Rotten floor joist ends

[RedwoodRenovation]

Hi,

First post to the forum, have been reading it for a while and have decided to take the plunge!

I've got some joist ends which are rotten at the external wall end, where they go into the 18 inch stone wall. I've removed the cement render from the outside and will be repointing and rendering in lime!

I'm thinking of removing six inches from the end of each joist and slipping in a new wall plate and then using joist hangers to re-hang the joists from that.

Question is, can you use a 6 inch wall plate and if so, what is the best method to bolt it to the wall?

Thanks

Graham

 

[FamilyWiggs]

Hi Redwood and welcome to the forum.

I had a similat problem with a main beam. We supported it, cut out the rotten end, scarfed in a new section (with steel plate bolted to the bottom just to be sure), dug out the socket, wrapped the end in plastic( :shock: ) and mortared it back in.

Guess you could do similar with the joists? I'll try and dig out a photo and post it.

NB you shouldn't take my advice as I am a non-expert; the others will be along shortly!

 

[RedwoodRenovation]

Hi FamilyWigs,

There are quite a lot of joists and this will probably need doing in another room next to it, I'll find out when I take the ceiling down next week!

I've been looking at putting a 6 inch oak beam in and maybe using stainless steel bar with resin injection to hold it on. I've not spoken to my engineer about this yet, as I only discovered the problem just before Christmas.

I was interested in others advice.

Thanks

Graham

 

[Flyfisher]

Another non-expert view; is it possible or practical to insert the new wall-plate some way into the supporting wall such that the wall itself bears the weight of the joists and floor? Any fixings would then only require the strength to hold the wall-plate in place until the joists are fixed to it.

 

[Gervase]

The commonest method is to acrow the offending joist, cut off the offending end with a shallow angle running from the top and then scarf in a new piece that will fit into the socket vacated by the rotten end, using a new oak pad underneath if the wall plate has rotted. The new is secured to the old by plywood cheekpieces screwed to both or by steel fishplates bolted through with 10mm bolts. If the joist is to be visible and you don't want too much ironmongery on display, you can also use a portable morticer to cut a groove down the middle of old and new and put a thicker steel fishplate inside the timbers, bolting through from the outside. That's the more fiddly approach, however. The ultimate in fiddliness is to use stainless steel rebar as dowels through both pieces, held in place with epoxy - ideal for visible carved oak beams and the like.

 

[RedwoodRenovation]

Hi Gervase,

There is no wall plate at the moment, the ends of the joists go into the stone wall, which was cement rendered in 1954 and has resulted in rotting them.

I've removed the cement render. As I've stripped the room, I noticed the rotten joist ends and thought that if I introduced a six inch wall plate and bolted it to the wall, I could just simply saw the ends off and then rehang the joists onto the new wall plate.

The only question I have is what is the best method to securely attach the six inch beam to the wall? I mentioned the stainless steel threaded bar, as I've used that in the past, with timber connectors to fix joists in the past, but normally for splicing bigger lengths not just the last 6 inches.

Thanks

Graham

 

[Penners]

Presumably you want to use a 6-inch thick wall member so as to support the joists, which will - after the rotten ends have been cut off - be short of the wall by several inches?

If that's an accurate explanation of your plans, then I can only say (as a complete amateur) that I don't like the sound of it.

If some or all of the joists terminate some inches from the wall, resting on a support member that's bolted to the wall, I suspect that the "turning moment" on the support beam will be considerable. It would therefore need to be extremely securely fixed to the wall, with sizeable spreader plates on the outside to resist any risk of pull-through. You could perhaps improve the situation by using a very deep beam, but I suspect this could be aesthetically troublesome.

IMO it would be far more advisable to follow Gervase's advice (and he's a professional) by scarfing new pieces on to the ends of the joists, resting within the existing sockets in the stone.

 

[middi]

The most unobtrusive way to fix a wall plate against an existing wall is to have simple but hevy duty ( 8/10mm) flat 90deg angled brackets countersunked and attached to the back of the oak plate by two stainless steel coach bolts ( coach screws if you do not want to see any ironwork). The 90deg lug ( min 100mm in length 50mm wide) to be pushed and "sealed" in a corresponding cavity cut out of the wall.
Ideally one bracket corresponding to one joist . The joists can then be screwed( pegged?) to the wall plate from above

 

[Matt Green]

I've removed the cement render from the outside and will be repointing and rendering in lime!

just to be sure here... Well done for removing the cement, where was the water coming from and has that been sorted out before you start any repairs?

Matt

 

[RedwoodRenovation]

Hi Matt,

Yes, the water has several options for getting into the building!

There is only one downpipe for the guttering, along the entire length of the front of the house. Then there is the concrete paved area, which is at least 6 inches too high and needs to be removed. Thirdly, there is the problem with the render and lack of proper pointing and there are now some holes in the wall, which can't be patched up, as it's too cold!

I haven't mentioned the additional work being done under the insurance, as the house was damaged by fire on 4th July 2009 (yes, that long ago!) so the house has no roof and is covered by scaffolding and a temporary roof. I'm removing one of the chimneys, all the way from the pot to the ground floor, hence my discovery of the rotten ends of the floor joists!

I'll have to update the website so you can have a look at the details. During the weekend I found some newspaper from February 1859 which was in a upstairs cupboard. I'm having some problems dating the house, but it's on an OS map from 1857. Which is rather amusing, as when I bought it, it was advertised as circa 1899! Just shows you how much the estate agents know...

Cheers

Graham

 

[headgear]

I've recently discovered that wind driven rain is a bigger deal than I had previously supposed. Must have been my sheltered upbringing :wink: You may want to have a look at BS 8104 1992 before removing that render from your stone walls; at least give yourself a chance of designing an appropriate replacement!
Lots of work has been done to model the hygrothermal conditions in single leaf masonry walls, but I fail to find anything that is other than specific to a given site and/or material; and all the models treat the wall as a homogeneous mass for moisture and heat transport. Might be OK for concrete or brick, but I don't believe it for stone.

 

[Stephen]

Setting aside the issue of the water ingress itself (no doubt you will resolve this before any joist repairs) there are various possible options.

1
Simply splice on new ends and put new ends (adequately protected) back into the pockets in the wall.
[In terms of splicing new ends there are various methods including cutting off the rotten end and bolting a new timber alongside (overlapping the joint and adequately bolted for a sufficient distance to prevent a bending moment around the joint area), or end connecting and placing plates along the joists over the joint (and to an adequate distance either side to prevent bending moment) to provide the required strength to the joint.]

2
Splice on new ends but fill pockets and hang joists on joist hangers so that the timber is not in contact with the wall at all.

3
Cut out a channel and install a wall plate (adequatley protected) and rest the new joist ends on this.

4
Fill pockets and install a 'ledge' to the wall face under the joist ends (supporting the new ends) so that only the rear face of the ledge itself will be in contact with the wall and therefore in need of protection.

Options 1 and 2 leave the joists supported individually in the wall and therefore creating spot loads. Probably involves more work than options 3 or 4.

Options 3 or 4 create a spread load (the wall plate or ledge) and is perhaps easier and less labour intensive.

In all instances ensure the cut ends of joists are treated and protected (i.e. isolating membrane) from direct contact with the wall (that may remain wet). Any timber (e.g. the wall plate or ledge) will need adequate protection/isolation from direct contact with the wall.

Options 3 and 4 are more likely to leave better air circulation around the joist ends.

There is no right or wrong way, but you must consider what suits the situation best and is most practical to undertake.

Hope this helps.

Stephen

 

[RedwoodRenovation]

Thanks for all the information and the feedback, but there has been progress on the floor joists debacle!

Found out, after taking the chimney down to ground level, that there is another floor on top of the with the rotten joist ends!

I've never seen anything like this, but when I dropped the ceiling, it seemed like a normal floor, but it's had another floor laid on top it, laying on studs.

I'll post some pics to let you see.

Cheers

Graham