extension floor joists

[trevw]

Hi,

I am doing a side extension, the specified joists for the first floor are 200x75 over a 4.2m span, the reg drawings specify joist hangers on both the new extension wall and where they hang from the old external cavity wall..

my problem is that the floor level needs to match the inside and the top of the new joist height would then fall just below mid course on the old cavity wall (as does the bottom of joist, typically ), I was wondering about the following options:

1) cut holes for the joists in the wall and build them in (cons: time consuming, damp issues?, joist movement?)
2) get oversized joist hangers (225m deep) so the joists drop lower (cons:joist not holding the top of the hanger in the wall/ will building inspector like it?)
3) put hangers in course above and notch the bottoms more than the 5mm or so needed to get a level run for the plasterboard (cons:weakens the joist, will building inspector like it?)

other?

I will of course check with the building inspector before doing anything non-standard but wondered if any of you had any suggestions on the best way forwad?

cheers

Trev

 

[noseall]

b.c. will allow you to build-in the joists on a non external wall, so just line up the TOPS of the joists. the ceilings can be levelled through by alternative means if required.

at tuther end (external wall) you will either be lucky with the block courses or you will need to cut a block down in order to make the hangers work, or use lightweight coursing bricks.

whatever the solution, you make the masonry suit the hanger or joist, not tuther way round.

 

[trevw]

thanks noseall, don't think I am going to be lucky on the external wall either but will ask the brickies to put in a cut down course..

just remembered, another suggestion I heard was to cut slots in the brick mid course for the masonry hangers using a 9" grinder or similar.. is this a good idea? I'm obviously willing to build in the joists if that is the only way but anything easier would be welcome!

On building them in, was figuring I would work out my level, ping a chalk line along the wall, cut sides of each slot with grinder (with suitable blade) then drill out tops and bottoms with a smallish bit in an sds drill? or is there an easier way... should I clear down to the next mortar course and then 'build up' to my required level instead?

thanks for the advice

Trev

 

[^woody^]

Hangers are put in an existing wall to suit the required height, and do not have to go into a joint. Drill and 2" bolster does it.

Or just fix an 8x2 timber to the wall at the required level with rawl bolts, and fix your hangers onto this

 

[trevw]

cool, thanks - I am a little concerned about cutting in the hangers as the bricks in the old external wall are all frog down and at the level of the cut the hanger would be going into the frog if that makes sense..

the 8x2 bolted to the wall sounds easier than cutting the holes for the hangers and possibly easier to get a nice level through than building in or hangers?

can you tell what size rawl bolts you would use and at what spacing? M12 do? in between every joist (400 spacing)?

thanks

Trev

 

[^woody^]

M12's at 600 spacings and staggered over the depth of the timber ie 1st 1/3 down, 2nd 1/3 up, 3rd 1/3 down etc - like this . ' . ' . ' . '

 

[trevw]

that's great, one more question if that's okay..? (last one promise )

hangers to use.. standard leg jiffy/speedy hanger or something similar?
http://www.screwfix.com/app/sfd/cat/pro.jsp?cId=101228&ts=10616&id=62724

If so, should the straps be long enough (long leg?)to be bent over and fixed to the top and back of the 8x2" plate? or can they just be nailed with square twist nails on the face of the plate..

thanks again

Trev

 

[^woody^]

They will do. The hangers only need a fixing on the front and top, not down the back as well.

40mm clout nails will do - the load is downwards and not pulling on the hanger , so twist nails are not necessary

 

[trevw]

thanks for all the suggestions/info woody and noseall - looks like I've got a busy weekend ahead!

Trev

 

[Penelopejean]

We are having an extension built on very similar lines but are having a floating floor in our new ensuite built above an existing ceiling in our sitting room. The old exterior wall is breeze block not brick(as it was tile hung). There is no opportunity to put a wall plate bearer thingy like this problem above here. The builder has used timber joist hangers and screwed them into the breeze block. The joists are moving when you walk on the WPB above and causing a horrible squeak over one particular joist where the shower tray will go. We want to tile the ensuite floor so don't want any movement. The builder has now taken up the ply( and was not happy as it's glued down!) to find the squeak but how can he make the floor more rigid? He has put in a row of noggins where there is a join in the WPB but are more needed and what else maybe?
The builder has now suggested that he puts the grotty split WPB down back after all this! Am I being fussy or what?!