Roof issues - what are the options?

[STEVEROG]

I have a 1930 built bungalow that I guess in its early life had a slate roof. The slates got replaced with Redland 49's some time ago.

Looking at the roof it sags a bit from gable end-to-end and also from ridge to gutter point. I guess its been this way for many years.

Inside theres a purlin half way down the rafters. This is actually in two pieces that are simply nailed together. Everything is 4" x 2" (rafters and purlin). There's noticable bending on this purlin and the joint is pants.
The ridge length and hence purlin length is about 8 metres. There's a binder, again a 4"x2", directly beneath the purlin. This is supported on the walls at each end of the building and also at around the centre of the ridge by corridoor walls but there is only one upright supporting strut from the purlin to this binder.

I will be getting the roof tiles re-newed in the next few months, I wondered if it would be worth sorting out the timber structure? Not sure how much needs doing (a) Rip the whole lot off and start again (b) Replace the purlin with something more substantial and perhaps put some steels in place of the wimpy binder and support the new purlin on this (c) something else.

??????

 

[noseall]

You haven't mentioned rafter length?

It sounds like you either need to beef up the purlin or fit deeper rafters.

Is there a way of supporting the purlin mid-span?

 

[STEVEROG]

Rafter length is 5.5m.

Its definately possible to support the existing rafer (or a replacement) at the mid span point as the two brick walls of the bungalow corridoor run right down the centre of the building (front to back) with the ridge running left-to-right. Currently theres a binder timber running parallel to the ridge along the ceiling joists. This binder is supported of the corridoor walls. There's one strut supporting the purlin pretty much directly over the wall.

 

[noseall]

At 5500mm long and even with a mid-span purlin, 100mm x 50mm rafters would not be adequate by todays' standards.

Beefing up the purlin will certainly help, though a timber fella will need mid-span support as you are unlikely to buy the section required or buy it in one piece.

or.......

It may be simpler to fit a steel purlin with a timber plate fixed to the top flange.