Loft floor joists help

[Speediii]

Hello all,

I would like to add joists across my loft that sit in the walls either end of the loft. These joist will not sit on the current floor, they will be raised so i can get all the insulation in. I would then like to add wooden floor to create the floor rather than boarding. I need joists approx 4m long however I cannot get them up the stairs, I don't think I will have enough room as the stairs spiral.

Question is if I cannot get the in the loft in 1 piece and i cut then, how would I attach them together to keep them very strong?

 

[Deleted member 174758]

Presumably you have woeked out the required cross section for a metre span, so I'll take that as a given.

I think I'd view this the same way I'd view doing joist repairs by sistering joists, namely the joist halves must have a metre or more of overlap and they require three coach bolts to join them in the overlap.we'd normally opt for C24 (where C16 was specified) to gain additional stiffness and ideally glue and screw any floor to the top of these (D4 PU glue). That leaves you humping at least 2.5 metre timbers up your stairs. Can you do that? BTW none of this will meet building regs for habitable spaces without having a structural engineer do the calcs

 

[Speediii]

Yes I can get 2.5m up the stairs.

Why wouldn't this pass building regulations?

 

[Deleted member 174758]

Why wouldn't this pass building regulations?

If you convert a loft to a habitable space you need to meet the building regulations, which includes having done calculations on loading, head height, etc. If you are just doing a loft storage space it isn't a habitable space.

 

[cdbe]

Lot of messing. Consider, depending on access etc, removing a few roof tiles at the eaves and feeding them through or cutting a small area out of a bedroom ceiling and feeding them up through a window. I've had 4m plus RSJ's up both ways.

As above, fine if it's storage but if it's in any way habitable a proper conversation is the only way to go.

 

[Speediii]

I want to use the space for storage for now with the view of making it habitable when the kids are older, this is why i want to put in a new layer of joist and have a floor on top of them. I don't relly want to and neither do i think i can work on the existing joists. Too scared to mess with them tbh

I have seen the joists below, will be calling them tomorrow and possibly pacing an order. I will be making holes in the walls and have these joists sit in the gaps.

6x2 Treated Timber C24 Regularised Sawn Joist 47x150mm

Our 47mm x 150mm kiln dried C24 regularised treated timber joists are planed with eased corners for smooth handling. If the specified lengths are not available from stock then we will provide the closest to the length required but ensure we supply the total meterage. If you have any specific...

diybuildingsupplies.co.uk

 

[cdbe]

Joists probably not adequate for the span.

 

[Speediii]

Sorry i posted a wrong link, it's the 8x2 joists not the 6x2, I really should have checked this before posting.

8x2 Treated Timber C24 Regularised Sawn 47x200mm - 3.6m

Our 8x2 Treated Timber C24 Joists are ideal for use in structural framing, as joists and beams, and a variety of other uses due to it’s sturdy C24 strength grading. Sourced from FSC or PEFC sources, our 8x2 timber is kiln-dried for straightness and strength, and are regularised to achieve an...

diybuildingsupplies.co.uk

Kind of found a solution to getting the joists up, we will try the back room window. If that does not wok then removing tiles as you stated above is the way we will go.

Do we have to place noggins at a certain length when fitting the joists? Is there a specific type of insulation needed to go between the wood in the ceiling before it is covered with plywood or plasterboard?

 

[Deleted member 174758]

Do we have to place noggings at a certain length when fitting the joists?

Assuming your intention is to stiffen the floor you need solid strutting, not noggins - noggins is in walls, normally. On a length such as this a single row of solid strutting down the centre line of the room suffices. The strutting should ideally be from the same material as the joists (i.e 8 x 2in C24), or failing that be of the same thickness but no less than 80% of the height (i.e 6.5 x 2in) to perform adequately. The fit between the joists needs to be very snug. Herringbone strutting is a bit better, but a lot more time consuming to install

 

[Speediii]

These are not noggins? I was planning on adding these down the centre using the same material. I need approx 13 joists but planned on ordering 16

http://thebuckstop.net/gallery2/var/resizes/IMAG0679.jpg?m=1422478810

 

[Deleted member 174758]

Solid strutting in normally done as a single row (or sometimes multiple rows), like this:

Herringbone strutting (the other main technique) looks like this:

Note that in both cases the strutting is installed in more or less a straight line. Not random. The function of strutting is to prevent joists under heavy load from twisting by transferring somevof the load into the adjacent joists. In order to do this efficiently and consistently the strutting must be installed in a (more or less) straight line.

The example you referenced (see below) isn't really solid strutting as we install it in the UK (to meet Building Control requirements) so I have no idea whether it would work as well or whether it would be given approval:

Maybe it would be OK if you were installing a diaphragm floor, but even there trying to nail into the strutting accurately would be an absolute nightmare (and if you hit the edges of any of the timbers with a nail but don't sink into the timberit can result in a point in the floor which creaks), so I doubt it has any advantages

 

[Speediii]

The herringbone strutting seems a little advanced to me to be honest, I don't think I can do that.

How is the solid strutting in a single row done? Do I install the joists in the wall or hangers then add pieces of the joists in a straight line or is the row i single piece and the joists attached in pieces?

I googled the picture I posted and seems easier to do, I can drill either side of the joists