Sistering floor joists

[Ooops]

Hi Guys

Could anyone tell me whether sistering floor joists (2x4's) is good practice or not? If it is considered ok then how is the best way to join them?

 

[mattysupra]

could you explain what you mean by sistering? We all have different saying up and down the u.k and im not familiar with this one.

 

[Ooops]

Sistering = Instead of replacing an old joist, I have read (on a different website) that you can lay a new one along side it and fix it to the existing one. The joists in my case are on the ground floor and are fixed to the sill with a skew nail.

 

[masona]

Why do you need extra joists? Are the old joists rotted?

 

[Ooops]

Some of them yes although not too bad. They have woodworm. I'm having them all treated tomorrow. The are structurally sound. I am going to lay insulation between the joist but would this be detrimental to the airflow?

 

[masona]

Have you check that the wallplate is not rotted on the bottom oft he sleeper walls? Poke a small screwdriver, the most common rot is on the bottom which you cannot see.

 

[kevnurse]

Sistering is used mainly to level a floor where the joists have sagged or the house has subsided. The principle is that, if the sister is not full length, the original joist still carries the weight to the wall plate; it just happens to be out of true. If your problem is rotting joists, I would suggest steel plates fitted to both sides of the joist such that they sandwich the joist. Bolting the plates together, through the joist, will make a solid base for the floor above. Some joists will require full length braces, while others might need only a few feet, depending on the degree and extent of damage or rot. Other opinions might differ from mine.

 

[Ooops]

Thanks masona and kevnurse. I did a search on this site before starting the job and saw masona that you had already advised somebody to check the wall plate with a screwdriver. I'm not sure what a wallplate is Is it the piece of wood that runs along the brick walls that the joists are fixed to? I have a brick wall then a layer of slate and then some timber. If it is then they have no rot at all.
How is the best way to sister the joists together? Can I just use nails or should I bolt them? If I do have to bolt them which bolts should I use? Can you tell that I've never done this before?

 

[mattysupra]

I asked earlier what you mean by as sister joint so you could explain what one is to get of the tech speak of most pro's. As a diy forum most people dont understand tech and pro terms. Try and keep it simple so every one understands. Hence you dont understand what ' masona' means by the wall plate. Im sure he will translate for you. Its all very simple but to the adverage person its a different language. lets try and keep it simple

 

[masona]

Here, scroll down to > 3 Ground Floors > 1920s

 

[mattysupra]

Very nice link masona.

 

[Ooops]

That is a fantastic link masona, thanks

Ok mattysupra point taken. I had never heard of sistering before (not on a diy forum anyway) until I read it on a different website. I was using a search engine and put in "how to replace floor joists" and a website came up with that suggestion (sistering). Anyway at least a few other people now know what sistering is. Me being a below average person can only understand things when they are simple anyway. I'll keep it in mind for the future, cheers.

 

[Ooops]

By the way I forgot...

I had asked whether laying insulation between the floor joists was a good idea or not. The chap who came to treat the joists this am advised that it would restrict the airflow around them and could cause the timber to sweat.