Core drilling hole in supporting pillar?

[reg091]

The only way I can run cooker hood ducting in new kitchen extension is to run through a 300mm x 300mm brick pillar that holds up a newly installed steel lintel (wall knocked through).

This rings alarm bells: the ducting should be 150mm diameter and surely I shouldn't be core drilling a hole that is half the size of the pillar?!

Tell me I am being paranoid, or even better, tell me the max diameter hole I could drill (If I can safely drill a 100mm hole then I will have to reduce the ducting diameter for that section - not a good idea for the hood, but better than the house collapsing!).

 

[Notch7]

I doubt you can do that safely.

Only way to know is have a structural engineer confirm.

I assume the hole would need to be at ceiling height, in which case is that not about where the end of the steel is bearing.

 

[bernardgreen]

Could you biiuld a second column next to the one you are going to drill through. Lose a bit of space but at least the space will not be filled with collapsing wall

 

[reg091]

No, The steel comes below ceiling height (plasterboarded and skimmed). So, if run duct along ceiling it would hit the steel. So I have to do that and then drop down inside wall cupboards to get below steel before I 90 degree through the side of the cabinet and into the pillar approx 50cms below bottom of steel.

 

[23vc]

Not a structural engineer but I’m sure Notch is correct, the area below the steels is either going to consist of padstones or need to be a sound base for the weight distribution of the steels.
I’d go for extending the size of the pillar with a bit of boxing/studwork as per Bernard. I’ve had to do similar on mine.

 

[^woody^]

A 300 pier is substantial for a domestic load. If you actually needed a 300 pier, then there is no way you can cut any hole in it.

Normally the idea is to design the support so that a pier is not required, but too late now. And always best to put beams above the ceiling not below.

 

[tony1851]

Whether or not you can drill a hole through the pier depends on 2 main factors:

1. The load the pier is carrying from the steel beam. If you drill a hole - say - 100mm diameter, you will be losing 1/3 the cross-sectional area at that point. Whether or not the remaining brickwork each side of the hole will be sufficient to take the increased compressive stress it will be subject to depends on the crushing strength of the brick (usually quoted in the calculations you will have, in N/mm²) and the grade of mortar used.

2. It will also depend on how concentric the load from the beam is on the pier. In an ideal world, the load from the steel beam will go directly down the centreline of the pier so that the compressive stress is equally spread over the whole cross-section. In practice, this never happens; the steel beam will bend very slightly upwards where it rests on the padstone. This means that most of the load will be towards the inner edge of the padstone, while the load will decrease towards the outer edge of the padstone. The net result is that there is an 'eccentricity' in the load going down the pier, which tends to cause the pier to 'buckle' and so reduces its load-bearing capacity.

The short answer is that it would be perfectly possible for your SE to do the number crunching to check wheher or not your idea is feasible; in practice he won't do this because he'll be taking on a further liability, and why should he? In reducing the cross-sectional area, you will be increasing the local stress and may be taking it uncomfortably close to its allowable limit, which is not a good idea. Common sense says find another way.

 

[Ian H]

Is that the only outside wall? What’s above it?

 

[reg091]

See pic. The hood will be to the right of the pic and the ducting has to go up into the celiling above it and then down inside a cupboard close to the pillar you see on the left. It is that pillar that I have to drill through.

Behind the hood is a bathroom with no easy exit for a duct to the outside.

Above the ceiling is a bedroom with laminate floor and I don't really want to rip that up.

 

[Notch7]

Im not understanding, isnt your proposed duct hole either above the steel or just beyond the end of it.

Can you not go into the ceiling void and get above the steel.

 

[reg091]

I can't go beyond the end of the steel as it sits on that pillar and the is against (or further) the back wall.

I hadn't thought of going over it but coming out the other side of it will be where fascia used to be before the extension was added. I think the conservatory roof beams come down to a new gulley joining where the fascia used to be.

EDIT: better explanation (sorry!). Was a bungalow now with bedrooms above. So above that beam is where the sloping roof came down to fascia and soffet.Now conservatory has been joined to where that fascia was.

So a possibility is to go into the ceiling, along to the left towards the beam and vertically out through the sloping roof. But that involves roof work, condensation trap etc and that is beyond my diy skills.

 

[^woody^]

.... Los of technical stuff.....

Surely if you could cut a 100mm hole and leave a 200mm pier, it would have been designed/built like that in the first place?

 

[^woody^]

See pic. The hood will be to the right of the pic and the ducting has to go up into the celiling above it and then down inside a cupboard close to the pillar you see on the left. It is that pillar that I have to drill through.

Behind the hood is a bathroom with no easy exit for a duct to the outside.

Above the ceiling is a bedroom with laminate floor and I don't really want to rip that up.

View attachment 158174

That's a poxy design and work. Who wants massive piers and deep downstands.

Anyway, you can cut your hole in the top corner of the steel above the sensor. Difficult but do-able

Or if the joists are running in your favour, up and over in the ceiling void.
Why you are saying that it would be a bit disruptive is beyond me, surely it's better than living with the alternative eyesore for ever.

 

[tony1851]

Surely if you could cut a 100mm hole and leave a 200mm pier, it would have been designed/built like that in the first place?

No, because a 200 x 300 pier would have a much higher slenderness ratio (ie height/width) and so would have a reduced allowable compressive strength.

 

[^woody^]

No, because a 200 x 300 pier would have a much higher slenderness ratio (ie height/width) and so would have a reduced allowable compressive strength.

What does that actually mean? And I thought I knew a bit about this stuff.

Here's what I mean. If the beam did not need a 300mm pier, it wouldn't have one.