Jilly Posted September 27, 2022 Share Posted September 27, 2022 I have to have a flat roof as per the planning permission, but the surface covering isn't specified. My options are: Felt and bitumen. Old fashioned but tried and tested. We know of a roofer who does this. Rubber. Fibreglass. Can anyone give me your experience/advice with these options please? Link to comment Share on other sites More sharing options...
SteamyTea Posted September 27, 2022 Share Posted September 27, 2022 11 minutes ago, Jilly said: Fibreglass Is a manufacture, but properly done GRP will outlive the building easily. How big is the area? 1 Link to comment Share on other sites More sharing options...
joe90 Posted September 27, 2022 Share Posted September 27, 2022 +1 to GRP (if done properly). 1 Link to comment Share on other sites More sharing options...
Tetrarch Posted September 27, 2022 Share Posted September 27, 2022 Vote for Rubber for me I self-installed an L-shaped flat roof 20 years ago on my previous house (still going strong). Recently, I've installed rubber onto two outside buildings It's cheap, completely waterproof and easy to install, my only real criticism is that the flashing and finishing accessories are expensive. Regards Tet 1 Link to comment Share on other sites More sharing options...
Canski Posted September 27, 2022 Share Posted September 27, 2022 If it’s not seen and has no roof penetrations I’d go with edpm if you want it to look nice and have any complicated penetrations I’d go with grp 1 Link to comment Share on other sites More sharing options...
Gus Potter Posted September 27, 2022 Share Posted September 27, 2022 9 hours ago, Jilly said: I have to have a flat roof as per the planning permission, but the surface covering isn't specified. My options are: Felt and bitumen. Old fashioned but tried and tested. We know of a roofer who does this. Rubber. Fibreglass. Can anyone give me your experience/advice with these options please? Hi Jilly. My own thoughts are: Have a Firestone rubber roof on part of my own house, from memory it was the thickest they offered 1.5mm thick. Performing well so far. Also, as I did it myself know how to fix it if hit by astoroid. Fibreglass, yes does well, but less easy maybe for DIY / local builder to maintain? Also edge detailing and you need the weather to be ameniable as the resin cures If you want have a look at Sika Sarnafil, you get an approved installer to install, bit more expensive but is a well tried and tested system. Felt and bitumen.. used to do this but the weak points can be the seems / joints. For me I would go for a more modern system even though old sckool at times myself. 1 Link to comment Share on other sites More sharing options...
Thorfun Posted September 28, 2022 Share Posted September 28, 2022 doesn't the structure underneath make a difference? I was told by 3 different roofers that due to the timber frame building and potential movement GRP wasn't suitable and all recommended a single-ply membrane. not sure on the validity of the claims but if 3 of them independently said it it must hold some truth, no? 1 Link to comment Share on other sites More sharing options...
SteamyTea Posted September 28, 2022 Share Posted September 28, 2022 27 minutes ago, Thorfun said: but if 3 of them independently said it it must hold some truth, no? No. Just happened to ask 3 roofers that had never attempted, or had attempted but failed, a GRP roof for an uneducated opinion. To do GRP properly you ned to get someone that knows what they are doing, you don't get your kitchen fitter to pour your foundation. 1 Link to comment Share on other sites More sharing options...
joe90 Posted September 28, 2022 Share Posted September 28, 2022 5 minutes ago, SteamyTea said: Just happened to ask 3 roofers that had never attempted, or had attempted but failed, I agree, I have done quite a few GRP roofs and really like the method and product but it must be done in very dry conditions and accurately with the mix, not something you can bodge (and get away with). Look in any harbour and you will see very many old fibreglass boats still floating 🤔🤷♂️. 1 Link to comment Share on other sites More sharing options...
PeterW Posted September 28, 2022 Share Posted September 28, 2022 46 minutes ago, Thorfun said: doesn't the structure underneath make a difference? I was told by 3 different roofers that due to the timber frame building and potential movement GRP wasn't suitable and all recommended a single-ply membrane. not sure on the validity of the claims but if 3 of them independently said it it must hold some truth, no? Depends on the roof size. It also needs to be properly designed and structured. If there is any steps or other stress points in the design then they need to be built in to allow any differential movement. There are some out there that think that the use of EPDM allows a roof to move and stretch more than any other product which is untrue - it will stretch to a point but when properly bonded down it can tear. A proper 2 layer GRP (ie 2 layers of 450gsm CSM) will bond to the underlying OSB and become a single structural membrane - it will move with the structure but remember that most movement will be downward compression/ settlement on a TF so it will all move together. 1 1 Link to comment Share on other sites More sharing options...
joe90 Posted September 28, 2022 Share Posted September 28, 2022 If you do go with GRP use a roofer that specialises in that material 1 Link to comment Share on other sites More sharing options...
SteamyTea Posted September 28, 2022 Share Posted September 28, 2022 32 minutes ago, PeterW said: A proper 2 layer GRP (ie 2 layers of 450gsm CSM) I would specify 3 layers. May seem more than needed, but I still see external cladding I made over 40 years ago in service. The main reason for the extra lay is to allow for overlaps and more resin overall. You also get more material to play with if you need to do some extra sanding or trimming. 1 Link to comment Share on other sites More sharing options...
Nick Laslett Posted September 28, 2022 Share Posted September 28, 2022 21 hours ago, Jilly said: I have to have a flat roof as per the planning permission, but the surface covering isn't specified. My options are: Felt and bitumen. Old fashioned but tried and tested. We know of a roofer who does this. Rubber. Fibreglass. Can anyone give me your experience/advice with these options please? Like so many aspects of house building, there is no right answer. I read most of the threads here on the topic and was not able to draw any firm conclusions. We went with the Sika Trocal single ply product. https://gbr.sika-trocal.sika.com I did the plywood deck, which I feel is where most of the cost is. A Sika approved specialist installer took one day to install the covering. I will upload some photos later. Of course this roof covering has only been on since March, so I have no idea about the longevity of this solution. 1 1 Link to comment Share on other sites More sharing options...
Dreadnaught Posted September 28, 2022 Share Posted September 28, 2022 I chose felt and bitumen after talking through the various options with Bauder. My impression was felt and bitumen was a good solution if you have lots of fiddly bits on the roof. And I had 9x rooflight up-stands to detail in my flat roof. In my case, I was reassured by the independent (and unannounced, even to me) inspections of the installer's work by the manufacturer. Whatever system you go for, make sure you get a 20+ year transferrable guarantee from the manufacturer, not just the here-today-gone-tomorrow installer. 3 1 Link to comment Share on other sites More sharing options...
jack Posted September 28, 2022 Share Posted September 28, 2022 Short version: I think the choice of roof covering is probably a lot less important than the choice of roof installer. We went with Resitrix, which is a textured, reinforced EPDM layer over modified bitumen. As documented here more than once, the product is great. It's been up there over 7 years, and is still looking bombproof. The problem was that the product wasn't installed all that well. I'd raised questions about the quality of a number of the joint when it was first finished, especially around some of the outlets. I wasn't happy with the answers they gave, so I got the local rep out to inspect. He sent me an email confirming that the installation was of the high quality expected from their authorised installers. A few months later, we woke up the morning after a large downpour to water dripping around the downlights in our bedroom and the main bathroom. Two of the joined areas I'd expressed concerns about turned out to be even worse than I'd thought might be the case. The installers came out to rectify. I made them re-do the other similar joins: upon removing the original joins to replace, it appeared that another two had almost completely given way and would be be leaking in the very near future. I was up on the roof again just last weekend patching some joins that I wasn't happy with: Resitrix is clearly an amazing product, but the installation - both the details chosen, and then the way they were implemented by the installer - completely let the product down. 40 minutes ago, Dreadnaught said: Whatever system you go for, make sure you get a 20+ year transferrable guarantee from the manufacturer, not just the here-today-gone-tomorrow installer. Also, double-check what the guarantee covers. We have a transferable, insurance-backed guarantee, but it only covers materials. I don't know whether that's typical, but if so, it's of limited use. 1 1 Link to comment Share on other sites More sharing options...
joe90 Posted September 28, 2022 Share Posted September 28, 2022 6 minutes ago, jack said: I think the choice of roof covering is probably a lot less important than the choice of roof installer. I agree and although I prefer GRP it still has to laid properly hence my opinion earlier about a company that specialises in GRP. 1 1 Link to comment Share on other sites More sharing options...
Jilly Posted September 28, 2022 Author Share Posted September 28, 2022 (edited) On 27/09/2022 at 13:04, SteamyTea said: Is a manufacture, but properly done GRP will outlive the building easily. How big is the area? 18m2 with block cavity walls Edited September 28, 2022 by Jilly Link to comment Share on other sites More sharing options...
SteamyTea Posted September 28, 2022 Share Posted September 28, 2022 22 minutes ago, Jilly said: 18m2 with block cavity walls Quite small then. 1 Link to comment Share on other sites More sharing options...
Kelvin Posted September 28, 2022 Share Posted September 28, 2022 We are using the Alwitra Elevaon V stuff. We have 64sqm to cover with one rooflight. I’ve seen it fitted on a few buildings and it looks very good. 1 Link to comment Share on other sites More sharing options...
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