corrugated roof construction

[wayt43]

Project is to replace a damaged, leaking flat garage roof. The roof consists of a thin fibreglass layer supported by OSB panels, which in turn rest on purlins and joists. The roof doesn't drain properly and the fibreglass has cracked, leading to the underlying OSB rotting. The joists were obviously treated with something and still seem to be OK.

I want to replace with sloping corrugated roof, preferably galvanised steel. For simplicity the slope can be from one side to the other instead of a ridge.

I already know that I can buy corrugated sheets which will span the entire width of the garage (only about 2.5 m) but what is the minimum amount of support I can get away with? It would be nice to only have to bolt the steel down on either side and not have to build a sloping rafter/purlin support structure.

What would be a durable and relatively simple method to build up the wall on one side and fill in the triangular gap at either end? The tops of the cement sheets are about 10 cm thick so I thought about using narrow breeze blocks, but not sure how well they would stand up to wind or getting knocked about. Maybe bolt some angle irons on the interior side to support the blocks laterally?

 

[noseall]

what is the minimum amount of support I can get away with? It would be nice to only have to bolt the steel down on either side and not have to build a sloping rafter/purlin support structure.

Lol. It's not just about the weight of the sheets, which are relatively light. It's more to do with snow and wind loading. Granted, the weight will be reduced but you don't want a roof that is diaphragming and wafting about, shaking everything around it to bits.

Look at a simplistic concrete sectional garage with metal purlins and you'll get the idea of what's needed. Bear in mind that your fixing points for any purlin arrangement will be at the very top of the structure - meaning weak and not much integrity or weight to secure to. You may have to elongate any wall brackets in order to secure adequately.

 

[Diver Fred]

For your quoted roof and length of sheet - top, middle and bottom. If you only fix at top & bottom the roof will move in wind and leak. Also it will not support much weight loading.

 

[Tigercubrider]

Maybe I am not aware of all of the problems, but isn't there a supplier of "kits" for this sort of thing?

A mate recently spent a fortune on repairing his flat roofed house, basically a turn of the century semi with a flat roof, parapet wall and small apex roofed attic type room that has a door to the roof. We spent ages chatting about it. Given the amazing amount of flat roofed buildings still being built because they are cheap, doesn't someone make a modular system to convert flat to sloping using bolt together components?

 

[foxhole]

Project is to replace a damaged, leaking flat garage roof. The roof consists of a thin fibreglass layer supported by OSB panels, which in turn rest on purlins and joists. The roof doesn't drain properly and the fibreglass has cracked, leading to the underlying OSB rotting. The joists were obviously treated with something and still seem to be OK.

I want to replace with sloping corrugated roof, preferably galvanised steel. For simplicity the slope can be from one side to the other instead of a ridge.

I already know that I can buy corrugated sheets which will span the entire width of the garage (only about 2.5 m) but what is the minimum amount of support I can get away with? It would be nice to only have to bolt the steel down on either side and not have to build a sloping rafter/purlin support structure.

What would be a durable and relatively simple method to build up the wall on one side and fill in the triangular gap at either end? The tops of the cement sheets are about 10 cm thick so I thought about using narrow breeze blocks, but not sure how well they would stand up to wind or getting knocked about. Maybe bolt some angle irons on the interior side to support the blocks laterally?

You will need at least 3m lengths to span 2.5m at an angle.

 

[noseall]

Given the amazing amount of flat roofed buildings still being built because they are cheap

Flat roofs are not all that cheap.

 

[Tigercubrider]

They're certainly not when they start to leak.
We moved into. 12million quid building (we already owned the land) about 8-10 years ago. Flat roof. The bloody thing leaked like a sieve every year until I left. It had a sort of butyl ? Liner on the roof, punctuated by various bits of plant. I don't understand why, even if a building has a flat roof for plant, they don't add something like a smoking shelter or bus stop over the kit and divert the worst weather to areas that can be defended.

 

[wayt43]

Maybe I am not aware of all of the problems, but isn't there a supplier of "kits" for this sort of thing?

A mate recently spent a fortune on repairing his flat roofed house, basically a turn of the century semi with a flat roof, parapet wall and small apex roofed attic type room that has a door to the roof. We spent ages chatting about it. Given the amazing amount of flat roofed buildings still being built because they are cheap, doesn't someone make a modular system to convert flat to sloping using bolt together components?

I've just looked into getting some timber mono pitched roof trusses and these would have come to several hundred quid with delivery, but these are a spec suitable for actual houses or extensions. I only need something light weight.

Any advice for constructing a simple triangle type truss out of Unistrut or scaffold poles? This could be done on the cheap if buying used.

Or if not, what is the obvious solution I am missing?

 

[cdbe]

Build up wall and gables in timber and clad externally with cement board or pvc, use 4x2 rafters, row of noggins down the centre to fix the sheets. Leave a few of the existing joists or add some ties to stop the walls spreading. Might be easier to do a duo pitched roof then you only have the ends to infill. It could also be just me but having an "open" ridge with plenty of airflow means I don't suffer from tin roof rain.

This is one of mine, I know it doesn't look that pretty at the moment but it will be cladded when time/funds allow:

Inside, I built the roof structure from a load of free pallet wood:

The rusty bit that all the junk is lying on is the original roof member which keeps the walls together.

 

[wayt43]

Looks like timber it is..

I have come up the following design (see sketch). Scale is bit off but you get the idea. Notable points:

• The existing joists are bolted directly to the top surface of the cement wall. I would rather avoid drilling into this wall. The H-shaped uprights will be thick, fit closely around the joist ends and top of the wall, with some mortar spread around the base of the wood, to reduce flex and provide extra stability.
  
• I wasn't going to bother having any purlins on top of the new pitched rafters, and the corrugated sheets would get fixed directly into each rafter (each rafter is roughly 800mm apart), do you think this will be sufficient to prevent the sheets from getting blown off? To keep things simple for myself I would rather double up the number of rafters (i.e. install them on every joist instead of every other one, giving about 400 mm spacing) rather than provide purlins.
  
• What minimum rafter thickness would be advisable? The existing joists are about 70 mm high x 45 mm thick.

 

[lostinthelight]

For your quoted roof and length of sheet - top, middle and bottom. If you only fix at top & bottom the roof will move in wind and leak. Also it will not support much weight loading.

If really good thick sheets I would agree but with lots of cr@p available for diy I would have two between the wall plates, for .5mm sheets 1m max spacing it recommended