Roof sag

[AnthonyL]

I'm holding back on purchasing a bungalow because it has a slight sag in its roof.

It may be serious, it maybe minor. Vendor is looking at getting local repair man in to fix it.

Everything that I read is that a professional is required to determine the cause and remedy.

Problem is "what professional?". Seems to be lots of people who do slates, tiles or general roofing repairs. Is the NFRC worth it? I'm wary of trade associations. Not even sure which category to search for.

Roof is concrete tiled. It is a 1968 build but the vendor has spare tiles in the garage so there is a possibility it has been retiled. The roof space is fairly open but with struts at the edges. The sag is about mid-way, not readily obvious and the ridge itself is straight.

[AnthonyL]

You reckon someone may have taken them out to create headroom? Is that common?

I wonder if they were taken out and the struts put in. Sounds like a Mr Bodge job if anyone did that!

[Tim Watts]

I'd go for a roofer personally.

[fred]

No. Get an engineer. He'll do the calculations and will have insurance if he makes a bollix of it.

How old is the house? How long has it had the sag? If the house is of amy age and the roof hasn't collapsed and the saddle back isn't too bad I'd live with it.

[AnthonyL]

As stated in my OP which had been snipped when you replied.

[Syd Rumpo]

Make sure it wasn't originally slate - which is lighter - then re-roofed with tiles.

Cheers

[GB]

Can you get a surveyor to look at it? Won't you be getting a survey done before purchase?

[alan_m]

When I had my roof replaced the roofer demonstrated that the slates that came off were approx the same weight as the tiles that went on.

[Tim Watts]

I had my plain tiles changed to interlocking - at quite a bit less weight.

[harry]

When roof trusses first came out, lots were undersized and the roof sagged. (ie too few trusses/too far apart.) Some were not installed correctly. Sometimes it matters not as long as things don't get worse.

One thing that happens is as the roof sags, the tiles are twisted and break. If he has spare tiles, this may be happening.

Or some nitwit may have cut bits out of the trusses (check in loft) Or plate nails/gang nails may have let go/corroded. (*check in lofT) Or someone has removed a (truss)supporting partition wall.

Look under the eves in the center of the building and see if there's any sign of "spread" ie the bottom of the rafters moving outward. Gaps, bodge cover ups of cracks etc

Nobody is going to fix this without removing the entire roof. They can only stop it where it is by putting in additional supports.

It's all a matter of degree, only and experienced roofer can say if there's a problem or not.

[News]

In message , AnthonyL writes

A friend of mine lives in a typical Victorian terrace, with one large tie beam in the loft, running from front to back. He boarded the loft for hobby use, and found the tie beam was in the way, so removed it by sawing flush at both ends.

That was thirty years ago, house and roof are still in place, but I'm glad I don't live there.

[AnthonyL]

Some good points there and the spare tile issue is interesting - either they've been in the garage for 50 yrs or he's had to keep up with a stock.

Which takes me back to my original question - NFRC or what? NFRC seems to not specify structure but rather the tiling/slating or am I misreading it. I'm not buying the house until I get a report as to why there's a problem and what's involved in fixing it.

[harry]

No-one is really going to be able to say. When these things were bought, they were/should have been installed as per manufacturer's recommendations. They have probably disappeared by now. (But you could check) They usually have their name stenciled onto the components.

So, you can only go by what a reliable and experienced roofer tells you. The rest will cover their arse and have lots of caveates.

If it was me & I was desperate to have the place, would beat the price down for this reason and than install additional strenghteners as a precautionary measure. (There's lots can be done).

However you may well have the same problem in reverse if/when you come to sell the place.

[Andrew Gabriel]

Someone I used to know wanted to put a loft ladder in, but there was this giant beam in the way across the loft floor. He was rather alarmed when the two ends sprung a few inches apart as he finished sawing through it. So was the surveyor he eventually got around after lots of his friends told him that was a really bad idea. Some piece of sheelwork was manufactured to hold the two ends and stop them separating any further. I don't think they dared to try to pull them back together.

[Andrew Gabriel]

They are heavier (and get even more heavy when wet), but most slate roofs were built plenty strong enough to support concrete tiles. It could be that the OP's wasn't, or has been modified and now no longer is.

[AnthonyL]

I went to have a close look yesterday. Helpfully there is a retired RICS surveyor who lives a few houses down and he came as well. The houses are all identical.

Apparently there used to be a frame holding hot and cold water tanks (it is a bungalow) and the frame was wedged between the rafters and running across the width of the roof. The purlins (just one each side and fairly low) are also too long to be one piece of timber so they are joined at around where the frame was.

The frame has been removed without any replacement of support. The RICS guy had put blocks under his purlins where the tank was.

It seems that the bow of the timber worked in favour of the sag on one side but against the sag on the other.

There are otherwise regular "under purlin struts" along the length of the roof, except where the water tank frame was.

I feel a lot more comfortable that whilst I cannot reverse the sag readily (it is slight but obviously the rafters have taken a bit of extra strain), I understand the reason and it can be readily and inexpensively prevented from worsening.

It seems silly that blocks were not put in place as standard design instead of relying on a water tank frame to provide that bit of support at that point.