How to strengthen joists ?

[nicola armstrong]

Hi, I am refurbishing my loft and I believe I need to strengthen the joists before I put t&g chipboard flooring down. The open space will be used as a kids tv area and a bit of storage, so nothing heavy duty.

As you can see from the attached pics, there are 4 x 2 binders laying across the 4 x 2 joists (i incorrectly called them 'floor beams' on the attached pics!).

I am meeting the carpenter next week and I would love to have an idea of the correct way to do this before I meet him.

Could anyone possibly advise me what the best way would be to strengthen the joists?

Thanks, Nicky.

 

[Ian H]

Why would you want your kids to watch TV up there?

Do a proper conversion or stick to storage.

 

[Doggit]

and why have you got two threads going.

 

[JohnD]

for storage (but not a habitable room, which has to meet building regulations) you can cross-batten it with timbers laid at right angles to the existing joists, and screwed tightly down at every point. This will stiffen the deck and help spread the load, reducing the risk of cracked ceilings. If you floor it with 18mm ply, also screwed tightly down this will also help stiffen it. You should lay insulation between both layers of joists before flooring. This will give you 200mm total, which is quite good.

If it is very dirty you might like to remove the old insulation and clean the loft first to reduce dust.

 

[nicola armstrong]

Hi JohnD, thanks for the advice, much appreciated. Please excuse my ignorance but: for the cross battening, would fitting these battens along with the new 18mm t&g be good enough to replace the existing binders (i.e. i'll remove the binders and replace them with the cross battens and boards, giving an equal or better strength than the binders themselves)?

Or would the cross battens be the same size timber as the binders (2 x 4)?

 

[nicola armstrong]

Hi Doggit, I posted a similar thread yesterday but i made a couple of mistakes on it (v. sorry).

I asked diynot to delete the previous thread this morning, which they helpfully did very quickly. I waited for this to be deleted before I posted the new (this) thread so hopefully there were not 2 threads on at the same time. If you did see both threads at the same time then I sincerely apologise for any confusion caused.

Hi Ian H, thanks so much for your thoughts - much appreciated.

 

[Doggit]

You could possibly put some acrow props in the room below to support the ceilings, take out the binder that are keeping the ceiling stiffened, add glued and screwed 4x2s on top of the existing ones, install 200mm of insulation between the joists, and then follow JohnDs suggestion of screwing down 18mm ply. Another option might be to move the binders so they sit under the purlins (or install new ones, and then take the old ones out), and then just increase the joists in the centre section. You could also put in a small dwarf wall from the purlins down to the repositioned binder.

 

[nicola armstrong]

Ah yes that sounds really good - many thanks these sound very sensible options. I'll chat with the chippy and get moving soon.

Thanks so much for the input Doggit and JohnD, this has been really helpful !

 

[endecotp]

I grew up in a house where the large loft had been boarded for storage and then gradually made more and more habitable - e.g. as a darkroom, and eventually old carpets were laid up there (easier than taking them to the dump). But fundamentally, in the winter it was freezing cold and in the summer it was boiling hot, so it was never appealing as a place for us kids to play or "hang out" despite there being a stereo and my sister's collection of LPs. And ours had much less insulation than you have, so your temperature extremes will be greater.

 

[JohnD]

I'd prefer to leave the binders, and add cross battens of the same size. If the battens are a bit bigger (for example decking timber is widely available and cheap) the flooring can pass over the binders.

The height above and beyond the binders is so limited that you need not treat it as floor.

If you do much hammering and levering, the ceilings will probably crack (or fall down if they are L&P), so use screws not nails. Another reason I wouldn't remove the binders, they are probably spiked down with big skew nails.

 

[nicola armstrong]

Hi JohnD thanks for the reply (sorry I just logged back in today).

So do you mean the cross battens will be basically adding what will look the same as the binders, then lay the flooring onto both?

i.e. we have existing 4 x 2 binders and will add 4 x 2 cross battens at adjacent to the binders (and 90 deg to the joists)?

Normally battens would be much slimmer, but we will use 4 x 2 purely to achieve level floor (we do want the flooring to go beyond the binders and just beyond the perlins (the perlins will just be painted).

Hope that makes sense !!

 

[Doggit]

You could add another cross batten outside of the binders, just below the purlin for neatness. But be careful; those binders may not be the same size as a modern 4x2 piece of wood, and if you add them in the same direction as the binders, you'll strengthen the floor, but not as much as if you glue and screw along it's whole length.

 

[nicola armstrong]

thanks again Doggit...

sorry just one last question, excuse my ignorance - so is it stronger to put the new 2 x 4s on top of the joists (i.e. at 90 deg to the binders) or is it stronger to put the new 2 x 4 in line with the binders (i.e. at 90 deg to the existing joists)...

and I'll check the binder dimensions against new 2 x 4.

and thanks so much for everyone's advice, this is a great forum.

 

[Doggit]

If you were able to carefully remove the binders by supporting the ceiling below first, and then putting the new joists on top of the old ones - along the complete length - then there's no question that they'd be stronger. But if you leave the setup as is, then I suspect there's possibly not a lot of difference between John's and my method, and johns would certainly be easier to do. The problem becomes when someone extends the use of the loft, and makes more use of it than was originally intended, and that's what you've got to keep in mind.

 

[nicola armstrong]

OK understood - starting tomorrow. Thanks !!!