Roofing Help

[Parm]

Not sure this is the correct section or not but here goes anyway !

I'm planning to build a new workshop very soon as the old ones had it now, prefab concrete panels sinking into ground because it's built on rubbish foundation.

The roof will be 18mm ply covered with felt. Can anyone tell me what the correct technique is for felt application.

I was planning to nail the first layer of sand faced felt to the ply and then cover with a torch on cap sheet as the top layer. Internet research suggests this is correct and in keeping with the relevant standards, in times gone by I've always stuck both layers with hot bitumen.

Can anyone confirm if this is correct or advise otherwise as I quite like the simplicity of torch on system and not having to glue the first layer.

Any help much appreciated

 

[CompoSimmonite]

Forget felt.
I have two flat dormers on my house. After the last leak had them redone with fibreglass and wished I'd opted that route years ago. The roofers laid waterproof chipboard floorboarding so interlocking. I queried why not ply but chipboard is use because a smooth surface and better than ply to take the fibreglass. Two layers of course matting followed by smooth matting and gel coat.
Very easy to DIY - GOOGLE will find all the information you need about technique but other than the preformed edgings not much different than say any other fibreglass work. Think of it this way - felt has a life span of around 10 years before it need replacing. How often does the hull of a fibreglass boat need replacing - 50-60 years life at least ! Same with fibreglass cars. Company who did my work charged less than neighbour paid for felt and has 25 year gauarantee.

Paul h

 

[Barlidge]

Or another alternative that I was thinking of for mine when it needs doing is EPDM, need to factor in the adhesive as well though.

http://www.ebay.co.uk/sch/i.html?_o...firestone+epdm+&_nkw=firestone+epdm+&_sacat=0

 

[AndyStobbs]

No mention of flat or apex roof?

 

[Parm]

Sorry folks it's a single pitch flat roof with an approximate solve of about 14 degrees

 

[Parm]

Forget felt.
I have two flat dormers on my house. After the last leak had them redone with fibreglass and wished I'd opted that route years ago. The roofers laid waterproof chipboard floorboarding so interlocking. I queried why not ply but chipboard is use because a smooth surface and better than ply to take the fibreglass. Two layers of course matting followed by smooth matting and gel coat.
Very easy to DIY - GOOGLE will find all the information you need about technique but other than the preformed edgings not much different than say any other fibreglass work. Think of it this way - felt has a life span of around 10 years before it need replacing. How often does the hull of a fibreglass boat need replacing - 50-60 years life at least ! Same with fibreglass cars. Company who did my work charged less than neighbour paid for felt and has 25 year gauarantee.

Paul h

Sounds very interesting, will look into it

 

[AndyStobbs]

Would just do it in mineral felt myself. Start at the bottom, go upward.

 

[Parm]

GRP system seems quite costly. Felt is estimated to cost around £100 all in while resin for GRP is around £500 plus other bits n bobs

 

[Parm]

Would just do it in mineral felt myself. Start at the bottom, go upward.

Felt seems to be hot favorite at the moment

 

[brightspark]

Felt seems to be hot favorite at the moment

it will be if u do it with a blow torch

 

[Parm]

it will be if u do it with a blow torch

Yes very good, I walked into that one !

 

[BrokenBiker]

have you thought about corrugated bitumen sheets?

my neighbour had a chippie in to build their shed and they used these, look like fibreglass but the guy reckons they are made from some woven plastic mesh and soaked in bitumen, guranteed weather proof for 10 years and fairly cheap too.

its what i will be using when i finally get round to making mine

 

[Parm]

have you thought about corrugated bitumen sheets?

my neighbour had a chippie in to build their shed and they used these, look like fibreglass but the guy reckons they are made from some woven plastic mesh and soaked in bitumen, guranteed weather proof for 10 years and fairly cheap too.

its what i will be using when i finally get round to making mine

I have looked into these but won't realy fit in to the grand scheme of things. I deadly I would like a pitched roof with tiles which for me is straight forward to do, but the height I need to give me the correct slope means that part of the workshop will obstruct the neighbors.

A lw angle flat roof is way forward. Does any one know if it's correct to nail down the first layer and then use bitumen or torch on cap sheet???

 

[rockweasel]

have you thought about corrugated bitumen sheets?

my neighbour had a chippie in to build their shed and they used these, look like fibreglass but the guy reckons they are made from some woven plastic mesh and soaked in bitumen, guranteed weather proof for 10 years and fairly cheap too.

its what i will be using when i finally get round to making mine

I've got experience of felt, bitumen sheeting (onduline/coroline), asbestos tiles and tin roofing. Not installing them all but I can see examples of each from where I live. My neighbor's onduline is about 12 years old. Looks ok. A bit saggy at the edges. It softens over time. My barn's felt roof is a patchwork mess. Asbestos tiles over the road are old but still in place. My money would be on a corrugated tin roof. A farmer told me they tend to get condensation underneath them, so if it's laid on top of an existing roof make sure that one is waterproof.
Lots of choices depending upon budget and how long you want it to last. I like the sound of rain, so I'll be saving up for a tin roof )

 

[AndyStobbs]

Its only a workshop, I would use single layer of felt, padded at all edges/corners with a piece underneath. Felt tacks to hold it down, battens on top if you live in tornado alley.
Gutters! If your last workshop sunk, then this one probably will too. Keeping the ground dry is the single best way to minimize this.

 

[Cobbs]

http://www.forticrete.co.uk/concrete-roof-tiles-and-slates/centurion®-low-pitch-roof-tile.aspx

These tiles will go down to VERY low pitches.

 

[morph]

Box profile tin is between £5-£10 sq/m so why mess around with anything else? It will last forever and is incredibly easy to install with a cordless drill and a bag of tecks?

 

[CompoSimmonite]

Look at what is used on industrial buildings.
On my carport I have fibreglass box profile sheets and allows an useful amount of light in. Bought from a company who specialise in surplus industrial materials so whilst brand new was quite reasonable - £160 for a large "L" shaped carport.
Neighbour has EDPM. Unfortunately the people who installed it simply attached around the edges so wind gets underneath (via air bricks, roof ventilation etc) and it blows up then collapses so is noisy plus I don't think the constant movement bodes well for long term life. Moral of story is with EDPM ensure glued down in the middle as well as securing at edges.
Friends have a massive ex factory that is clad in insulated box profile steel. They use it for industrial storage and keep documents as well as other items for customers who don't have the space themselves. Surprisingly whilst it gets cold it doesn't suffer from condensation even when they use blown heaters for staff working in there.
My garage is done in steel profiled sheets and condensation is terrible. Mate had his garage done last year an company used similar steel profile sheets but the inside is coated with some sort of moisture absorber. Even the plain steel profiled sheets over wood (OSB is OK if on exposed to water - timber merchants will have better quality than B&Q !) would work well.

Paul H