Building a new garage roof - adding a slight peak?

[hanvyj]

I have a garage that's about 4.5m by 7m. It's currently leaking like a sieve.

It has 50 by 150 beams at varying distances of 550 - 600 spacing that span the 4.5 m. That's covered with OBS, which has corrugated bitumen sheeting length-wise atop that.

On initial inspection, it all looked good (it hadn't rained recently!) but I soon found it leaked a lot, this has since got worse. The slope is almost zero. There's not much sag, but the water still pools.

Over summer, the worst affected beam, which had a huge knot in it, developed a large crack. I had a friend down so we sistered it on either side. A bodge, but hopefully one to stop the roof coming down...

But I'm using the garage as a workshop more and more, and I have an old car in there. I don't want everything to get wrecked because it's all sitting in a swimming-pool of water.


I was trying to work out what geometry I could construct that would be sensible and within regulations and I came across this:

http://www.ebay.co.uk/itm/181633752...trkparms=gh1g=I181633752632.N7.S1.M342.R1.TR2

It's the exact length I'd need, and allow me to add a slight peak to the roof with this long-wise as a ridge beam.


I've got a few questions.

1) Stupid idea? Should I stick with a bunch of 4.5m joists? I'd have to commit soon.

2) How would I get it up there? Is there any way I could do it without hiring a lift? (I'm on a budget)

3) I understand from building regulations I'd need to keep the whole building under 2.5m (It backs onto a council owned road at the back)? Neighboring garages are higher, so I probably could obtain it: Would I have to show them sensible plans if I get PP? Would it need inspecting? I understand it costs about £150, which I wouldn't like paying...

At the border, the building height is about 2.25m. At the garden side of the garage, it's higher than 2.5 (land drops a little). Is there any way I could find out if it already has planning permission? Given the zero slope, I'd have to build up somewhere.

4) A friend of mine is convinced I should build a light-weight super-structure on top of the existing rafters. I'm not sure they're cut out for spanning the current distance, let alone supporting more roof. Should I consider this?

5) Can anyone suggest a decent surface? If the slope does end up 5 degrees. I'm not impressed with the bitumen sheeting, and it seems expensive. EPDM might be a better option?

I was originally looking at shingles, but PP won't allow as high as a 15 degree slope.

6) The OBS boarding is soaked through, and has some places where the screws have punched through a few chips - but could this be re-used? It's all very new by the looks of things.

I've got potentially a big project, not sure how to approach it within the limits of budget, being sensible, and planning permission.

Cheers.

 

[freddiemercurystwin]

Add tapered firrings battens to the top of your existing joists or add a series of diminishing sized joists perpendicular battens on top. This is a normal way to add a fall.

You will be able to get tapered firrings cut to suit at a local timber mill.

 

[hanvyj]

Add tapered firrings battens to the top of your existing joists or add a series of diminishing sized joists perpendicular battens on top. This is a normal way to add a fall.

You will be able to get tapered firrings cut to suit at a local timber mill.

Thanks. You think the existing 150x50 joists are sturdy enough? I ask because every data-table I read on roof spans says they should reach less than 3m (e.g. here http://www.home-extension.co.uk/tech2.html)

No need for the steel

 

[freddiemercurystwin]

Your post is quite confusing, your post title says the garage is new, but the post reads like it’s an existing garage?

I have a garage that's about 4.5m by 7m. It's currently leaking like a sieve.

If it is new build then 50x200 joists @ 400 centres will be OK. You can just do them higher on one side to achieve a fall.

Technically at that size you are bordering requiring Building Regs approval.

A steel beam down the middle I suspect will need to be deeper than a 203, more like 300. If there is a garage door at the end then your long beam will need to sit on another beam above the door at the end.

EDPM is a fine choice, don’t go any lower than 1:80, even then that is hardly any fall.

 

[hanvyj]

Your post is quite confusing, your post title says the garage is new, but the post reads like it’s an existing garage?

Sorry for the bad wording. Garage is not new, I was trying to say I'm putting a new roof on. Should have said I'm replacing an existing roof. I'm trying to work out how much of the old roof I can actually use (rafters etc).

If it is new build then 50x200 joists @ 400 centres will be OK. You can just do them higher on one side to achieve a fall.

Technically at that size you are bordering requiring Building Regs approval.

It's already built, can't remember what time, maybe in the 80s? The roof (OBS, beams & bitumen sheets) has clearly been replaced at least within the last few years but has been soaked by rain a lot.

I assume I don't need planning permission given it's already a structure and was in the documents when we bought the house?

I fear the current beams are insufficient because everywhere I look it says use 50x200 at 400, wheras the current beams are 50x150 at 600 (more in one case). Plus I've already had one crack.

A steel beam down the middle I suspect will need to be deeper than a 203, more like 300. If there is a garage door at the end then your long beam will need to sit on another beam above the door at the end.

Good to know. I might stay away from that idea. The garage door already has a steel beam across it that's around 130 by 90, it spans a 3m gap. So not sure that's sufficient.

Thanks for the comment.

 

[hanvyj]

Pictures for context:

Showing beam repair:

outside showing pooling (last year)

 

[freddiemercurystwin]

Is there much sag on the existing joists? It doesn’t look like it? There are millions of existing roofs built that would not comply nowadays. As you say the one joist that cracked, cracked on a knot. I would be inclined just to add tapered firrings battens to the top of your existing joists or add a series of diminishing sized joists perpendicular battens on top. This is a normal way to add a fall.

 

[hanvyj]

Is there much sag on the existing joists? It doesn’t look like it? There are millions of existing roofs built that would not comply nowadays. As you say the one joist that cracked, cracked on a knot. I would be inclined just to add tapered firrings battens to the top of your existing joists or add a series of diminishing sized joists perpendicular battens on top. This is a normal way to add a fall.

There's not too much sag, no, I think most of the issues is with the length-wise slope being too shallow and the joists aren't quite lined up perfectly causing a sag on the long edge rather than the short edge.

I'll stick to that and keep it simple. Thanks.

 

[catlad]

600 centres is to much for those sheets why not add more joists the same size as whats there already.

 

[hanvyj]

600 centres is to much for those sheets why not add more joists the same size as whats there already.

I think I might, probably the best solution.

 

[tony1851]

When you do replace the covering, don't use those bitumen-impregnated corrugated sheets ('Onduline'?),

They're rubbish, particularly on zero slope. Use EPDM or similar.