Anyone seen this sarking board before?

[paralucent]

I had another idea: to screw hooks into the rafters then stretch net curtain wire between them. The wire could easily be shortened if the board looks too saggy. This is more within my comfort zone than working with wood.

 

[robinbanks]

Fit them back into place to what useful end though?

 

[paralucent]

Do they not provide insulation? If not then what is the point of them?

 

[JohnD]

Tilers batten is quite cheap, and readily available. If you cut it to a tight fit, it would wedge in.

 

[DiyNutJob]

I had another idea: to screw hooks into the rafters then stretch net curtain wire between them. The wire could easily be shortened if the board looks too saggy. This is more within my comfort zone than working with wood.

The good thing about DIY is you can do whatever you like so long as you don't do damage or violate regulations. Often you can come up with solutions better than the pro's and cheaper. You can absolutely use hook/ring screws and strings. With an X configuration for the string, you can support multiple panels.

 

[DiyNutJob]

Fit them back into place to what useful end though?

More tidy looking so that they don't get in your way. They are fitted in a certain way for a reason. Unless better reasons are found, best to stick to the original arrangement.

 

[datarebal]

Looks like insulation board as it used to be called .
We have used it years ago over the top of old rafters , counter battens on top ,batten then slated.
The building was an old disused mill on Wiltshire . The idea was to use it as a museum . Rafters were impressive , old ships timbers and the like . So on show to all.
Generally you would not leave floating ends .
Support them anyway you can. No need for mastic . (Ever)

 

[robinbanks]

Do they not provide insulation? If not then what is the point of them?

It looks to be about 10 mm thick and has unsealed joints; its effective insulative value in that application will be close to zero. You also don't appear to have a warm roof construction, so from "make the house warmer" perspective it'll be about as useful as buying some sheets of modern Celotex (a sheet of polyisocyanurate foam that tends to be foil covered or attached to the back plasterboard) and leaning them up outside agaisnt the wall of the house

For aesthetic value, by all means push them back into place and pop a screw into the rafter, sticking out to retain it but if youre after making the loft space warmer you should consider insulating between and underneath the rafters with a dedicated modern product. The difficulty in converting the loft to a useful warm space, however, is that trussed lofts tend to require a lot of work because of all the wood in the way