Is there a wood preserver that does not have an adverse effect on roofing felts ?

There's are quite a few water based wood preservative treatments on the market, just Google water based wood preservative. Most are for garden use and have a colour and wax additive but you could also consider using a preservative designed for treating the cut end grain of tanalised timber. Water based treatments are not as effective as spirit based ones but they wont react with bitumen based felt.