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Splicing ceiling Joists

10/11/18       
Ricardo Member

I need to create an independent ceiling using 2x4" with maximum span of 4.5m. Can I rely on the strength of an overlapped, glued and mechanically joined splice in the middle of the span to be strong enough.

The joists will be spaced at 300mm centres and will hold 2 layers of 15mm plaster board. I would prefer to nail them as there are about 30 to do and given the the glue strength wonder if bolts would be overkill.

Thanks in advance for any advice

10/11/18       #2: Splicing ceiling Joists ...
Pat Gilbert

Run that by the building department. That is not going to work at all.

10/11/18       #3: Splicing ceiling Joists ...
BH Davis  Member

No............not only will it sag and break at the joint but will most likely put you in prison for manslaughter when it falls on someone's head and kills them.

Even full length 2x4 joists over nearly a 15' span would likely fail with that much weight. I suspect that framing codes would have that as a 2x8 requirement given the double drywall layers.

I recently used 2x4 ceiling joists on a 7'+ wide room. One single layer of 1/2" drywall. Worked fine but I would not have used 2x4's if it had to have a 2nd layer of drywall for some reason.

BH Davis

10/12/18       #4: Splicing ceiling Joists ...
Adam

Couple of things

This is a professional woodworking site. Some of us are carpenters as well as cabinetmakers, joiners, stairbuilders, etc.

The vast majority of people on here are from the US. That's why you see mostly inches & feet.

You are from a mostly metric country. I'm thinking the UK maybe, because you start with a 2x4 then switch.

You are describing a nightmare of a ceiling. Check all of your dimensions. Wallboard is typically 10mm(3/8"),13mm(1/2"), or 16mm(5/8"). Those are the worldwide standards.

Most countries use 13mm(1/2"). Australia and New Zealand use really poor 10mm.

Your framing is crazy. It will not be code in any country.

You could use what's called a hanging beam in AU/NZ. You put a big beam up above the ceiling midspan and hang continous 2x4's from it. You should be able to buy 2x4's 4.5m long in most parts of the world.

No one will allow you to glue framing timbers together. If there is a fire the glue will fail. Most of us on here could glue up a beam, but its got to be done with the proper glue and certified.

You can nail plate(the teethed ones) butted 2x4's together. They have to be the correct size. It is up to code in many countries. That is how trusses are made.

Do you plan on ever having someone access above the ceiling? Why are there double sheets of plasterboard?

You need to have someone with more experience actually look at this ceiling before attempting such a plan.

10/12/18       #5: Splicing ceiling Joists ...
Ricardo Member

Thank you very much for your replies and explanations.

I added a a link of the soundproofing construction which I am trying to achieve.

The reason I was hoping to splice was that 2x4" joists are only available in 2.4m and 4.8m length and I hoping to save on costs and wastage by using the shorter and splicing, but it seems, from your comments, that this is unlikely to work and potentially dangerous. The reasoning was that I have seen many illustration of using metal splice plates, but this will get expensive and so was hoping there may be an alternative solution. I did think of but jointing and using spiked multinail-type plates on either side, but thought this would actually be weaker than glue and bolts.

Thanks again for all your insights


View higher quality, full size image (1280 X 720)

Soundproof construction

10/12/18       #6: Splicing ceiling Joists ...
BH Davis  Member

I have to question how good the sound proofing is going to end up being. I've been down this road and it is very difficult to accomplish true sound deadening from one space to another. A lot depends upon the type/pitch of the noise you are trying to reduce. Higher pitches and shorter, sharper sounds are the most difficult to isolate.

The two best components of the design are the isolated joist framing and the double drywall with the acoustic rubber in between. By the way in the US you can actually buy pre-made acoustic double layer dryway although it is 5 to 6 times the cost of standard drywall.

The acoustic wool is better than either fiberglass or loose cellulose (tightly compressed cellulose works better).......but not by a whole lot. When I last worked with the stuff a couple years ago my research showed that it only had a decibel reduction rating of around .5 to 1 decibel per inch. So if you can only squeeze in a couple inches of the stuff you aren't going to see much benefit.

And I repeat that a 2x4, whether spliced or one piece full length, is not going to be safe construction. Possibly 2x6 after some additional thought on the matter though.

BH Davis

10/12/18       #7: Splicing ceiling Joists ...
Adam

Where are you located?

The 90 x 45 pine will support floor loads of 1.6m @ 600 centers. You can't double the number and get to 3.2. Beam loading doesn't work that way. You are trying for 4.5m.

I would use a floor joist calculator. The total load would be similar. They both have a wallboard ceiling and the subfloor will be about the same weight as the 2nd layer of wallboard.

Based on your plan with continous 2 x 4's the 1st sheets will at best bow the ceiling big time. The 2nd sheets will drop it on your head while you are putting them up.


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