Joists into wall

[Yorkblade]

Hi,

Soon I'll be adding joists to my extension and wondered if anyone had some advice.
I have seen suggestions of a ledger board and hangers, I have also seen people suggest cutting a hole into the existing wall to rest the joist on there. The latter sounds the most structurally sound.

If I did do this, would the joist just need to go circa 100mm in, wrapped in DPM and then mortar into place?

I have reposted here after a very kind user informed me it may have been in the wrong location

 

[martygturner]

I would for the sake of ease use hangers ...leveling a ledger board up is a matter of cutting two slots at either end to put bolts through then level and drill through all the other fixings.

 

[Deleted member 174758]

Soon I'll be adding joists to my extension and wondered if anyone had some advice.
I have seen suggestions of a ledger board and hangers, I have also seen people suggest cutting a hole into the existing wall to rest the joist on there. The latter sounds the most structurally sound.

It makes little difference, structurally.

With the joist in pocket technique it is more difficult to level your joists through, you will have to repair the masonry around the pocket afterwards, and it us highly advisable to use treated joists on exterior walls and to envelope wrap the ends of the joists in roofing felt where they go into the pockets before installing them. To emphasise the problems with this method, just think about the problem of placing a 4000mm joist into two holes in a 3800mm wide room for a moment, given that you need 100mm bearing at each end and you'll begin to understand how much masonry you may need to chop out and make good

With the ledger and joist hanger approach it is far easier to level the joists through, there us no masonry to chop out and repair afterwards but in ropey masonry it may be necessary to use resin anchors as opposed to Rawlbolts. For this technique you ideally need to use treated timber for the ledger and to protect the back of the ledger with DPM on exterior walls, but the joists needn't be treated. This approach doesn't work too well on really rough (i.e. not flattish) masonry

As a chippy I find the ledger method to be less work and faster. In addition it doesn't require the use of a heavy breaker and masons tools (or a brickie) to create and infill the pockets

 

[Yorkblade]

Brilliant!
Thank you, the latter does seem the most practical approach. It was the structural side I was concerned about. I would have opted for the resin and dpm as well.

Thank you all for your time. Really appreciate it

 

[Deleted member 174758]

There is another alternative which sometimes gets used in buildings which have issues with dry rot persisting in the masonry (TBH we are talking about really old buildings with lime mortar): instead of using a timber ledger and joist hangers a steel angle plate (something like 150 x 150 x 5mm) is fixed to the masonry using Rawlbolts or resin anchors and the joist ends are simply rested on the flat of the angle. The joists are kept in position by having solid strutting between the joists. This approach keeps the timber out of contact with the "infected" masonry, but it isn't a cheap approach and is always a 2 (or more) man job.

 

[martygturner]

Sorry I may have misunderstood your proposal, don't run the joists from old house to new front wall, run them from side to side and do a double joist at the old building end to take the flex out on the change from the brick of the gap to the new suspended floor....You will need to ventilate the space below and a cross draught is essential, joists should always run in the direction of airflow, otherwise a moisture line builds up on the back of the joist. , . Make sure you bottom batten your joists before you shove them in, so that your insulation has something to rest on if you are using rigid. I would consider very carefully insulation at this point.

Personally I prefer draping the joist with roofing membrane ( felt in old speak) and then slab matting to rigid foam as you don't need an gap sealant and the matting if compressed when you put it in moves with the joist.

eg

 

[@tlan]

joists should always run in the direction of airflow

Wrong, joists should go over the shortest distance.

 

[martygturner]

wrong you pop in piers

 

[@tlan]

Nope, you use binders.

 

[Justin Passing]

If you did the "hole partway through the block wall" method, if external you'd have a cold spot = condensation where your joist end is. Bad!

 

[Deleted member 174758]

If you did the "hole partway through the block wall" method, if external you'd have a cold spot = condensation where your joist end is. Bad!

That's one of the reasons why you have to envelope wrap the ends