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Garage roof replacement - advice?

Discussion in 'Roofing and Guttering' started by MrPloppy, 25 Jan 2008.

  1. MrPloppy

    MrPloppy

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    Hello chaps,

    I've decided I'm going to replace the garage roof; it's asbestos cement, and its leaking pretty badly. I know about the disposal procedures for the panels, so that's not a problem.

    I'm going to replace the sheets with that Coroline corrugated stuff. The first thing I notice about the stuff is that it looks really flimsy but I guess it should work.

    I've been going through the procedures, and trying to adapt what I've got at the moment. The purlins are metal and the current sheets are attached to these using skyhooks, those 'J' shaped hooks. I believe it's best to use those special nails for fixing the Coroline onto the roof, so I'm going to bolt wooden joists onto the metal frame, and nail into that.

    First question is whether that's a good idea.

    Next bit is that the purlins are about 120cm apart, or 4 feet. This suggests that I need extra purlins in place, as the wickes "how-to" leaflets suggest 450mm ~ 600mm spacings. I don't particularly want to do this, as I'm sure it'll add to the cost (there is a tight budget on this!). Indeed, I can see this being a lot of hard work as I'll have to somehow attach these extra purlins to the exterior walls, and I'm not sure how this can be done - is this an easy job? Do I have to remove some of the exterior walls so the joists can get slotted in?

    Third bit concerns the slope of the roof. It's one of these pre-fabricated garages, (a double one, approx 5m wide), and the slope is very gentle, probably around 5-10 degrees. The leaflets say I should have boarding to go across the whole lot and then put the coroline sheets on top of that. I think this is the way I should go, but I'm not sure if the thing with the purlins still applies. What boarding do I use? Can 6mm exterior plywood do, or do I have to go the whole hog and use that OSD roofing boards at 20 a shot? The prices are roughly the same, but I'm worried whether the weight would cause a problem.

    As I say, my budget is tight. My current estimate is for around 300, but that doesn't include any joists or boarding.

    Any advice would be greatfully received. I'll be starting this when the weather improves, probably Easter weekend.

    Cheers,

    MrP.
     
  2. Deluks

    Deluks

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    Sounds like you have the same garage as me. Rockfaced concrete panels slotted into concrete stanchions on top of which the angle iron trusses attach to?

    The coroline bitumen sheets (if that's what you mean) are perfect for a reroof like this, they are cheap and durable. However they do need supporting at regular intervals as the instructions say.

    You could use timber bolted in between the trusses to make extra support for the sheets, then fix the sheets to these. If you can track some some angle iron of similar size (will be cheap from a steel supplier) then even better. These will then need to be drilled and bolted into place. I assume you have a drill, you will also need some HSS bits to drill through the steel.

    You could always reuse the bolts that were used to fix the asb sheets, or track down some new ones.

    The bitumen sheets can be screwed down, if you pre-drill them and use roof sheet screws with the plastic caps.



    Sheeting the roof is another good idea, and won't require any additional supports if you use at least 18mm thick boards. Use wbp plywood or t&g OSB boards, then you'll need to underlay and felt over this as if you were refelting a flat roof (use good quality felt though!)

    Fixing to the steel isn't such a problem if you use self tapping screws, they might need a small pilot hole in the angle iron though. Which will require a bit of marking out/planning as you go along.

    I'd go easy on the easter eggs and budget £400 at least. ;)
     
  3. MrPloppy

    MrPloppy

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    Thanks for the reply Deluks.

    I went to a local builders merchants to price up how much the boarding will cost, and I think I'll need to save more than just Easter Eggs to get that lot up there! :confused: (especially if it has to be 18mm!)

    The chap asked what it was for, and he then suggested I just lay down some wooden beams, say 3"x2" from front to back - the metal joists are left to right, so I put these on in the opposite direction. Then I can space them however often is required and it'll save me a ton of money! Great stuff.

    So this is my plan now - get very long (5 metre) 3x2 beams (treated, of course), and lay them on the top of the metal beams. I can put them every, say 2-3 feet widthways. Interspaced with these, I can put extra wood beams running in the opposite direction (the same direction as the metal beams) however often I need for good support - they don't necessarily need to be attached to the metal purlins already in place (the metal purlins are 4ft apart, too wide for the sheets to go on). So basically I'm putting a whole new frame on the top.

    Once the frame is in place, I can cover the lot with the Coroline Bitumen sheets.

    Does this sounds like a good plan? :eek:

    The only question that remains really is how to attach those wooden beams (front to back) to the metal purlins (left to right). You say about these self tapping screws? Will that be enough? I've not seen anything like that, but I'll take a look.

    Thanks again.

    MrP
     
  4. drewroof

    drewroof

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    either self tapping screws or nuts and bolt drilled through will do it,
     
  5. MrPloppy

    MrPloppy

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    Yeah - just looked these up; seems they will do the job! Great stuff.
     
  6. Deluks

    Deluks

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    Sounds a little more complicated than it need be. Why build a complete new frame work on top of the existing framework? Just fill the gaps in the existing framework and fix the roof sheets to that. Will be cheaper as you won't have to buy all that wood.

    Just to confirm, as I read it. The rafters (the ones which go from wall to peak) are 4ft apart, and the angle iron supporting purlins (the ones that connect the rafters) are also 4ft apart. So your roof is made up of 4ft 'squares'. Or thereabouts.

    If you can halve these into 4ft x 2ft sections, then you'll get away with a thinner board. 11mm osb or half inch plywood.

    What price were you quoted for the boarding?

    A picture would be helpful here.
     
  7. MrPloppy

    MrPloppy

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    Actually I was speaking to someone at work today and he suggested exactly that. He showed me those brackets the beams slot into - the ones you attach to the walls with bolts. It certainly simplifies it!

    Sorry for the confusion; I may be getting terminology mixed up here - the roof is almost flat; perhaps a 5 degree incline. There is no peak. I guess the 'purlins' I refer to are the joists? Rafters?! Sorry. These metal C-shaped beams go straight across from wall to wall, and are 4ft apart. Guess I can just shove some more in as above.

    I shall endevour to put pics on later tonight.

    Cheers and thanks again.

    MrP.
     
  8. iaink

    iaink

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    i am looking to use the same roofing. Go to c&a building plastics they have your j bolts
     
  9. hampshiresparrow

    hampshiresparrow

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    Anyone know how long coroline is expected to last? I have some on my garage - certainly looks like that or some very similar stuff. It has started to go porous especially at the bottom edges. I suppose that gets more water running over it that the high up bits.

    Can I paint it to prolong its life, and if so what do you suggest?

    It's been up there since 1993. I bought the house since then.

    HS
     
  10. Deluks

    Deluks

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    You've had at least 15 years usage then, normally it would start to be on the way out now, but until it actually starts causing problems, just leave it in place. They are made from bitumen so any bitumen paint or tin of repair mastic should do the trick.
     
  11. Daniel B

    Daniel B

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    Hello guys,

    I seem to be in a very very similar situation.

    I bought a house last year, and it has a double garage, internal dimensions are about 18ft by 16ft, but it leaks badly.

    It is a prefab garage, probably from around the 70's, and I am led to believe has concrete/asbestos roofing.

    These Coroline sheets appear to be a maximum of 2M long, is that right?
    I was thinking it would make the most sense to get sheets that spanned the full length of the garage, and so eliminate a dreaded join, and the seemingly soon to follow leak.
    If they are only 2m long each, how do you get a water tight seal??

    Mine too has a very very minor slope, and I was wondering about trying to increase this, or if I managed to get single sheets, I imagine this would no longer prove an issue.

    Also, my local council helpfully don't provide a disposal service at any charge, any idea of how much I would need to pay a private firm to take the sheets away, and whether I would need to get them down first?
    Just a ballpark figure would be handy.

    I'll try and take some pictures at the weekend, and maybe we can share info on the best methods forward, I'll take exterior and internal shots so you can see the construction, and maybe laugh :LOL:

    Many thanks

    Dan
     
  12. Daniel B

    Daniel B

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  13. Deluks

    Deluks

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    If you can take the asbestos sheets down yourself it will obviously save you money. Wear a mask etc, gloves. Wet the sheets on both sides if poss and don't break or cut them.

    Good practice to wrap them in 1000 gauge poly (dpm sheet will do) and tape up.

    You might find a local waste disposal company to take them away, or you could hire a covered skip. Be sure to let them know that you'll be putting asbestos in it though, as they may not allow it.

    If you know of a local landfill site, and have a mate with a van, you might be able to take them straight there, with a couple of £20 notes to buy the helpful men some refreshments. That's where they end up anyway.

    I make screwfix about £3ish more per sheet. wickes will deliver over £45 so no contest, SF will be cheaper on the fixings though, you can get 50 screws with plastic caps for under £5 But like mentioned earlier, you could reuse the angle brackets and bolts that the asb. sheets use (give em a wash first)

    2m is as long as they come afaik. You might get away with a sheet and half overlapped, give at least 300mm overlap and use some silicone or gutter sealant under the overlaps.
     
  14. BK12

    BK12

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    I have exactly the same issue (want to replace a shallow sloping asbestos roof with Coroline corrugated bitumen sheets).

    Just wondering how it all went?
     
  15. rubberroof

    rubberroof

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    I supply rubber roof kits, and the cost is around £350 inc vat and delivery. Its a 1 piece rubber membrane that adheres to OSB-3 ideally. The kit also includes adhesives and trims.

    I have a free instruction guide I can offer anyone if they wanted to look into this option. We sell dozens of these kits every week, and proving very popular.

    Life expectancy is 50 years plus.

    Hope this helps
     
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