Pilot hole into a roof joist at mid-span

[Elandrel]

I’ve caught the edge of a roof joist with a pilot hole I drilled vertically up from the floor below. The hole is into the mid span of the roof joist around 3m in from each supporting wall (I think, I’ll need to check later). The hole is c. 15mm to 20mm deep and 2.5mm diameter. The joist is around 2”x3”.

The cold water tank sits on three of these joists. I nicked the centre one of the three. The other two are spaced at around 450mm centres.

I drilled two more 2.5mm pilot holes 60mm apart on the centre-line of the same joist at approximately the same location after I realised I was an inch off.

I realise now that there might be a crack risk I need to be worried about as I'm in the higher risk tension zone of the joist? I don't want to exaggerate the risk as it can't be uncommon that people nick these joists when doing DIY. I can’t see any evidence of a crack. But equally, I don't want to dismiss a risk that I should be concerned about. How much of a concern is there? Should I look into fitting a metal plate as a precaution in case of high winds putting additional load on the roof?

I’ll get a photo later.

 

[Deleted member 323070]

I suspect that most potential respondents will wait for the photo.

 

[Deluks]

2.5mm?

Not worth worrying about.

 

[Elandrel]

I've attached two photos. One shows the pilot hole almost at the edge of the joist as evidenced by minor side wall breakout (see orange circled area). The second photo shows the general location, including water tank; the general joist locations are shown by the orange lines and the hole location with an arrow. A support for the centre of the roof is shown just to the right of the water tank. The tank is on a plinth; it isn't the full height of the insulation.

The roof span is 7m. Two 2" x 3" joists have been used to span the gap. The two are nailed together with an 800mm overlap at the roof span centre. There is no wall support mid span. The tank is a 40 gallon cold water header supported on three of the joists.

Is it usual to have such small roof joists (2" x 3")? Especially with no mid span support and supporting a cold water tank?
There may be mid span support for the other joists from a combination of stud or masonry walls beneath. But the one shown has no mid span support as is runs above a corridor.

 

[Elandrel]

Another angle showing more of the surrounding roof structure down the centre-line.

 

[Deleted member 323070]

Is it usual to have such small roof joists (2" x 3")?

How long has it been like that?

 

[Elandrel]

Looks like I may have a roof design where the loft floor load is transferred to either a central vertical struts (a "king post"?) or two smaller vertical struts c. 3m in from the side walls ("queen posts"?). If so, then the 3"x2" joists can be treated as two separate 3.5m sections carrying only the imposed loads between the side walls and the central strut. The joist I drilled into is supported by the queen posts.

I checked the roof and oddly there are a few joists that are not connected by either a king post or queen posts. Which has me wondering if they are an unsupported 7m span. All the joists are connected by lengths of 2"x3" that run the length of the roof space about 3m in on either side. But these are nailed down into the joists below. The joists would therefore tend to pull away downward from the runner under gravity over time?

Any thoughts on whether I have a combined king post / queen post design from the photos? If so, then the 2"x3" joists aren't carrying much load and my pilot hole shouldn't be significant.

 

[Elandrel]

How long has it been like that?

It has been like that since it was built in the 60s as far as I can tell. So 65 years. And no doubt your point is that it hasn't fallen down yet. Which is a point well made.