Risk associated with making a hole in a wall
Risk associated with making a hole in a wall
(OP)
Hi. I'm curious about whether there is any unacceptable risk associated with making a rectangular hole in an external house wall.
In the picture, the wall is a no fines wall. That is, its made off pebble aggregates (20mm dimmer) coated in cement. There are many voids. It's a wall developed by the construction firm Wimpey in the UK. So, it's type of concrete wall, but not solid throughout. The wall is 340mm thick.
You see that there is a lintel over a length of 1800mm which covers a door way and a window opening. Note that the back wall to the left of the left edge of the door way goes for about 30 feet to the left, and the wall, to the right of the right side of the window opening goes about 20 feet to the right. Effectively we are looking at a doorway and a window opening in a 56 feet long wall.
There are two rectangular holes marked on the wall, each 200mm long by 55mm deep that go right through the wall. The bottom hole is hole "B" and it's at 60mm from the floor level. Now, if I make a hole in this position I have no worries about risking any structural problem. Now, hole "A" is in a position that is 30mm from the edge of the window opening right edge. The question is, would making that hole present a risk? My intention is to make a metal box of 10mm thick steel to fit in the rectangular hole, but is there a risk associated with making the hole, before I get to put in the steel box?
Hole "A" is almost tantamount to taking a notch out of the wall 250mm long, where there is a gap on the left of that notch( i.e the window opening).
I'm not asking for any calculations or any approval to make hole "A". I'm just seeking a knowledgeable person to express an opinion about whether making hole "A" represents a risk that should not be taken. I could probably make the hole in two goes, that is doing the right half first, putting in a supporting box, then doing the left half and putting in another supporting box. I do realize that no one may wish to give an opinion. Thanks.
In the picture, the wall is a no fines wall. That is, its made off pebble aggregates (20mm dimmer) coated in cement. There are many voids. It's a wall developed by the construction firm Wimpey in the UK. So, it's type of concrete wall, but not solid throughout. The wall is 340mm thick.
You see that there is a lintel over a length of 1800mm which covers a door way and a window opening. Note that the back wall to the left of the left edge of the door way goes for about 30 feet to the left, and the wall, to the right of the right side of the window opening goes about 20 feet to the right. Effectively we are looking at a doorway and a window opening in a 56 feet long wall.
There are two rectangular holes marked on the wall, each 200mm long by 55mm deep that go right through the wall. The bottom hole is hole "B" and it's at 60mm from the floor level. Now, if I make a hole in this position I have no worries about risking any structural problem. Now, hole "A" is in a position that is 30mm from the edge of the window opening right edge. The question is, would making that hole present a risk? My intention is to make a metal box of 10mm thick steel to fit in the rectangular hole, but is there a risk associated with making the hole, before I get to put in the steel box?
Hole "A" is almost tantamount to taking a notch out of the wall 250mm long, where there is a gap on the left of that notch( i.e the window opening).
I'm not asking for any calculations or any approval to make hole "A". I'm just seeking a knowledgeable person to express an opinion about whether making hole "A" represents a risk that should not be taken. I could probably make the hole in two goes, that is doing the right half first, putting in a supporting box, then doing the left half and putting in another supporting box. I do realize that no one may wish to give an opinion. Thanks.






RE: Risk associated with making a hole in a wall
That is a "must know".
Will there be a structural member vertical between floor and the lintel between the door and window? Not just a door trim or window trim and water-proofing, but afull length structural member that the trim and flashing will attach to?
RE: Risk associated with making a hole in a wall
I noted in an earlier posting that changing the load regime of an existing structure can have some unanticipated effects and the owner should be advised that some cracking of the existing wall above the opening may occur.
Dik
RE: Risk associated with making a hole in a wall
A wall of 340mm thickness is 1706Cm long, 5181mm high. Near the middle of that wall there is a rectangular opening that is 1800mm long in the horizontal and 2050mm in the vertical. Atop which is a lintel.
If you cut a rectangular notch into that wall, starting at the right edge of the opening, that is 250mm in horizontal length and 85mm in vertical length, the bottom of that notch at say 1030mm from the floor - would that notch present some sort of structural risk?
This in a case where the top of the wall is holding up the edge of a roof? Force on top of wall unknown.
( No support of the lintel in the middle, only the ends.)
Strictly, I'm not seeking to cut a notch. At any rate, I think in this case, the risk is a function of how I go about making the hole. As has been alluded to. It's how I go about making that hole. In which I may need instructing.
RE: Risk associated with making a hole in a wall
What is the existing foundation? How are you impacting them? You could be overloading portions of it and if supported by grade beams you could be causing portions of it to crack and fail, in flexure or shear.
If the existing wall is on piles, there could be 'arching action' occurring between the piles, with little or no loading going to the grade beams. What lateral support is provided to or by the wall? You need more information.
Once the needle beam is correctly installed, it's just a matter of carefully removing portions of the wall as required. It may be a matter of providing some temporary lateral support of the remaining wall, etc. The openinc can be made by sawcutting or removal of the CMU units.
I've attached a design development sketch that I've used with other works; the sketch is illustrative only and very preliminary.
The reason for the pockets noted in my first post was to provide bearing support for the lintel, steel or concrete...
Dik
RE: Risk associated with making a hole in a wall
EDIT: Given that there is a space under the lintel, I will (if required in the interests of reducing risk) be able to put under the lintel on the right hand side a prop (An acro prop here in the UK). That prop can be tightened to exert an amount of upward pressure on the lintel. So, when I create that 220mm x 85mm hole there is some measure of support on the right hand side of the lintel. After the hole is made the intention is to put a steel box inside the rectangular hole made of 10mm thick steel plate. Then run pipes through the hole.
RE: Risk associated with making a hole in a wall
Now, I'm looking at this problem as a lintel support problem, perhaps that is good enough. My intention to create a hole may be considered as effectively cutting a notch at notch #5 position.
My analysis is this: Any hole above the shelf line is effectively a notch which leaves the lintel held up by a cantilever made by a section of the wall. Below that line there is no cantilever. Any hole made below the shelf line is relatively a small risk. The risk increases the higher it is up the wall. At # 15, a notch, there is no support for the lintel and the lintel falls. Now, at notch #5, the depth of the cantilever wall support is 850mm and the length of the cantilever is 250mm. This cantilever is shown by the darker lines in the drawing. The drawing also shows where I would put a prop, between the lintel and the shelf top surface.
Now, let me try to put words in your mouth and see if they can be accepted. These words are: "If you create a hole at notch # 5, place a prop in the position shown to be doubly sure that the lintel will not move. Do not just rely on the cantilever."
EDIT: It would probably be wise to install two props, sitting on a beam, so the load would be spread along the shelf top. That shelf in my case is actually the top of the concrete, that is the wooden shelf board is removed at present.
EDIT: I could play safer and create a hole in # 3 position, avoiding the creation of a cantilever.
RE: Risk associated with making a hole in a wall
Also, if I put in a box made of 10mm thick mild steel into the new hole, I suppose that may need to be made to exert some upward pressure on the cantilever, before the props are removed. Would that be correct? Thanks.
RE: Risk associated with making a hole in a wall
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
https://www.facebook.com/AmericanConcrete/
RE: Risk associated with making a hole in a wall
RE: Risk associated with making a hole in a wall
Even if it doesn't crack when you make the opening, without proper detailing you could easily cause issues down the road. Buildings are not static.
If it is easy and risk free as you say then getting a qualified person to investigate will cost a minimal fee. It should also be a small fee to find out if it is easy or not. If an engineer looks at it and quotes you a high price to do the work then maybe it wasn't so easy and risk free as you thought.
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
https://www.facebook.com/AmericanConcrete/
RE: Risk associated with making a hole in a wall
RE: Risk associated with making a hole in a wall
I agree. The 30mm strip of wall should be regarded as having no strength particularly with 20mm diameter aggregate and many voids. Whether the wall can perform satisfactorily with the notch would depend on the lintel reaction and the shear strength and tensile strength of the wall. Without a lot more information about the loads and material properties, I would consider the cutting of Hole 'A' to be a risk not worth taking.
BA
RE: Risk associated with making a hole in a wall