Sistering Joists

[onabudget]

Hi all, I'd like some advice on the following please

1) I'm adding some additonal joists in my old house mated (side bv side) to the existing 4.3 metre 9*1.5 inch joists

The new joists are 9 by 2 as while the ceilings were down I noticed the existing had dropped slightly possibly caused by the notching or general age hence I wanted to add in some additonal supports.

I am putting the new joists in fully supported on both ends (onto an intermediate wall and into the other house wall) so running the same span as the original joists.

I would like to attach and bolt to the existing joists but where should I position the bolts over the 4.3 metre span (middle or top or bottom) of the joist. I was going to use M10 coach bolts and have some two inch square large washers that will hopefully spread the load. Is this ok and how many bolts should I use over the span?


2) To support the joists while the bridging wood is removed I have acro'd the joists being worked on and noticed that the drop is less. Should I drill and bolt while the joists is undergoing the acro prop support or let the existing joist relax before bolting?

thanks very much

 

[RonnyRaygun]

There's no real load on the bolts as you're bearing the new joists onto existing walls, so 1200 centres centrally in the joist would be fine.

If you want a level floor and flat ceiling it would make sense to prop your existing joists level and then drill and bolt through, then screw your floor to the new joists.

225 x 50 would be fine by themselves over 4.3m...

 

[onabudget]

Thanks very much for that help,

Just one more question re your comments about the loading on the bolts, if I acro the floor joists it moves a little upwards if I drill and bolt the new joist while the old one is acro'd then when I remove the acro won't a load be placed on the bolt as the old joists try's to drop a little and pulls against the new joist in a downwards fashion. I'm going to try and acro the new joists as much as possible under the partition wall keeping the crown up while making sure it sits on it's end bearing is this all ok.

For the bits of the bridging I'm replacing (it's solid) and under a partition block wall so I cannnot get in to nail in the correct fashion, will screws from the sides be ok and is there any benifit is doubling up the bridging sizes in terms of width and adding addtional bridging?

I wanted to double up some of the joists with the addtional timber as there are some very worrying size holes next to existing large notches on the long joists that support the floor an intermediate partition wall balanced on it, I'd rather be safe than sorry. I thought the 225by50 was good for the floor weight only over that span and not for having an intermediate wall balanced on it as well.

Thanks

 

[RonnyRaygun]

Thanks very much for that help,

Just one more question re your comments about the loading on the bolts, if I acro the floor joists it moves a little upwards if I drill and bolt the new joist while the old one is acro'd then when I remove the acro won't a load be placed on the bolt as the old joists try's to drop a little and pulls against the new joist in a downwards fashion.

Yeah, it will a bit...difficult to work out how much, although, if the ceilings and floorboards are screwed to the new joists you have taken the majority of the load off the old ones anyway.
Toothed plate connectors are a good idea between the joists and there would be no harm in bolting at 600mm centres if you are worried.

Or you could get some 250mm deep joists and allow the extra depth to take up the sag in the existing ones.

I wanted to double up some of the joists with the addtional timber as there are some very worrying size holes next to existing large notches on the long joists that support the floor an intermediate partition wall balanced on it, I'd rather be safe than sorry. I thought the 225by50 was good for the floor weight only over that span and not for having an intermediate wall balanced on it as well.

Ah, you didn't say there was a wall on the joists too...

 

[Richard C]

I’d avoid jacking the old joists too much, it’s difficult to reverse any sagging that’s already taken place & you will stress the timber which could result in cracks & other problems elsewhere. Deeper sister joists or battening them is probably the best way to go if you want to level things up; use timber connectors as advised but I would alternately stagger the connecting bolts 50% either side of the centre line.

 

[RonnyRaygun]

I would alternately stagger the connecting bolts 50% either side of the centre line.

Agreed, 1/3 2/3 staggered is better...