Quick roofing felt question

will_uk · 27 Oct 2008

Hi guys,

Just a very quick question for someone if they've got a moment

Basically, I've finished building the structure for a flat roof on a small workshop/shed. Plan to get it felted with the help of a friend who's experienced with torch on stuff (he's away for a week or so at the moment).

Anyway, I know that the torch-on felts and underlay are different to the normal stuff you buy for sheds etc and the cold-adhesive ones too.

But, can I use as a very temporary 'first' layer a roll of (quite thin) normal 'traditional' underlay? Then when I can get my friend over, a further layer of proper torch underlay followed by a torch on top layer?

Only reason I ask is because I have a roll of this already from a while back, plus I was hoping it'd help protect the roof a bit from any rain we may have over the next week or two.

Any tips most appreciated

Will

Leadman · 27 Oct 2008

I wouldn't waste your time and just get your self a tarpaulin to cover over your roof to keep the water out till your mate gets back and does a proper job
Cheers
Dave

Xenon · 27 Oct 2008

Some manufacturers insist you have a nailed layer if not using a torched vent layer.

So, a layer of felt nailed at 300mm centres, and 150mm centres around perimeters won't hurt.

will_uk · 28 Oct 2008

Cheers Guys,

I had thought of getting a tarpaulin but I was hoping that a layer of this underlay (which I've got already) might help (ie, 3 layers in total including this)

Xenon said:
Some manufacturers insist you have a nailed layer if not using a torched vent layer.

So, a layer of felt nailed at 300mm centres, and 150mm centres around perimeters won't hurt.

Hi Xenon,

What's the torched vent layer out of interest?

Are you saying that basically I should be ok with the layer of underlay felt nailed on straight to the ply deck - just tack it into place every 300mm (like a grid) and 150mm around the edges. I was planning to take it up to just over the upstands and maybe slightly down the edge?

If the end result was to be a torched on felt system, would the next layer of underlay (proper torch type stuff) be either nailed on as well, or torched onto this old underlay that I've got hanging around?

Many thanks for taking the time to reply

Will

Xenon · 28 Oct 2008

Just torch the 2 layers onto the layer you nail down. Take the nailed layer to the base of the 'arris'. You can run it up any upstands as a temp measure, but cut it back when the roof is installed.

The grid you mention is correct, you won't require a vented (holed) layer if you nail the first.

A vent layer is a quick way of partially bonding the roof, although most decent HT systems nowdays do not require it, as the will have enough ability to move with the deck.

The old style flat roofs used to be frame bonded/vent layer to stop splitting, but felts have advanced well beyond this requirment nowdays.

will_uk · 28 Oct 2008

Cheers Xenon,

That makes sense (the 'vent' layer bit) - I guess it helps to stop air bubbles/blisters too?

I'll do as you've suggested - run it up the upstands for the moment (to help keep it dry temporarily), and then cut it back when the roof is properly felted.

Am I fairly OK with this underlay if it isn't a 'torch' specific type(?), I guess worst case it can be quite easily removed later on but would rather avoid this if possible.

It's only a fairly thin 'traditional underlay' (wickes type rubbish I'm afraid).

Many thanks for taking the time to repy - much appreciated

I'll probably be doing this after work today so hope it's not too cold!

Cheers,

Will

Xenon · 28 Oct 2008

That makes sense (the 'vent' layer bit) - I guess it helps to stop air bubbles/blisters too?

With the old felts, yes.

If it is a weak felt you are nailing, when they torch the underlay on, they need to focus the heat on the roll to stop the nailed layer disintegrating.

will_uk · 28 Oct 2008

Cheers Xenon, much appreciated - I must owe you a pint by now!

It's raining (and dark, cold..) tonight so haven't been able to nail this underlay on, fingers crossed one night this week or saturday/sunday latest (!).

Out of interest, *if* I can't get hold of my friend to do this job (he's away for a week and is always quite a busy guy..), how much roughly would you say I'd be looking at to felt an 8x10ft (2.4x3m) flat roof if I get someone to do it for me?

It's a sound structure on a garden workshop ('shed') - based in West London/Surrey.

Will

Xenon · 28 Oct 2008

You'd be looking at £550 with quality felt if i was doing it. Thats with good access. Anything more would be a bit strong, significantly less would make me question quality.

GSUTTY8 · 21 Oct 2011

Sorry to pick up an old thread but having a small extension done off a conservatory and joiner told me he would "sort the roof out for me"...

Now the structure is complete and flat roof constructed but I didnt realise he wouldnt be felting/finishing it

So I now have a 1.5mx1.5m roof which needs felting - what would in your opinion be a cheap/reasonable price?

RedHerring2 · 21 Oct 2011

My advice is to start a new topic in this forum with your own questions.

Don't drag up old threads and don't tap into other's threads, it's called hijacking.

Alastairreid · 21 Oct 2011

GSUTTY8 said:
Sorry to pick up an old thread but having a small extension done off a conservatory and joiner told me he would "sort the roof out for me"...

Now the structure is complete and flat roof constructed but I didnt realise he wouldnt be felting/finishing it

So I now have a 1.5mx1.5m roof which needs felting - what would in your opinion be a cheap/reasonable price?

£200...£250. or diy with epdm.

http://www.rubba-seal.co.uk/

diynot

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Quick roofing felt question

RedHerring2

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