Bowed Roof

[obliquegeek]

Hi All,

We've got a section of roof over the old garage that is slowly starting to bow (pic attached). We had the felt roof replaced about a year ago and fell out with the person doing it over this, so we can't go back to them.

This is probably a stupid question, but Is this a job for a general builder or a roofer? Best we've had so far is 'just stick an extra pole in the middle'

Thanks.

 

[jj4091]

Is it the whole roof or just the canopy. If it is just the canopy then it would appear that an extra support may be all it needs. You could try borrowing or hiring an Acrow prop and see if you can jack it up level before installing something permanent.

 

[Harry Bloomfield]

We've got a section of roof over the old garage that is slowly starting to bow (pic attached).

Deflection of a beam, under loading is quite normal, but that looks as if it is excessive. I assume the beam is timber(?), and it may have been originally installed with a bow in it, but with the bow down, instead of up - so it becomes near straight, under load.

You could try the acro prop, mentioned above, tightening the acro gradually over several weeks, to see how it reacts. Watch for the any signs of it lifting off the two poles at either end, at stop at the first sign of that. If that proves satisfactory, your next step, is to replace the acro, with a permanent prop, near the middle.

For the permanent prop, you could use either an alloy or galv steel scaffold pole, cut to exact length, with a made up steel spreader brackets, for the base, and another for the top, so they can be fixed in place.

How did you fall out with the guy doing the felting? The bowing, wasn't his fault.

 

[obliquegeek]

The rest of the roof is fine, it's just the metre that protrudes out past the walls.

Ideally didn't want to add an additional pole as it's in front of the window and a parking space.

It used to be straight/flat a few years ago, then slowly started bowing.

 

[obliquegeek]

How did you fall out with the guy doing the felting? The bowing, wasn't his fault.

No, appreciate the bowing wasn't his fault, but he said he would sort it while replacing the roof, as part of the cost of the job. Seemed like the ideal time to do it while the roof was stripped off. Also damaged a few things, generally left things in a mess (broken tiles, broken fascia, broken front step, tar everywhere). Actual main part of the roofing was fine. At the same time removed a chimney on the side of the house, which again was left a bit of a mess that I had to finish in the end.

 

[obliquegeek]

Slightly more recent pic of the roof, it's definitely getting worse over time.

 

[freddiemercurystwin]

What's the construction inside, which way are the joists running? Might be able o get a post to work on the step rather than dead centre but you need to know how it's been constructed in anycase. If you insist on not having a post then it's likely to involve extra wok to insert bigger joists running the whole span.

 

[^woody^]

Probably a fundamental design issue that won't be corrected unless rebuilt better.

General builder, who is knowledgeable in first fix roof structure.

 

[Ivor Windybottom]

Instinctively it does look a bit thin for its span, it was possibly inadequately designed from day one, was already at its limit and a few rolls of roofing felt were enough to tip it over the edge.

The only quick cheap fix option would be to stick another pole in the middle.

The all-out perfection option would be to strip the thing back completely, remove the timber joist and replace it with steel, ending up with the same slimline look without the sag.

The middle option would be to add a timber or steel joist underneath it, after shortening the existing poles. Clad it with UPVC to match the rest.

Regardless, the poles look a bit puny. I reckon that 1960s builder was watching the budget a bit too closely.

 

[Ivor Windybottom]

Actually it doesn't look like it's original. Someone's later add-on, a chucked together project.

 

[obliquegeek]

No idea on the construction. I originally assumed that there would just be wooden joists running front to back, that seems to make the most sense, but seeing as the roof is completely flat until after the wall, then suddenly dips, maybe not. How would I find out?

 

[obliquegeek]

the poles look a bit puny.

They're not actually doing anything, you can wobble them. They don't feel like they are attached to anything.

Terhe

Actually it doesn't look like it's original. Someone's later add-on, a chucked together project.

Maybe right I think there is a similar house (attached) a few doors down with a much smaller overhang and doesn't sag.

I guess a post is looking the simplest option. I'm loathed to strip the roof back as it is less that a year old.

 

[Dereekoo]

No idea on the construction. I originally assumed that there would just be wooden joists running front to back, that seems to make the most sense, but seeing as the roof is completely flat until after the wall, then suddenly dips, maybe not. How would I find out?

Have you any idea what the size of that support timber is and what is the span between the posts and although the cantilevered section is bowed at the front I assume its level at the back

 

[Harry Bloomfield]

They're not actually doing anything, you can wobble them. They don't feel like they are attached to anything.

Oh, dear - that doesn't sound good!

 

[Ivor Windybottom]

My guess is it's a single joist running between the posts, another attached to the house and joists between them.

The non-destructive option without a third post would be a new joist under it. Would probably need to be metal, as two thin lengths of wood aren't much stronger than one, it would still bend unless the wood was really tall, so metal is probably the only way.

The issue with all these fixes is that it's now curved. If you jack the centre with an acro prop then the ends will probably lift too, you'll end up with it still bent but higher, resting entirely on the new centre prop.

The real solution would be to not be starting from here, i.e. it should have been built right in the first place.