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to DIY or to not DIY flat roof repair

  • 02-12-2025 05:22PM
    #1
    magicbastarder
    Moderators, Category Moderators, Arts Moderators, Sports Moderators, Paid Member Posts: 55,566 CMod ✭✭✭✭


    i've a 1950s semi-d, with a flat roof garage on the side, with a probably half inch thick layer of what i think is asphalt on top.

    over the last ten years or so i've done several patch repair jobs, usually with some torch-on, as the asphalt has obviously aged over the years and is pulling away from the side wall of the house and cracking; so when the rain hits the side of the house and runs down the wall, we get leaks in the garage through those cracks.

    i've had four or five roofers come to give me quotes; most of them told me a torch on job would be absolutely fine, on top of the existing asphalt (which a couple pointed out can remain as a vapour barrier), and just use lead flashing around the edges to sheet the water onto the torch on - but would i be right to be dubious about fixing the torch on to a surface which is already shrinking and cracking?

    one line of thought i have is that the issue is around the edge; doing a torch-on job for the whole roof is - to a large extent - fixing a problem that is not there. would cutting a channel and fixing the lead flashing in place, be straightfoward enough a job for a reasonably competent DIYer to tackle? especially since only one of the companies who suggested the torch-on route ever got back to me with the quotes…

    the other company which did get back to me quoted for an EDPM roof; so obviously a more significant cost than torch-on - but that was minimum 5k ex vat, and i have noticed that the lead flashing work in that quote is worth less than 15% of the total quote.

    TL;DR

    would doing a lead flashing repair job be adequate enough, and could i tackle that myself?

    as you can see from the photos below, the cracks have migrated down onto the flat part of the roof in places, especially in the corner pictured.

    PXL_20251202_151055955.jpg PXL_20251202_151238586.jpg


Comments

  • #2
    magicbastarder
    Moderators, Category Moderators, Arts Moderators, Sports Moderators, Paid Member Posts: 55,566 CMod ✭✭✭✭magicbastarder


    bump?



  • #3
    DC999
    Registered Users, Registered Users 2 Posts: 1,634 ✭✭✭DC999


    I did my folks 4m x 5m kitchen extension and I'm only a decent DIY-er, so it's deffo do-able. And it's leak free.

    Went with this stuff in the end (neighbour had it and liked it): Lava 20 Kits - Owl Waterproofing. Paints on with brushes and rollers - it's very sticky and you need to bin anything it touches.

    • Got OSB18mm and boarded that directly over the existing roof. Just got long screws into the existing rafters. Takes a bit of time to find all those. Did nothing else to the existing leaking roof
    • Added 90 degree OSB 'upstands' as our roof has 4 parapet walls. That was slow to cut them to size.
    • I know a roofer and he recommended doing those steps for our roof
    • Then added the Lava 20 onto those. They have very good Youtube training videos - watch a lot of them if doing it.
      • You add a primer, then paint it on
      • Need to use their mastic in between gaps in OSB or at edges. We used like 3 times more of those than the kit comes with. But I was paranoid of leaks at edges of the roof
      • All the edges / gaps, get a 'bandage' that gets more LAva20 on top
      • The edges take time so get properly sealed. They sell light fiber glass lengths to cover the gaps from horizontal to vertical

    Worked out great and is leak free. But took agessssss. Likes days of work once the roof is ready to be painted. And once you open the tub, it lasts a few days at most.

    Without a doubt we did a better job than a 'pro' who would have spent 2 days on it. But downside is time. That said, once you get one layer of the Lava 20 onto it, it's waterproof. Can do the 2nd layer at a later stage (but will need an unopened can). And it cost us about 1700 quid (from memory) including the OSB. Quotes were 5-10k.

    I was looking at EPDM for DIY. But looking back, I would have struggled. Anything you can paint in is more forgiving for edges.

    PM me if you are going with the LAva20 or a similar paintable sealant and I'll send you more info. Did it a few months ago so need to remind myself the steps I took.



  • #4
    magicbastarder
    Moderators, Category Moderators, Arts Moderators, Sports Moderators, Paid Member Posts: 55,566 CMod ✭✭✭✭magicbastarder


    cheers - as mentioned, i'd hope to get away with not actually resurfacing the roof as a whole, as the vast majority of the flat section is fine. but that lava 20 kit might be up to the job of a more permanent repair than i had been doing?

    i should have mentioned - the roof pictured above is asphalt on top of probably 4 inch reinforced concrete.



  • #5
    standardg60
    Registered Users, Registered Users 2 Posts: 6,589 ✭✭✭standardg60


    Issue with flashing there is because it's a flat roof water is likely to seep back under it.

    Me I'd try a roll of dpc folded into the angle and then a haunch of strong sand and cement mix with waterproofer on top.



  • #6
    10-10-20
    Registered Users, Registered Users 2, Paid Member Posts: 10,141 ✭✭✭✭10-10-20


    Just for you... Steve Roofer heard your call... 😆

    https://youtu.be/zaf-aRhVv-E?si=MI0_4PCUrgBgm5q-


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  • #7
    magicbastarder
    Moderators, Category Moderators, Arts Moderators, Sports Moderators, Paid Member Posts: 55,566 CMod ✭✭✭✭magicbastarder


    Cheers!



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