screwing into ceiling joist

[rjlwest]

I have a studfinder, a bosch gms120 but it's readout is inconsistent, the place I'd like to screw is about 1.5m from a light and it seems to think there is a livewire everywhere. Would I need to go into the loft to mark out where the joists are? can i just knock on the ceiling and accurately find one? is there a common logic to wire placement leading to a light or should I try and find where the wire leads? or should the bosch be working and I'm just using it wrong?

 

[Belboz]

How long are the screws?

Generally, there will be cable leading to and from your light fitting which could be tacked to the side of the joists or just lying flat beside them on the ceiling plasterboard. Chances are you will have wiring going to the light from the switch and wiring either side of the fitting going to the next light fitting (looping) Where these cables need to go through a joist, there will be a hole with the cable going through it. That hole should be drilled so as not to weaken the joist structure so ought to be above the height of the plasterboard underneath by quite a few mm.

Chances are your detector is hitting on the cables lying parallel with the joists. In a normal installation, save for those holes, there shouldn't be any issue screwing into the centre of the actual joist (because the cables will either by lying beside them or tacked to their sides) but long screws could screw into a cable if you are unlucky enough to be screwing into that part of the joist where there is a cable going though the drilled hole.

Does that make sense?

 

[PrenticeBoyofDerry]

I have a studfinder, a bosch gms120 but it's readout is inconsistent

Most of them are.

the place I'd like to screw is about 1.5m from a light and it seems to think there is a livewire everywhere.

They could well be

Would I need to go into the loft to mark out where the joists are?

You could and identify if any cables are in the area

can i just knock on the ceiling and accurately find one?

I doubt it

is there a common logic to wire placement leading to a light or should I try and find where the wire leads?

There are regulations on where they should be and how they are protected against damage, but those regulations are not always followed and depending on the age of the installation they may not have existed then

or should the bosch be working and I'm just using it wrong?

It will work to a limited ability, nothing I would trust with any confidence with my life.

What is it you wish to screw into ceiling?
If I am in doubt, I would measure exactly where I wanted to fit to, pierce the ceiling with a pilot hole, small thin shafted screwdriver. Then go into loft space see where the hole has appeared and but a brace or noggin between joists to catch the screw location. Alternative is to go it to loft, find a suitably located joist, pierce joist at an angle inward to joist, Then you have the location of your fixing position below.

 

[rjlwest]

all good information cheers. looks like I'll have to go i into the loft for this one.

its to hang a punchbag, what Im screwing is some of those wall anchors, I have absolutely no experience with them though.

 

[PrenticeBoyofDerry]

For punchbag, I would be putting a strong brace across the joists and bolting bag up with nuts/bolt. Otherwise it is not going take the stress.

 

[rjlwest]

its this thing

i thought it might be enough

 

[JohnD]

you might consider going into the loft, and bridging a short piece of timber on two or more of the joists, and hanging your swing off that, with a large eyebolt and an even larger nut and washer on the upper surface. You can use a screw-closing carabiner to hang off the eyebolt, so it is readily removable.

Suspending it from two joists will greatly reduce the risk of cracking the ceiling or bending the joist.

edit
too slow

and the fastening in your pic looks like it is intended for screwing into brick or concrete, not wooden joists.

 

[rjlwest]

whats the best way to connect timber to the 2 joists? and what you do mean by larger nut and washer on the upper surface?

 

[Tigercubrider]

Bear in mind that the ceiling joists are quite weak.
They are only designed to hold up the ceiling, whereas the downstairs ceiling has sturdier joists as a floor is above.

Spread the load as much as possible

 

[JohnD]

eyebolt

and to prevent the nut sinking into the timber, a large washer or steel plate under the nut

Flanged locking nut

 

[JohnD]

see also //www.diynot.com/diy/threads/suspending-load-between-2-rafters.331770/#post-2464414

 

[rjlwest]

thanks chaps

 

[Ian H]

If the joists sit on a solid wall you will want to put it as close to the wall as you can.

 

[rjlwest]

I'm just about to add the brace, what are those lines there? it looks like plaster but it's on top of some black mat. I ant to chisel it away so I have a level floor, is that advisable?

 

[JohnD]

How old is the house? (this is important) and is the plaster greyish white, in ripples, bulging up above the black lines?

And are the black lines thin wood, about an inch wide?

Don't chisel anything away, and don't use a hammer up there.