Sagging Roof

[KMBoro]

Been looking at a property that is pretty cheap to be fair - the vendor has been honest (up to a point) about some structural problems. He said that the slate roof was taken off in the 1980s and replaced with a concrete tile but obviously the woodwork in the roof was not suitably strengthened and the roof has sagged.
I have had one or two roofers have a look from the outside and had some varied ball park figures quoted - one said he would replace the roof for £8000, another told me there was no need to replace the roof, rather he would take off the tiles, strengthen the roof, re-felt it and put on the existing tiles, job done for £3500.
My worry is that there is something worse lurking beneath the roof in terms of the structural integrity of the house. I did notice that one of the bedroom walls seemed to be bowing at the top. The house has been on the market for a long time, originally priced at £170k, but now is offers around £100k. Obviously I would get a building survey, but anyone got any thoughts as to whether I should just walk away....I would have thought that if it was as simple as getting the roof strengthened for £3.5k then either the vendor would have got that done or a builder would have snapped up what would surely be a bargain

 

[KenGMac]

KMBoro, hi.

Your comment as regards the bedroom wall bowing at the top? could be indicative of roof spread?

Roof spread occurs when the weight of the roof causes the external, front and rear walls to move outwards. If you consider a roof as a closed triangle with the ceiling tie connecting the bottom ends of the rafters, this design maintains equilibrium in the roof structure, should the ceiling tie fail, or be removed, or the ceiling joists are not connected correctly to the bottom of the rafters [at the external wall heads] then the unrestrained load on the afters will in effect push the external walls outwards.

With me so far? I hope so, I have only seen a few cases of roof spread, all in England or in Northern Ireland, never seen it in Scotland, so far?

Remedy is going to be a load more expensive than a simple re-roofing plus the roofers thoughts on Strengthening the roof structure, a repair could entail a partial demolition of the external walls and their re-building to a plumb condition.

If it is roof spread I for one would run not just walk away?

Ken

 

[KMBoro]

Thanks Ken, really helpful