Joist Size and brick gauge

[Adrian80]

Hi guys,

Looking for some advice,

Building an extension and just getting to first floor level.

Because i want to match up the new and old floor levels up, i need to decide what joist sizes to use.

The SE has specified 7x2 c16 at 400 centres.
This would be fine one side, as i intend to bolt a big bit of timber to the old wall and and use joist hangers.

But because the other side is on an angle, i was going to rest the joists on the blocks.

However a 7x2 joist doesnt fit in with brick gauge. So can i pack the bottom of the joists with more timber to get the right height. (personally i think this sounds a bit crap, and not likely to pass building control)

or

do i pack it out with slate, is 2 inches of slate a lot to make up.

or do i just get 9x2 joists and sit them straight on the blocks?

if i use 9x2 can i increase the centres?

Span ranges from 2.7 m to 3.5m

Your advice as always is greatly appreciated..

Thanks
A

 

[tony1851]

Packing the underside of joists with bits of timber never seems quite right.
9x2 would be OK on those spans at up to 500 centres.

 

[garyo]

Do the tops of your joists align with the coursing - have you looked in to the dims of masonry joist hangars that are available - e.g.

http://www.insulationplace.co.uk/Simpson-Strong-Tie-Masonry-Supported-Joist-Hanger-JHM-50x200mm.html

 

[Adrian80]

I agree packing with timber just doesnt seem right..

I have looked at loads of hangers, but the only ones that allow a rake or an adjustable rake are light duty.

Yes the top of the joists is level with brick work, so it needs to match in..

 

[^woody^]

What is "just getting to first floor level?" Are you there yet?

If not, then alter the blockwork to suit the joist level - alter the gauge, or run a course of split blocks around

I can't understand why you just want to randomly change the joists. Normally you should match the existing joists so that floor and ceilings are the same.

If you are using aerated blocks, then the blocks can be notched/sawn afterwards to whatever level you like

 

[garyo]

I was in a similar position - the existing house had 100mm deep joists, and the new extension had 195mm deep joists.

I'm using aerated 3.5N blocks so ended up cutting 40mm slivers of blocks to get the block work up to the right height. (edited to add - you can buy 65mm thick coursing 3.5N blocks too - you may be lucky and these will get you to where you need to be)

Don't forget to factor in the depth of your various flooring choices.

 

[Adrian80]

thanks guys for your help much appreciated, Going to notch all the blocks to get the course right..

Cheers
A

 

[theoldun]

JOISTS..
DON’TS.
Don’t notch the blocks. Don’t notch the joists. Don’t pack a joist more than 3mm to bring to level. Don’t attempt to match the gauge to the joist. Match the gauge to suit the joist. Don’t sit joists at 500mm centres. Will not suit size of chipboard or plasterboard, and you will need 22mm chipboard and 15mm plasterboard or noggins to all long edges of 12.5mm plasterboard. Don’ use timber to masonry hangers unless working on shared party wall. Acoustic and fire regulations. Note 450mm of masonry on top of hangers before any load applied Don’t place first and last joist tight against wall. Don’t overlap joists on partition wall

DO
Do have joists regulised. Do crown joists before placing. Do set joists out to floor and plasterboard size Do level out across tops of all joist before strapping. Do leave 25 to 50mm gap between first and last joist and external wall. Do work gauge to joist, either by cutting top course and turning block over as bed joint, or use slip blocks 40mm thick, course blocks 65mm thick or dolly blocks 140mm thick, or cut your own slips, or as said cut top block to suit Do use size of joist specified. Do pay attention to beam fill and mastic joint. Do set out accurately trimmers for soil pipes etc..
That’s all you need to know.
Regards oldun

 

[Adrian80]

Thanks old un,

very good points, started cutting slips to get to the right level.
Good point about plasterboard, will keep at 400 centers.

All very helpfull, will take some pictures. and post

Cheers
A