Replacing common floor joists

[andy1971]

Hi,

I’m a newbie here and I’d be very grateful for some advice as I need to replace joists that hold up the upstairs floor in my rubble stone cottage. I found a previous discussion that I found very useful here

Unlike Minkeycat, my common joists don’t just drop in to a protruding beam on the outside wall - in my cottage, they sit in a hole in the stonework itself on the outside wall. At the other end, they sit in a pocket in the bridging joist (thanks for the terminology, MikeG) with something I believe is called a bare-faced tenon and diminishing haunch.

My question is how physically does the replacement common joist get into position, given that it is longer than the distance between the outside wall and bridging joist, and can’t just be dropped in from above? Is it pushed further into to the bridging joist at an angle, which would allow it to be moved to a horizontal position, and then withdrawn out a few centimetres from the bridging joist whereby the other end would then (hopefully) slot into the stonework in the outside wall? I think this must be the case as the “pocket” in the bridging joist seems to be deeper than the tenon itself which would allow for this method.

 

[Lacan07]

Usually when replacing upper floor joists you have to knock a hole out in the wall, the joist goes partially out the wall and back in again to be straightened.

You really want the 'entrance' for the new joist to be opposite the wall where the joist is seated.

Obviously you prop the ceiling first before removing the old joist.

 

[Toby Newell]

At the other end, they sit in a pocket in the bridging joist (thanks for the terminology,

Not that it matters, but FYI 'bridging joist' more often called 'spine beam' these days, or traditionally 'bresummer beam' or simply 'bresummer'. And despite repairing, replacing and strengthening floor joists being part of my job, replacing beams gives me the willies, as does anything that requires props, so I will let others explain.

 

[Toby Newell]

I am sure you have been advised correctly, but have you got a second opinion? Many bad looking joists and beams are perfectly serviceable underneath as the heartwood is often less attacked by rot and pest. Often strengthening in place is possible.

 

[Toby Newell]

Hi,

I’m a newbie here and I’d be very grateful for some advice as I need to replace joists that hold up the upstairs floor in my rubble stone cottage. I found a previous discussion that I found very useful here

Unlike Minkeycat, my common joists don’t just drop in to a protruding beam on the outside wall - in my cottage, they sit in a hole in the stonework itself on the outside wall. At the other end, they sit in a pocket in the bridging joist (thanks for the terminology, MikeG) with something I believe is called a bare-faced tenon and diminishing haunch.

My question is how physically does the replacement common joist get into position, given that it is longer than the distance between the outside wall and bridging joist, and can’t just be dropped in from above? Is it pushed further into to the bridging joist at an angle, which would allow it to be moved to a horizontal position, and then withdrawn out a few centimetres from the bridging joist whereby the other end would then (hopefully) slot into the stonework in the outside wall? I think this must be the case as the “pocket” in the bridging joist seems to be deeper than the tenon itself which would allow for this method.

View attachment 13097

Hi, can you show the diminishing haunch please? That's not a joint I am familiar with outside of furniture. Interesting, I thought they might of used a double tennon rather than a haunch to reduce lateral movement.

 

[andy1971]

Thanks for all your replies. Just to clarify, we are not replacing the spine beam. Just the smaller joists. We will need to remove the floorboards above. More photos attached.

 

[Toby Newell]

I cannot see from here obviously, impossible to tell if they are ok or not. They look pretty straight. If they are rotted then no one has touched them afterwards as the surface looks almost perfect (relative to their age) Still can't see any haunching... nice floorboards.