Boarding out a loft

[Doggit]

I suspect you really know the answer; in an ideal world, they'd be continuous, but manueverability in the loft may not allow that, so just do the best you can. Use 4" screws, and sink them in about halfway into the new joists, and give a good layer of PVA glue in between them.

 

[Ian H]

When you board the floor think if there is an point going beyond the purlins. You could save money there and if your insulating the rafters you would probably come down vertically at the purlins anyway.

 

[OldKettle]

I suspect you really know the answer; in an ideal world, they'd be continuous, but manueverability in the loft may not allow that, so just do the best you can. Use 4" screws, and sink them in about halfway into the new joists, and give a good layer of PVA glue in between them.

Thanks. I realised that the link I posted ages ago didn't work. This is the timber that I was thinking of using, is it suitable? It's not quite long enough to span the supports, but maneuverability is probably not an option, so maybe I should find something longer?

http://www.wickes.co.uk/Wickes-Sawn-Kiln-Dried-45-x-95-x-2400mm-Single/p/107187

When you board the floor think if there is an point going beyond the purlins. You could save money there and if your insulating the rafters you would probably come down vertically at the purlins anyway.

Thanks. I've not really planned to board past them at the moment, as I don't need the extra storage, so I'll probably just leave them for now.

 

[Doggit]

That's the stuff; but you'll get it cheaper and longer at a wood yard.

 

[OldKettle]

Hi,
I've finally gotten around to buying the stuff and hopefully getting started. I have bought the following to deepen the joists (100mm deep):

https://www.wickes.co.uk/Wickes-Sawn-Kiln-Dried-47-x-100-x-3000mm-Single/p/107542

and these boards:

https://www.wickes.co.uk/Wickes-P5-T+G-Chipboard-Flooring-18-x-600-x-2400mm/p/164516

The only question I have now, is the best way to join the new timbers to the existing joists.

Originally I was going to screw vertically through the new timber and the joist, with 150mm long screws (so vertically straight through the new timber and 50mm vertically into the joist).

It has also been suggested to me to instead cut pieces of ply, attach them alongside, and screw horizontally into the new timber and the original joist.

Which of these is better?

Does screwing vertically potentially weaken the joist (and the new timber)?

If alongside is better, could I use a nail plate, rather than cutting pieces of ply?

Any thoughts would be really appreciated (I had hoped to get started this evening, but want to make sure that I get this right).

EDIT: Also, if I am to use ply at the sides, would this stuff be OK?

https://www.wickes.co.uk/Structural-Softwood-Plywood-CE2+-18x1220x2440mm/p/120945

 

[TicTac]

It has also been suggested to me to instead cut pieces of ply, attach them alongside, and screw horizontally into the new timber and the original joist

That's good for sistering alongside joists that need leveling, but there's normally a level piece of joist somewhere to start with. This trick isn't a good idea for boarding out lofts. The 150's sunk slightly into the wood will work fine (a pilot hole in the top joist is sensible), and the wood you've got will also work nicely. Sods law says that you'll get a joint in between 2 joists, so you'll need a noggin for support, and then glue the joint.

 

[endecotp]

Other options that avoid needing such longs screws include screwing diagonally, and screwing vertically but with a deep (50mm?) hole larger than the screw.

 

[OldKettle]

That's good for sistering alongside joists that need leveling, but there's normally a level piece of joist somewhere to start with. This trick isn't a good idea for boarding out lofts. The 150's sunk slightly into the wood will work fine (a pilot hole in the top joist is sensible), and the wood you've got will also work nicely. Sods law says that you'll get a joint in between 2 joists, so you'll need a noggin for support, and then glue the joint.

Other options that avoid needing such longs screws include screwing diagonally, and screwing vertically but with a deep (50mm?) hole larger than the screw.

Thanks to both of you. If I sink the screws vertically, how far into the original joist is too shallow/deep? I suppose there is not too much of an issue with horizontal force, so could I go fairly shallow? 25mm? (125mm screw)

If I can screw vertically, it will save me a lot of effort, but if there is any risk to the integrity of the original joist, I'll happily spend the day cutting up some plywood.

 

[TicTac]

There are no problems with integrity screwing into the joists, but 150mm screws will be quite thick, hence drill a pilot hole first in the top joist. As you've got 100mm joists sink then in below the surface, and that'll put them about 60mm in the old joist, and that should be okay. A bit of wood glue first wouldn't go amiss though; bit of belt and braces.

 

[Keithmac]

This glue is excellent and not too expensive, buy two and if you don't need the second bottle you can always take it back for a redund!

 

[OldKettle]

There are no problems with integrity screwing into the joists, but 150mm screws will be quite thick, hence drill a pilot hole first in the top joist.

Thanks. The screws I plan on getting are 6mm, so I was looking to drill pilot holes with a 3mm bit.

Should I ideally drill the pilot hole down into the original joist too, to minimise the risk of splitting? (I'm having trouble finding a 3mm bit longer than 100mm).

EDIT: Finally found these (4x119 or 5x132). Are either of them appropriate for 6x150 screws?

https://www.screwfix.com/p/erbauer-hss-drill-bits-4-x-119mm-2-pack/5943v

https://www.screwfix.com/p/erbauer-hss-drill-bit-5-x-132mm/7607v

 

[endecotp]

I use these. They generally don’t need pilot holes: https://www.screwfix.com/p/turbo-ii...k-multipurpose-screws-5-x-80mm-100-pack/3843h

 

[TicTac]

You only need a pilot hole in the upper joist, those screws will self drill into the lower joist quite easily. It's the shank of the screw that needs the pilot hole to stop any splitting.

 

[OldKettle]

Many thanks!

Is a 4mm pilot hole ok for a 6mm screw?

 

[TicTac]

Try 3mm first.