I think to strengthen your roof would be quite an undertaking and the consequences of getting it wrong could be disastrous. To do any sort of work like this you would need to get your local council's Building Control involved. They will want detailed drawings and almost certainly calculations from a structural engineer, I fear this would be expensive as I think you would need to employ an architect to draw up the plans. Do you absolutely need to alter the roof?

It's  normal practice to align the ceiling joist with the rafters so that they act as a tie otherwise the rafters rely solely on the fixing into the wall plate which is far from ideal. Also with your roof the two braces under the purlins look like an afterthought.

You really need to get someone to look at this and it's just possible that your local councils building control officer would come out and have a look without charging you. They certainly used to but Councils are so strapped for cash these days there may be a charge, but even if they do charge I think it would still be the cheapest way to get some proper advice.

thescruff wrote on Jun 26^th, 2017, 4:23pm:


No, never used to be 2 houses, no purlins have been removed.....

The strange thing is that both purlins have joins, like half join, one half holding the other half up........problem with one purlin is that the join is the wrong way round for the support, in other words the prop is holding up the half that is lapped over the other half.....

Have decided to take the easier route now, replace with imitation slate (weight for weight) of original covering.......

Thanks for all input, this has been invaluable in helping to reach a sensible decision !!!