Soil pipe through ledger board

[jayc89]

I need to fit new floor joists into a room which will become our ensuite. The old ones aren't suitable to support a bath and they're in the wrong direction to route the soil pipe. The room's 4.3m x 3.8m. I have two options;

 

- 3.8m 97 × 202 posi joists secured to 4.3m ledger board. These will allow me to run the soil pipe through the webs and straight out the perimeter wall. Is more expensive and will take longer to be delivered.

- 4.3m 72 × 220 solid timber joists secured to 3.8m ledger board. Would need to rotate the joists 90 degrees so I can run the soil pipe parallel to them, which means they'd have a longer span and I'd need to core through the ledger board (and wall behind) for the soil pipe to exit. I can get these delivered this week, to be fitted over the weekend.

 

Given a 72 × 220 ledger board, could I cut a 110mm hole through it? Or could I effectively fit 2x ledger boards to the wall, with a gap where the soil pipe will exit the wall?

 

 

 

[Russell griffiths]

Why are the longer joists less thick ??

are you putting them at closer centres ?

regarding the hole, drill in through the board and add additional anchors either side to take the load of each joist. 

 

Have you worked out the deflection over that span ?

[jayc89]

1 hour ago, Russell griffiths said:

Why are the longer joists less thick ??

are you putting them at closer centres ?

regarding the hole, drill in through the board and add additional anchors either side to take the load of each joist. 

 

Have you worked out the deflection over that span ?

 

Posi joists were designed for under 8mm deflection.

Solid joists were designed (by me) using the LABC table, picking the joist size suitable for the span at 600 centres and I'd fit them at 400 centres. 

How can I calculate the deflection of the solid joists myself?

[jayc89]

Some American calculator suggests the solid joist deflection would be around 6mm. Although there was a lot of conversion between mm and inches to get that. 

[saveasteading]

3 hours ago, jayc89 said:

How can I calculate the deflection of the solid joists myself?

You shouldn't need to, as the design guide will already have done that. Joists are designed 1. not to break. 2 not to deflect unpleasantly. the second is usually critical so will not deflect more than 1/360.  Even then, some of that is permanent due to furniture, and any bounce is less.  So for 3600 span, the max defect is 10mm  etc.

[Mr Punter]

I am doing similar but need an extract duct hole.  The floor is in place and I plan to drill through the ledger but if it is a pain I will chop a section out with cordless circular saw.

[jayc89]

34 minutes ago, saveasteading said:

You shouldn't need to, as the design guide will already have done that. Joists are designed 1. not to break. 2 not to deflect unpleasantly. the second is usually critical so will not deflect more than 1/360.  Even then, some of that is permanent due to furniture, and any bounce is less.  So for 3600 span, the max defect is 10mm  etc.

 

Agreed, but I thought 8mm or span x 0.002 is typically recommended around here, not whatever LABC would accept (which I assume is what the span tables work to).

 

That being said, the solid joists I'm looking at have a max span of 3.946m at 600 centres, or 4.512 at 400 centres, so my span of 3.8m at 400 centres should be well within that tolerance?