Jack Arch - Acrows?

[bmb4cjt]

Hi,

I need to replace the loose set of cut bricks forming overhand above this PVC window with a lintel (mainly for aesthetic purposes) before rendering. My feeling is the Jack arch is self supporting especially as the bricks below are loose, would you place some acrows in whilst taking the loose ones out to place the lintel or not needed?

 

[tell80]

The arch is self-supporting. No Acrow needed.
Removing the loose & uneven bricks, & mortaring back in bricks that fit the gap above the window frame is necessary for rendering.
A steel flat bar would suit as a lintel - see metals4u.

The upper light in that frame must be able to swing fully open - its maybe a potential means of escape.

Make sure a Bellcast is used above the opening - above all rendered openings..

 

[bmb4cjt]

Cheers @tell80 that's brill

 

[^woody^]

A flat arch does not self-support

 

[bmb4cjt]

@^woody^ I'll wack an acrow in just to be safe. In this area, know there isn't masses of load with the wall being small but would the original timber framed window have been bearing the load for that wall? There's a large timber lintel on the internal skin but nothing except the jack arch and a the loose bricks under on the outer. There are some more traditional arches on other window openings on the side of the house.

 

[Nozzle]

A flat arch does not self-support

What is the objective of such an 'arch' if it doesn't self support? I mean why go to the bother of building such a thing, for no evident gain.

This isn't a rhetorical question, or a question to nit-pick at your knowledge. It's a question purely of curosity.

Nozzle

 

[^woody^]

What is the objective of such an 'arch' if it doesn't self support? I mean why go to the bother of building such a thing, for no evident gain.

This isn't a rhetorical question, or a question to nit-pick at your knowledge. It's a question purely of curosity.

Nozzle

Mainly decorative. The support is mainly from friction, so its probably not true to say there is no self support, but there is little performance in the same way as a typical arch - the bricks tend to easily slide down.

Sometimes called a Chamber Arch as a slight chamber may be introduced to avoid the illusion of it sagging. But even so, its not an "arch".

 

[Deleted member 292770]

A steel bar as a lintel wont do . It’ll rust and blow the render off in no time.

 

[^woody^]

@^woody^ I'll wack an acrow in just to be safe. In this area, know there isn't masses of load with the wall being small but would the original timber framed window have been bearing the load for that wall? There's a large timber lintel on the internal skin but nothing except the jack arch and a the loose bricks under on the outer. There are some more traditional arches on other window openings on the side of the house.

Its like with just normal brickwork, sometimes it can just hold up with friction if you are quick and don't bang it about too much. You need to have a close look at it and assess it.

Even if it's a bit loose, you can sometimes knock some timber wedges into the joints to stiffen it up enough.

 

[bmb4cjt]

Sound, I'll place an acrow and bought a prestressed concrete lintel for the opening (1.5m) to replace the loose bricks, rendering chap felt his beading would adhere better to it anyways. I'll just take it easy.
Cheers for the help

 

[tell80]

Flat arches do self support.
With or without a chamber, the building trade name for such a construction is Flat Arch.

 

[tell80]

metals4u and similar steel stockists supply varnished and SS metal bars.

 

[stuart45]

Why's everyone calling a Camber arch a Chamber arch?

 

[tell80]

Agreed, camber is the usual name but, fair play, chamber is an alternative name. Chamber was already on the page so I stayed on page with it.

 

[stuart45]

Must admit I always say Camber, because of the slight camber at the base, although I've heard Jack and Skewback used. Done properly they are still an arch. A segmental one with the top and bottom extended. They are set out on the segment of a circle, so the arch is in there.