Roof tile choice - roof weight

Afternoon all

Following on from another similar roof weight question, we will be having our bungalow roof replaced shortly at the same time as our attached neighbours [same tile/colour] the existing roof that I believe is the original, has Redland 49s.

Neighbour has suggested using a lighter tile as there are a couple of rafters that have sagged slightly over time, nothing major, but just about noticeable. It would appear that the Redland Renowns are a little lighter and are of a similar style.

Would there be any real benefit from choosing a different tile?
Are there any issues with using the Renown instead? I can see that it is a slightly larger format to the 49s.
Would it be a simple enough task for the roofer to sister a new rafter alongside the sagging ones whilst the roof was off so that the roof plane is straightened up?

Thanks

[Building regs application will be made and loft insulation added to]

There is no reason why not, but no point either.

A couple of sagging rafters are unlikely to be related to the tile weight, so ensure that there are not other causes.

Yes a new rafter can be added to the side of a sagging one, but the potential problem with this is that you end up with a hump from a new straight rafter amongst others which are slightly bowed from age. You see it more only when the tiles are on.

Good roofers will pack the tile battens up to remove any major dips

Woody, thank you. There has indeed been a little roof spread previously but this has been dealt with a while back.
Its good to know that there is an alternative of packing the battens if necessary, I shall mention this to the roofer.