andyscotland

Thanks - Coventry is a bit far for me but I'd not come across the product before. Looks interesting. Have you used it / do you rate it?

I'm probably being dense but I still can't quite picture exactly what the layers would be and how they'd meet/overlap. Do you mean: Resin, mat, resin to the centre of each board when on the ground leaving a border round all sides. Then top coat 95% of that area, again on the ground Then fit to the roof once that's all cured Then resin, mat/bandage, resin along all the joins and untreated border areas and onto the roof trims Then what - just topcoat the join areas / topcoat the whole thing / something else? Just trying to get my head round it. If I leave a border on all the boards there'd still be a fair bit of wood that could get wet between putting the first board on the roof and being ready to do the final coat(s)?

You mean just do a coat of the resin (without matting etc) as the boards go down just to temporarily waterproof them? And then apply a full coat of resin & matting (as if going directly onto the wood) once the OSB layer is complete? That's an interesting idea. I could possibly tolerate the cost of a bit of extra resin if it reduced the risk of moisture problems. Would the final resin coat bond OK to the initial one if it was a day or two later - would I have to sand or otherwise prepare it once it had cured? Still a bit more cautious about the idea of entirely coating the boards before they go up. As you say, unless I was very careful masking off the tongues and grooves I can imagine that'd be a bit of a nightmare to fit together. And can't quite get my head round the robustness and appearance of the end result once all the board joints and screw heads are covered. A little nervous about doing anything too far outside "standard" as well, in case it causes me problems when Building Control come to inspect. In fact thinking about it - would it be better to break the roof into sections and do the complete buildup on each one at a time - pick an area, lay the insulation and OSB, fully GRP it before moving to the next area? Presumably would need to take care that each section was well joined to the ones either side. Feels like that would be a bit of a hybrid between the two ideas - fewer joints than doing the individual boards before they go up, and no screw heads to cover afterwards. Is that worth exploring?

Thanks, some really helpful advice here. Looks like that specific product doesn't meet the fire rating I need but very good to know of someone who's used a PU membrane and been happy with it! @Conor @scottishjohn @JSHarris thanks for the helpful tips. It's a new OSB deck going down, it won't be there weeks before but I won't manage to get it done in a single day. It's an awkward shaped roof abutting the house with every side angled and rooflight upstands. So a lot of sheets and trims to measure and cut. Plus the insulation and VCL is held down by screwing down through the OSB, so I'll have to cut and fit all of that at the same time too. I was hoping if I choose a fairly dry week and put a decent tarp over it at night/if the weather changes with space for some airflow between deck and tarp that would be ok? Not had much experience yet, but I have a shed and a valley gutter (over a narrow void between us and the neighbour so wouldn't be the end of the work if the waterproofing wasn't perfect) that I'm planning to do first for practice. As I understand it, that's supposedly one of the benefits of the polyurethane resin - as it's pre-mixed and moisture cured it's not so sensitive to environmental conditions. They advertise an initial drying time of 2-8 hours. I guess as it's immediately rain resistant once the mat is covered they can manufacture on the basis there's not the same need to get it to cure rapidly so can produce a slower/less volatile chemical reaction. I'm also wondering if the moisture-cure might give a little more tolerance for any slight dampness in the sheathing... Would that work? Feels like it'd conflict with the idea that a big benefit of GRP is the total absence of joints. I'd have to go back over all the fixings too, I guess - could be quite a lot to redo by the time it's all on the roof and screwed down. I'm using tongue and groove, 2400x600, so there's quite a lot of board joints...

Thanks - I'm getting a flavour of that just from this relatively small project but it's not put me off so far... As you say it's proving very rewarding!

I'll soon be ready to do the flat roof covering on my project. I'm going to use a wet-applied product, in particular because it's an L-shaped roof with several rooflights on site-built upstands and I like the idea of not having any seams / joints in the final finish. I had been going to use GRP, but have come across advertising for a couple of polyurethane-based resins e.g. Ultraflex http://www.ultra-flex.com/ It looks like they're the same basic concept as GRP - applied over a chopped strand matting etc - but according to the marketing with a few benefits: Moisture curing so instantly rain resistant - attractive in Edinburgh where it's not uncommon to get rain even if the forecast says it'll be dry Usable as soon as you open the tin - no catalyst mixing etc Resultant membrane is highly flexible - I've read that one concern with GRP vs e.g. EDPM is that because it's more rigid you can get more issues with expansion/contraction and related noises. Although my roof area's not that big, 7m x 3m on the longest side of the L. But my project spans across an existing building and a new section with new rafters - potentially there'll be a little bit of shrinkage movement at first so the idea of a more flexible covering is attractive. But apart from their own marketing I can't really find anyone online talking about / using polyurethane products - everyone seems to go for standard GRP. Does anyone on here have any experience with these? The ultraflex one is BBA/NHBC certified and meets my fire resistance criteria, so presumably it should be OK. It'd just be nice to feel a bit more confident people actually used / recommended it - I'm always cautious about putting too much weight on what a manufacturer says!

Hi everyone, I'm part way through a self-build garage conversion and small 4 sqm timber frame utility room extension. Probably the first of many projects we'll do here! The garage conversion is actually a re-conversion, after we moved in it turned out the previous owners had had it done by cowboys with no building warrant. So had to start by stripping it all back to the original garage and starting again. One of those gifts that kept on giving - as I took down the old work I found issues including big areas of wall stuffed with rolled up newspaper where they'd presumably run out of insulation, VCL against the outer wall so the plasterboard battens were rotting from condensation, ceiling noggins/dwangs made of old table legs and some electrics that had clearly been on fire. Presumably it was all too wet with condensation to take hold! My personal favourite was lifting the cheap laminate to find a disintegrating timber lid over a 2m x 1m x 2m deep vehicle inspection pit in the floor.... Anyway, now well underway putting it right - the old stuff is stripped, pit infilled, the stick-built timber frame for the extension is almost complete and I'm starting to strip and replace the roof deck (with alterations to rafters for some new rooflights). Doing it pretty much all myself with a bit of labouring help, I did most of the design / specs / warrant application too after a lot of research, though with help and certification from a brilliant Structural Engineer. Sadly he's just retired. Trained and used to work in theatre and event production, so picked up a lot of carpentry, welding, painting, moulding etc type skills. I primarily worked as a spark, did my City & Guilds in Electrical Installation. Done quite a lot of quite major DIY too over the years, but this is definitely the most challenging thing I've taken on. One day I'd love to self-build an actual house, though by the time I've done everything I want to here I probably won't want to move! I've been occasionally lurking round here in the past, looking forward to being a member and helping to answer questions where I can as well as asking some!