Cat flap cut through weakens single skin brick wall?

[Safety First]

Apologies for rubbish drawings....

TLDR-
Single skin brick wall 2.15m wide x 1.05m tall, under some load, and on dubious slab/footings.

Will cutting a catflap through it, say 1 brick above slab, weaken the wall significantly?

I am thinking chain drill and gingerly knock out.


Long form
Over the last year (plus) I have re roofed a pretty rough single skin lean to out the back of our house. It's a small corridor with storage left and right then a door out to garden.

It was half glass roof and half tiles. East side timber and glass 'conservatory' built on 105cm high brick. Normal tiles on West side over full height brick walls.

It is now tiles across entirely given my timber framing loading on the dwarf wall.


The probably very shallow slab and minimal footings worry me re weakening the wall with
The dwarf wall has no cracks in it now.

 

[tony1851]

Depends how big your cat flap needs to be.

 

[freddiemercurystwin]

Is this one of those joke threads?

 

[Safety First]

Deadly serious.
Our cat is fat, and that's that.

I know about the 'triangle' load spreading voodoo, having removed lintels above fireplaces.

Wondering if it would be very bad, for instance, to remove the lowest brick on the slab.

The cat is old and wouldn't enjoy a catflap 3 bricks high.

 

[mattylad]

If your worried then put a cat lintel in

 

[freddiemercurystwin]

Otherwise it could be catastrophic!

 

[tony1851]

Deadly serious.
Our cat is fat, and that's that.

I know about the 'triangle' load spreading voodoo, having removed lintels above fireplaces.

Wondering if it would be very bad, for instance, to remove the lowest brick on the slab.

The cat is old and wouldn't enjoy a catflap 3 bricks high.

Cutting a hole one brick wide x two bricks high at the base would not affect the wall.
Just drill the mortar joints out instead of hacking it away

 

[Safety First]

Thanks Tony,
AI advised very much against removing the lowest brick currently on the slab. I assume it gathers this knowledge from nerds who talk Bricks online. It never takes the p155.

As my lion is so tall, it looks like I can leave the bottom two courses intact and sit the catflap on 2nd brick up. AI says this is good as the forces of the wall will largely bear around the hole.

I know this all a bit bonkers, but I need to be cautious as the project is pretty much finished and I have so far done well. I can't tell how much structural redundancy there is so need to go carefully.

 

[freddiemercurystwin]

I built a step outside for our cat.

 

[Safety First]

You think I should put the hole through higher, and so maybe build a step?

 

[stevie888]

OP if you're worried then take out 1 whole brick for the top part of the hole and the bricks above will span that untill hell freezes over. Doesn't matter now what you do below so 2 half bricks on the next course and a whole brick below that. You now have a 9inch square hole.

Cut the mortar out as Tony advises and go gently: you may damage the wall making the hole if you're kack-handed but its presence is not going to matter at whatever level suits your cat.

 

[robinbanks]

AI advised very much against removing the lowest brick currently on the slab

Then it's talking absolute cobblers. I asked ChatGPT about removing a single brick from the bottom course, and alternatively one from the next course up, which was safer? It said removing the one from course two, because the wall would still be supported by the row of brick below..
..like the foundations do nothing to support removal of a brick from row one..


The most serious threat to the structure and integrity of your single brick wall will be the process by which you remove the bricks. Powering an 18kg breaker through the wall will have a very different outcome to cutting a hole from both sides using a 9 inch diamond wheel aligned with the mortar perps in one row and cutting to leave two half bats on the row below

 

[Safety First]

Then it's talking absolute cobblers. I asked ChatGPT about removing a single brick from the bottom course, and alternatively one from the next course up, which was safer? It said removing the one from course two, because the wall would still be supported by the row of brick below..
..like the foundations do nothing to support removal of a brick from row one..


The most serious threat to the structure and integrity of your single brick wall will be the process by which you remove the bricks. Powering an 18kg breaker through the wall will have a very different outcome to cutting a hole from both sides using a 9 inch diamond wheel aligned with the mortar perps in one row and cutting to leave two half bats o

Then it's talking absolute cobblers. I asked ChatGPT about removing a single brick from the bottom course, and alternatively one from the next course up, which was safer? It said removing the one from course two, because the wall would still be supported by the row of brick below..
..like the foundations do nothing to support removal of a brick from row one..


The most serious threat to the structure and integrity of your single brick wall will be the process by which you remove the bricks. Powering an 18kg breaker through the wall will have a very different outcome to cutting a hole from both sides using a 9 inch diamond wheel aligned with the mortar perps in one row and cutting to leave two half bats on the row below

I agree that AI is highly flawed in many cases.
It does though, always scour the totality of the information you give it. In this case particularly, including that the foundations and slab are dubious.

Fully appreciate and thanks for the cautious anti-percussive removal methods.

The loading and geometry, building and removal of bricks isn't obvious!

Thanks all again.

 

[mattylad]

I'm no expert however leaving the bottom brick in may help when it's raining so water does not flood in through the cat flap.

Do conservatories (I assume that's what it is) not have a DPC?

 

[robinbanks]

I agree that AI is highly flawed in many cases.
It does though, always scour the totality of the information you give it.

I agree, and I work with various models daily. It generally gives an answer designed to be pleasing, and you can get it to make alterations the outcome based on how you phrase the question (and you then interpret the response which introduces another slant..) but it is indeed a useful tool, like a cautious 10 year old that's read the entire internet

One thing is certain; an AI has never built a wall, nor knocked a hole in one. Dodgy foundations or not, if the wall is presently standing, putting a 200x200 hole in it will have no discernible effect, even if the hole were made right at the end of a leaf so there was only brickwork on one side of the hole it wouldn't fall down, unless the mortar is completely shagged and can be wriggled out with a pencil. Even if the foundations were made of sand, there would be no change, because a hole of that size just doesn't have a significant enough effect on the transmission of self-weight load down the wall. By the time you're at the bottom of the bricks on the row below the load triangle will have closed up again..

If you want to be ultra careful, you could look at hiring a large core drill and drilling through the wall (no hammer) - cat flaps can be fitted to round holes