Renew existing lead flat roof?

[Agile]

I have a flat lead roof about 2m x 2m over a dormer window.

The lead is not in very good condition being about 90 years old and last year I needed to add several areas of mastic to stop it leaking.

There are two upstands about 40 mm high which I would rather like to remove.

My question is would it be better to remove the upstands and flatten the lead and then overlay it with a new layer of top felt or to remove the lead completely?

If I do completely remove the lead then what is considered the best flat roofing material to be used nowadays?

I have previously done areas of flat roofing myself with the traditional hot bitumen three layers of felt but it seems many roofers now use a single layer of torch on modern material.

Tony

 

[alan333]

Personally I'd strip the lead and felt it, you won't get the lead flat enough to overlay, and felt won't stick too well. Others will suggest single layer rubber or epdm solutions but I've never worked with those so can't comment. My original gripe with the single layer stuff I had dealings with about 30 years ago (Sarnafil IIRC) had problems like when a bird pecked through a small corner or something. With traditional felt you had a chance the next layer would still be watertight.

A lot of roofers use torch on cos it's pretty good these days if you get polyester based stuff, and it saves messing about with tar boilers etc. If your roof is planks then nail a layer of underlay then torch an intermediate layer then a cap sheet, and offset your laps. If your surface is sheets like ply or similar you can skip the nailed layer but tape the joints of the boards using strips of your torch on underlay. Done properly (including good edge flashings and welted drips) you'll probably get 25 - 40 years from it.

 

[catlad]

The upstands you are referring to are probably mop rolls which is what the lead is dressed over and can be removed once the lead is removed, at that point if you wish you can add celotex insulation and the ply over the top and then go with alan 333 suggestion. And with such a small area to do you could do that with a hand held rothenburger being a plumber.

 

[Agile]

The 40 mm upstands have the lead taken up about 25 mm on each side. Then an inverted "U" cover sheet over the top.

There are adjoining tiles on two sides and the underside of the tiles is only about 30 mm above the lead. So there is not enough space to add any insulation unfortunately.

So I am still not sure that the advice is definitely to use three layer rather than these single layer modern types. One disadvantage is that with only 4 sq m I would probably have to buy a very long roll and hardly use any of it.

Any more or other suggestions?

Tony

 

[alan333]

The 40 mm upstands have the lead taken up about 25 mm on each side. Then an inverted "U" cover sheet over the top.
There are adjoining tiles on two sides only about 30 mm above the lead. So there is not enough space to add any insulation unfortunately.
So I am still not sure that the advice is definitely to use three layer rather than these single layer modern types. One disadvantage is that with only 4 sq m I would probably have to buy a very long roll and hardly use any of it.

The inverted "U" can be removed using a spade, then remove the upstands as catlad says.
The adjoining tiles can probably be moved up if you want. Remove two rows for access and move the battens for row 1 up accordingly.
Torch on felt 2mm underlay come in rolls of 15m IIRC, so if you nailed one layer of it upside down, then torched one layer on top of that, by the time you used more doing the upstands under the tiles you'll probably use towards half a roll. Cap sheet tends to be 8m rolls so you'll probably use about 2/3 by the time you do upstands and welted drips.
If you decide to fit insulation make sure you have one layer under the insulation as a vapour barrier.

BTW the underlay I bought recently was about £25 per roll, and the cap sheet about £30.

 

[geraldthehamster]

If you're doing it yourself, I'd recommend insulating, overboarding and using EPDM.

Cheers
Richard

 

[Agile]

Good point about moving tiles up a bit.

But even so would hardly let me use more than about 25mm of insulation.

Its has a 100 mm gap inside before the ceiling plaster which I hope will enable me to push some insulation into the gap.

But depending on what I find when removing the lead I may lift a couple of boards and pour in some shreadded insulation board which I have. I cannot see any disadvantage in using it but it is not a mainstream product but just a one man recovery business!

Tony

 

[datarebal]

strip the lead. to much thermal movement eventually will cause the felt to fail.

 

[Agile]

Torch on felt 2mm underlay come in rolls of 15m IIRC, so if you nailed one layer of it upside down, then torched one layer on top of that, by the time you used more doing the upstands under the tiles you'll probably use towards half a roll. Cap sheet tends to be 8m rolls so you'll probably use about 2/3 by the time you do upstands and welted drips.
If you decide to fit insulation make sure you have one layer under the insulation as a vapour barrier.

BTW the underlay I bought recently was about £25 per roll, and the cap sheet about £30.

 

[Agile]

So could I use two layers of cap sheet with the lower one upside down?

That would be a more efficient purchase method. Just one 8 m roll.

But looking at Ebay for supplies what exactly should I be looking for?

Assuming those shown as "shed felt" are not suitable, there seems little correlation between names and specifications.

About the only common spec is a ( usually ) 4 mm thickness. Am I likely to go far wrong buying anything 4 mm thick and described as torch on?

How about this?

http://www.ebay.co.uk/itm/Roofing-F...257?pt=LH_DefaultDomain_3&hash=item4adc688cf9

Tony

 

[alan333]

So could I use two layers of cap sheet with the lower one upside down?
That would be a more efficient purchase method. Just one 8 m roll.

No. Assuming you're only laying two layers then they'll both need torched, and it won't torch upside down. If you're laying three layers however, then you can use pretty much any old thing (including cap sheet upside down) as your first nailed layer.
If your roof is 2m x 2m you won't get two layers and edges from an 8m roll.

Try a roofing merchant for your felt, there are quite a few Asphaltic branches around the country.

 

[Agile]

But f I could get it to fit, not sure of exact size but will measure exactly as may be more like 1.8m square, then could I not nail upside down cap sheet as the first layer?

Any comments on the type of sheet I linked to above?

Tony

 

[alan333]

Yes you could nail cap sheet upside down as the first layer but you need more than one waterproofing layer on top of it.

The felt you linked would be fine.

 

[Agile]

But what should I look for which is the single sheet torch on that is often

How thick is it?

Can it be laid directly onto wooden boards?

Tony

 

[datarebal]

in my opinion torch on isn't a diy job.. especially if you value your house. it is pretty irresponsible to advise anyone its a diy job.
epdm is definitely a safe diy job though.