Building Joists in

[glangri2]

Hi Knowledgable Ones.

I am close to fitting the first floor joists in my extension, and the BCO has suggested a Ledger board & Hangers to attach to the existing gable end wall, and then to build the other ends into the new wall.

I have 2 questions;

1 - The inner skin of the new wall is made of light weight Aerated blocks (3.6Kn), and the joists are going to be 220x38. Is it OK to sit the joists straight onto the blocks, or should I do a course of Concrete Blocks for them to sit on?

2 - I am going to 'Double up' on the 3 middle joists, just in case I ever decide to partition off the room above. If I double up the joists, do I use a wider hanger at the ledger board and fit 2 joists into it, or do I use a hanger for each, and just fit them as close together as possible ?

Cheers
Gary

 

[simonjay]

Hi Knowledgable Ones.

I am close to fitting the first floor joists in my extension, and the BCO has suggested a Ledger board & Hangers to attach to the existing gable end wall, and then to build the other ends into the new wall.

I have 2 questions;

1 - The inner skin of the new wall is made of light weight Aerated blocks (3.6Kn), and the joists are going to be 220x38. Is it OK to sit the joists straight onto the blocks, or should I do a course of Concrete Blocks for them to sit on?

2 - I am going to 'Double up' on the 3 middle joists, just in case I ever decide to partition off the room above. If I double up the joists, do I use a wider hanger at the ledger board and fit 2 joists into it, or do I use a hanger for each, and just fit them as close together as possible ?

Cheers
Gary

I prefer building in at both ends if possible - it's more solid. Round here you see lots of extensions going in with holes knocked in the original house wall to take joists. However, ledger board and hangers are OK of course.

In theory the lightweight blocks can usually take the joists direct (but check for the crush load since 38mm is quite narrow), but I built in an engineering brick under each to spread the load a bit. Cutting lightweight blocks is easy to do this.

You can get wide hangers for doubled-up joists. Of course if you build them in at both ends, no problem.

Simon.

 

[theoldun]

No need to use concrete blocks, 3.5N aerated block plenty good enough.
If you want to double up 38mm joists use a 75mm wide hanger. You might have to trim arris on bottom of joists Rattle few bolts and bulldogs through them to stop any possible squeaking. Use standard leg 225mm long hangers, nail every hole with sheradised 30x3.7 square twisted nails
oldun

 

[glangri2]

In theory the lightweight blocks can usually take the joists direct (but check for the crush load since 38mm is quite narrow), but I built in an engineering brick under each to spread the load a bit.

I am thinking of stepping up to 47mm Joists, and increasing the spacing to 600mm from 450mm.

Joists are the same price per metre regardless, so why pay for 6 more than necessary