Uneven floor joists/structural engineer

velaine

We live in an old converted Victorian house. We want to lay engineered wood planks on the ground floor and taken up the dodgy chipboard subfloor to replace with plywood (no original floorboards)..

Upon removing the subfloor underneath the issues start.  Although not rotten, some joists are uneven (dipping into the middle, different heights from the next. The largest difference is 2-3cm.Also the cement  the fireplace sits in is raised above the joists and the hearth? Doesn't quite sit directly on top 

Also one piece of wood supports 3 joists at one end

Do we need a structural engineer to come and look to see if it's safe/offer solutions?

Will try and upload a photo.

Thanks in advance 

velaine

This is a photo of the joists holding the longer joists bit not attached to the wall and the fireplace 

ThisIsWeird

They look otherwise to be in very good order?
You don't plan to retain the hearth?
Anyhoo, provided the joists aren't sagging or moving under your weight, but are simply uneven, then the simplest solution would be to 'sister' additional jousts alongside the uneven ones, glued and screwed through sideways, and ensuring that these are dead straight and level with the rest.
A straight forward job for a chippy. No SE required.
All that rubble should also come out to ensure the best air flow in that underfloor void. And you should take the opportunity to add insulation under there, I understand the two common methods being to either drape a mesh over and down the sides of each joist, and fill with loft type insulation, or better I think would be to neatly cut rigid insulation like Celotex to tap down tightly half the joist depth, leaving it flush with the top surface. Use exp foam to fill any gaps, and seal around the perimeter. 
If the joists are actually springy, then you may possibly require an additional support wall under there, but again that should present no issues.
Finally, ensure the grill vents on the outside walls are clear - keep that void looking as healthy as it currently appears 
I'd get a few chippies around for their thoughts and to quote. If you remove all the boards and clear the room, it'll be a nice job for them.

ThisIsWeird

If you wish to remove the hearth, I guess your two options are to either chisel off material from its top, or to raise the rest of the floor. The first option seems more obvious.

Section62

velaine said:

This is a photo of the joists holding the longer joists bit not attached to the wall and the fireplace 

Looks quite normal to me.  The piece going across (called a 'header') is sometimes 'doubled up' (i.e. two pieces side-by-side), but that isn't always necessary.

The floor structure isn't original and has been replaced at some point.  The dipping/different heights could be caused by poor quality materials or workmanship, but hard to say from one picture.

Excessively notching or drilling (which shouldn't be necessary with a suspended floor) joists weakens them and can cause dipping or bounciness - so if there are more pipe runs than the one in the foreground of your picture then that would be something to take a look at.

stuart45

As Section62 said, poor quality timber or workmanship. Has the look of a not too good job. Joists should be laid crown up. Minimum of 150mm from bottom of joists to oversite. Noggins fixed through each side, not top. All debris from demolished sleeper walls and lager cans removed.

Keep_pedalling

stuart45 said:

As Section62 said, poor quality timber or workmanship. Has the look of a not too good job. Joists should be laid crown up. Minimum of 150mm from bottom of joists to oversite. Noggins fixed through each side, not top. All debris from demolished sleeper walls and lager cans removed.

The Tennants larger can could be a clue to the poor quality 🤪

velaine

Thanks. All. I suspect poor quality workmanship as I understand the developers went bankrupt when the converted the building back in 2000. There is some bounce in the floor and there is another set of pipes for a another radiator an

Fyi we don't want to remove the fireplace. The concrete the fireplace is on is bigger than the fireplace. This picture  might be better and about 1 cm higher than the floor  will be even with ply and planks. 

I will look into arranging some visits from flooring expert in the area 

Section62

velaine said:

Fyi we don't want to remove the fireplace....

If that's a redundant (but still live) gas supply to a fire then you might want to consider getting the pipework properly capped off/completely removed, whilst the floor is up.