Joist replacement in stone wall

[welshcottage]

I'm sure there are several answers to this same question so appreciate the help.

We have a 'bouncy' floor in one room, we knew this when we bought the property and ultimately was caused by a bad damp problem and partially rotted joists, which we now have the time and money to replace.

The room is about 4mx3m and the joists runs long ways.

They are currently located directly into the stone, which is typically Victorian rubbish on the inside! There is no support beam part way across etc.

We will be replacing around 50% of these at least and have had different opinions on fixing and general solutions of. These are:

Cuts out, enlarge hole use a little damp proof membrane around end of joist and wiggle into place, the overlap by my rough calculation would be a bout 2 inches at each end does not seem enough?

Use wall hangers, tricky as stone is not the easiest and made up of lots of smaller pieces not big lumps.

Add a wooden batton using 6x2 at each end and runs new joists using modern hangers, quite like this idea and seems quite simple but massive weight in the fixings.

Use option one but also add a beam half way through for extra support, not convinced needed.

All opinions welcome thank you

 

[welshcottage]

Just to add damp problem has been sorted was due to a bank of earth and now dried out!

 

[welshcottage]

Well took plunge.

Pulled down ceiling, before it fell down was a little crumbly!

Origional joists are about 5 inch by 2 that would explain the bouncy ness as they moved a pantry wooden wall in the 70s! So thinking will need 9x2 joists rondo a proper job

 

[vinn]

You've got several issues to deal with here.

What do you mean: " a bank of earth has now dried out" - is the earth still banked against your outside wall surface?
I ask because its almost useless doing interior remedial damp work when the cause might still be in place - why not post a photo of the banked earth and exterior surface?

All your joists will now need replacing - make a selection from a joist span table.

The thing is unless the upper floor is removed or supported you cannot fix a ledger and hangers (on both sides of the room), which would be the way to go.
What kind of flooring is it - T&G etc?

Propping and cutting joist tails to slide in a ledger would work - but depends on further variables. Come back if you are still interested.

 

[welshcottage]

Hi I struggle to post pics, but yes the bank was removed about 3 years ago now, has been allowed to dry out and now return deter with a lime mortar mix.

I'm happy to remove the floor complete makes no real difference as after inspecting makes most sense to replace all the joists in one go, the floor board are old and very hard, likely oak.

I like the idea of ledgers and hangers just need to work out best way of attaching as the wall on the inside is made of relatively small stone and lots of old mortar so lack of fixing points, any thoughts on this would be great

 

[vinn]

Work out where your joists hangers will fall and use the joist bay spaces for fixing the ledger bolts.
Open up pockets in the joist bays, and fill with a packed sand and cement and chippings mix.
Allow 24 - 48 hrs to dry, and then offer up the ledger using expanding bolts into the pockets.
Line the back of the ledger with DPC material.

 

[welshcottage]

Seems sensible.

Effectively, I could enlarge the existing pockets left by the old joists, to accommodate the ledger. I have some DPM so again makes sense. Thank you.

Sounds daft question but is there a specific type of expandable bolts just thinking of them shearing and how many should I use is their a rough formula, just thinking there will be some weight after everything is installed!

 

[vinn]

Fischer or Rawl.
4 or 5 fixings.

 

[welshcottage]

Able to add a couple of PICs, please see state of wall, and a closeup of where one of the joist has dropped over time. the cross pieces I added when we bought he property just to add some strength, which it has done short term.

The ledger still seems easier than making bigger pockets.

Just seems in my mind a wall pocket is stronger than a wall ledger, probably not, same principal as kitchen cupboards lots of vertical stress rather than horizontal, just my brain over thinking. I located some Rawl m16 bolts which seem a fair size.

Questions:

1 - I have checked the charts and 9 x 2 is the correct for the span, should I use same for the wall hanger, makes sense too just want to ask ?

2 - If I enlarge slightly the pockets and fill with concrete mix right back, should I use two fixings per pocket to hold on the ledger? is there a minimum number I should be using, space between?

3 - Floorboards are being treated with woodworm and dry rot treatment as we have done in the rest of the house, and we will only reuse the better ones probably about 70%

4 - After seeing the Pics any other advice?

are to be removed later today!

 

[tony1851]

Why not just use the same socket-holes for your new joists? If you are using 9"x2"s, you can notch the ends of the joists down to 5" without there being any problem. The tricky bit would be the clearance to get the joists in - that depends on how much wall-thickness you have to play with. You can have the cut-down ends 6-8" long if that helps manouver them in. If you can get at least 2" bearing, that would suffice.

 

[welshcottage]

Hi Tony, in reality that would be easier if I can do that.

The current beams go back about 6 inches so should be enough to make a ledge of 3 maybe 4 inches with a little fettling and jiggling.

Would cutting down not take away from integrity of the beam if down to 5 inches

 

[vinn]

1 - yes
2 - 1/packing
simply space them out.

 

[welshcottage]

Many thanks

 

[tony1851]

Would cutting down not take away from integrity of the beam if down to 5 inches

Strange as it may seem, the answer is - no.

Look at it this way; you currently have 5" deep joists. They have not collapsed, but are a bit springy.
If your joists are 9" deep for the vast majority of their span, they will deflect (ie bounce) far less than the 5" deep joists,
even though you have cut them down to 5" at the bearings.

The only force on the timber at the bearings is shear force, and with domestic floor joists, that is never an issue.
Cut down to 5" x 2" at the bearing, a C16 joist would support about 5.5 kn (approx 1/2 ton) before it failed in shear.