Flat roof - again.

[Dave Plowman (News]

Have a felted flat roof which was constructed some 30 odd years ago. So past its sell by date.

Very wary of roofers in general, so looked for recommendations.

Contacted the architect who designed the conversion, who despite being over 80 is still working. His chap came round, had a good look, and we agreed a price. But not a date, as he was busy.

Patched the roof again with Aquapol or whatever.

Six months on, still no start date.

Now another leak, so just want it fixed.

Given my age and the uncertain future at the moment, I'm not now willing to pay for the very best, ie glassfibre. Well done three layer felt will likely see me out.

Got a quote from a firm who can do it soon. Came as a PDF and here's a quote from the spec:-

Date: 02/03/2022 Quote. Number: 00123 Please find below our estimate for proposed roofing works: ? Remove all moss/lichen of the flat roof and place in rubbish bag ? Supply & install 25kg tub of bitumen self adhesive primer onto the OSB boards ? Supply & install GEKO high-performance breathable tac down 3B underlay ? Supply & install GEKO high-performance torch on 2mm underlay ? Supply & install GEKO high-performance torch on mineral black capping sheet ? Supply & install blue treated batten around whole perimeter of the flat roof ? Supply 18mm clout nails ? Supply & install drip cards ? Supply 2? brush ? Supply 19kg Calor gas bottle ? Install 12? up-stands around the whole perimeter of the outlet to ensure watertight ? Ensure all the felt is bled with a 2mm bead ? All labour included ? All waste removed from site ensuring site is left clean and tidy ? 15-year guarantee on the flat roofing works carried out ? 0% deposit ? Payment upon completion.

How does that look to our experts?

Seems odd they don't mention removing the old felt?

Also not sure about the perimeter. There are parapet walls, with lead flashing over the upstand. It was well constructed initially, so I'd not expect any timbers to need replacing. The decking is marine ply and feels very sound when walking on it.

Also couldn't find GEKO felt by Googling.

[Andrew]

Make sure the lead flashing can be 'turned up' to allow the new felt to be run up the wall at least 150mm, without tearing the lead. If it is, it needs to be repaired by gas welding/soldering, not a run of mastic.

[Fredxx]

Did he mean IKO?

Is there any reason you don't go for EPDM?

[Theo]

Perhaps:

(never heard of them)

Theo

[Roger Mills]

Yes, I noticed they didn't mention removing the existing felt. But I don't know how they'd apply the adhesive primer to the OSB if they didn't!

Anyway, it looks like a professional quote where they have specified all the materials and consumables to be used. Most quotes don't have that level of detail. They sound as if they know what they're doing.

[Robin]

Your bit of London has a fair few loft conversions so I'd be inclined to ask if people have had problems with the flat roof and, if not, for the name of the firm that did the work. In London bound to get a lot of don't knows (tenants, buyers) and variations on "bugger off". But round here there's just a handful of firms who do the vast bulk of conversions and will at least have people who are used to slapping it on ;) -- Robin reply-to address is (intended to be) valid

[Dave Plowman (News]

I'd say there are hundreds of firms who do this sort of work in the area. My problem is wanting a decent job at a decent price. I've been ripped off by roofers in the past - and know of others too. And that all the ones I've had a personal recommendation for seem to be busy. Meaning they are likely the best ones.

Just keeping my fingers crossed they are OK.

[Dave Plowman (News]

The bit from the quote was a copy and paste from the PDF.

It's a material I don't know, unlike felt and glass fibre. And no one I've asked has pushed it. Either felt or glassfibre. The latter about three times the cost.

[Andrew]

Roofers don't seem to like EPDM or Fibreglass because they are stuck in the past with their 'torch on' mentality.

Using EPDM or F/Glass means you have to have new 18mm decking, or overlay existing sound decking with some

11mm OSB, whereas a new built up felt roof can be added to the existing deck (if it is dry) after pulling the old felt off and scraping with a spade.

[Fredxx]

EPDM is very popular, and I'm surprised no one has suggested it. It's incredibly simple and by all accounts reliable. There are loads of YouTube videos of installation.

The only issue perhaps is the difficulty to put on top of a felt roof, without being able to (or choosing not to) remove all of the old felt.

[Theo]

A Youtube rabbit hole delivered me to:

In particular there's some interesting comments about overlay systems: if your old roof is solid, it's possible to lay eg EPDM over the top without having to strip off the old - you can put insulation boards over the top and then EPDM on that. There are also liquid roofing products, like: Ah, some prices: Theo

[John Miller]

They mention OSB board. Around here, roofers seem to just overlay the existing roofing felt with these boards rather than strip the old felt which is a time-consuming & dirty job. The new felt then goes on top of the OSB boards. Perhaps that is what your quote includes. Just ask them?

[fred]

Why not just ask him for references and check them out ?

[Andrew]

If the existing roof is a cold roof (with cross ventilation) then slapping insulation on top of the existing felt and covering with new felt is total waste of insulation. This sort of nonsense is even mentioned on the Energy Savings Trust Website.

Unless the cross ventilation is sealed you still have outside air temperature between the existing roof and the insulation.

If you seal the ventilation without adding a vapour-proof membrane on the warm side of the ceiling (ie overboard inside with foil-backed plasterboard with double sided tape to seal all the edges) you will end up with all manner of rot problems.

[Theo]

Yes, you have to actually seal the insulation, otherwise that's no point. I'm assuming somebody doing this knows that.

If you have an insulated cold roof and you slap insulation on top, you're making a hybrid roof. You need to make sure the timber in the middle isn't going to get damp as it has access to neither warm air from below or fresh air ventilation from the outside.

If it's an uninsulated roof you turn it into a warm roof, but that still needs the sides filling to stop warm air from inside encountering cold surfaces (eg fascia) and condensing.

If you have an existing uninsulated felt flat roof (eg in a shed) and it's still intact, that can be the vapour membrane underneath the insulation. Saves having to strip it off. That assumes the deck underneath has enough airflow from inside to prevent moisture, and is not covered by something impermeable (foiled plasterboard or vinyl paint).

Theo

[Dave Plowman (News]

For some reason many seem unwilling to remove the old felt. One fibreglass company said they'd put OSB on the top of it as a base for the fibreglass.

[Dave Plowman (News]

The roof started leaking a couple of days ago. Time is of the essence.

This chap says he will start tomorrow.

The stories I've heard from my architect, who is a pal, is that the building trade in general in London is a bit of a mess after Brexit. Lack of skilled and other labour (and not just a question of paying more). So you can't pick and choose as easily as once.

[Theo]

I think they don't like removing it because:

- it's time consuming and annoying

- it needs to be cleaned up enough for the new surface

- now you have a roof's worth of felt to dispose of - need to pay for a skip

- when it's off they need to get the new roof down asap, which is not good to do in the winter when chances of rain are high.

- unless you're going to pay for scaffolding plus a temporary roof, they need to get it off and the new surface down in one day, because they can't leave it open to the elements. Scraping it all off and installing the new roof makes for a very long day.

Theo

[Andrew]

By the time a leak from a failing felted flat roof appears inside it has already been quietly seeping through and damaging the deck for quite some time (usually).

End-of terrace across the road had scaffolding front and back installed

2 days ago because a couple of Marley Modern interlocking concrete tiles on 37 degree pitch roof had beenn loiosened by Eunice.

Yesterday at 8AM a van with 9 'Romanians' turned up and by 1PM they had stripped the entire roof, front and back, ripped off all the 1976 sarking felt and battens, added breathable membrane, new battens, put the tiles back, rebedded all the ridge tiles and mortared the tiles ends at the gable end. Nice tidy mortaring too. The only 'defect' was that they removed the end gable clips and didn't replace them. These are important to stop the end row from being dislodged in a storm and hitting someone on the head. Other than that it was an amazingly quick job. A typical UK tradesman and his apprentice would have take over a week, or even two.

[PeterC]

<big snip>

I hope that teir roofing is better than their spelling.