repairing 1st floor joist

[ajrobb]

I removed bathroom/bedroom partition and exposed the floorboards to reveal rot (picture upload not working). At least top 50mm of 165mm joist is completely rotten. It is a 1978 Wimpey end terrace with joists running between party wall and end wall. The rot is adjacent to the end wall and is obviously the result of a leaking shower.

If I lift the floorboards and take down the sagging ceiling I can get good access. Can I DIY? I'm thinking an Acro supporting the mid point of the joist, support the rotten end by tying to a 2x4 stud across adjacent joists. Cut the joist 600mm (2') from visible rot (about 1.5m from the end). Splice a new section with joist splice plates.

If there are no noggins, should I raise the Acro while splicing the joist to pre-tension the joint?

Where can I get splice plates? SabreFix SP82 look suitable but can't find a supplier.

 

[ajrobb]

I have now taken down the ceiling. No great loss there - it was only 9.5mm plasterboard with neither adhesive nor joint tape at the walls. This has revealed that the rotten 'joist' is actually a pair of 165x45 joists bolted together with 3 coach bolts along the 3.6m span. The joist centres are at 400mm spacing and there are wooden herringbone trusses mid-span. The water got between the joists and both are rotten. The rotten section extends about 800mm from the wall.

I have not found a direct source for this timber. The nearest is TP, who might plane down some 170.

How should I repair this pair of joists?

 

[Static]

Try Alsfords for the timber.. always found them fairly helpful..
Maybe Expemet for the splice plates (http://www.expamet.co.uk/product/builders-metalwork/structural-fixings/splice-plates)

Repairing the double joist just think of it as a 165x90 timber.. so either bolt new double joist together before splicing it in or order wider timber..

 

[ajrobb]

Been quoted £180 for splicing new timber at different lengths and laminating with 5 coach bolts. I already bought some splice plates so I'll attach a pair over each joint afterwards.

 

[alittlerespect]

Hi

You need to be careful - the detail you describe for the joists is normally indicative of a load bearing system and you would be best advised to get a Structural Engineer to comment on your proposed method of repair before carrying out any work.

Regards

 

[ajrobb]

the detail you describe for the joists is normally indicative of a load bearing system

There was a Paramount partition running along this pair of joists with extra layers of 12.5mm Soundbloc on each side and a bath on one side (above the rot). There will be a staggered stud partition with 2 layers of 12.5mm Soundbloc on each side. The ceiling above is hung on roof trusses.

 

[Static]

As you are fairly close to the supporting wall the moment transfer over the splice should be fair small.. so splice plates should be sufficient.. (if you were doing this mid span may need something beefier)..

Might want to stagger the joists to allow for a better connection, ie make the two new joists different lengths by about 150-200mm and bolt thro) then add the 4 splice plates .. make sure you bolt the new pieces together as the existing has been done so they work together..

Does your builder proposes different?

 

[alittlerespect]

Hi

Its not the load but more the shear factor that will determine the best means of repairing the timber joists!

I would still recommend obtaining comments from a Structural Engineer, if you don't like what they have to say, you don't need to employ them and then you will have to accept the risk associated with any action that you take!

Regards

 

[ajrobb]

It's not the load but more the shear factor that will determine the best means of repairing the timber joists!

Most of the stress in a beam is due to bending moments rather than shear. The most likely place of failure is mid-span at the bottom where tension is greatest. For instance, engineered joists have very little shear load capacity.

However, near the supports, the shear loads are at their greatest while the bending moments reduce.

 

[2929twin]

Check out; Joist-repair.co.uk They sell steel angles that bolt onto end of rotten joists.

 

[alittlerespect]

Hi

Not when your cutting off the end of the beam! Tension is in the bottom section of the beam which has nothing to do with shear!

Good luck with whatever action you decide to take!

Regards

 

[Static]

Lol.. love how this turned into an engineering debate..

Anyways,, so long as adequate nails/screws are used in the splice connection then shear wouldnt be an issue.. as bending and creating a more continuous member to limit deflection would be the more critical factors..

Unless ajrobb has failed to mention that the beam has some massive point load near the support

 

[ajrobb]

Lol.. love how this turned into an engineering debate..

Sorry, I was a mechanical engineer in a past life.

Unless ajrobb has failed to mention that the beam has some massive point load near the support

No, it was a Paramount partition and will be a staggered stud partition wall (distributed load). The nearest point load was the HWC (now gone) a metre from the other end but sitting on the next joist. Oh, and a share of the bath but again that will be centred over the next joist.

 

[alittlerespect]

Hi

I wasn't going to say any more on this subject but I will just so that I have a clear conscience - my first comment stands - get some advice from an SE.

The choice is yours as is the risk!

Goodbye!

 

[ajrobb]

get some advice from an SE

I have an SE doing a structural survey on a flat we are buying. I'll ask his advice.

I've been failing to upload some more photos. The old timbers were almost completely rotten where water got between them. Anything would be better than that. Maybe the partition was holding up the floor rather than the other way round.

The only splice plates I could find were oversized (about 100mm deep). I've put one splice plate across the bottom of each joint. After I got the first screw in one end, I pushed the other end of each splice plate up against the joist. This initially buckled the splice plates slightly before I got all the screws in. With all the screws in, the plates are flat again and the temporary prop has lifted slightly off the floor (1mm or so). The joists are also overlapped and bolted.