Sistering old floor joists

[Window]

Hello all,

I am new here and just wanted to ask about sistering joists. I've had a look through the forum and can't see anything relating to what I'm after.

My bedroom floor is sagging in the middle the house was built just before the 1800.

I was thinking about just sistering but as you can see from the photos the joists aren't straight so wont sit flush.

This will be done from above rather than below as these are old photos and the celling has been repaired so don't really want to disturb it.

I was thinking about getting some 4x2 timber to sister and use M12 coach bolts with screws as well

Any help would be grateful

 

[motorbiking]

What is the length of the run? I'd be tempted to make an engineered joist with ply to keep the weight down.

 

[Window]

The run is 3850mm

With regards to the bow in the joists how would you get around that?

 

[Lower]

I'd bolt the sister joists at either end and then pack at points along the length and coach bolt together through the packers. I wouldn't try and straighten the bowed joists.

 

[Window]

Sorry for the newbie question but what do you pack it with?

Can you sister joists at either end and then add another sister joist every 1000mm for example

 

[Window]

I'd bolt the sister joists at either end and then pack at points along the length and coach bolt together through the packers. I wouldn't try and straighten the bowed joists.

I understand, just had one of those moments. I think that will be the best way.

Thank you

 

[Lower]

Sorry for the newbie question but what do you pack it with?

Can you sister joists at either end and then add another sister joist every 1000mm for example

No, the sister joists needto be the same length as the originals and be continuous without any joins, unless you sister on both sides. If you sister on both sides you can have joins, as long as the joins are offset.

Packers should be solid timber, same height as the joists, as long as you can make them, just cut to the correct thickness.

 

[motorbiking]

The run is 3850mm

With regards to the bow in the joists how would you get around that?

You insert 2-4 Engineered I beam joist between the existing and then use herringbone straps to attache to the existing beams.
It will be a lot lighter and stronger than solid 4 x 2 or 6 x 2.

This kind of thing.

FinnJoist I-Beam Floor Joists - Sydenhams - Timber Engineering

Sydenhams are an established builder's merchants who can assist with all of your building project needs, offering a range of products and services.

www.sydenhams.co.uk

Sistering will also work, but its going to be a lot of weight.

 

[Window]

Coach bolts or structural screws to secure the joists together

 

[motorbiking]

nuts, bolts and washers ideally.

 

[cdbe]

You're going to struggle a bit with that and getting any "sistering" effect if they're not clamped tightly together. Obviously when you remove the floor boards they would pull together but that would ruin your ceiling. I'd just leave those old things for the ceiling and drop some new ones on masonry hangars. I don't know what depth you have but something like 7x3 may be needed.

 

[Dereekoo]

No need to sister, sistering only really required if you are trying to repair existing joists or do not want to put new wall supports in, putting joists by the side or even in the middle of the existing spacing will double the strength of floor supports

 

[Window]

Its all going to be replaced with new joists, better to do it right.

Thank you for all the response

 

[cdbe]

A wise choice, that is pretty bad!

 

[Deleted member 174758]

I've heard of leaving allowance beneath skirtings for laminate flooring, but does laminate actually come that thick?