Sagging Joists - Do I need a Professional Opinion?

CoastingHatbox

There's a lot of information to condense into this post, but I'm going to try and keep this short and sweet. Slow leak in bathroom resulted in a rotten joist. We've removed the ceiling below, and although the rot is contained to a very small area, we have serious misgivings about the floor under the bathroom in general.

It is a 70s house of very typical construction. It is a typical joisted floor. 7 joists 2.66m in length support the bathroom. The joists are 170mm x 48mm and spaced 45cm apart, measured centre to centre.

The joists are supported by exterior wall at one end and a supporting intermediate wall at the other. Two of the joists at one end of the intermediate wall are 10mm higher than they are at the exterior wall. They bend upwards sharply enough as the reach the supporting wall to distort the floor boards. Largest recorded deflection in the joists (superimposed load, no live load, N.B empty bath) is 13mm. I understand according to building regs, this should be no more than 8mm.

The joists have multiple notches mostly outside of the safe notching areas. In the worst case 6 notches. There is one hole bored through some of the joists for electrics, just outside the safe area for holes but in very close proximity to notches.

The joists are made from fairly knotty timber. In one of the joists, with a quick inspection I can see 11 knots, most of them sizeable.

Two of the joists looked to have distorted along the grain and around the knots - one of them quite badly, kicking out it's original vertical positioning by a centimetre at the base. For 2/3 of the span the vertical looks quite plumb. It's over the other 1/3 of the span it kicks out and gets increasing worse as you reach the end of the span.

Having noted what was happening with the supporting wall and the two joists being higher, I did some crude measurements of the ceiling in the other room (similar span) and that too looks to be sagging by ~10mm. (It's difficult to be exact with the ceiling in situ).

The original plan was to replace the two joists affected by rot, sorting out the plumbing and electrics in the process so they are not illegally notched, but now I'm thinking I need a professional to advise on the structural aspect. Obviously, cost is a concern, as are plans to gently rennovate the remainder of the house (we've just commited a good chunk on replacement double glazing). Ultimately though, we want to know the structure is safe and worth investing in.

Do I need a structural engineer to take a look?
Thanks

Doozergirl

It might just be cheaper to replace the joists if you're worried about them, rather than pay someone to tell you to replace them... 

That said, all houses move and the tolerances applied during fitting don't apply 50 years down the line.  

Maybe get a visual inspection rather than any type of report.  

Mickey666

Having removed the ceiling below why not just reinforce the floor structure by inserting new joists?   Either by sistering the existing ones or inserting new ones in between the existing ones, ie so the floor joists are spaced about 20cm apart.  Probably overkill but it won't do any harm to over-engineer things and the cost of a few joists will be a lot less than getting a structural engineer to inspect and write a long-winded report.  It'll be the most solid floor in the house

fenwick458

just get a builder/joiner in to have a look at replacing them, get your advice from them. pointless seeking advice of an engineer I can almost guarantee you they will just tell you to replace them, just to cover themselves. and also charge you for it!

CoastingHatbox

I don't think my original post does justice to how bad it looks.

We've had a builder round to look at it ... well, he was here to build a garden wall. He looked at it and said the state of the timber was shocking and that 'the builders have used whatever wood they had lying around'. He is going to provide a quote. We're reasonably well satisfied the best course of action is probably to replace them all. Additional joists would mean every block at that level has a piece chipped out of it or attaching joist hangers. Sistering the joists and some block work maybe an option.

I'm concerned more about that supporting wall than the joists themselves.The joists under the bathroom are angling upward as they cross the partition wall into the next room and the joists from the adjacent room look like they are angling upwards as they cross back the other way.

Over the weekend I think I'll fill the bath and see how much more deflection we see and maybe strip off some of the plaster from the supporting wall so we can see how much movement there is in that structure. And go from there.

I don't necessarily want a report, more some re-assurance that the house is structurally sound or, some guidance on what we can/should do to improve structural issues.

Doozergirl

If you're worried about your 1970s house, you should see the state of 1870s houses behind the walls.   You'd be astounded at how they're still standing when the mortar in the walls is crumbling away.  Yet they still stand.  

I don't think you need an entire rebuild.  I appreciate that renovation can be like pulling on a loose thread in clothing.  You have to stop somewhere though.   Your house doesn't need to meet current regs and houses stand perfectly well with a lot less in the way of original joist thickness than yours will have.   

We've had to carry out repairs where nothing we could do would stand up according the SE's computer.   The proof is in the pudding though.  The pudding is time.  

Sounds like you might want the SE for a bit of reassurance.