Re-roofing a shed

[PeterC]

A few years ago I posted about this; now I need to do something this year - before my tuit gets dripped on from the brand new crack! The roof is corrugated asbestos cement, single pitch, about 8 deg. Size is 7' wide by 10' down the pitch and has only one, mid-point, support.

Now, as mentioned to me before, I've been looking at cement fibre panels as being the nearest type to the present ones, but it seems that the pitch is shallow for the 3" ones and they seem to need a lot more support.

Are there any other products worth looking at? Steel seems rather thin and prone to rust; Onduline would need a full deck.

Actually, I was wondering about using OSB 3 deck flush with the outsides of the walls, overhang the panels a bit and use gravel board to protect the OSB and joists - would that work.

As for the pitch, the sheets would be long enough to have about 40cm overlap and that might e enought to stop water being blown up and under.

Any pointers, please?

[Bob Minchin]

Osb decking and EPDM works well.

[Tim Lamb]

I suspect the existing support and pitch would not have met the requirements for asbestos cement anyway. The big 6 fibre cement sheets I have used seem little different in rigidity to the asbestos they were replacing.

[David]

I used powder coated steel for my shed roof and there is no sign of rust so far.

No need for full boarding, either.

See

and

for a rough idea.

Deep excavation would be required (probably) to find the supplier, but it is generally used for industrial and agricultural buildings.

The shed roof is a little over engineered, and safe for several people to walk on at the same time.

If you look at the typical agricultural building then the whole thing is usually held up by minimal timber (presumably to reduce costs).

Cheers

Dave R

[PeterC]

Given the requirements of fibre cement, I'd wondered about the differences from asbestos cement. Big 6 is OK for the pitch, but on the size of shed might be a bit strange(?). Looks as if the 'domestic/DIY', 3 version can't handle the span. The old roof has been OK for, reallistically, about 60 years. Mind, I'm not too worried about another 60 years - that'd make me nearly 130!

[PeterC]

I'm not surprised - must be the biggest 'brick shithouse' in the world! I really like the construction of the roof - it's really versatile for use inside and just looks right.

OK, thanks, I'll look at steel again as an option. The FS sheets are an awkward width: 3 won't do it and 4 would be ridiculous.

[Tim Lamb]

The shallowest pitch recommended for agricultural use is 12.5 deg.

I'd think the support spacing requirement is based on snow loading rarely encountered here. Just do it! Alternatively get some joist hangers and put up more purlins.

Steel roofing, in some weather conditions, (cold night after a humid day) will suffer from condensation.

[PeterC]

Yes, could do that. Another 2 would help a lot. If I were to use a full deck, I'd need another joist for the 'horizontal' (transverse) join in the deck.

If the pitch criterion is about water being blown back up, a 40cm overlap and some sealant should fix that.

That's what concerned me - I don't want me tools rusting!

[Steve Walker]

You never saw Manchester Arndale before the IRA blew it up then?

[PeterC]

I didn't - was it bad? It wasn't DIY anyway.

[Steve Walker]

Take a look at the 3rd and 4th pictures at

A DIYer wouldn't have done what the architect specified!

[PeterC]

Oh, I see - concrete grunge. The Victorians could build a sewage pumping station and was a work of art and could have lasted for centuries. Nowadays we fo for fugly that, in some merciful cases, falls down in a few decades.

Yes, one look and run!

[AnthonyL]

I've just been around Papplewick Pumping station - a fine example of Victorian grandeur never intended for public viewing:

The defunct reservoir is like a cathedral inside and no bricks were cut!

Some nice YouTube videos available if you like steam and Victoriana.

[Steve Walker]

Yes, although not so much the concrete as the acres of yellow tiles covering it. Even concrete can sometimes be made to look good.

If it looks right, it often is right. The Victorians certainly knew how to build things that both lasted and were beautiful at the same time.

[PeterC]

Cheers, I'll have a look later. There's something about 'proper' engineering that modern crapstacks lack. Menai Bridge had to be strengthened when lorries became too heavy, but otherwise is still good. Some modern bridges fall down during construction!

[PeterC]

Well, getting there slowly - the rain, the rain! On my own, so shunting the old sheets around (once I'd managed to see off

65-yo, rather thick, nails) whilst keeping the place rainproof has been arduous. Lucky that I got a cheap tarpaulin from TS>

The long sides were hacked roughly to pitch then mortared up to the roofing sheet, so plenty in there as it fills a ridge of the corrugation. I need to matchit more closely to the OSB so, when there's sufficient fine weather, I'll slide the old sheets to one side, use a 3m straight timber as a guide and fill in. What would be the best mortar to use? I prefer ready-mixed powder as the ready-to-use will be heavier and I have a rucksack as transport! Would this stuff be OK?

Polyfilla seems a bit naff for this purpose!