more tricky because the bricks had a slight arch to them 

[Gus Potter]

23 hours ago, Russell griffiths said:

In a former life I was a bricklayer, I remember

You probably did this many times.. so will know what your doing.

 

23 hours ago, Russell griffiths said:

This can probably be explained better by

To jog your memory they are Halfen channels or similar.

 

 

[GEO-PAR]

Cheers for all the feedback guys. I don't know if this makes much difference to your suggestions above but my lintels are going to be chunky beasts (I want the traditional cottage look where you get very deep external reveals).  For the doors, they're H210 x D325 and for the windows they're H210 x D230.  

 

 

I'm currently exploring two options: 

 

01: Purchase stone in 50mm thickness to act as a veneer.  There will be a joint to the underside but i'll need a drip detail anyway so I'm thinking I can obscure as the drip. We did this on a big commercial project I worked on where most of the facade was stone faced precast but we had traditional hand-set stone for the two entrances.  They made timber moulds, placed the stones in the mould, and then pour concrete over the top. Unfortunately I'm too small fry for the company that did it to be interested but I have found a much smaller pre-caster that have said they'll price it up.  Not 100 percent sure this is going to be the cheapest option but exploring it at the moment.  It feels like the most robust option and will enable me to put lifting eyes in so I can telehandler them into position with less risk of damage to the stone. 

 

Option 02: This is based on your suggestion above: Metal angle that is cut into the stone.  I'm thinking it might be a good idea to weld some rods to the angle and chem fix them to the stone to prevent any rotation or slipping (or am I over thinking / is this a bit daft?).  It feels to me like this could be a much cheaper solution to be fair. Not sure what size angle I'll need for my size of lintels - Will have to ask the S.E I guess

Cheers

 

 

 

[GEO-PAR]

Had a quote come back on making the lintels into stone veneered pre cast - £6k!  🤦‍♂️

 

Spoke to my S.E about notching the back of the stone for a steel L Section and he thinks it won't be any different than the original method drawn at the top of this thread.  He said if my steel deflects it will crack the stone regardless of whether it's notched in the back or above. 

 

He suggested instead sticking with the original plan at the top of this thread, but oversizing the steel catnik CN71A above the stone lintel (so it has like a 300mm bearing instead of 150) and keep about a 10-15mm gap above.  I worry it might look a bit shit with my stone jointing being so tight but equally don't want cracked stone lintels with how much they cost! 

 

Am I over thinking this?