How to replace parts of a timber frame

[RogerS]

Some of the frame members at the cottage are rotten and need replacing.

Two cross beams and one upright.

The originals were tenoned and morticed into other parts of the frame but clearly I can't dismantle the entire Meccano kit so how can I carry out the repair?

There must be a way to do it without resorting to metal brackets etc but I can't see it.

Many thanks

 

[jasonB]

Looks like all the affected timbers have tennons on them. To retain a tennon on one end it will be best to cut the damaged length of timber away then scarf in a new piece that has a tennon on the end. If you need to replace a whole timber then you will have to start thinking about loose tennons at one or both ends.

Jason

PS you may want to get that wiring looked at, its probably not upto part P :wink:

 

[RogerS]

If you need to replace a whole timber then you will have to start thinking about loose tennons at one or both ends.

Jason

How do you get the loose tenons into the wood that frames the new piece? Do I need a dematerialiser/rematerialiser from Rutlands? :wink:

 

[OLD]

The tv program The House that John Rebuilt (john revell on discovery) covered this problem from memory scarfing in and stainless rod with injection resin glue were used as the oak had gone very hard.

 

[Anonymous]

Brick and timber frame is belt and braces really. Unless your collapsed joint is showing as a structural problem, with other cracks and building movement etc. I'd quietly cover it up and paint the outside black.
Prob with houses like this is that once you start remedial work there is no stopping. You could end up dismantling the whole building. If you do, make sure you keep a record of everything :roll:

cheers
Jacob

 

[RogerS]

The tv program The House that John Rebuilt (john revell on discovery) covered this problem from memory scarfing in and stainless rod with injection resin glue were used as the oak had gone very hard.

Yes...I've seen this stuff and was wondering if it was any good.

 

[RogerS]

Brick and timber frame is belt and braces really. Unless your collapsed joint is showing as a structural problem, with other cracks and building movement etc. I'd quietly cover it up and paint the outside black.
Prob with houses like this is that once you start remedial work there is no stopping. You could end up dismantling the whole building. If you do, make sure you keep a record of everything :roll:

cheers
Jacob

Good point, Jacob...trouble is the engineer/purist in me wouldn't rest easy knowing that it was as bad as it is!

 

[CHJ]

The only time I have done a similar 'repair' on a horizontal timber I removed the rotten member completely, bricks didn't move but I placed a few wedges in void for a day whilst replacement timber was sorted.

Replacement timber was inserted in two half sections 'back and front' with loose tenons cut to fit half mortice in rear member and a driven fit in the vertical mortices, the outer member was then fitted with wedged pegs so that it pulled tight up to back member.

The brickwork infill was 'pointed' at the inner section fit to limit any future movement and the same on completion with outer brickwork. As far as I am aware it's still there some 40 yrs later.

Just make sure any horizontal members are not proud of the infill to trap water, or if they are chamfer the top face to spill it outboard.

Edit: If both of your cross beams are fitted in the same vertical I would make the cross beams solid and halve the vertical to facilitate fitting.

Fitting the rear vertical member first as reference for the horizontals then cap it with the outer to trap the horizontals in place.

 

[jasonB]

You would have to have open backs to the mortices if you went for loose tongues, the joint could be held together with stainless coach screws into counterbored holes then the plug left slightly proud as a dummy peg.

Jason

 

[Mike.C]

Old,

The tv program The House that John Rebuilt (john revell on discovery) covered this problem from memory scarfing in and stainless rod with injection resin glue were used as the oak had gone very hard.

I saw that program, and if I remember rightly it was the conservation officer who recommended that he got it repaired that way.

Roger are the bricks in between each beam cladding panels, or are they full bricks?

Cheers

Mike

 

[RogerS]

Chas..not sure I follow you totally. Any references to anything on the web, do you know?

Mike...the brick infill panels aren't structural but simply something to fill the hole. I fully expect to remove them to replace the timber.

Roger

 

[CHJ]

Variations on this concept Roger.

Whether the 'back member' has half mortices or full depth with just a capping strip is dependant on your assessment of the particular job and as mentioned whether the brick is surface panel or full thickness, but looking at it they look like timber frame thickness only infills. You may want to brace the inside of the wall to support the mortar skim whilst you are banging around.

The stainless 'screws' motioned and plugs is a good idea, far easier than wedging tapered pegs, they weren't around when I last had to to stop daylight entering from places other than the windows.

A Structural engineer may see stainless inserts and epoxy fillers as the ultimate strength way of doing it, but lets face it, IMO the structure is not moving far with the existing rotten wood and anything you are likely to replace it with will be better, just make sure you don't encourage additional water ingress.

 

[engineer one]

what about using some thing similar to the ronseal window resins roger.

as jacob says as soon as you start, you will find even more problems.

although i agree with the idea of making it perfect, there is a great deal to be said for accepting that these things have lasted some time in the state they are in, so reinforcing may be the most practical and pragmatic way of doing it.

the important thing is to ensure that the wood is sound internally, and then stop it deteriorating outside.

good luck

paul :wink:

 

[inventor]

Is that lime mortar between all those bricks? I hope so, portland cement will rot those beams quickly!

Any of the suggested ways of joining the chunks of timber - stainless screws, studding and resin, or wooden plugs through the scarf - will work fine. However, I agree with the chap who said, "Do nothing". I'd spend at least a year thinking about how to fix this house before taking out a beam. The house down the road here waited 40 years between the discovery of major rot and the repair!

 

[RogerS]

Thanks guys for all the suggestions.

In response to some of the comments/questions....

...ideally I would leave well alone if it weren't the fact that some of the rot does allow a lot of water ingress and also the surveyor for the building society isn't that way inclined (ie leave alone) and so there's some retention on the mortgage.

Mostly it is lime mortar between bricks but I suspect that they've used Portland to fill in gaps and holes in the beams. No worries as that will all be fetched out and epoxy filler put in, wire brushed to simulate grain

How about a tusk tenon at each end (or similar) and swivel the horizontal into place?

Someone suggested keeping the horizontals as one piece and splitting the vertical but I think that that will create an inherent weakness in the building as most forces are downwards, I think, and it could cause the verticals to bow.

I suspect that in the final analysis it will be a combination of all methods!

For those interested, I'm nearly there setting up the blog and even a webcam if I'm adventurous. More info to follow.

 

[Keith Smith]

If you are going to take the bricks out above you could remove the offending cross member, fit loose tenons to each end, making the half that projects very slightly tapered.

Cut the mortises in the cross beam so they go right to the end, a bit like a cross between a bridle joint and a mortise, again slightly tapered to match the tenon.

The cross beam will slot in from above and you can peg both sides of the joint. You could also glue it, I would, but the joint takes the strain and doesn't rely on the glue.

I'm not a fan of glues and fillers in old buildings, a lot of these fancy glues have an expected life of 25 years, thats less than half a moment in the life of a building like the one you have.


Keith

 

[devonwoody]

Remember iron and oak is a disaster waiting to happen. No experience but stainless has been mentioned so I suppose thats why.

 

[Dibs-h]

The timber repair splices are definetly the way to go - some of my friends who are structural engineers, vouched for them, as I was a bit dubious.

Problem with in-situ repairs is that there aren't that many alternatives. Besides, I would suspect that Epoxy and SS rods would outlast me and the kids.

Dibs

 

[RogerS]

I had a couple of local timber frame repairers round to see what they would do and also to ask how they get around the tenon 'problem'. This was one approach given (and apologies if you guys have already suggested it but me being rather obtuse failed to 'get it').

The right hand end of the beam is cut square to the upright. It is then morticed upwards but not all the way through. The loose tenon then goes into this mortice and slides over into the mortice in the upright. It is then wedged and pegged.

Both recommended using lime mortar and a micro-porous paint to fill in external splits. Neither recommended using epoxy as a filler.

One of them also made a rather inspiring recommendation to get some large needles (as in those used to inject cattle/horses etc) and connect them to an upended container of preservative. Drill a very thin hole coming in from the direction of any rot etc and let a slow drip feed go into the wood. A kind of intravenous drip.

 

[inventor]

One of them also made a rather inspiring recommendation to get some large needles (as in those used to inject cattle/horses etc) and connect them to an upended container of preservative. Drill a very thin hole coming in from the direction of any rot etc and let a slow drip feed go into the wood. A kind of intravenous drip.

If you do need to stop rot, you might consider using boron. It can be injected into old beams and can be inserted as rods to provide long term protection. I've just put boron rods into some rotting softwood windows. I'll let you know if it works in forty or fifty years.

I think I'd rather have boron in my house than something with a very long name!