ETC Posted June 19 Share Posted June 19 7 hours ago, Russell griffiths said: Have you considered closed cell spray foam sprayed to the underside of the osb, whithin the webs of the posi joist 50mm pir on top of joist and 150 spray foam inbetween. very little height build up then. your box gutter shape needs changing to vertical sides, with no horizontal epdm stuck under that parapet. Don’t…..just don’t. 2 Link to comment Share on other sites More sharing options...
ETC Posted June 19 Share Posted June 19 20 hours ago, Mulberry View said: Here's a rough idea of what I propose. If this could work, it would be the preferable option. Horizontal Parapet wall on the green lines.... Integral gulleys on the thick red lines. Outlet into the denoted hopper. Flat roof falling in the direction of the red arrows... Very roughly this. The scale is off and the measurements are for guidance. We had planned to fit 200mm PIR into the main roof, so I guess we need to do the same in the flat roof area? 120mm meets our declared as-designed SAP, but we want to do much better than that. I've shown the PIR cut at an angle so as to keep the 200mm thickness as far as possible, but oversailing onto the EPS inner skin of the Nudura. Of course I realise I'd have to place firrings under the Plywood for the fall. Keep in mind there is an outer unifying 50mm skin of EPS to go on in addition to that drawn, this will cover the external timbers. What width should the Parapet be? From the centreline of the Nudura outwards it would be roughly 200mm without needing that inward overhang and might allow the PIR to oversail a bit more. We would run the EPDM up the adjoining walls of the two-storey building. If the Parapet can be kept to 250mm maximum as denoted, it would leave 80-100mm underneath the structural opening of the window. Also, depending on what height the Parapet would need to be in relation to the insulation and gutter depth, it might not even need to be as funky as I've drawn it. @ETC - I would be very happy to pay your rates to do a proper detail drawing if you think a version of this/your idea could work. Any good? You’ll have a massive cold bridge there I’m afraid. Are your joists laid to a fall? Link to comment Share on other sites More sharing options...
Russell griffiths Posted June 19 Share Posted June 19 1 hour ago, ETC said: Don’t…..just don’t. What don’t you like, I’ve recently been on a job where it’s been used in a flat roof situation condensation risk done, no problem whatsoever. Link to comment Share on other sites More sharing options...
Jilly Posted June 19 Share Posted June 19 Might Aerogel be worth considering? Link to comment Share on other sites More sharing options...
SteamyTea Posted June 19 Share Posted June 19 6 minutes ago, Jilly said: Might Aerogel be worth considering? Unless it is the genuine article, not the stuff that is in a blanket, it is never worth considering. Pretend it does not exist. 1 Link to comment Share on other sites More sharing options...
ETC Posted June 19 Share Posted June 19 30 minutes ago, Russell griffiths said: What don’t you like, I’ve recently been on a job where it’s been used in a flat roof situation condensation risk done, no problem whatsoever. https://hoa.org.uk/advice/guides-for-homeowners/i-am-improving/spray-foam-roof-insulation/ https://commonslibrary.parliament.uk/spray-foam-insulation-and-mortgages/ https://www.which.co.uk/reviews/insulation/article/spray-foam-insulation-ajTlp7t5K7lT Link to comment Share on other sites More sharing options...
ETC Posted June 19 Share Posted June 19 13 hours ago, Dave Jones said: replace the window for a wider/narrower one to give you some height ? Good example of an architect drawing being total crap when it comes to the reality of building. It’s always the architect who gets the flack! 1 Link to comment Share on other sites More sharing options...
Mulberry View Posted June 19 Author Share Posted June 19 @ETC My sketch is getting a bit ugly now I'm tippex'ing and scrawling, but what would be the effect of reducing the insulation on the flat roof to, say 150 or 175mm when the rest of the house is at 200mm? If I could do something like below, with 100mm base layer of PIR forming the bottom of the gutter and the Parapet be 150mm above this, I'd be in the ballpark of 275mm total height, 75mm under the window at the worst point. Keep in mind this is ICF, in my original sketch I thought it was sufficient to have made the PIR lap over the EPS inner skin of the ICF. Link to comment Share on other sites More sharing options...
Mulberry View Posted June 19 Author Share Posted June 19 Am I right in saying that a hopper could only be used with a parapet wall in this scenario? Link to comment Share on other sites More sharing options...
Dave Jones Posted June 20 Share Posted June 20 6 hours ago, ETC said: It’s always the architect who gets the flack! in fairness who drew this really poor design element? minor change in shape and size of those windows to butt up the roof would have saved a lot of cost and hassle from the start. 1 Link to comment Share on other sites More sharing options...
Mulberry View Posted June 20 Author Share Posted June 20 5 hours ago, Dave Jones said: in fairness who drew this really poor design element? minor change in shape and size of those windows to butt up the roof would have saved a lot of cost and hassle from the start. Dave, again, please stop posting here. It's not helpful. The fact that you think those 2 roofs should be joined shows that you do not have a good idea of how the design works and therefore should not try to give advice. Link to comment Share on other sites More sharing options...
Kelvin Posted June 20 Share Posted June 20 10 minutes ago, Mulberry View said: Dave, again, please stop posting here. It's not helpful. The fact that you think those 2 roofs should be joined shows that you do not have a good idea of how the design works and therefore should not try to give advice. Quite. It is what it is so has to be solved that way. 1 Link to comment Share on other sites More sharing options...
Mulberry View Posted June 20 Author Share Posted June 20 (edited) 25 minutes ago, Kelvin said: Quite. It is what it is so has to be solved that way. Indeedy, and the fact that I am facing this problem doesn't write the whole design off. As someone who is not a 'tradie', this has been an ambitious build and far harder than a straight-forward square/rectangle building would have been, but that doesn't take away from how pleased we are with how it is turning out. Edited June 20 by Mulberry View 1 Link to comment Share on other sites More sharing options...
Russell griffiths Posted June 20 Share Posted June 20 15 hours ago, ETC said: https://hoa.org.uk/advice/guides-for-homeowners/i-am-improving/spray-foam-roof-insulation/ https://commonslibrary.parliament.uk/spray-foam-insulation-and-mortgages/ https://www.which.co.uk/reviews/insulation/article/spray-foam-insulation-ajTlp7t5K7lT This is not the same situation. new build, not a 1930’s semi that needs the airflow through the roof space. 1 Link to comment Share on other sites More sharing options...
Russell griffiths Posted June 20 Share Posted June 20 What’s to stop you dropping the 100mm insulation between the top chords of the posi’s then putting 100mm over the top foam the bottom 100mm to the pos’s then a bit of further details from below, foam all gaps to the walls with illbruck foam, not the cheap nasty open cell stuff. 1 Link to comment Share on other sites More sharing options...
Mulberry View Posted June 20 Author Share Posted June 20 1 hour ago, Russell griffiths said: What’s to stop you dropping the 100mm insulation between the top chords of the posi’s then putting 100mm over the top foam the bottom 100mm to the pos’s then a bit of further details from below, foam all gaps to the walls with illbruck foam, not the cheap nasty open cell stuff. Would be lovely to gain that much space back, but what about the insulation under the VCL? Everyone seems to say that's a no no. Link to comment Share on other sites More sharing options...
torre Posted June 20 Share Posted June 20 Won't you also need some additional height for flashing where the parapet meets the main wall? Maybe look at alternatives to a parapet if it's too tight - could you create a fall from front to back so that all the water drains to the rear (see pic) or fall towards the front into a hidden gutter without a parapet. (Not an architect by the way!) 1 Link to comment Share on other sites More sharing options...
AppleDown Posted June 20 Share Posted June 20 15 minutes ago, Mulberry View said: Would be lovely to gain that much space back, but what about the insulation under the VCL? Everyone seems to say that's a no no. Have a watch of this guy's channel - knows his stuff: Link to comment Share on other sites More sharing options...
ETC Posted June 20 Share Posted June 20 5 hours ago, Russell griffiths said: This is not the same situation. new build, not a 1930’s semi that needs the airflow through the roof space. Try getting a mortgage! Link to comment Share on other sites More sharing options...
ETC Posted June 20 Share Posted June 20 14 hours ago, Dave Jones said: in fairness who drew this really poor design element? minor change in shape and size of those windows to butt up the roof would have saved a lot of cost and hassle from the start. Perhaps. But the size and shape could have been determined by factors we are not privy to. Link to comment Share on other sites More sharing options...
ETC Posted June 20 Share Posted June 20 5 hours ago, Russell griffiths said: What’s to stop you dropping the 100mm insulation between the top chords of the posi’s then putting 100mm over the top foam the bottom 100mm to the pos’s then a bit of further details from below, foam all gaps to the walls with illbruck foam, not the cheap nasty open cell stuff. No….no…..and no again. How many times do I have to say no do not build like this. You will get problems with interstitial condensation if you build like this. 1 Link to comment Share on other sites More sharing options...
ETC Posted June 20 Share Posted June 20 3 hours ago, torre said: Won't you also need some additional height for flashing where the parapet meets the main wall? Maybe look at alternatives to a parapet if it's too tight - could you create a fall from front to back so that all the water drains to the rear (see pic) or fall towards the front into a hidden gutter without a parapet. (Not an architect by the way!) Nope. Makes the problem worse. 1 Link to comment Share on other sites More sharing options...
Kelvin Posted June 20 Share Posted June 20 (edited) You really want to keep this as simple as possible with the water going to one place ideally if that’s possible. My previous house was part of a converted series of barns. The barns opposite us had a relatively complicated roof with several valleys and flat bits. Rather than try and get all the water to run in one direction at either end they built so it ran down and in several directions and off the building down 4 different downpipes. Consequently they ended up with multiple weak points rather than one and all of them leaked. The worst was a downpipe that ran inside and between the walls of two of the houses. That inevitably failed and both houses ended up with water damage. The eventual fix was remove everything they had done rebuild the roof to get the water to drain into a single deep gutter either end of the building. This was also all done in lead as I remember. The only issue was access to clear any blockages. See picture below. This was after it was re-done. Every single hopper also failed at some point as they were made out of wood and painted. Edited June 20 by Kelvin Link to comment Share on other sites More sharing options...
Kelvin Posted June 20 Share Posted June 20 Link to comment Share on other sites More sharing options...
Mulberry View Posted June 20 Author Share Posted June 20 1 hour ago, ETC said: Perhaps. But the size and shape could have been determined by factors we are not privy to. I'm starting to think this roof may have to be open and into a short gutter. I'm fast running out of time. Link to comment Share on other sites More sharing options...
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