If the wall plate of the flat roof is level with the wall plate of the existing house can you make the two wall plates the same height then you will need to strip off some roof tiles and run the new joists through butting and fixing them up to either the roof rafter or the ceiling joist on top of the house wall plate.
Fixing flat roof joists.
This is a completion video of a flat roof framing.
Repairing roof joists yourself.
Rotten roof joists are a severe problem and commonly lead to underlying issues and damage to opposing structures.
This is a long video but it will show you how to do it.
And tie it into your hip roof.
Boarding to be fastened on top of flat roof joists with a depth to width ratio greater than 4 the allowable clear spans have been calculated in accordance with bs 5268 2 2002 structural use of timber part 2.
Make sure you offset yo.
To fix the joists and rafters down on to the wall plates they should be toe or skew nailed to the top plate like below.
Set out the ceiling joists onto the wall plates the ceiling joists are installed before the rafters as they will stop the roof spreading and also give something for you to lay planks across to stand on when building the roof.
If extra weight is the problem additional joists or rafters can be added to shore.
When it comes to flat roof repair options simple patch repairs for flat roofs such as those on garages or extensions can cost a few hundred pounds.
This is a completion video of a flat roof framing.
While it is not entirely impossible to take on a diy roof joist repair replacing or repairing a damaged roof joist is a complicated procedure that requires precision.
Code of practice for permissible stress design materials and workmanship and bs 5268 7 2 1989 structural use of timber section 7 2.
However given the nature of flat roof repair costs it can sometimes make sense to replace the entire roof.