Rotten rafters under internal skielings

[larry]

Hello everybody

I'd love some advice.

As part of works upstairs I recently took out an internal sloped lath and plaster ceiling in our 1920s house. 

This is in the middle of the original house and the wall is a single skin two storey wall with a timber wall plate and rafters sitting atop. 

To the left is a new two story extension which continues the line of the sloping ceiling which becomes an external wall/roof.

However two years ago we had work done to repair what seemed to be a leaking valley. I only noticed this through a very small amount of evidence in the loft. The rafters in the loft all look pretty sound. 

Clearly the leak in the valley bad been there for some time as the left most rafter is completely done as is part of the wall plate.

The second rafter looks impacted but clearly is giving strength. 

I guess the external roof is helped by the new extension running to the left.

There are some cracks also in some of the good timbers. 

The rot is now bone dry and I have removed anything that came off in my hand without force. 

What I want to do is leave most of the rafters exposed (probably painting the rafters??) to let light across the top to a new landing. We are planning a suspended ceiling above..

Questions are:

1 opinions on the rotten bits and potential repairs or ways to strengthen them and treatment??

2 opinions on need and if so methods to deal with the two rafters that have length wise cracks

3. Ideas to insulate underneath the valley

4. What else am I missing??

 

 

 

I don't think the rot looks like dry rot and no evidence of spread. It's clearly stable enough as has been like this for at least a couple of years without problems. 

 

 

[larry]

I should add, the walls underneath might have moved around a bit over the last ten years, but not signs of progression anywhere as far as I can see. The extension meant taking out a lot of the external wall which you can imagine is to my left from most of the photos. Similarly, most of the wall underneath this was taken out also in a later development.