How to fix joists to a gable end

[Mr Spoons]

Lots of questions about timer sections and joist hangers...

I plan to put new joists in my loft (sitting on raised wall plates, so I have a nice strong floor that doesn't interfere with the trusses), but due to the dimensions etc, the last joist will run parallel to the gable end, about 800mm away. The joists are 2" x 8" on 400mm centres as per BCO span tables.

What I am planning to do is run some 800mm sections of 2"x6" (2" smaller to avoid hitting the joist of the last truss) between the last joist and the gable end wall at 90^ to the joist/wall, sort of like a noggin arrangement. I plan to use speedy joist hangers

to attach the

800mm sections to the last joist, but I am not sure how to attach the other end to the gable wall. The way I see it is there are 2 options :

1) use hangers like this

directly bolted to the gable wall. If I went down this route, should I use expansion bolts, or just some 3" x 12 screws into a good anchor?

or

2) Use something like expansion bolts to bolt 2"x8" joist sections to the gable wall as a batten, then use speedy hangers of both ends of the 800mm sections. If I were to do this, how far apart should the bolts into the gable end be?

The second question I have is about loading. The joists are on 400mm centres and that fits with the BCO span tables. If I were to do this thing with the

800mm sections, given that one end is bolted to the masonry in some way, is the final joist considered to be taking more load as the next joist is 800mm away (although it is actually the wall?) I was thinking that because the final "joist" is in fact the gable wall, that it would the best place to put the heaviest things.

The third question I have is about the 800mm sections. As their span is only

800mm (wall to final joist) would 400mm centres be sensible?

The fourth question relates to the loft hatch opening which has a new joist either side which are 800mm apart. To support the floor across this span (chip boards seem to require supporting every 400mm) and I better off :

(a) putting a proper joist in that runs between the wall plates and a pair of noggins just before/after the loft hatch opening

or

(b) Putting in a series of 2" x 6" noggins between the new joists either side of the loft hatch.

My instinct here is (a), because at least one end of the joist would be transferring weight to the walls, even though the other end is transferring load to adjacent joists via the noggin. With arrangement (b) all the weigh in the 800mm void between the joists is transferred to the adjacent joists, so I essentially have joists on 800mm centres.

Thanks in advance for any thoughts on this...

[dom]

I'm in the process of putting in various levels of mezzanine floor in a chapel. For the wall ends of the joists I'm using the multi-truss hangers directly to masonry fixed with 4 of these per hanger

is the solution I specified in my full plans application to Building Control.

It's the more expensive solution, but the wallplate approach would end up looking ugly around windows (one area of mezzanine has to cut horizontally across the tall gothic windows, so extra joists either side with noggins across the windows - but set back a little, then some cunning joinery to close the floor up to a window glazing bar).

A pre-exisitng area of mezzanine that had to be replaced did use the wallplate aproach just as you describe - although one 4 meter section of which was supported with a grand total of just 2 expansion bolts to hold up a whole 4m by 4m floor. I suggest you use a few more - maybe 2 for every joist on the wallplate, evenly spaced horizontally and staggered vertically.

(The comedy didn't stop there with the old mezzanine - the stud wall supporting the other edge of the floor was simple 50*75mm studs, single top and bottom plate, laid directly on the chapel's original timber suspended floor, parallel to and between the joists. Oh and some double doors in them, no attempt to stiffen/strengthen the studwork. Then the electrician butchered the studs away to almost nothing. God must have been dedicating a fair bit of will power to holding it all up. I suspect what actually happened was what was only intended as a ceiling, ended up being boarded over to use as a floor).

Your Q2 sounds like you need an extra joist to carry the 800mm noggins, and Q3 400mm centres on noggins does sound right, Q4 sounds either way to me, provided the full length joists are doubled up and you're not pushing the nearest full spans into "extra duties".