Loft joist questions

[Homerdoh]

I've just taken down my kitchen ceiling as part of my refurb and am wondering what's the best way to do the new joists?
I store quite a bit of "junk" up there and it's accessible by a flight of alternate stairs so it does have regular foot traffic, therefore needs to be able to take a reasonable load.
My plan was to upgrade existing 75 x 45 joist to 145 x 45 joists, I have offered the new joists up, sat onto wall plate and screwed to the old joists.
Went up to assess and there seems to be a hell of a bounce in them, I know it will improve with flooring down but am still worried about movement affecting the new plastered ceiling below, The old joists had a binder which I cut out as it was in the way of getting the new joists in, the binder obviously was serving a purpose but I don't really want to fit a new one across the new joists as it would interfere with the floorboards.
Should I just get rid of the old joists and fit noggins between the new joists?
Also should I run the new joists under the purlin props? as at present it's supported by a short 75 x 45 across 4 old joists (see pic)

Any suggestions / advice appreciated,

Regards

Loads of pics to give you a better idea.

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[Homerdoh]

Forgot to mention the span across the kitchen is 3.3m, the other side of the intermediate wall is the lounge which will be getting the same work done, the span across the lounge is 3.7m

Regards

Homer

 

[tony1851]

If it's for storage, 145x45 should be OK on that span. They will stiffen up a bit when the flooring goes down as that tends to spread the load, and it's unlikely it will affect your ceiling
You should try and maintain the purlin prop.

 

[Homerdoh]

Maintain the purlin prop as it is or run new joists under?

Would you recommend noggins?

Regards

Homer

 

[maltaron]

As Tony says, 6 x 2 is OK for storage but you need 7 x 2 for normal floor at that span and 8 x 2 on the lounge. Plus herringbone or solid strutting half way. ( Sorry, not into foreign measurements, you will have to convert))

 

[Homerdoh]

Oh dear, now we're up to 8x2 joists over the lounge which means I'd have to use 8x2's over the kitchen as I deffo don't want a step in the loft floor!

Regards

Homer

 

[tony1851]

Personally, I'd be OK with 6x2s over that span.
Remember that the standard tables give joist sizes/spans for domestic loading of 30 lbs/sq ft over the whole span of the floor. When you are working under a roof, it is highly unlikely that the floor will be loaded with the full domestic loading right up to the eaves because of the lack of headroom.
Also, OP won't be putting furniture in such as wardrobes etc.

 

[tony1851]

Maintain the purlin prop as it is or run new joists under?

Would you recommend noggins?

Regards

Homer

If it's not causing any bend in the existing joists, leave it as it is and just work round it.

 

[Homerdoh]

Maintain the purlin prop as it is or run new joists under?

Would you recommend noggins?

Regards

Homer

If it's not causing any bend in the existing joists, leave it as it is and just work round it.

Had a think about it today and my OCD kicked in and I decided I won't be able to sleep at night knowing the purlin prop is supported by crappy bits of would in the middle of my nice new joists, so I'm getting rid of all the old joists and fitting new, At least now I'll be able to use full height noggins,(OCD again)

Question is, the new 145 x 45 joists sat on the wall will be about 6mm lower than the bottom of the prop so do I:

Pack the difference and if so what with and where?(above or below joist?)
Cut out existing prop and fit new at correct length.
Just let the whole thing drop 6mm

Regards

Homer